Document:

<PAGE>

                                EXHIBIT 10(18)
                  Fifth Amendment to Business Loan Agreement
  between Registrant and Bank of America, Texas, N.A., dated January 14, 1999
<PAGE>

                                                                   EXHIBIT 10.18

                  FIFTH AMENDMENT TO BUSINESS LOAN AGREEMENT
                          (RECEIVABLES AND INVENTORY)

     This FIFTH AMENDMENT TO BUSINESS LOAN AGREEMENT (RECEIVABLES AND INVENTORY)
("Amendment") is executed and entered into on January 14, 1999, by and between
  ---------
Bank of America, Texas, N.A. (the "Bank") and Aztec Manufacturing Co. (the
                                   ----
"Borrower").
---------

                                   RECITALS:

     A.   The Borrower and the Lender are parties to that certain Business Loan
Agreement (Receivables and Inventory) dated as of June 28, 1996 (as amended and
as the same may be further amended, renewed, extended, restated, or otherwise
modified from time to time, the "Loan Agreement") pursuant to which the Lender
                                 --------------
agreed to provide to the Borrower a secured revolving credit facility in the
maximum aggregate principal amount of $10,000,000 and a secured term loan
facility in the amount of $10,000,000.

     B.   The indebtedness of the Borrower to the Lender pursuant to the Loan
Agreement is secured by liens on the Borrower's property as described in that
certain Security Agreement: Receivables, Inventory and Equipment (Borrower);

     C.   Each subsidiary of the Borrower is a Pledging Party and a Guarantor
under the terms of the Loan Agreement.

     D.   The Borrower has requested that the Lender provide additional loans to
the Borrower as set forth herein and amend certain provisions of the Loan
Agreement, and, subject to satisfaction of the conditions set forth herein, the
Lender is willing to make such additional loans available to the Borrower and
amend the Loan Agreement.

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto hereby agree as
follows:

                                  ARTICLE I.

                                  Definitions
                                  -----------

     Section A.  Definitions.  Unless otherwise defined in this Amendment, each
                 -----------
capitalized term used in this Amendment has the meaning given to such term in
the Loan Agreement (as amended by this Amendment).
<PAGE>

                                  ARTICLE II.

                                  Amendments
                                  ----------

     Section A.  Amendment to subsection 1.1(a) of the Loan Agreement.
                 ----------------------------------------------------
Effective as of the date hereof, subsection 1.1(a) of the Loan Agreement is
                                 -----------------
hereby amended and restated to read in its entirety as follows:

          (a)    Fifteen Million Dollars ($15,000,000.00), or

     Section B.  Amendment to Section 1.4 of the Loan Agreement.  Effective as
                 ----------------------------------------------
of the date hereof, Section 1.4 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

          1.4    "Pledging Party" means the Borrower and each subsidiary of the
                  --------------
     Borrower who is party to a security agreement in favor of the Bank pledging
     to the Bank such subsidiary's accounts, inventory, equipment, and other
     related assets.

     Section C.  Amendment to Section 2 of the Loan Agreement.  Effective as of
                 --------------------------------------------
the date hereof, each of the following sections in Section 2 ("LOAN AMOUNTS AND
                                                   ---------
TERMS") of the Loan Agreement is hereby amended and restated to read in its
entirety as follows:

          2.     LOAN AMOUNTS AND TERMS

          2.1    Line of Credit Amount.
                 ---------------------

                 (a) During the availability period described below, the Bank
          will provide a line of credit (the "Line of Credit") to the Borrower.
                                              --------------
          The amount of the Line of Credit is equal to the amount of the
          Borrowing Base.

                 (b) The Line of Credit is a revolving line of credit for
          advances with a within line facility for letters of credit. During the
          availability period, the Borrower may repay principal amounts and
          reborrow them.

                 (c) Each advance must be for at least One Hundred Thousand
          Dollars ($100,000.00) or an integral multiple thereof, or for the
          amount of the remaining available Line of Credit, if less.

                 (d) The Borrower agrees not to permit the outstanding principal
          balance of the Line of Credit, plus the outstanding amounts of any
                                         ----
          letters of credit, including, without limitation, amounts drawn on
          letters of credit and not yet reimbursed, to exceed the Borrowing
          Base. If on any day such outstandings exceed the Borrowing Base, then
          within five (5) days of such day the Borrower will pay the excess to
          the Bank. The Bank may apply payments received from the Borrower under
          this Paragraph to the obligations of the Borrower to the Bank in the
          order and the manner as the Bank, in its discretion, may determine.

