<PAGE>   1
                                                                   EXHIBIT 10.28

                         AMENDMENT NUMBER SIX TO THIRD
                     AMENDED AND RESTATED CREDIT AGREEMENT

     This AMENDMENT NUMBER SIX TO THIRD AMENDED AND RESTATED CREDIT AGREEMENT
(this "SIXTH AMENDMENT"), dated as of December 17, 1999 (the "EFFECTIVE DATE"),
is entered into among SOUTHDOWN, INC., a Louisiana corporation ("BORROWER"), the
banks and financial institutions parties hereto that are signatories to the
Credit Agreement (as defined below) (collectively, the "BANKS," and WELLS FARGO
BANK, N.A., a national banking association, as agent for the Banks hereunder
("AGENT").

     WHEREAS, Borrower, the Banks, and Wells Fargo Bank, N.A., as agent,
heretofore have entered into that certain Third Amended and Restated Credit
Agreement, dated as of November 3, 1995, as amended by (a) that certain Letter
Agreement, dated as of February 29, 1996, (b) that certain Amendment Number Two
to Third Amended and Restated Credit Agreement, dated as of September 30, 1996,
(c) that certain Amendment Number Three to Third Amended and Restated Credit
Agreement, dated as of August 6, 1997, (d) that certain Amendment Number Four to
Third Amended and Restated Credit Agreement dated as of May 14, 1998 and (e)
that certain Amendment Number Five to Third Amended and Restated Credit
Agreement dated as of December 18, 1998 (as amended, the "CREDIT AGREEMENT");

     WHEREAS, Borrower has requested, among other things, that the Credit
Agreement be amended to (a) permit the Borrower to enter into a $250,000,000
revolving credit facility and revise certain provisions of Articles 1, 4, 5, 6
and 7, (b) and (c) make other amendments to the terms and conditions of the
Credit Agreement as set forth herein; and

     WHEREAS, subject to the terms and conditions contained herein, the Banks
are willing to so amend such provisions of the Credit Agreement.

     NOW, THEREFORE, in consideration of the mutual covenants, conditions, and
provisions hereinafter set forth, the parties hereto agree as follows:

                                   ARTICLE 1
                                  DEFINITIONS

     1.1 DEFINITIONS FOR THIS SIXTH AMENDMENT. Any and all initially capitalized
terms used herein shall have the meanings ascribed thereto in the Credit
Agreement, as amended hereby, unless specifically defined herein.



                                       1                         SIXTH AMENDMENT
<PAGE>   2


                                   ARTICLE 2
                       AMENDMENTS TO THE CREDIT AGREEMENT

     2.1 Section 1.1 of the Credit Agreement hereby is amended by deleting in
their entirety each of the defined terms on EXHIBIT A hereto attached.

     2.2 Section 1.1 of the Credit Agreement hereby is amended by adding each of
the defined terms on EXHIBIT B hereto attached in alphabetical order.

     2.3 Section 1.1 of the Credit Agreement hereby is amended by amending and
restating each of the following defined terms to read as set forth below:

          "'AGENT' or 'ADMINISTRATIVE AGENT' means Wells Fargo Bank, N.A., and
     its permitted successor or successors as administrative agent for the
     Banks."

          "'BANK' and 'BANKS' means any of the financial institutions which
     either now or in the future are parties to this Agreement."

          "'ISSUING BANK' means Wells Fargo Bank, N.A. or any other Bank that,
     on behalf of all Banks having a share of the Revolving Credit Facility
     Commitments, issues a Letter of Credit requested by Borrower hereunder."

          "'MATERIAL ADVERSE CHANGE' means and refers to a material adverse
     change in the business, Assets, operations, business property, or
     conditions (financial or otherwise) of Borrower and its Subsidiaries, taken
     as a whole, as compared with the business, Assets, operations, business
     property, or conditions (financial or otherwise) of Borrower and its
     Subsidiaries, taken as a whole as of December 31, 1998."

          "'UCC' means the Texas Uniform Commercial Code, as amended or
     supplemented from time to time, and any successor statute."

          "'WELLS FARGO' means and refers to Wells Fargo Bank, N.A., a national
     banking association."

     2.4 The Credit Agreement hereby is amended by deleting Subsections 2.5(e)
therefrom and substituting the following Subsections 2.5(e), (f), and (g) in
lieu thereof and Subsection 2.5(f) of the Credit Agreement is hereby renumbered
Subsection 2.5(h):

          "(e) It is the intention of the parties hereto to comply with
     applicable usury laws, if any; accordingly, notwithstanding any provision
     to the contrary in this Agreement, the Notes or in any of the other Loan
     Documents securing the payment hereof or otherwise relating hereto, in no
     event shall this Agreement, the Notes or such other Loan Documents require
     or permit the payment, taking, reserving, receiving, collection, or
     charging of any sums constituting interest under applicable laws which
     exceed the maximum amount permitted by such laws. If any such excess
     interest is called for, contracted for, charged, taken, reserved, or
     received in connection with the Loans evidenced by the Notes or in any of
     the Loan Documents,



                                       2                         SIXTH AMENDMENT
<PAGE>   3

or in any communication by the Agent, any Issuing Bank or the Banks or any other
Person to Borrower or any other Person, or in the event all or part of the
principal or interest thereof shall be prepaid or accelerated, so that under any
of such circumstances or under any other circumstance whatsoever the amount of
interest contracted for, charged, taken, reserved, or received on the amount of
principal actually outstanding from time to time under the Notes or any other
Loan Document shall exceed the maximum amount of interest permitted by
applicable usury laws, then in any such event it is agreed as follows: (i) the
provisions of this paragraph shall govern and control, (ii) neither Borrower nor
any other Person now or hereafter liable for the payment of the Notes or any
obligation arising under this Agreement shall be obligated to pay the amount of
such interest to the extent such interest is in excess of the maximum amount of
interest permitted by applicable usury laws, (iii) any such excess which is or
has been received notwithstanding this paragraph shall be credited against the
then unpaid principal balance of the Notes or other obligations arising under
this Agreement, as applicable, or, if the Notes or other obligations arising
under this Agreement, as applicable, have been or would be paid in full,
refunded to Borrower, and (iv) the provisions of this Agreement, the Notes and
the other Loan Documents, and any communication to Borrower, shall immediately
be deemed reformed and such excess interest reduced, without the necessity of
executing any other document, to the maximum lawful rate allowed under
applicable laws as now or hereafter construed by courts having jurisdiction
hereof or thereof. Without limiting the foregoing, all calculations of the rate
of the interest contracted for, charged, collected, taken, reserved, or received
in connection with the Notes, this Agreement or any other Loan Document which
are made for the purpose of determining whether such rate exceeds the maximum
lawful rate shall be made to the extent permitted by applicable laws by
amortizing, prorating, allocating and spreading during the period of the full
term of the Loans or other obligations arising under this Agreement, as
applicable, including all prior and subsequent renewals and extensions, all
interest at any time contracted for, charged, taken, collected, reserved, or
received. The terms of this paragraph shall be deemed to be incorporated in
every document and communication relating to the Notes, the Loans or any other
Loan Document.

     (f) Texas Finance Code, Chapter 346 (formerly Tex. Rev. Civ. Stat., Title
79, Chapter 15), which regulates certain revolving loan accounts and revolving
triparty accounts, shall not apply to any revolving loan accounts created under
the Notes, this Agreement or the other Loan Documents or maintained in
connection therewith.

     (g) To the extent that the interest rate laws of the State of Texas are
applicable to the Loans or any other obligations arising under this Agreement,
the applicable interest rate ceiling is the weekly ceiling (formerly the
indicated rate ceiling) determined in accordance with Tex. Rev. Civ. Stat.,
Title 79, Article 5069- 1D.003, also codified at Texas Finance Code, Section
303.301 (formerly Article 5069-1.01(a)(1)), and, to the extent that this
Agreement, the Notes or any other Loan Document is deemed an open end account as
such term is defined in Tex. Rev. Civ. Stat., Title 79, Article 5069-1B.002(14),
also codified at Texas Finance Code Section 3.01.001(3) (formerly Article
5069-1.01(f)), the Agent and the Banks retain the right to modify the interest
rate in accordance with applicable law."



                                       3                         SIXTH AMENDMENT
<PAGE>   4

     2.5 The Credit Agreement hereby is amended by deleting Article 4
(Representations and Warranties of Borrower) therefrom and substituting the
Article 4 (Representations and Warranties) set forth on EXHIBIT C hereto
attached in lieu thereof.

     2.6 The Credit Agreement hereby is amended by deleting Article 5
(Affirmative Covenants of Borrower) therefrom and substituting the Article 5
(Covenants) set forth on Exhibit D hereto attached in lieu thereof.

     2.7 The Credit Agreement hereby is amended by deleting Article 6 (Negative
Covenants of Borrower) therefrom and substituting the following Article 6 in
lieu thereof:

                      "ARTICLE 6. Intentionally omitted."

     2.8 The Credit Agreement hereby is amended by deleting Section 7.1 (Events
of Default) therefrom and substituting the Section 7.1 (Events of Default) set
forth on Exhibit E hereto attached in lieu thereof.

     2.9 Section 10.2 of the Credit Agreement hereby is amended by deleting the
phrase "(the "Indemnified Liabilities")" and replacing such phrase with the
following:

     "(the "Indemnified Liabilities," WHICH TERM SHALL INCLUDE ANY INDEMNIFIED
     LIABILITIES RESULTING FROM ANY IDEMNITEE'S NEGLIGENCE)."

     2.10 Each reference to "CALIFORNIA" in Sections 11.9 and 11.10 of the
Credit Agreement hereby is amended to read "TEXAS."

     2.11 Each reference to "LOS ANGELES" in Sections 11.9 and 11.10 of the
Credit Agreement hereby is amended to read "HARRIS."

     2.12 The Credit Agreement hereby is amended by deleting Section 11.13
(Changes in Accounting Principles) therefrom and substituting the following
Section 11.13 in lieu thereof:

          "11.3 Intentionally Omitted."

     2.13 Section 11.17 of the Credit Agreement hereby is amended by adding the
following paragraph at the end thereof:

          "NO ORAL AGREEMENTS. THIS WRITTEN LOAN AGREEMENT, TOGETHER WITH THE
NOTES AND THE OTHER LOAN DOCUMENTS EXECUTED IN CONNECTION HEREWITH, REPRESENTS
THE FINAL AGREEMENT BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE
OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL AGREEMENTS OF THE PARTIES.

          THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES."