                                      ***

                                       2
<PAGE>

     2.3  Conditions to Each Extension of Credit.  Before each extension of
          --------------------------------------
credit under the Line of Credit, the Borrower will deliver a Borrowing
Certificate in the form of Exhibit A hereto completed in a manner satisfactory
                           ---------
to the Bank by telecopy at the telecopy number set forth on the signature pages
hereto.

     2.4  Repayment Terms.  The Borrower will repay in full all principal and
          ---------------
any unpaid interest or other charges outstanding under the Line of Credit no
later than the Expiration Date.

     2.5  Letters of Credit.  The Line of Credit may be used for financing
          -----------------
standby and/or commercial letters of credit with a maximum maturity not to
exceed one year beyond the Expiration Date.  The aggregate face amount of all
letters of credit outstanding at any one time (including, without limitation,
amounts drawn on letters of credit and not yet reimbursed) may not exceed Two
Million Dollars ($2,000,000.00).  The Borrower agrees:

          (a) any sum drawn under a letter of credit may, at the option of the
     Bank, be added to the principal amount outstanding under the Line of Credit
     pursuant to this Agreement.  Such amount will bear interest and be due as
     described elsewhere in this Agreement;

          (b) if there is a default under this Agreement, to immediately prepay
     and make the Bank whole for any outstanding letters of credit;

          (c) the issuance of any letter of credit and any amendment to a letter
     of credit is subject to the Bank's written approval and must be in form and
     content satisfactory to the Bank and in favor of a beneficiary;

          (d) to sign the Bank's form Application and Agreement for Standby
     Letter of Credit (or any similar form as requested by the Bank) in
     connection with and as a condition to the issuance of each letter of
     credit;

          (e) to pay any issuance and/or other fees that the Bank notifies the
     Borrower will be charged for issuing and processing letters of credit for
     the Borrower;

          (f) to allow the Bank to automatically charge its checking account for
     applicable fees, discounts, and other charges arising or accrued in respect
     of letters of credit; and

          (g) to pay the Bank a non-refundable fee equal to one percent (1.0%)
     per annum of the outstanding undrawn amount of each standby letter of
     credit and one-quarter of one percent (0.25%) per annum of the outstanding
     undrawn amount of each commercial letter of credit, each such fee payable
     quarterly in advance, calculated on the basis of the face amount
     outstanding on the day the fee is calculated.

     2.6  Term Loans.  The Bank agrees to provide term loans to the Borrower
          ----------
(the "Term Commitment") in the amounts of (a) Ten Million Dollars
      ---------------
($10,000,000.00) (the

                                       3
<PAGE>

"Term Loan A") and (b) Ten Million Dollars ($10,000,000.00) (the "Term Loan B";
 -----------                                                      -----------
the Term Loan A and the Term Loan B are referred to collectively herein as the
"Term Loans").
 ----------

     2.7   Availability Period.  The Term Commitment is available in two
           -------------------
disbursements as follows:

          (a)  the Term Loan A shall be made in one disbursement from the Bank
     between the date of this Agreement and June 30, 1996, and

          (b)  the Term Loan B shall be made in one disbursement from the Bank
     between January 14, 1999 and _________________, 1999.

     2.8  Purpose.  The Term Loan A shall be used to refinance existing
          -------
indebtedness, to finance capital expenditures previously made, and for working
capital purposes.  The Term Loan B shall be used to repay indebtedness
outstanding under the Line of Credit on the date of disbursement.

     2.9  Term Loan Repayment Terms; Prepayment.
          -------------------------------------

          (a)  (i)  The Borrower will repay the principal amount of the Term
          Loan A in seventy-one (71) successive monthly installments of One
          Hundred Thirty-Eight Thousand Eight Hundred Eighty-Nine Dollars
          ($138,889.00) starting August 1, 1996.  On July 1, 2002, the Borrower
          will repay the remaining principal balance of the Term Loan A.

               (ii) The Borrower will repay the principal amount of the Term
          Loan B in eighty-four (84) successive monthly installments starting on
          the first day of the month following the disbursement of the Term Loan
          B and continuing on the first day of each month thereafter as follows:
          (A)  the first eighty-three (83) installments shall be in the amount
          of One Hundred Nineteen Thousand Forty-Seven and 62/100 Dollars
          ($119,047.62); and the final installment shall be for the remaining
          principal balance of the Term Loan B.

          (b)  The Borrower may prepay the either of Term Loans in full or in
     part at any time in an amount not less than One Hundred Thousand Dollars
     ($100,000.00) or an integral multiple thereof.  Any such prepayment will be
     applied to the Term Loan A or the Term Loan B, as designated by the
     Borrower, to the most remote installment of principal due under this
     Agreement.