                                       4                         SIXTH AMENDMENT
<PAGE>   5

                                   ARTICLE 3
                            AMENDMENTS TO THE NOTES

          3.1 Each reference to "CALIFORNIA" in Sections 14 and 15 of the Notes
hereby is amended to read "TEXAS."

3.2 Each reference to "LOS ANGELES" in Section 15 of the Notes hereby is amended
to read "HARRIS."

                                   ARTICLE 4
                              CONDITIONS PRECEDENT

          4.1 CONDITIONS PRECEDENT TO THE EFFECTIVENESS OF THIS SIXTH AMENDMENT.
The effectiveness of the provisions of this Sixth Amendment is subject to the
fulfillment, to the satisfaction of Agent, of each of the following conditions:

               4.1.1 The Agent shall have received a certificate from a
          Secretary or Assistant Secretary of Borrower attesting to the
          resolutions of Borrower's board of directors or an authorized
          committee authorizing the execution and delivery of this Sixth
          Amendment.

               4.1.2 The Agent shall have received counterparts of signature
          pages of this Sixth Amendment duly executed and delivered by Borrower
          and Banks constituting Majority Banks.

               4.1.3 The Agent shall have received a certificate from a
          Responsible Officer certifying that:

                    (a) the representations and warranties, as amended hereby,
               of Borrower contained in the Credit Agreement and the Loan
               Documents, to the extent that it is a party thereto, are true and
               correct in all material respects at and as of the date of the
               effectiveness of this Sixth Amendment, as though made on and as
               of such date (except to the extent that such representations and
               warranties expressly relate solely to an earlier date);

                    (b) neither an Event of Default, as amended hereby, nor an
               Unmatured Event of Default, as amended hereby, has occurred and
               is continuing on the date of the effectiveness of this Sixth
               Amendment;

                    (c) on the date of the effectiveness of this Sixth
               Amendment, no Material Adverse Change has occurred, as a result
               of one or more acts or occurrences; and

                    (d) the Credit Agreement and each of the Loan Documents to
               which Borrower is a party are in full force and effect.






                                       5                         SIXTH AMENDMENT
<PAGE>   6

               4.1.4 The Agent shall have received the written opinions, dated
     as of the Effective Date, of counsel to Borrower, in form and substance
     satisfactory to Agent and its counsel.

                                   ARTICLE 5
                                 MISCELLANEOUS

     5.1 EXECUTION IN COUNTERPARTS. This Sixth Amendment may be executed in any
number of counterparts, each of which when so executed and delivered shall be
deemed an original. All of such counterparts shall constitute but one and the
same instrument. Delivery of an executed counterpart of the signature pages of
this Sixth Amendment by telecopier shall be equally effective as delivery of a
manually executed counterpart. Any party delivering an executed counterpart of
the signature pages of this Sixth Amendment by telecopier thereafter also shall
deliver promptly a manually executed counterpart, but the failure to deliver
such manually executed counterpart shall not affect the validity,
enforceability, or binding effect of this Sixth Amendment.

     5.2 NO OTHER AMENDMENT. Except as expressly amended hereby, the Credit
Agreement shall remain unchanged and in full force and effect. To the extent any
terms or provisions of this Sixth Amendment conflict with those of the Credit
Agreement, the terms and provisions of this Sixth Amendment shall control. This
Sixth Amendment shall be deemed a part of and hereby is incorporated in the
Credit Agreement.

     5.3 SEVERABILITY AND INTERPRETATION OF AMENDMENTS. It is the intention of
the parties hereto to comply with Section 11.1 of the Credit Agreement. Whenever
possible, each provision of the amendments contained in this Sixth Amendment
shall be interpreted in such manner as to be effective and valid in accordance
with Section 11.1 of the Credit Agreement. If any term or provision of any
amendment contained in this Sixth Amendment is held not be effective because
such term or provision required the consent of all Banks pursuant to Section
11.1 of the Credit Agreement, such term or provision shall be fully severable
and shall not affect the enforceability of the remaining terms and provisions.

     5.4 GOVERNING LAW. This Sixth Amendment shall be governed by, and construed
and enforced in accordance with, the laws of the State of Texas and applicable
federal law.

     5.5 NO ORAL AGREEMENTS. THIS WRITTEN AGREEMENT, TOGETHER WITH THE NOTES AND
THE OTHER LOAN DOCUMENTS EXECUTED IN CONNECTION HEREWITH, REPRESENTS THE FINAL
AGREEMENT BETWEEN THE PARTIES AND MAY

                                       6                         SIXTH AMENDMENT

<PAGE>   7

NOT BE CONTRADICTED BY EVIDENCE OF PRIOR, CONTEMPORANEOUS OR SUBSEQUENT ORAL
AGREEMENTS OF THE PARTIES.

     THERE ARE NO UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

                            [SIGNATURE PAGES FOLLOW]


                                       7                         SIXTH AMENDMENT
<PAGE>   8

     IN WITNESS WHEREOF, the parties hereto have caused this Sixth Amendment to
be executed and delivered as of the date first set forth above.

                                        SOUTHDOWN, INC.
                                        a Louisiana Corporation



                                        By
                                          -------------------------------------
                                        Name:
                                        Title:


                  [SIGNATURES CONTINUE ON THE FOLLOWING PAGE]





               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]

                                                                 SIXTH AMENDMENT


<PAGE>   9


                                        WELLS FARGO BANK, N.A.,
                                        in its individual capacity and as Agent



                                        By
                                          -------------------------------------
                                        Name:
                                        Title:


                  [SIGNATURES CONTINUE ON THE FOLLOWING PAGE]






               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]



                                                                 SIXTH AMENDMENT

<PAGE>   10

                                        SOCIETE GENERALE, SOUTHWEST
                                        AGENCY, as an Issuing Bank



                                        By
                                          -------------------------------------
                                        Name:
                                        Title:


                  [SIGNATURES CONTINUE ON THE FOLLOWING PAGE]




               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]




                                                                 SIXTH AMENDMENT
<PAGE>   11

                                        CREDIT SUISSE FIRST BOSTON
                                        (formerly known as Credit Suisse)



                                        By
                                          -------------------------------------
                                        Name:
                                        Title:


                  [SIGNATURES CONTINUE ON THE FOLLOWING PAGE]




               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]



                                                                 SIXTH AMENDMENT
<PAGE>   12

                                        CREDIT AGRICOLE INDOSUEZ
                                        (formerly known as Caisse Nationale De
                                         Credit Agricole)



                                        By
                                          -------------------------------------
                                        Name:
                                        Title:


                  [SIGNATURES CONTINUE ON THE FOLLOWING PAGE]






               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]



                                                                 SIXTH AMENDMENT
<PAGE>   13

                                        SUNTRUST BANK, ATLANTA




                                        By
                                          -------------------------------------
                                        Name:
                                        Title:


                  [SIGNATURES CONTINUE ON THE FOLLOWING PAGE]





               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]



                                                                 SIXTH AMENDMENT
<PAGE>   14

                                        PARIBAS
                                        (formerly known as Banque Paribas)



                                        By
                                          -------------------------------------
                                        Name:
                                        Title:


                                        By
                                          -------------------------------------
                                        Name:
                                        Title:


                  [SIGNATURES CONTINUE ON THE FOLLOWING PAGE]






               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]




                                                                 SIXTH AMENDMENT
<PAGE>   15

                                        PNC BANK NATIONAL ASSOCIATION



                                        By
                                          ------------------------------------
                                        Name:
                                        Title:


                  [SIGNATURES CONTINUE ON THE FOLLOWING PAGE]




               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]



                                                                 SIXTH AMENDMENT
<PAGE>   16

                                        THE BANK OF NOVA SCOTIA



                                        By
                                          -------------------------------------
                                        Name:
                                        Title:


                  [SIGNATURES CONTINUE ON THE FOLLOWING PAGE]






               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]



                                                                 SIXTH AMENDMENT
<PAGE>   17

                                        BANKBOSTON, N.A.



                                        By
                                          -------------------------------------
                                        Name:
                                        Title:






               [THIS IS A SIGNATURE PAGE TO AMENDMENT NUMBER SIX
              TO THE THIRD AMENDED AND RESTATED CREDIT AGREEMENT]

                                                                 SIXTH AMENDMENT

<PAGE>   18

                                   EXHIBIT A

                          DEFINED TERMS TO BE DELETED

"BROOKSVILLE PLANT"

"CAPITAL EXPENDITURES"

"CAPITALIZED LEASE"

"CAPITALIZED LEASE OBLIGATIONS"

"CEMENT PLANTS"

"CHANGE OF CONTROL"

"CONSOLIDATED CURRENT ASSETS"

"CONSOLIDATED CURRENT LIABILITIES"

"CONSOLIDATED NET INCOME"

"CONSOLIDATED TANGIBLE NET WORTH"

"CONTINGENT OBLIGATION"

"CONTINUING DIRECTORS"

"CONTRACTUAL OBLIGATION"

"CONTRIBUTED CALIFORNIA ASSETS"

"DAMAGES"

"DEBT"

"DISQUALIFIED STOCK"

"ENVIRONMENT"

"ENVIRONMENTAL PROTECTION STATUTE"

"EPA"

"ERISA AFFILIATE"

"EXCHANGE SUBORDINATED DEBT"

                                       A-1                       SIXTH AMENDMENT


<PAGE>   19

"EXISTING SUBORDINATED DEBT"

"FAIRBORN PLANT"

"FIFTH AMENDMENT"

"FIFTH AMENDMENT CLOSING DATE"

"FOURTH AMENDMENT CLOSING DATE"

"FREE CASH FLOW RATIO"

"FUND," "TRUST FUND" OR "SUPER FUND"

"FUNDED DEBT"

"HAZARDOUS SUBSTANCE"

"HAZARDOUS WASTE"

"HEDGE AGREEMENTS"

"INDENTURE"

"INTANGIBLE ASSETS"

"INTEREST EXPENSE"

"INVESTMENT"

"JUNIOR PAYMENT AMOUNT"

"KCC"

"KNOXVILLE PLANT"

"LEVERAGE RATIO"

"LIEN"

"LYONS PLANT"

"MEDUSA"

"MEDUSA ENTITIES"

"MERGER"

                                       A-2                       SIXTH AMENDMENT
<PAGE>   20


"MERGER AGREEMENT"

"MMRI"

"MOODY'S"

"MULTIEMPLOYER PLAN"

"NET ISSUANCE PROCEEDS"

"NONCANCELLABLE LEASE"

"ODESSA PLANT"

"OPERATING LEASE"

"PBGC"

"PENSION PLAN" OR "PLAN"

"PENSION PROTECTION ACT"

"PERMITTED ACQUISITIONS"

"PERMITTED JUNIOR PAYMENTS"

"PERMITTED LIENS"

"PERMITTED PAYMENT MEASUREMENT PERIOD"

"PERMITTED PREFERRED STOCK"

"PERMITTED TRANSACTIONS"

"POLLUTION CONTROL BONDS"

"PREFERRED STOCK"

"PROHIBITED PREFERRED STOCK"

"QUALIFIED OFFERINGS"

"RELATED TERMINALS"

"REMEDIAL ACTION"

"REPORTABLE EVENT"

                                       A-3                       SIXTH AMENDMENT

<PAGE>   21

"SARA"

"S&P"

"SDW AGGREGATES"

"SDW CALIFORNIA SUBSIDIARIES"

"SDW CEMENT"

"SDW CONCRETE"

"SDW FINANCE"

"SDW FINANCE SUBORDINATED DEBT"

"SDW FINANCE SUBORDINATED NOTE"

"SENIOR SUBORDINATED NOTES"

"SERIES A PREFERRED STOCK"

"SERIES B PREFERRED STOCK"

"SERIES C PREFERRED STOCK"

"SERIES D PREFERRED STOCK"

"SPECIFIED SUBSIDIARIES"

"SUBORDINATED DEBT"

"SUBORDINATED INDENTURE"

"TERMINATION EVENT"

"THIRD AMENDMENT"

"THIRD AMENDMENT CLOSING DATE"

"VICTORVILLE PLANT"

                                        A-4                      SIXTH AMENDMENT

<PAGE>   22

                                   EXHIBIT B

                           DEFINED TERMS TO BE ADDED

     "ADJUSTED CONSOLIDATED EBITDA" means, for the relevant period, the sum of:
(a) the Consolidated Net Income for such period, (b) Consolidated Interest
Expense, (c) all taxes measured by income to the extent included in the
determination of such Consolidated Net Income and (d) all amounts treated as
expenses for depreciation and the amortization of intangibles of any kind for
such period to the extent included in the determination of such Consolidated Net
Income for the relevant period; provided, however, that Consolidated Net Income
shall be computed for the purposes of this definition (i) without regard to
non-recurring costs incurred in connection with any acquisition or non-cash
write-ups and write-downs, and (ii) without giving effect to extraordinary
losses or extraordinary gains for such period.

     "BUSINESS DAY" means (a) for all purposes, any day other than Saturday,
Sunday, and any other day on which commercial banking institutions are required
or authorized by Law to be closed in Houston, Texas, San Francisco, California
or New York, New York, and (b) in addition to the foregoing, in respect of any
LIBOR Rate Borrowing, a day on which dealings in United States dollars are
conducted in the London interbank market and commercial banks are open for
international business in London.

     "CHANGE OF CONTROL" means and refers to the occurrence of one or more of
the following events: (a) any sale, lease, exchange, or other transfer (in one
transaction or a series of related transactions) of all or substantially all of
the assets of Borrower to any Person or related group for purposes of Section
13(d) of the Exchange Act (a "Group"), together with any Affiliates thereof, (b)
the shareholders of Borrower shall approve any plan or proposal for the
liquidation or dissolution of Borrower (other than a liquidation or dissolution
pursuant to a Reincorporation Merger), (c) any Person or Group, together with
any Affiliates thereof, shall, as a result of a tender or exchange offer, a
merger, consolidation or similar transaction, open market purchases, privately
negotiated purchases, or otherwise, have become the beneficial owner (within the
meaning of Rule 13d-3 under the Exchange Act), directly or indirectly, of
securities of Borrower representing at least thirty percent (30%) of the Voting
Stock of Borrower, or (d) a majority of the members of the Board of Directors
shall not constitute Continuing Directors. For purposes of this definition,
"Board of Directors" does not include any committee thereof.

     "COMPANIES" means, at any date of determination thereof, Borrower and each
of its Subsidiaries, and "Company" means any of the Companies.

     "CONSOLIDATED INTEREST EXPENSE" means, for the relevant period, for
Borrower and its Subsidiaries, without duplication, the amount of all costs,
fees and expenses paid by Borrower and its Subsidiaries in such period which are
classified as interest expense on the consolidated financial statements of
Borrower and its Subsidiaries, all determined in accordance with GAAP.

     "CONSOLIDATED NET INCOME" means, for any period, the net income (or net
loss) of the Borrower and its Subsidiaries for such period taken as a single
accounting period determined in accordance with GAAP.

                                       B-1                       SIXTH AMENDMENT
<PAGE>   23

     "CONSOLIDATED NET WORTH" means, on any date of determination, all amounts
that would be included under shareholders' equity on a consolidated balance
sheet of Borrower as determined in accordance with GAAP.

     "CONSOLIDATED SUBSIDIARY" means, at any date any Subsidiary or other entity
the accounts of which are consolidated with Borrower in its consolidated
financial statements prepared in accordance with GAAP.

     "CONTINUING DIRECTOR" means and refers to (a) any member of Borrower's
board of directors who was a director of Borrower on the Closing Date, and (b)
any person who becomes a member of the board of directors after the Closing Date
if such person was appointed or nominated for election to the board of directors
by a majority of the Continuing Directors, but excluding any such person
originally proposed for election in opposition to the Continuing Directors in an
actual or threatened election contest relating to the election of the directors
of Borrower (as such terms are used in Rule 14a-11 under the Exchange Act) and
whose initial assumption of office resulted from such contest or the settlement
thereof.

     "CONTRACTUAL OBLIGATION" means, as to any Person, any provision of any
security issued by such Person or of any agreement, instrument, or undertaking
to which such Person is a party or by which it or any of its property is bound.

     "CURRENT FINANCIALS" means, at the time of any determination thereof, the
more recently delivered to Banks of either (a) the consolidated Financial
Statements of Borrower and its consolidated Subsidiaries for the fiscal year
ended December 31, 1998, and the nine-month period ended September 30, 1999; or
(b) the Financial Statements required to be delivered under SECTIONS 5.1(a) or
5.1(b), as the case may be.

     "DEBT" means (without duplication), for any Person, the sum of the
following: (a) all liabilities, obligations, and indebtedness of such Person
which in accordance with GAAP should be classified upon such Person's balance
sheet as liabilities in respect of (i) money borrowed, including, without
limitation, the Principal Debt, (ii) obligations of such Person under Capital
Leases, (iii) obligations of such Person issued or assumed as the deferred
purchase price of property, all conditional sale obligations, and obligations
under any title retention agreement (but excluding trade accounts payable
arising in the ordinary course of business and deferred federal and state income
taxes), and (iv) all non-contingent obligations (and, for purposes of SECTIONS
8.10 and 9.4 and letters of credit, banker's acceptances and other similar
instruments issued to support Debt, all contingent obligations) of such Person
to reimburse any bank or other Person in respect of letters of credit, banker's
acceptances and similar instruments; (b) all obligations of the type referred to
in CLAUSES (a)(i) through (a)(iv) preceding of other Persons for the payment of
which such Person is responsible or liable as obligor, guarantor, or otherwise;
and (c) all obligations of the type referred to in CLAUSES (a)(i) through CLAUSE
(a)(iv) and CLAUSE (b) preceding of other Persons secured by any Lien on any
property or asset of such Person (whether or not such obligation is assumed by
such Person), the amount of such obligation being deemed to be the lesser of the
value of such property or assets or the amount of the obligation so secured. For
all purposes of this Agreement, Debt of any Person shall include the Debt of any
partnership or joint venture in which such Person is a general partner or a
joint venturer, unless such Debt is expressly made non-recourse to such Person.


                                       B-2                       SIXTH AMENDMENT
<PAGE>   24

     "DEBTOR RELIEF LAWS" means the Bankruptcy Code of the United States of
America and all other applicable liquidation, conservatorship, bankruptcy,
moratorium, rearrangement, receivership, insolvency, reorganization, fraudulent
transfer or conveyance, suspension of payments or similar Laws from time to time
in effect affecting the Rights of creditors generally.

     "DISTRIBUTION" for any Person means, with respect to any shares of any
capital stock or other equity securities issued by such Person, (a) the
retirement, redemption, purchase, or other acquisition for value of any such
securities, (b) the declaration or payment of any dividend on or with respect to
any such securities, and (c) any other payment by such Person with respect to
such securities.

     "ENVIRONMENTAL CLAIM" means any written notice, claim, demand, action,
suit, complaint, proceeding or other communication by any person alleging
liability or potential liability arising out of, relating to, based on or
resulting from (i) the presence, discharge, emission, release or threatened
release of any Hazardous Materials at any location, or (ii) circumstances
forming the basis of any violation or alleged violation of any Environmental Law
or Environmental Permit. "Environmental Law" means any applicable Law that
relates to (a) the condition or protection of air, groundwater, surface water,
soil, or other environmental media, (b) the environment, including natural
resources or any activity which affects the environment, (c) the regulation of
any pollutants, contaminants, wastes, substances, and Hazardous Substances,
including, without limitation, the Comprehensive Environmental Response,
Compensation, and Liability Act (42 U.S.C. Section 9601 et seq.) ("CERCLA"), the
Hazardous Materials Transportation Act (49 U.S.C. Section 1801 et seq.), the
Resource Conservation and Recovery Act (42 U.S.C. Section 6901 et seq.)
("RCRA"), the Clean Water Act (33 U.S.C. Section 1251 et seq.), the Clean Air
Act (42 U.S.C. Section 7401 et seq.), the Toxic Substances Control Act (15
U.S.C. Section 2601 et seq.), the Federal Insecticide, Fungicide, and
Rodenticide Act (7 U.S.C. Section 136 et seq.), the Safe Drinking Water Act (42
U.S.C. Section 201 and Section 300f et seq.) and the Rivers and Harbors Act (33
U.S.C. Section 401 et seq.), the Oil Pollution Act (33 U.S.C. Section 2701 et
seq.) and analogous state and local Laws, as any of the foregoing may have been
and may be amended or supplemented from time to time, and any analogous future
enacted or adopted Law, or (d) the Release or threatened Release of Hazardous
Substances.

     "ENVIRONMENTAL LIABILITIES" means all liabilities in connection with or
relating to the business, assets, presently or previously owned, leased or
operated property, activities (including, without limitation, off-site disposal)
or operations of the Borrower and each Subsidiary, whether vested or unvested,
contingent or fixed, actual or potential, known or unknown, which arise under or
relate to matters covered by Environmental Laws.

     "ENVIRONMENTAL PERMITS" means all permits, licenses, registrations, and
other governmental authorizations required for any of the Companies to conduct
its business and operations under Environmental Laws.