                                      ***

     2.13 Long Term Rate.  The Borrower may elect to have all or portions of the
          --------------
principal balance of the Term Loan A bear interest at a rate equal to the lesser
of (a) the Maximum Rate or (b) the Long Term Rate, subject to the following
requirements:

          (a)  The interest period during which the Long Term Rate will be in
     effect will be for the remaining term of the Term Loan A.

          (b)  The "Long Term Rate" means a fixed interest rate equal to the
                   --------------
     Bank's Cost of Funds Rate in existence at the time the Long Term Rate is
     selected

                                       4
<PAGE>

     plus one and one-quarter percent (1.25%).  "Cost of Funds Rate" means the
                                                 ------------------
     rate then quoted by the Bank at which the Bank can acquire United States
     dollars in any domestic market for a period equal to the applicable
     interest period and in an amount of the portion of the Term Loan A subject
     thereto, adjusted for such reserves as the Bank may deem appropriate.

          (c)  Each Long Term Rate portion will be for an amount not less than
     Two Hundred Fifty Thousand Dollars ($250,000.00).

          (d)  Any portion of the Term Loan A bearing interest at the Long Term
     Rate will not be converted to a different rate during the applicable
     interest period.

          (e)  The Borrower may prepay any Long Term Rate portion in whole or in
     part in the minimum amount of One Hundred Thousand Dollars ($100,000.00).
     The Borrower will give the Bank irrevocable written notice of the
     Borrower's intention to make any such prepayment, specifying the date and
     amount of such prepayment.  The notice must be received by the Bank at
     least five (5) banking days in advance of the prepayment.  All prepayments
     of principal on the Long Term Rate portion will be applied on the most
     remote principal installment or installments of the Term Loan A then
     unpaid.

          (f)  Each prepayment of a Long Term Rate portion will be accompanied
     by payment of all accrued interest on the amount of the prepayment and a
     prepayment fee (as calculated by the Bank in its discretion) to be equal to
     the present value of the amount (if any) by which:

               (i)  the additional interest which would have been payable on the
          amount prepaid had it not been prepaid exceeds

               (ii) the amount of interest which would accrue on the amount paid
          if it were reinvested from the date of prepayment through its original
          maturity at a then prevailing rate equal to the interest rate yield on
          like term U.S. Government Treasury securities determined by the Bank
          based on information from either the Telerate or Reuters information
          services, The Wall Street Journal, or other information sources the
                    -----------------------
          Bank deems appropriate.

     The Bank is under no obligation to actually reinvest any prepayment.

          (g)  If at any time during any applicable interest period the Long
     Term Rate shall exceed the Maximum Rate and thereafter the Long Term Rate
     shall become less than the Maximum Rate, the rate of interest payable shall
     be the Maximum Rate until the Bank shall have received the amount of
     interest it otherwise would have received if the interest payable had not
     been limited by the Maximum Rate during the period of time the Long Term
     Rate exceeded the Maximum Rate.

     2.14 Libor Rate.  The Borrower may elect to have all or portions of the
          ----------
principal balance of the loans bear interest at a rate equal to the lesser of
(i) the Maximum Rate or (ii) the Libor Rate plus (i) seven-eighths of one
                                            ----
percent (0.875%) with respect to the Line of

                                       5
<PAGE>

Credit or (ii) one and one-quarter percent (1.25%) with respect to the Term
Loans (the "Eurodollar Rate"), subject to the following requirements:
            ---------------

          (a)  The interest period during which the Eurodollar Rate will be in
     effect will be (i) 1, 2, 3, or 6 months with respect to the Line of Credit
     or (ii) 1, 2, 3, 6, or 12 months with respect to the Term Loans.  The last
     day of the interest period will be determined by the Bank using the
     practices of the London interbank market.

          (b)  Each Eurodollar Rate portion under a loan will be for an amount
     not less than Five Hundred Thousand Dollars ($500,000.00) or an integral
     multiple thereof.

          (c)  The Borrower shall irrevocably request a Eurodollar Rate portion
     no later than 11:00 a.m. Dallas, Texas time two (2) banking days before the
     commencement of the interest period.

          (d)  The "LIBOR Rate" means the interest rate determined by the
                    ----------
     following formula, rounded upward to the nearest 1/100 of one percent.
     (All amounts in the calculation will be determined by the Bank as of the
     first day of the interest period.)