     "ERISA AFFILIATE" means any Person or trade or business (whether or not
incorporated) which is a member of Borrower's or any Company's controlled group
or affiliated service group with Borrower or any Company within the meaning of
Section 414(b), (c), (m) or (o) of the Code.

     "FINANCIAL STATEMENTS" means balance sheets, statements of operations,
statements of shareholders' investments, and statements of cash flows prepared
in accordance with GAAP, which


                                       B-3                       SIXTH AMENDMENT

<PAGE>   25

statements of operations and statements of cash flows shall be in comparative
form to the corresponding period of the preceding fiscal year, and which balance
sheets and statements of shareholders' investments shall be in comparative form
to the prior fiscal year-end figures.

     "FOREIGN PENSION PLAN" shall mean any plan that (including, without
limitation, any superannuation fund) or other similar program established or
maintained outside the United States by Borrower or any Company primarily for
the benefit of employees of Borrower or any Company residing outside the United
States, which plan, fund or other similar program provides, or results in,
retirement income, a deferral of income in contemplation of retirement or
payments to be made upon termination of employment, and which plan is not
subject to ERISA or the Code.

     "HAZARDOUS SUBSTANCE" means (a) any substance that is designated, defined
or classified as a hazardous waste, hazardous material, pollutant, contaminant
or toxic or hazardous substance under any Environmental Law, including without
limitation, any hazardous substance within the meaning of Section 101(14) of
CERCLA, (b) petroleum, oil, gasoline, natural gas, fuel oil, motor oil, waste
oil, diesel fuel, jet fuel, and other petroleum hydrocarbons, (c) regulated
asbestos and asbestos-containing materials in any form, (d) polychlorinated
biphenyls, or (e) urea formaldehyde foam.

     "LAWS" means all applicable statutes, laws, treaties, ordinances, tariff
requirements, rules, regulations, orders, writs, injunctions, decrees,
judgments, opinions, or interpretations of any Governmental Authority.

     "LEVERAGE RATIO" means and refers to, as of the last day of any fiscal
quarter of the Borrower, the ratio of (a) the aggregate amount of Consolidated
Debt as of such day, to (b) Consolidated EBITDA for the four immediately
preceding fiscal quarters (including such quarter).

     "LIEN" means and refers to any lien, mortgage, pledge, security interest,
charge, or encumbrance of any kind or any other type of preferential arrangement
that has the practical effect of creating a security interest (including any
conditional sale or other title retention agreement or any lease in the nature
thereof).

     "LITIGATION" means any action by or before any Governmental Authority.

     "MATERIAL ADVERSE EVENT" means any set of one or more circumstances or
events which, individually or collectively, result in any (a) material
impairment of the ability of the Borrower to perform any of its payment or other
material obligations under the Loan Documents or the ability of Administrative
Agent or any Bank to enforce any such obligations or any of their respective
Rights under the Loan Documents, or (b) material and adverse effect on the
business, properties, condition (financial or otherwise) or results of
operations of the Companies, in each case considered as a whole.

     "MOODY'S" means Moody's Investors Service, Inc. or any successor thereto.

     "MULTIEMPLOYER PLAN" means and refers to a "multiemployer plan" as defined
in Section 4001(a)(3) of ERISA or a "multiemployer pension plan" as defined in
Section 3(37) of ERISA or Section 414 of the Code, or any similar type of plan
established and regulated under the laws of any

                                       B-4                       SIXTH AMENDMENT


<PAGE>   26

foreign country, that is maintained for employees of the Companies or any ERISA
Affiliate of any Company.

     "NON-RECOURSE DEBT" means (a) Debt (other than Capital Lease Obligations)
of a special purpose Subsidiary created or acquired after the Closing Date
incurred in connection with the acquisition or construction by such Subsidiary
in the ordinary course of business of fixed assets used in the manufacture and
distribution of building products and (b) any renewals and refinancings of such
Debt; provided that (i) the holders of such Debt described in clauses (a) and
(b) agree that they will look solely to the fixed assets so acquired with such
Debt, (ii) any Liens securing such Debt are permitted pursuant to SECTION 5.10,
(iii) such Debt is not Debt, in whole or part, of any other Company, (iv) such
Debt is not secured by any Lien upon any property or assets of any other
Company, and (v) such Debt is not supported in any way by any other Company,
including any undertakings or guarantees, and provided further that no such Debt
of such Subsidiary shall be considered "Non-Recourse Debt" if (y) any default
with respect to such Debt would allow or require any other Debt which is owed by
such Subsidiary or one or more of the other Companies to be accelerated or
otherwise made payable in advance of its stated maturity, and (z) any other
Company owes Debt to such Subsidiary.

     "OBLIGATION" means all present and future indebtedness, liabilities, and
obligations, and all renewals and extensions thereof, or any part thereof, now
or hereafter owed by Borrower to Administrative Agent, or any Bank arising from,
by virtue of, or pursuant to any Loan Document, together with all interest
accruing thereon, fees, costs, and reasonable expenses (including, without
limitation, all reasonable attorneys' fees and expenses incurred in the
enforcement or collection thereof) payable under the Loan Documents.

     "OTHER CREDIT AGREEMENT" means the Revolving Credit Agreement dated as of
December 17, 1999 among Borrower, various lenders, and Wells Fargo Bank (Texas),
National Association, as administrative agent and various lenders and as may be
amended, extended, modified, or restated.

     "PLAN" means any pension plan as defined in Section 3(2) of ERISA, which is
maintained or contributed to by (or to which there is an obligation to
contribute of) the Companies or an ERISA Affiliate, and each such plan for the
five year period immediately following the latest date on which Companies or an
ERISA Affiliate maintained, contributed to or had an obligation to contribute to
such plan.

     "PRINCIPAL DEBT" means, on any date of determination, the aggregate unpaid
principal balance of all Borrowings under the Revolving Credit Facility.

     "REGULATION D" means Regulation D of the Board of Governors of the Federal
Reserve System, as amended.

     "REGULATION U" means Regulation U of the Board of Governors of the Federal
Reserve System, as amended.

     "REINCORPORATION MERGER" is defined in SECTION 5.11.

                                       B-5                       SIXTH AMENDMENT
<PAGE>   27

     "RELEASE" means any spilling, leaking, pumping, pouring, emitting,
emptying, discharging, injecting, escaping, leaching, dumping, disposal,
deposit, dispersal, migrating, or other movement into the air, ground, or
surface water, or soil.

     "REPORTABLE EVENT" shall have the meaning specified in Section 4043 of
ERISA or the regulations issued thereunder in connection with a Plan that is
subject to Title IV of ERISA, excluding events for which the notice requirement
is waived under subsections .22, .23, .25 and .27 of PBGC Regulation 4043.

     "REPRESENTATIVES" means representatives, officers, directors, employees,
attorneys, and agents.

     "RIGHTS" means rights, remedies, powers, privileges, and benefits.

     "S&P" means Standard & Poor's Ratings Services, a division of The McGraw
Hill Companies, Inc., a New York corporation.

     "SCHEDULE" means, unless specified otherwise, a schedule attached to this
Agreement, as the same may be supplemented and modified from time to time in
accordance with the terms of the Loan Documents.

     "SIGNIFICANT SUBSIDIARY" means, at any time, any Subsidiary that, together
with its Subsidiaries, (a) accounted for more than 5% of the revenue of the
Companies determined on a consolidated basis for the then most recently
completed fiscal year of the Borrower, or (b) was the owner of more than 5% of
the assets of the Companies determined on a consolidated basis at the end of
such fiscal year of the Borrower, all as shown in the case of (a) and (b) on the
consolidated financial statements of the Borrower and its Subsidiaries for such
fiscal year.

     "SUBORDINATED INDENTURE" means the Indenture dated as of March 19, 1996,
among the Borrower, as issuer, and State Street Bank and Trust Company, as
Trustee, as amended, pursuant to which the Borrower's Subordinated Notes were
issued.

     "SUBORDINATED NOTES" means the Borrower's Series B 10% Senior Subordinated
Notes, due in 2006.

     "SUCCESSOR CORPORATION" is defined in SECTION 5.11.

     "UNFUNDED CURRENT LIABILITY" means with respect to any Plan, the amount, if
any, by which the value of the accumulated plan benefits under the Plan
determined on a plan termination basis in accordance with actuarial assumptions
at such time consistent with those prescribed by the PBGC for purposes of
Section 4044 of ERISA, exceeds the fair market value of all plan assets
allocable to such liabilities under Title IV of ERISA (excluding any accrued but
unpaid contribution).

     "WHOLLY-OWNED" when used in connection with any Subsidiary shall mean a
Subsidiary of which all of the issued and outstanding shares of stock (except
shares required as directors' qualifying shares) shall be owned by Borrower or
one or more of its Wholly-owned Subsidiaries.

                                      B-6                        SIXTH AMENDMENT
<PAGE>   28

                                   EXHIBIT C

                                   ARTICLE 4

ARTICLE 4 REPRESENTATIONS AND WARRANTIES. To induce Banks to enter into this
Agreement and to make the loans herein provided for, Borrower hereby represents
and warrants to the Administrative Agent and to each Bank that:

     4.1 FINANCIAL CONDITION. The Current Financials present fairly the
consolidated financial condition of Borrower and its consolidated Subsidiaries,
and the consolidated results of their operations and cash flows, as of and for
the portion of the fiscal year ending on the date or dates thereof (subject only
to year-end audit adjustments). All such Financial Statements including the
related schedules and notes thereto, have been prepared in accordance with GAAP
applied consistently throughout the periods involved (except as approved by such
accountants or Responsible Officer, as the case may be, and as disclosed
therein) Neither Borrower nor any of its consolidated Subsidiaries had, as of
the dates of the consolidated balance sheets referred to above, any Contingent
Obligation, contingent liabilities, or liability for Taxes, long-term leases, or
unusual forward or long-term commitments, which are material to Borrower and its
consolidated Subsidiaries taken as a whole and are not reflected in the
foregoing statements or in the notes thereto and are required by GAAP to be so
reflected.

     4.2 NO CHANGE. Since September 30, 1999, there has been no material adverse
change in the business, operations, assets, or financial or other condition of
the Companies taken as a whole.