                    LIBOR Rate =        London Rate
                                 ---------------------------
                                 (1.00 - Reserve Percentage)
     Where,

               (i)  "London Rate" means the interest rate (rounded upward to the
                     -----------
          nearest 1/16th of one percent) at which the Bank's London Branch,
          London, Great Britain, would offer U.S. dollar deposits for the
          applicable interest period to other major banks in the London
          interbank market at approximately 11:00 a.m. London time two (2)
          banking days prior to the commencement of the interest period.

               (ii) "Reserve Percentage" means the total of the maximum reserve
                     ------------------
          percentages for determining the reserves to be maintained by member
          banks of the Federal Reserve System for Eurocurrency Liabilities, as
          defined in Federal Reserve Board Regulation D, rounded upward to the
          nearest 1/100 of one percent.  The percentage will be expressed as a
          decimal, and will include, but not be limited to, marginal, emergency,
          supplemental, special, and other reserve percentages.

          (e)  The Borrower may not elect an Eurodollar Rate with respect to any
     portion of the principal balance of any loan which is scheduled to be
     repaid before the last day of the applicable interest period.

          (f)  Any portion of the principal balance of a loan already bearing
     interest at the Eurodollar Rate will not be converted to a different rate
     during its interest period.

                                       6
<PAGE>

               (g)  Each prepayment of an Eurodollar Rate portion will be
          accompanied by the amount of accrued interest on the amount prepaid,
          and a prepayment fee equal to the amount (if any) by which

                    (i)  the additional interest which would have been payable
               on the amount prepaid had it not been paid until the last day of
               the interest period, exceeds

                    (ii) the interest which would have been recoverable by the
               Bank by placing the amount prepaid on deposit in the London
               interbank market for a period starting on the date on which it
               was prepaid and ending on the last day of the interest period for
               such portion.

               (h)  The Bank will have no obligation to accept an election for
          an Eurodollar Rate portion if any of the following described events
          has occurred and is continuing:

                    (i)  Dollar deposits in the principal amount, and for
               periods equal to the interest period, of an Eurodollar Rate
               portion are not available in the London interbank market; or

                    (ii) The Eurodollar Rate does not accurately reflect the
               cost of an Eurodollar Rate portion.

               (i)  If at any time during any applicable interest period the
          Eurodollar Rate shall exceed the Maximum Rate and thereafter the
          Eurodollar Rate shall become less than the Maximum Rate, the rate of
          interest payable shall be the Maximum Rate until the Bank shall have
          received the amount of interest it otherwise would have received if
          the interest payable had not been limited by the Maximum Rate during
          the period of time the Eurodollar Rate exceeded the Maximum Rate.

     Section D.  Amendment to Section 3.1 of the Loan Agreement.  Effective as
                 ----------------------------------------------
of the date hereof, Section 3.1 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

          3.1  Unused commitment fee. Subject to the provisions of Section 11.12
               ---------------------
     hereof, the Borrower agrees to pay a fee on any difference between Fifteen
     Million Dollars ($15,000,000) and the amount of the Line of Credit it
     actually uses, determined by the average loan balance maintained during the
     specified period. The fee will be calculated at one-quarter of one percent
     (0.25%) per year. This fee is due on October 1, 1996 and on the first day
     of each following January, April, July and October until the Expiration
     Date.

     Section E.  Amendment to Section 4.2 of the Loan Agreement.  Effective as
                 ----------------------------------------------
of the date hereof, Section 4.2 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

          4.2  Personal Property Supporting Guaranty.  The obligations of Aztec
          -------------------------------------
     Industries, Inc., Aztec Industries, Inc. - Moss Point, Automatic
     Processing, Incorporated,

                                       7
<PAGE>

     The Calvert Company, Inc., Gulf Coast Galvanizing, Inc., Arkgalv, Inc.,
     Arbor-Crowley, Inc., Aztec Group Company, Aztec Holdings, Inc., Aztec
     Manufacturing Partnership, Ltd., Aztec Manufacturing-Waskom Partnership,
     Ltd., Rig-A-Lite Partnership, Ltd., Atkinson Industries, Inc., Arizona
     Galvanizing, Inc., Hobson Galvanizing, Inc., International Galvanizers
     Partnership, Ltd., and Drilling Rig Electrical Systems Partnership, Ltd.
     (collectively, the "Guarantors") to the Bank will be secured by all
                         ----------
     equipment, fixtures, inventory, accounts, receivables and related assets
     the Guarantors now own or will own in the future, as further defined in the
     security agreement executed by the Guarantors.

     Section F.  Amendment to subsection 5.3(b) of the Loan Agreement.
                 ----------------------------------------------------
Effective as of the date hereof, subsection 5.3(b) of the Loan Agreement is
                                 -----------------
hereby amended and restated to read in its entirety as follows:

          (b)    Approximately 15 days prior to each Due Date, the Bank will
     mail to the Borrower a statement of the amounts that will be due on that
     Due Date (the "Billed Amount"). The calculation will be made on the
                    -------------
     assumption that no new extensions of credit or payments will be made
     between the date of the billing statement and the Due Date, and that there
     will be no changes in the applicable interest rate.

     Section G.  Amendment to Section 8.1 of the Loan Agreement.  Effective as
                 ----------------------------------------------
of the date hereof, Section 8.1 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

          8.1    Use of Proceeds. To use the proceeds of the Line of Credit only
                 ---------------
     for the general working capital needs of the Borrower and its subsidiaries
     and to finance acquisitions permitted hereby.

     Section H.  Amendment to Section 8.6 of the Loan Agreement.  Effective as
                 ----------------------------------------------
of the date hereof, the first sentence of Section 8.6 of the Loan Agreement is
                                          -----------
hereby amended and restated to read in its entirety as follows:

     To maintain on a consolidated basis a Cash Flow Ratio of at least 1.75:1.0.

     Section I.  Amendment to Section 8.11 of the Loan Agreement.  Effective as
                 -----------------------------------------------
of the date hereof, Section 8.11 of the Loan Agreement is hereby amended and
                    ------------
restated to read in its entirety as follows:

          8.11   Treasury Stock. Not to purchase, redeem, or otherwise acquire
                 --------------
     for value any of its shares, or create any sinking fund in relation
     thereto; provided that the Borrower may otherwise acquire for value its
     shares for an aggregate purchase price not to exceed,, during the period
     from August 4, 1998 through and including July 1, 2001, the sum of (a)
     Seven Million Dollars ($7,000,000), plus (b) the proceeds of any key man
     life insurance policy for the purpose of funding the repurchase of its
     shares.

     Section J.  Amendment to Exhibit C of the Loan Agreement.  Effective as of
                 --------------------------------------------
the date hereof, Exhibit C of the Loan Agreement is hereby amended and restated
                 ---------
in its entirety to read as set forth in Exhibit 1 attached hereto.
                                        ---------

                                       8
<PAGE>

                                 ARTICLE III.

                             Conditions Precedent
                             --------------------

     Section A.  Items to be Delivered By Borrower.  Prior to or simultaneously
                 ---------------------------------
with execution and delivery of this Amendment, the Borrower shall deliver, or
cause to be delivered, to the Lender the following:

          1.     Officer's Certificates.  Due certification by the corporate
                 ----------------------
     secretary (or other duly authorized officer acceptable to the Lender) of
     the Borrower and each other Pledging Party (or the general partner of any
     Pledging Party) (a) attaching a copy of resolutions duly adopted by its
     board of directors approving the terms and conditions contained in this
     Amendment, (b) certifying that the certificate of incorporation, bylaws,
     certificate of limited partnership, and other constituent documents of the
     Borrower, such other Pledging Party, or its general partner (as applicable)
     as previously certified to the Lender remain in full force and effect
     without amendment, and (c) including a certification of incumbency of all
     officers who are authorized to act in respect of the corporate resolutions
     referenced above, including the name, office, and signature of each such
     officer.

          2.     Amendment Documents.  Each agreement, certificate, document, or
                 -------------------
     instrument required by the Lender to be executed or delivered by the
     Borrower or any other Pledging Party in connection with this Amendment (the
     "Amendment Documents"), duly executed or delivered by the parties thereto.
      -------------------

     Section B.  Other Conditions.  The effectiveness of this Amendment is
                 ----------------
subject to the satisfaction of each of the additional following conditions
precedent:

          1.     Continued Effect of Representations and Warranties.  All
                 --------------------------------------------------
     representations and warranties contained in any loan document (including,
     without limitation, the Loan Agreement, as amended hereby; all of such loan
     documents are referred to collectively herein as the "Loan Documents")
                                                           --------------
     shall be true, correct, and complete in all material respects (as
     determined by the Lender in its sole discretion) except as disclosed
     otherwise to the Lender in writing and as acceptable to the Lender or
     representations specifically relating to a prior date or no longer relevant
     due to the occurrence of an event or circumstances specifically permitted
     hereunder or by any other Loan Document;