     4.3 CORPORATE EXISTENCE; COMPLIANCE WITH LAW. Each of (a) the Borrower and
its Significant Subsidiaries (i) is duly organized, validly existing, and in
good standing under the laws of the jurisdiction of its incorporation or
formation, as the case may be, and (ii) has the corporate, company or
partnership power, as the case may be, and authority and the legal right to own
and operate its property, to lease the property it operates, and to conduct the
business in which it is currently engaged, and (b) the Companies (i) is duly
qualified as a foreign corporation and in good standing under the Laws of each
jurisdiction where its ownership, lease, or operation of property or the conduct
of its business requires such qualification, except to the extent that failure
to be so qualified is not reasonably likely, in the aggregate, to be a Material
Adverse Event, and (ii) is in compliance with all Laws except to the extent that
the failure to comply therewith is not reasonably likely, in the aggregate, to
be a Material Adverse Event.

     4.4 CORPORATE POWER; AUTHORIZATION; ENFORCEABLE OBLIGATIONS. Borrower has
the corporate power and authority and the legal right to make, deliver, and
perform the Loan Documents and to borrow hereunder and has taken all necessary
corporate action to authorize the Borrowings on the terms and conditions of the
Loan Documents and to authorize the execution, delivery, and performance of the
Loan Documents. The execution, delivery, and performance of the Loan Documents
will not contravene any provision of the charter or bylaws. No approval,
consent, exemption or authorization of, filing with, or other act by, or in
respect of, any Governmental Authority, is necessary or required in connection
with the Borrowings hereunder or with the execution, delivery, performance,
validity, or enforceability of the Loan Documents. The Loan Documents have been
duly executed and delivered on behalf of Borrower and constitute legal, valid,
and binding obligations of Borrower enforceable against Borrower in accordance
with their

                                      C-1                        SIXTH AMENDMENT
<PAGE>   29


respective terms, except as enforceability may be limited by applicable Debtor
Relief Laws and by equitable principles regardless of whether considered in a
proceeding in equity or at law.

     4.5 No Legal Bar; No Contravention. The execution, delivery, and
performance of the Loan Documents, the Borrowings hereunder, and the use of the
proceeds thereof, will not (a) violate any Laws (including, without limitation,
Regulation U, the Securities Act of 1933 and the Securities Exchange Act of
1934), or any Contractual Obligation of any Company, or (b) conflict with or
result in a default under, any Contractual Obligation, judgment, injunction,
order, decree or other instrument binding upon any Company or result in or
require the creation or imposition of any Lien (other than Liens permitted in
accordance with SECTION 5.10) on any of its or their respective properties or
revenues pursuant to any Laws or Contractual Obligation.

     4.6 No Material Litigation. No Litigation, investigation, or proceeding of
or before any arbitrator or Governmental Authority is pending or, to the
knowledge of Borrower, threatened by or against any Company or against any of
its or their respective properties or revenues (a) with respect to the Loan
Documents or any of the transactions contemplated hereby or (b) which is
reasonably likely to constitute a Material Adverse Event.

     4.7 No Default. No Company is in default under or with respect to any
Contractual Obligation in any respect which could be a Material Adverse Event.
No Event of Default or Unmatured Event of Default has occurred and is
continuing.

     4.8 Ownership of Property; Liens. The Companies taken, as a whole, have
good and indefeasible title to all their material assets reflected in the
Current Financials as being owned by them (except as sold or otherwise disposed
of in the ordinary course of business after the date of such Current Financials)
free of any Lien, except Liens permitted in accordance with SECTION 5.10.

     4.9 Taxes. Each of the Companies has filed or caused to be filed all Tax
returns which to the knowledge of Borrower are required to be filed (except for
state and local Tax returns where such failure to qualify and such failure to
file is not reasonably likely, in the aggregate for all such jurisdictions, to
be a Material Adverse Event), and has paid all Taxes shown to be due and payable
on said returns or on any assessments made against it or any of its property and
all other Taxes, fees or other charges imposed on it or any of its property by
any Governmental Authority (other than those the amount or validity of which is
currently being contested in good faith by appropriate proceedings and with
respect to which reserves in conformity with GAAP have been provided on the
books of the appropriate Companies, as the case may be, and those that could not
reasonably be expected to be a Material Adverse Event); and no Tax liens have
been filed and, to the knowledge of Borrower, no claims are being asserted with
respect to any such Taxes, fees or other charges which, in either case, is
reasonably likely to be a Material Adverse Event.

     4.10 Federal Regulations. No Company is engaged or will engage, principally
or as one of its important activities, in the business of extending credit for
the purpose of "purchasing" or "carrying" any "margin stock" within the
respective meanings of each of the quoted terms under Regulation U as now and
from time to time hereafter in effect. No part of the proceeds of any Borrowings
hereunder will be used for any purpose which violates, or results in a violation
of, the provisions of the Regulations of such Board of Governors. "Margin Stock"
(as defined in Regulation U) constitutes less than 25% of those assets of the
Companies which are subject to any limitation on sale, pledge, or other
restriction hereunder.

                                      C-2                        SIXTH AMENDMENT
<PAGE>   30


          4.11 Compliance with ERISA.

          (i) Each Plan (and each related trust, insurance contract or fund) is
     in substantial compliance with its terms and with all applicable laws,
     including ERISA and the Code; each Plan (and each related trust, if any)
     which is intended to be qualified under Section 401(a) of the Code has
     received a determination letter from the Internal Revenue Service to the
     effect that it meets the requirements of Sections 401(a) and 501(a) of the
     Code; no Reportable Event has occurred; no Plan which is Multiemployer Plan
     is insolvent or in reorganization; no Plan has an Unfunded Current
     Liability; no Plan (which is not a Multiemployer Plan) which is subject to
     Section 412 of the Code or Section 302 of ERISA has an accumulated funding
     deficiency, within the meaning of such sections of the Code or ERISA, or
     has applied for or received a waiver of an accumulated funding deficiency
     or an extension of any amortization period, within the meaning of Section
     412 of the Code or Section 303 or 304 of ERISA; all contributions required
     to be made with respect to a Plan have been timely made; neither any
     Company nor any ERISA Affiliate has incurred any material liability to, or
     on account of, a Plan pursuant to Sections 406, 409, 502(i), 502(l), 515,
     4062, 4063, 4064, 4069, 4201, 4204 or 4212 of ERISA or Sections 401(a)(29),
     4971 or 4975 of the Code or expects to incur any such material liability
     under any of the foregoing sections with respect to any Plan; no condition
     exists which presents a material risk to any Company or any ERISA Affiliate
     of incurring a material liability to or on account of a Plan pursuant to
     the foregoing provisions of ERISA and the Code; no proceedings have been
     instituted to terminate or appoint a trustee or administer any Plan which
     is subject to Title IV of ERISA; no action, suit, proceeding, hearing,
     audit or investigation with respect to the administration, operation or the
     investment of assets of any Plan (other than routine claims for benefits)
     is pending, expected or threatened that could reasonably be expected to be
     a Material Adverse Event; using actuarial assumptions and computation
     methods consistent with Part 1 of subtitle E of Title IV of ERISA, the
     aggregate liabilities of any Company and its ERISA Affiliates to all Plans
     which are Multiemployer Plans in the event of a complete withdrawal
     therefrom, as of the close of the most recent fiscal year of each Plan,
     would not exceed $25,000,000; each group health plan (as defined by Section
     607(1) of ERISA or Section 4980B(g)(2) of the Code) which covers or has
     covered employees or former employees of Companies or any ERISA Affiliate
     has at all times been operated in material compliance with the provisions
     of Part 6 of subtitle B of Title I of ERISA and Section 4980B of the Code;
     no lien imposed under the Code or ERISA on the assets of any Company or any
     ERISA Affiliate exists or is likely to arise on account of any Plan and
     neither any Company nor any ERISA Affiliate maintains or contributes to any
     employee welfare benefit plan (as defined in Section 3(1) of ERISA) which
     provides benefits to retired employees or other former employees (other
     than as required by Section 601 of ERISA) or any Plan the obligations with
     respect to which could reasonably be expected, either individually or in
     the aggregate, to cause a Material Adverse Event.

          (ii) Each Foreign Pension Plan, if any, has been maintained in
     substantial compliance with its terms and with the requirements of any and
     all applicable laws, statutes, rules, regulations and orders and has been
     maintained, where required, in good standing with applicable regulatory
     authorities, except where failure to do so could not reasonably be expected
     to be a Material Adverse Event. All contributions required to be made with
     respect to a Foreign Pension Plan have been timely made, except the failure
     of which to make could not reasonably be expected to be a Material Adverse
     Event. Neither any Company nor its subsidiaries has incurred any obligation
     in connection with the termination of or withdrawal from any Foreign
     Pension Plan, except such obligation that could not reasonably be expected
     to be a Material Adverse Event. The present value of the accrued benefit
     liabilities (whether or not vested) under each Foreign Pension Plan,
     determined as of the end of the

                                      C-3                        SIXTH AMENDMENT
<PAGE>   31

Borrower's most recently ended fiscal year on the basis of actuarial
assumptions, each of which is reasonable, did not exceed the current value of
the assets of such Foreign Pension Plan allocable to such benefit liabilities,
except if any such excess could not reasonably be expected to be a Material
Adverse Event.

     4.12 Investment Company Act, etc. None of the Borrower, any Person
controlling the Borrower, or any Subsidiary, is an "Investment Company" within
the meaning of the Investment Company Act of 1940. None of the Companies is
subject to regulation under (i) the Public Utility Holding Company Act of 1935,
(ii) the Federal Power Act, (iii) the Interstate Commerce Act, (iv) any state
public utilities code, or (v) any Federal or state statute or regulation,
limiting, in the case of CLAUSES (iii), (iv) AND (v), its ability to incur Debt
for borrowed money.

     4.13 Environmental Matters. Except as to matters which, individually, or in
the aggregate, are not reasonably likely to result in a Material Adverse Event,

          (a) The Companies have obtained all Environmental Permits with respect
     to the business in which they are engaged (the "BUSINESS") and with respect
     to the facilities and properties owned, leased, or operated by the
     Companies (the "PROPERTIES"), and the Business and all operations at the
     Properties are in compliance with all Environmental Permits and are
     otherwise in compliance with all Environmental Laws;

          (b) No Company has received any Environmental Claim with respect to
     any of the Properties or the Business or otherwise, nor does Borrower have
     knowledge or reason to believe that any such Environmental Claim will be
     received or is threatened; and

          (c) There are no past or present actions, activities, events,
     conditions, or circumstances, including, without limitation, the Release,
     threatened Release, emission, discharge, generation, treatment, storage, or
     disposal of Hazardous Substances at any location, that could reasonably be
     expected to give rise to liability of any Company under any Environmental
     Law or any contract or agreement.

     4.14 Year 2000 Compliance. Borrower has (i) initiated a review and
assessment of all areas within its and each of its Subsidiaries' business and
operations (including those affected by suppliers and vendors) that could be
materially adversely affected by the "Year 2000 Problem" (that is, the risk that
computer applications used by the Borrower or any of its Subsidiaries (or its
suppliers and vendors) may be unable to recognize and perform properly
date-sensitive functions involving certain dates prior to and any date after
December 31, 1999), (ii) developed a plan and time line for addressing the Year
2000 Problem on a timely basis, and (iii) to date, implemented in all material
respects that plan in accordance with that timetable.

     4.15 Purpose of Facility. Borrower will use all proceeds of Borrowings for
one or more of the following purposes: (i) to repurchase Borrower's Subordinated
Notes, (ii) to repurchase Borrower's common stock, and (iii) for working capital
and for general corporate purposes.

     4.16 Pari Passu Obligations; Senior Indebtedness. The claims and rights of
the Banks and the Administrative Agent against Borrower under this Agreement and
the Notes will not be subordinate to, and will rank at least pari passu with,
the claims and rights of any other unsecured creditors of Borrower with respect
to indebtedness which is not in any manner subordinated in right


                                      C-4                        SIXTH AMENDMENT
<PAGE>   32

of payment or security in any respect to the Obligation. The Obligation is
permitted in accordance with the terms of the Subordinated Indenture and
constitutes "Designated Senior Indebtedness" and "Senior Indebtedness" as such
terms are defined in the Subordinated Indenture. The Borrower hereby
specifically designates the Obligation as "Designated Senior Indebtedness" for
purposes of the Subordinated Indenture. This Agreement and the other Loan
Documents represent a "Bank Credit Facility" for purposes of the Subordinated
Indenture. So long as the Subordinated Indenture is in full force and effect,
all Borrowings are and will be made in compliance with the restrictions
contained in the Subordinated Indenture.

     4.17 Full Disclosure. All information furnished to the Banks in writing
prior to the date hereof in connection with the transactions contemplated hereby
does not, collectively, contain any misstatement of a material fact or omit to
state a fact necessary to make the statements contained therein, in the light of
the circumstances under which they were made, not misleading in any material
respect on and as of the date hereof.


                                      C-5                        SIXTH AMENDMENT
<PAGE>   33

                                   EXHIBIT D

                                   ARTICLE 5

ARTICLE 5 COVENANTS. Borrower covenants and agrees (and agrees to cause each
other Company to the extent any covenant is applicable to such Company) to
perform, observe, and comply with each of the following covenants, from the
Closing Date and so long thereafter as Banks are committed to fund Borrowings
under this Agreement and thereafter until the payment in full of the Principal
Debt and payment in full of all interest, fees, and other amounts of the
Obligation then due and owing, unless Borrower receives a prior written consent
to the contrary by Administrative Agent as authorized by Majority Banks:

     5.1 Financial Statements. Borrower shall furnish to the Administrative
Agent in Sufficient Quantity for each Bank:

          (a) As soon as available, but in any event within 95 days after the
     end of each fiscal year of Borrower, Financial Statements, showing the
     consolidated financial condition and results of operation calculated for
     Borrower and its consolidated Subsidiaries as at the end of such year,
     certified without a "going concern" or like qualification or exception, or
     qualification arising out of the scope of the audit, by independent
     certified public accountants of a nationally recognized standing; and

          (b) As soon as available, but in any event not later than 50 days
     after the end of each of the first three quarterly-periods of each fiscal
     year of Borrower, the unaudited Financial Statements showing the
     consolidated financial condition and results of operation calculated for
     Borrower and its consolidated Subsidiaries as at the end of each such
     quarter and the portion of the fiscal year through such date, certified by
     a Responsible Officer (subject to year-end audit adjustments);

all such Financial Statements to be prepared in accordance with GAAP applied
consistently throughout the periods reflected therein (except as approved by
such accountants or Responsible Officer, as the case may be, and disclosed
therein).

     5.2 Certificates; Other Information. Borrower shall furnish to the
Administrative Agent in sufficient quantity for each Bank:

          (a) Concurrently with the delivery of the Financial Statements
     referred to in SECTION 5.1(a) and (b), a certificate of a Responsible
     Officer (i) stating that, to the best of such officer's knowledge, the
     Companies during such period have observed or performed all of the
     covenants and other agreements applicable to such Companies, and that such
     officer has obtained no knowledge of any Event of Default or Unmatured
     Event of Default, except as specified in such certificate, and (ii) showing
     in reasonable detail the calculations supporting such statement in respect
     of SECTION 5.16;

          (b) Within five Business Days after the same are sent, copies of all
     Financial Statements and annual reports which Borrower sends to its
     stockholders, and within five days

                                      D-1                        SIXTH AMENDMENT
<PAGE>   34


after the same are filed, copies of all Financial Statements and reports which
Borrower may make to, or file with, the Securities and Exchange Commission or
any successor; and

          (c) Promptly, such additional financial and other information as any
     Bank may from time to time reasonably request.

     5.3 Payment of Obligations. Each Company shall pay, discharge, or otherwise
satisfy all material taxes, assessments and governmental charges or levies
imposed upon it or upon its income or profits, or upon any property belonging to
it, prior to the date on which penalties attach thereto, and all lawful material
claims which, if unpaid, might become a Lien upon the property of such Company;
provided that none of the Companies shall be required to pay any such tax,
assessment, charge, levy or claim (i) the payment of which is being contested in
good faith by appropriate proceedings and reserves in conformity with GAAP with
respect thereto have been provided on the books of the applicable Companies, as
the case may be, (ii) not yet delinquent or (iii) the non-payment of which, if
taken in the aggregate, could not reasonably be expected to be a Material
Adverse Event.

     5.4 Conduct of Business and Maintenance of Existence. None of the Companies
shall engage in any business if, as a result thereof, the business of the
Companies, taken as a whole, would not be substantially the same as that
conducted on the Closing Date. For purposes of this Section 5.4, the business of
the manufacture and distribution of building products shall be deemed to be
within the types of business conducted by the Companies on the Closing Date.
Each Company shall preserve, renew and keep in full force and effect its
corporate or partnership existence, as the case may be, and take all reasonable
action to maintain all rights, privileges, and franchises necessary or desirable
in the normal conduct of its business (other than those rights, privileges, and
franchises the failure of which to maintain could not reasonably be expected to
be a Material Adverse Event); provided that nothing in this Section shall
prohibit (i) the merger of a Subsidiary into the Borrower or the merger or
consolidation of a Subsidiary with or into another Person, (ii) the sale or
other disposition (whether by merger or otherwise) of the capital stock or
assets of any Subsidiary, if such transaction complies with the provisions of
SECTION 5.11 or (iii) the termination of the corporate existence of any
Subsidiary if the Borrower in good faith determines that such termination is in
the best interest of the Borrower and is not materially disadvantageous to the
Banks and if, with respect to each of the foregoing CLAUSES (i), (ii) and (iii),
after giving effect thereto, no Event of Default or Unmatured Event of Default
shall have occurred and be continuing. Company shall comply with all Contractual
Obligations and Laws, except to the extent that the failure to comply therewith
would not, in the aggregate, be a Material Adverse Event.

     5.5 Maintenance of Property; Insurance. Each Company shall (i) keep all
property useful and necessary in its business in good working order and
condition, except when failure to do so could reasonably be expected to be a
Material Adverse Event; (ii) maintain with financially sound and reputable
insurance companies insurance on all its property in at least such amounts and
against at least such risks as are usually insured against in the same general
area by companies engaged in the same or a similar business; and (iii) furnish
to each Bank, upon written request, full information as to the insurance
carried.

     5.6 Inspection of Property; Books and Records; Discussions. Each Company
shall (i) keep proper books of record and account in which full, true, and
correct entries in conformity with GAAP and all Laws shall be made of all
dealings and transactions in relation to its business and


                                      D-2                        SIXTH AMENDMENT
<PAGE>   35

activities; and (ii) permit representatives of any Bank to visit and inspect any
of its properties at any reasonable time and as often as may reasonably be
desired, and to discuss the business, operations, properties, and financial and
other condition of Borrower and its Subsidiaries with officers and employees of
the Companies and with its independent certified public accountants.

     5.7 Notices. Borrower shall promptly give notice to Administrative Agent
and each bank of:

          (a) The occurrence of any Event of Default or Unmatured Event of
     Default;

          (b) Any (i) default or event of default under any Contractual
     Obligation of any Company or (ii) Litigation, investigation, or proceeding
     which may exist at any time between any Company and any Governmental
     Authority, which in either case, is reasonably likely to be a Material
     Adverse Event;

          (c) Any Litigation or proceeding affecting any Company (i) in which
     the potential loss not covered by insurance could reasonably be expected to
     be $50,000,000 or more or (ii) in which injunctive or similar relief is
     sought which is reasonably likely to be a Material Adverse Event;

          (d) The occurrence of a Material Adverse Event.

Each notice pursuant to this Section shall be accompanied by a statement of a
Responsible officer setting forth details of the occurrence referred to therein
and stating what action Borrower proposes to take with respect thereto.

     5.8 Year 2000 Compliance. Borrower will promptly notify the Administrative
Agent in the event Borrower discovers or determines that any computer
application (including those of its suppliers and vendors) that is material to
its or any of its Subsidiaries' business and operations will not be Year 2000
compliant on a timely basis, except to the extent that such failure is not
reasonably expected to be a Material Adverse Event.

     5.9 Compliance with Laws. The Companies will comply with all laws, rules,
regulations, orders, writs, judgments, injunctions, decrees or awards to which
it may be subject, including laws relating to pension funds and Environmental
Laws, which, if violated, could reasonably be expected to be a Material Adverse
Event.