          2.     Absence of Default.  No default or event of default shall have
                 ------------------
     occurred and be continuing (after giving effect to this Amendment);

          3.     Corporate Proceedings.  All corporate proceedings taken in
                 ---------------------
     connection with the transactions contemplated by this Amendment and all
     other agreements, documents, and instruments executed and/or delivered
     pursuant hereto, and all legal matters incident thereto, shall be
     satisfactory to the Lender and its legal counsel; and

          4.     Additional Information.  The Lender shall have received such
                 ----------------------
     additional agreements, certificates, documents, instruments, and
     information as the Lender or its legal

                                       9
<PAGE>

     counsel, Jenkens & Gilchrist, a Professional Corporation, may reasonably
     request to effect the transactions contemplated hereby.

                                  ARTICLE IV.

                        Representations and Warranties
                        ------------------------------

     Section A.  Representations and Warranties.  The Borrower hereby represents
                 ------------------------------
and warrants to the Lender that, as of the date of and after giving effect to
this Amendment:  (a) the execution, delivery, and performance of this Amendment
and any and all other Amendment Documents executed and/or delivered in
connection herewith have been authorized by all requisite corporate action on
the part of the Borrower and will not violate the Borrower's certificate of
incorporation or bylaws; (b) all representations and warranties set forth in the
Loan Agreement and in the Loan Documents are true and correct in all material
respects as if made again on and as of such date (except as disclosed otherwise
to the Lender in writing and as acceptable to the Lender or representations
specifically relating to a prior date or no longer relevant due to the
occurrence of an event or circumstances specifically permitted hereunder or by
any other Loan Document); (c) no default or event of default has occurred and is
continuing; and (d) the Loan Agreement and the other Loan Documents (as amended
by this Amendment) are and remain legal, valid, binding, and enforceable
obligations of the Borrower.

                                  ARTICLE V.

                                 Miscellaneous
                                 -------------

     Section A.  Governing Law.   THIS AMENDMENT, AND ALL DOCUMENTS AND
                 -------------
INSTRUMENTS EXECUTED IN CONNECTION HEREWITH, SHALL BE GOVERNED BY AND CONSTRUED
ACCORDING TO THE LAWS OF THE STATE OF TEXAS, PROVIDED THAT TO THE EXTENT FEDERAL
                                             --------
LAW WOULD ALLOW A HIGHER RATE OF INTEREST THAN WOULD BE ALLOWED BY THE LAWS OF
THE STATE OF TEXAS, THEN WITH RESPECT TO THE PROVISIONS OF ANY LAW WHICH
PURPORTS TO LIMIT THE AMOUNT OF INTEREST THAT MAY BE CONTRACTED FOR, CHARGED OR
RECEIVED IN CONNECTION WITH ANY OF THE OBLIGATIONS, SUCH FEDERAL LAW SHALL
APPLY.

     Section B.  Agreement Remains in Effect; No Waiver.  Except as expressly
                 --------------------------------------
provided herein, all terms and provisions of the Loan Agreement and the other
Loan Documents shall remain unchanged and in full force and effect and are
hereby ratified and confirmed.  No delay or omission by the Lender in exercising
any power, right, or remedy shall impair such power, right, or remedy or be
construed as a waiver thereof or an acquiescence therein, and no single or
partial exercise of any such power, right, or remedy shall preclude other or
further exercise thereof or the exercise of any other power, right, or remedy
under the Loan Agreement, the Loan Documents, or otherwise.

     Section C.  Survival of Representations and Warranties.  All
                 ------------------------------------------
representations and warranties made in this Amendment or any other Loan Document
shall survive the execution and delivery of this Amendment and the other Loan
Documents, and no investigation by the Lender or

                                       10
<PAGE>

any closing shall affect the representations and warranties or the right of the
Lender to rely upon them.

     Section D.  Reference to Loan Agreement and Loan Documents.  Each of the
                 ----------------------------------------------
Loan Documents, including the Loan Agreement, the Amendment Documents, and any
and all other agreements, documents, or instruments now or hereafter executed
and/or delivered pursuant to the terms hereof or pursuant to the terms of the
Loan Agreement, as amended hereby, are hereby amended so that any reference in
the Loan Documents to the Loan Agreement shall mean a reference to the Loan
Agreement as amended hereby, and the term "loan documents" as used in the Loan
Agreement and as used in any of the other Loan Documents includes, without
limitation, the Amendment Documents.