     5.10 Limitation on Liens. The Companies shall not, directly or indirectly,
create, incur, assume, or suffer to exist any Lien upon any of its property,
assets, or revenues, whether now owned or hereafter acquired, except:

          (a) Liens for Taxes not yet due or which are being contested in good
     faith and by appropriate proceedings if adequate reserves with respect
     thereto are maintained on the books of the appropriate Companies in
     accordance with GAAP;

          (b) carriers', warehousemen's, mechanics', materialmen's, repairmen's,
     or other like Liens arising in the ordinary course of business which are
     not overdue for a period of


                                      D-3                        SIXTH AMENDMENT
<PAGE>   36

more than 30 days or which are being contested in good faith and for which
adequate reserves in accordance with GAAP, if any, have been set aside;

          (c) pledges or deposits in connection with workmen's compensation,
     unemployment insurance, and other social security legislation;

          (d) easements, rights-of-way, mineral reservations, restrictions, and
     other similar encumbrances, defects or irregularities of title which do not
     in any case (i) secure Debt or (ii) materially detract from the value of
     the property subject thereto or interfere with the ordinary conduct of the
     business of the Companies;

          (e) Liens (other than any Lien imposed by ERISA) incurred or deposits
     made in the ordinary course of business in connection with workers'
     compensation, unemployment insurance, and other types of social security;

          (f) statutory or common law banker's liens in the nature of rights of
     setoff arising in the ordinary and usual course of business of the
     Companies;

          (g) any Lien upon assets existing at the time of acquisition thereof
     or to secure the payment of all or any part of the purchase price thereof
     or to secure any Debt incurred prior to, at the time of, or within 90 days
     after, the acquisition of such assets for the purpose of financing all or
     any part of the purchase price thereof, so long as such Lien is limited to
     the assets so acquired;

          (h) Liens securing Acquired Indebtedness if such Liens secured such
     Acquired Indebtedness at the time such Acquired Indebtedness becomes an
     obligation of any Company and such Liens were not incurred in connection
     with, or in anticipation of, such Acquired Indebtedness becoming an
     obligation of a Company; provided, however, that such Liens shall not
     extend to or cover any assets of any Company other than the assets that
     secured the Acquired Indebtedness prior to such Acquired Indebtedness
     becoming an obligation of a Company;

          (i) Liens arising out of the refinancing, extension, renewal or
     refunding of any Debt secured by any Lien permitted by the foregoing
     CLAUSES (g) and (h), provided that such Debt is not increased and is not
     secured by any additional assets;

          (j) Liens in the nature of deposits with a trustee or other depository
     in connection with a redemption, payment, acquisition, repurchase or
     retirement for value of the Subordinated Notes; and

          (k) Liens, in addition to those otherwise specified in this Section,
     which in the aggregate do not secure obligations in excess of 10% of
     Consolidated Net Worth.

     5.11 Prohibition of Fundamental Changes. No Company shall, directly or
indirectly, enter into any transaction of merger or consolidation or
amalgamation, or liquidate, wind up, or dissolve itself (or suffer any
liquidation or dissolution), or convey, transfer, lease or otherwise dispose of,
whether in one transaction or a series of transactions, all or substantially all
of its assets, whether now owned or hereafter acquired, to or in favor of any
Person, except that:

                                      D-4                        SIXTH AMENDMENT
<PAGE>   37

          (a) Any corporation (including any Subsidiary of Borrower) may be
     merged or consolidated with or into Borrower (provided that, Borrower shall
     be the continuing or surviving corporation) or with any one or more
     Subsidiaries of Borrower (provided that, (i) if any such transaction shall
     be between a corporation (including any Subsidiary of Borrower) and a
     Wholly-owned Subsidiary of Borrower, the continuing or surviving
     corporation shall be a Wholly-owned Subsidiary of Borrower and (ii)
     immediately after each such transaction and after giving effect thereto,
     Borrower is in compliance with this Agreement and no Event of Default or
     Unmatured Event of Default shall have occurred and be continuing);

          (b) Borrower may be merged into a corporation ( the "SUCCESSOR
     CORPORATION") solely for the purpose of changing the Borrower's domicile (a
     "REINCORPORATION MERGER") as provided in Rule 145 (a) (2) of the Securities
     Act of 1933, as amended from time to time, and such Successor Corporation
     shall:

               (i) immediately after giving effect to such merger
          have-then-effective ratings (or implied ratings) published by Moody's
          and S&P applicable to such Successor Corporation's senior, unsecured,
          non-credit-enhanced, long term indebtedness for borrowed money, which
          ratings shall be Baa3 or higher (if assigned by Moody's) or BBB- or
          higher (if assigned by S&P);

               (ii) be a corporation organized and existing under the laws of
          the United States of America, any state thereof or the District of
          Columbia, and shall expressly assume, by amendment to this Agreement
          acceptable to the Majority Banks executed by the Borrower and such
          Successor Corporation and delivered to the Administrative Agent, the
          due and punctual payment of the principal of, and interest on, the
          Borrowings made hereunder and other amounts payable under this
          Agreement and the performance and observance of every covenant hereof
          on the part of the Borrower to be performed or observed and this
          Agreement shall remain in full force and effect;

               (iii) immediately after giving effect to such merger, no Event of
          Default and no Unmatured Event of Default, shall have occurred and be
          continuing;

               (iv) immediately after giving effect to such merger, all of the
          representations and warranties of the Borrower set forth in the Loan
          Documents shall be true and correct in all material respects as if
          made by such Successor Corporation; and

               (v) the Borrower shall have delivered to the Administrative Agent
          a certificate signed by a Responsible Officer and a written opinion of
          counsel satisfactory to the Administrative Agent (who may be counsel
          to the Borrower), each stating that such transaction and such
          amendment to this Agreement comply with this Section and that all
          conditions precedent herein provided for relating to such transaction
          have been satisfied; and

          (c) any Subsidiary may enter into any transaction of merger or
     consolidation or amalgamation, or liquidate, wind up, or dissolve itself
     (or suffer any liquidation or dissolution), or convey, transfer, lease or
     otherwise dispose of, whether in one transaction or a series of
     transactions, all or substantially all of its assets, whether now owned or


                                      D-5                        SIXTH AMENDMENT
<PAGE>   38
     hereafter acquired, to or in favor of any Person; provided that,
     immediately after each such transaction and after giving effect thereto,
     Borrower is in compliance with this Agreement and no Event of Default and
     no Unmatured Event of Default shall have occurred and be continuing.

     5.12 Subsidiary Debt. No Subsidiary of Borrower will incur or at any time
be liable with respect to any Debt, or to issue or have outstanding any
preferred stock, except: (i) Debt or preferred stock outstanding on the date
hereof; (ii) Debt or preferred stock of a Subsidiary issued to and held by the
Company or a Wholly-Owned Subsidiary; (iii) Debt or preferred stock of any
Person existing at the time such Person becomes a Subsidiary of the Company and
not created in contemplation of such event; (iv) refinancing, extension, renewal
or refunding of any Debt or preferred stock permitted by the foregoing clauses
(i) through (iii); (v) Non-Recourse Debt; and (vi) Debt or preferred stock in
addition to that set forth in clauses (i) through (v), if, after giving effect
thereto, the aggregate outstanding principal amount of Debt of all Subsidiaries
pursuant to this clause (vi) does not exceed 10% of Consolidated Net Worth.

     5.13 Subsidiary Dividends. No Company shall be a party to or enter into any
agreement, instrument or other document which prohibits or restricts in any way,
or to otherwise, directly or indirectly, create or cause or suffer to exist or
become effective any encumbrance or restriction on the ability of any Subsidiary
of Borrower to (i) pay dividends or make any other distributions in respect of
its capital stock or any other equity interest or participation in any
Subsidiary, or pay or repay any Debt owed to Borrower or any Subsidiary, (ii)
make loans or advances to Borrower or (iii) transfer any of its properties or
assets to Borrower or any Subsidiary (subject to the rights of any holder of a
Lien on any such properties or assets which Lien is a Permitted Lien) other than
(a) customary restrictions contained in purchase and sale agreements with
respect to the sale of assets or Capital Stock that relate to such assets or
Capital Stock for the period from and after the date of the execution and
delivery of such purchase and sale agreement until the date of the closing
thereunder, (b) restrictions on Subsidiaries not Wholly-owned by Borrower that
are acquired or created after the Closing Date, and (c) encumbrances or
restrictions binding upon any Person at the time such Person becomes a
Subsidiary (unless the agreement creating such encumbrance or restriction was
entered into in connection with, or in contemplation of, such Person becoming a
Subsidiary) provided that such encumbrances or restrictions shall not encumber
or restrict any assets of the Borrower or its other Subsidiaries other than such
Subsidiary.

     5.14 Compliance with ERISA. As soon as possible and, in any event, within
ten (10) days after any Company or any ERISA Affiliate knows or has reason to
know of the occurrence of any of the following that will or could reasonably be
expected to be a Material Adverse Event, Borrower will deliver to each of the
Banks a certificate of the chief financial officer of the Borrower setting forth
the full details as to such occurrence and the action, if any, that a Company or
any ERISA Affiliate is required or proposes to take, together with any notices
required or proposed to be given or filed by a Company, the Plan administrator
or any ERISA Affiliate to or with the PBGC or any other governmental agency, or
a Plan participant or any notices received by any Company or such ERISA
Affiliate from the PBGC or any other government agency, or a Plan participant
with respect thereto: that a Reportable Event has occurred (except to the extent
that Borrower has previously delivered to the Banks a certificate and notices
(if any) concerning such event); that a contributing sponsor (as defined in
Section 4001(a)(13) of ERISA) of a Plan subject to Title IV of ERISA is subject
to the advance reporting requirement of PBGC Regulation Section 4043.61 (without
regard to subparagraph (b)(1) thereof), and an event described in subsection
 .62, .63, .64, .65, .66, .66, .67

                                      D-6                        SIXTH AMENDMENT
<PAGE>   39

or .68 of PBGC Regulation Section 4043 is reasonably expected to occur with
respect to such Plan within the following 30 days; that an accumulated funding
deficiency, within the meaning of Section 412 of the Code or Section 302 of
ERISA, has been incurred or an application may be or has been made for a waiver
or modification of the minimum funding standard (including any required
installment payments) or an extension of any amortization period under Section
412 of the Code or Section 303 or 304 of ERISA with respect to a Plan; that any
contribution required to be made with respect to a Plan or Foreign Pension Plan
has not been timely made; that a Plan has been or may be terminated,
reorganized, partitioned or declared insolvent under Title IV of ERISA; that a
Plan has an Unfunded Current Liability; that proceedings may be or have been
instituted to terminate or appoint a trustee to administer a Plan which is
subject to Title IV of ERISA; that a proceeding has been instituted pursuant to
Section 515 of ERISA to collect a delinquent contribution to a Plan; that any
Company or any ERISA Affiliate will or may incur any material liability with
respect to, or on account of, the termination of or withdrawal from a Plan under
Sections 4062, 4063, 4064, 4069, 4201, 4204, or 4212 of ERISA or with respect to
a Plan under Sections 401(a)(29), 4971, 4975 or 4980 of the Code or Section 409,
502(i) or 502(l) of ERISA; or that Companies or an ERISA Affiliate will or may
incur a material liability with respect to a group health as defined in Section
607(1) of ERISA or under Section 4980B of the Code; or that a Company or an
ERISA Affiliate will or may incur any material liability pursuant to any
employee welfare benefit plan (as defined in Section 3(1) of ERISA) that
provides benefits to retired employees or other former employees (other than as
required by Section 601 of ERISA) or any Plan or any Foreign Pension Plan.
Companies will deliver to each of the Banks copies of any records, documents or
other information that must be furnished to the PBGC with respect to any Plan
pursuant to Section 4010 of ERISA. At the written request of any Bank, Companies
will also deliver to such Banker a complete copy of the annual report (and
related financial and actuarial statements and opinions and other supporting
statements, certifications, schedules and information) required to be filed with
the Internal Revenue Service on the Form 5500 series. In addition to any
certificates or notices delivered to the Banks pursuant to the first sentence
hereof, copies of any records, documents or other information required to be
furnished to the PBGC or any other governmental agency, and any material notices
received by Companies or any ERISA Affiliate with respect to any Plan shall be
delivered to the Banks no later than ten (10) days after the date such records,
documents and/or information has been furnished to the PBGC or any other
governmental agency or such notice has been received by Companies or the ERISA
Affiliate, as applicable. Each of the Companies shall insure that all Foreign
Pension Plans administered by it or into which it makes payments obtains or
retains (as applicable) registered status under and as required by applicable
law and is administered in a timely manner in all respects in compliance with
all applicable laws except where the failure to do any of the foregoing could
not, either individually or in the aggregate, reasonably be expected to cause a
Material Adverse Event.