     Section E.  Severability.  Any provision of this Amendment held by a court
                 ------------
of competent jurisdiction to be invalid or unenforceable shall not impair or
invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

     Section F.  Successors and Assigns.  This Amendment is binding upon and
                 ----------------------
shall inure to the benefit of the Borrower, the Lender, and their respective
successors in interest and assigns.  The Borrower may not assign any right,
power, duty, or obligation hereunder without the prior written consent of the
Lender.

     Section G.  Headings.  The headings, captions, and arrangements used in
                 --------
this Amendment are for convenience only and shall not affect the interpretation
of this Amendment.

     Section H.  Expenses of the Lender.  As provided in the Loan Agreement, the
                 ----------------------
Borrower agrees to pay on demand all reasonable, third party out-of-pocket costs
and expenses incurred by the Lender in connection with the preparation,
negotiation, and execution of this Amendment, the Amendment Documents, or the
other Loan Documents executed pursuant hereto and any and all amendments,
modifications, and supplements thereto, including, without limitation, the
reasonable fees of the Lender's legal counsel, and all reasonable costs and
expenses incurred by the Lender in connection with the enforcement or
preservation of any rights under the Loan Agreement, as amended hereby, or any
other Loan Document, including, without limitation, the reasonable costs and
fees of the Lender's legal counsel.

     Section I.  Counterparts.  This Amendment may be executed simultaneously in
                 ------------
one or more multiple originals, each of which shall be deemed an original, but
all of which together shall constitute one and the same agreement.

     THIS AMENDMENT, TOGETHER WITH THE LOAN AGREEMENT AND THE OTHER LOAN
     DOCUMENTS AS WRITTEN, REPRESENT 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.

                                       11
<PAGE>

     IN WITNESS WHEREOF, the Borrower and the Lender have caused this Amendment
to be executed and delivered by their duly authorized officers effective as of
the date first written above.

                              BORROWER:
                              --------

                              AZTEC MANUFACTURING CO.

                              By: /s/ DANA PERRY
                                  ----------------------------------------------
                              Name: DANA PERRY
                                    --------------------------------------------
                              Title: V.P. FINANCE
                                     -------------------------------------------

                              LENDER:
                              ------

                              BANK OF AMERICA, TEXAS, N.A.

                              By: /s/ RANDY WOODS
                                  ----------------------------------------------
                              Name: RANDY WOODS
                                    --------------------------------------------
                              Title: BANK OFFICER
                                     -------------------------------------------
                                       12<PAGE>

                                EXHIBIT 10(19)
                  Sixth Amendment to Business Loan Agreement
  between Registrant and Bank of America, Texas, N.A., dated February 3, 1999
<PAGE>

                  SIXTH AMENDMENT TO BUSINESS LOAN AGREEMENT
                          (RECEIVABLES AND INVENTORY)

     This SIXTH AMENDMENT TO BUSINESS LOAN AGREEMENT (RECEIVABLES AND INVENTORY)
(this "Amendment") is executed and entered into on August __, 1999, by and
       ---------
between Bank of America, N.A. (successor by merger to Bank of America, Texas,
N.A., the "Bank") and Aztec Manufacturing Co. (the "Borrower").
           ----                                     --------

                                   RECITALS:

     A.   The Borrower and the Bank are parties to that certain Business Loan
Agreement (Receivables and Inventory) dated as of June 28, 1996 (as amended and
as the same may be further amended, renewed, extended, restated, or otherwise
modified from time to time, the "Loan Agreement") pursuant to which the Bank
                                 --------------
agreed to provide to the Borrower a secured revolving credit facility and a
secured term loan facility.

     B.   The indebtedness of the Borrower to the Bank pursuant to the Loan
Agreement is secured by liens on the Borrower's property as described in that
certain Security Agreement: Receivables, Inventory and Equipment (Borrower);

     C.   Each subsidiary of the Borrower is a Pledging Party and a Guarantor
under the terms of the Loan Agreement.

     D.   The Borrower has requested that the Bank provide additional loans to
the Borrower as set forth herein and amend certain provisions of the Loan
Agreement, and, subject to satisfaction of the conditions set forth herein, the
Bank is willing to make such additional loans available to the Borrower and
amend the Loan Agreement.