     No Company or ERISA Affiliate shall, directly or indirectly, (a) terminate
any Plan so as to result in any liability to PBGC; (b) engage in any "prohibited
transaction" (as defined in Section 406 of ERISA or Section 4975 of the Code)
involving any Plan which would result in a liability for an excise tax or civil
penalty in connection therewith; (c) incur or suffer to exist any "accumulated
funding deficiency" (as defined in Section 302 of ERISA), whether or not waived,
involving any Plan; (d) allow or suffer to exist any event or condition, which
presents a risk of incurring a material liability to PBGC by reason of
termination of any such Plan; or (e) incur or likely incur withdrawal liability
under a Multiemployer Plan or incur liability respecting the insolvency or
reorganization of a Multiemployer Plan; and, in each of CLAUSES (a) through (e)
hereof, such liability, deficiency or risk, as the case may be, when taken
together with all other contingencies and facts relating to the Companies under
this Section, is a Material Adverse Event.

                                      D-7                        SIXTH AMENDMENT
<PAGE>   40

     5.15 Assignment. Borrower shall not assign or transfer any of its Rights,
duties, or obligations under any of the Loan Documents except pursuant to a
Reincorporation Merger in accordance with SECTION 5.11(b).

     5.16 Financial Covenants.

          (a) Leverage Ratio. Borrower shall not permit, as of the final day of
     any fiscal quarter of the Borrower, the ratio of: (i) the aggregate amount
     of Consolidated Debt as of such day, to (ii) Adjusted Consolidated EBITDA
     for the four (4) immediately preceding fiscal quarters, including the
     quarter then ended, to be greater than 3.00:1.00.

          (b) Consolidated Net Worth. Borrower shall not permit, at any time its
     Consolidated Net Worth to be less than Six Hundred Million Dollars
     ($600,000,000).

          (c) Interest Coverage Ratio. Borrower shall not permit, as of the last
     day of any fiscal quarter of the Borrower, the ratio of: (i) Adjusted
     Consolidated EBITDA for the twelve-month period ending on such date to (ii)
     Consolidated Interest Expense for such period to be less than 3.00 to 1.00.

     5.17 Transactions with Affiliates. No Company shall enter into any material
transaction with any of its Affiliates (other than transactions between or among
Companies), other than transactions in the ordinary course of business and upon
fair and reasonable terms not materially less favorable than such Company could
obtain or could become entitled to in an arm's-length transaction with a Person
that was not its Affiliate.

                                      D-8                        SIXTH AMENDMENT
<PAGE>   41

                                   EXHIBIT E

                                  SECTION 7.1

     7.1 EVENTS OF DEFAULT. The term "EVENT OF DEFAULT" means the occurrence of
any one or more of the following events:

          (a) Payment of Obligation. Borrower shall fail to pay all or any part
     of the principal of the Obligation when the same becomes due (whether by
     its terms, by acceleration, or as otherwise provided in the Loan Documents)
     or shall fail to pay any other part of the Obligation (including, without
     limitation, interest and fees) within three Business Days of when the same
     becomes due (whether by its terms, by acceleration, or as otherwise
     provided in the Loan Documents).

          (b) Misrepresentation. Any representation or warranty made or deemed
     made by any Company in any Loan Document shall prove to have been incorrect
     in any respect material to the Companies taken as a whole on or as of the
     date made or deemed made.

          (c) Covenants. The failure or refusal of Borrower (and, if applicable,
     any other Company) to punctually and properly perform, observe, and comply
     with:

               (i) Any covenant, agreement, or condition contained in SECTIONS
          5.7 AND 5.10 through 5.17; and

               (ii) Any other covenant, agreement, or condition contained in any
          Loan Document (other than the covenant to pay the Obligations
          addressed in SECTION 7.1(a) or the covenants addressed in SECTION
          7.1(c)(i)) and such failure or refusal shall continue unremedied for a
          period of 30 days after notice thereof shall have been given to the
          Borrower by the Administrative Agent or any Bank.

          (d) Default Under Other Debt. An Event of Default as defined in the
     other Credit Agreement shall occur or the Companies shall (i) default in
     any payment of principal of or interest on any Debt (other than the
     Obligation), beyond the period of grace (not to exceed 30 days), if any,
     provided in the instrument or agreement under which such Debt was created;
     provided that, such Debt shall be in the amount of $50,000,000 or more; or
     (ii) default in the observance or performance of any other agreement or
     condition relating to any such Debt or contained in any instrument or
     agreement evidencing, securing, or relating thereto, or any other event
     shall occur or condition exist, the effect of which default or other event
     or condition is to cause, or to permit the holder or holders of such Debt
     (or a trustee or agent on behalf of such holder or holders) to cause, with
     the giving of notice if required, such Debt or other indebtedness to become
     due prior to its stated maturity.

          (e) Debtor Relief. Any Company (a) voluntarily seeks, consents to, or
     acquiesces in the benefit of any Debtor Relief Law, other than as a
     creditor or claimant, (b) becomes a party to or is made the subject of any
     proceeding provided for by any Debtor Relief Law, other than as a creditor
     or claimant, that could suspend or otherwise adversely affect the Rights of
     Administrative Agent or any Bank granted in the Loan Documents (unless, in
     the

                                      E-1                        SIXTH AMENDMENT
<PAGE>   42

event such proceeding is involuntary, such proceeding remains undismissed,
undischarged, or unbonded for a period of 60 days); and (c) any Company shall
generally not, or shall be unable to, or shall admit in writing its inability
to, pay its debts as they become due.

          (f) Attachment. There shall be commenced against any Company any case,
     proceeding, or other action seeking issuance of a warrant of attachment,
     execution, distraint, or similar process against all or any substantial
     part of its assets which results in the entry of an order for any such
     relief which shall not have been vacated, discharged, stayed, or bonded
     pending appeal within 60 days from the entry thereof; or any Company shall
     take any action in furtherance of, or indicating its consent to, approval
     of, or acquiescence in, any such proceedings.

          (g) Employee Benefit Plans. The following shall occur: (a) Any Plan
     shall fail to satisfy the minimum funding standard required for any plan
     year or part thereof under Section 412 of the Code or Section 302 of ERISA
     or a waiver of such standard or extension of any amortization period is
     sought or granted under Section 412 of the Code or Section 303 or 304 of
     ERISA, Reportable Event shall have occurred, a contributing sponsor ( as
     defined in Section 4001(a)(13) of ERISA) of a Plan subject to Title IV of
     ERISA shall be subject to the advance reporting requirement of PBGC
     Regulation Section 4043.61 (without regard to subparagraph (b) (1) thereof)
     and an event described in subsections .62, .63, .64, .65, .66, .67 or .68
     of PBGC Regulations Section 4043 shall be reasonably expected to occur with
     respect to such Plan within the following 30 days, any Plan which is
     subject to Title IV of ERISA shall have had or is likely to have a trustee
     appointed to administer such Plan, any Plan which is subject to Title IV of
     ERISA is, shall have been or is likely to be terminated or to be the
     subject of termination proceedings under ERISA, any Plan shall have an
     Unfunded Current Liability, a contribution required to be made with respect
     to a Plan or a Foreign Pension Plan has not been timely made, Company or
     any ERISA Affiliate has incurred or is likely to incur any liability to or
     on account of a Plan under Sections 406, 409, 502(l), 515, 4062, 4063,
     4064, 4069, 4201, 4204 or 4212 of ERISA or Sections 401(a)(29), 4971 or
     4975 of the Code or on account of a group health plan (as defined in
     Section 607(1) of ERISA or Section 4980B of the Code) under Section 4980B
     of the Code, or any Company or ERISA Affiliate has incurred or is likely to
     incur liabilities pursuant to one or more employee welfare benefit plan (as
     defined in Section 3(1) of ERISA that provide benefits to retired employees
     or other former employees (other than as required by Section 601 of ERISA)
     or Plans or Foreign Pension Plans, a "default" within the meaning of
     Section 4219(c)(5) of ERISA shall have occurred with respect to any Plan,
     any applicable law, rule or regulation is adopted, changed or interpreted,
     or the interpretation or administration thereof is changed, in each case
     after the date hereof, by any governmental authority or agency or by any
     court (a "Change of Law"), or, as a result of a Change in Law, an event
     occurs following a Change in Law with respect to or otherwise affecting any
     Plan, insolvency or reorganization of a Multiemployer Plan, or any other
     event or condition shall occur or exist with respect to a Plan; (b) there
     shall result from any such event or events the imposition of a lien, the
     granting of a security interest, or liability or a material risk of
     incurring a liability; and (c) such lien, security interest or liability,
     either individually and/or in the aggregate, is, or could reasonably be
     expected to cause, a Material Adverse Event.

          (h) Judgments. One or more judgments or decrees shall be entered
     against any of the Companies involving in the aggregate a liability (not
     covered by insurance or not paid)

                                      E-2                        SIXTH AMENDMENT
<PAGE>   43


of $50,000,000 or more and all such judgments or decrees shall not have been
vacated, discharged, or stayed within 60 days from the entry thereof.

          (i) Change of Control. A Change of Control shall occur.


                                      E-3                        SIXTH AMENDMENT