     NOW, THEREFORE, in consideration of the mutual covenants and agreements
contained herein and for other good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto hereby agree as
follows:

                                   ARTICLE 1

                                  Definitions
                                  -----------

     Section 1.1  Definitions.  Unless otherwise defined in this Amendment, each
                  -----------
capitalized term used in this Amendment has the meaning given to such term in
the Loan Agreement (as amended by this Amendment).
<PAGE>

                                   ARTICLE 2

                                  Amendments
                                  ----------

     Section 2.1  Amendment to subsection 1.1(a) of the Loan Agreement.
                  ----------------------------------------------------
Effective as of the date hereof, subsection 1.1(a) of the Loan Agreement is
                                 -----------------
hereby amended and restated to read in its entirety as follows:

             (a)  Twenty-Two Million Dollars ($22,000,000.00), or

     Section 2.2  Amendment to Section 1.4 of the Loan Agreement.  Effective as
                  ----------------------------------------------
of the date hereof, Section 1.4 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

             1.4  "Pledging Party" means the Borrower and each subsidiary of the
                   --------------
     Borrower who is party to a security agreement in favor of the Bank pledging
     to the Bank such subsidiary's accounts, inventory, equipment, and other
     related assets; provided, however, that Pledging Party shall also mean and
                     --------  -------
     include CGIT Westboro, Inc. ("CGIT") from and after the date of the
     acquisition of CGIT by the Borrower, CGIT to execute and deliver to the
     Bank a guaranty, security agreement, financing statements and such other
     documents (including, without limitation, an officer's certificate as to
     CGIT's charter documents, resolutions and authorized signatures) required
     by the Bank to create and perfect a security interest in CGIT's accounts,
     inventory, equipment, and other related assets within ninety (90) days of
     the Borrower's acquisition of CGIT.

     Section 2.3  Amendment to Section 2.14 of the Loan Agreement.  Effective as
                  -----------------------------------------------
of the date hereof, Section 2.14 of the Loan Agreement is hereby amended and
                    ------------
restated to read in its entirety as follows:

             2.14 Libor Rate.  The Borrower may elect to have all or portions of
                  ----------
     the principal balance of the loans bear interest at a rate equal to the
     lesser of (i) the Maximum Rate or (ii) the Libor Rate plus (i) the
                                                           ----
     Applicable Libor Margin (as determined as provided in clause (j) below)
     with respect to the Line of Credit or (ii) one and one-quarter percent
     (1.25%) with respect to the Term Loans (the "Eurodollar Rate"), subject to
                                                  ---------------
     the following requirements:

                  (a)  The interest period during which the Eurodollar Rate will
          be in effect will be (i) 1, 2, 3, or 6 months with respect to the Line
          of Credit or (ii) 1, 2, 3, 6, or 12 months with respect to the Term
          Loans. The last day of the interest period will be determined by the
          Bank using the practices of the London interbank market.

                  (b)  Each Eurodollar Rate portion under a loan will be for an
          amount not less than Five Hundred Thousand Dollars ($500,000.00) or an
          integral multiple thereof.

                  (c)  The Borrower shall irrevocably request a Eurodollar Rate
          portion no later than 11:00 a.m. Dallas, Texas time two (2) banking
          days before the commencement of the interest period.

                                       2
<PAGE>

          (d)  The "LIBOR Rate" means the interest rate determined by the
                    ----------
     following formula, rounded upward to the nearest 1/100 of one percent.
     (All amounts in the calculation will be determined by the Bank as of the
     first day of the interest period.)

                    LIBOR Rate =           London Rate
                                 ---------------------------------
                                    (1.00 - Reserve Percentage)
     Where,

               (i)  "London Rate" means the interest rate (rounded upward to the
                     -----------
          nearest 1/16th of one percent) at which the Bank's London Branch,
          London, Great Britain, would offer U.S. dollar deposits for the
          applicable interest period to other major banks in the London
          interbank market at approximately 11:00 a.m. London time two (2)
          banking days prior to the commencement of the interest period.

               (ii) "Reserve Percentage" means the total of the maximum reserve
                     ------------------
          percentages for determining the reserves to be maintained by member
          banks of the Federal Reserve System for Eurocurrency Liabilities, as
          defined in Federal Reserve Board Regulation D, rounded upward to the
          nearest 1/100 of one percent.  The percentage will be expressed as a
          decimal, and will include, but not be limited to, marginal, emergency,
          supplemental, special, and other reserve percentages.

          (e)  The Borrower may not elect an Eurodollar Rate with respect to any
     portion of the principal balance of any loan which is scheduled to be
     repaid before the last day of the applicable interest period.

          (f)  Any portion of the principal balance of a loan already bearing
     interest at the Eurodollar Rate will not be converted to a different rate
     during its interest period.

          (g)  Each prepayment of an Eurodollar Rate portion will be accompanied
     by the amount of accrued interest on the amount prepaid, and a prepayment
     fee equal to the amount (if any) by which

               (i)  the additional interest which would have been payable on the
          amount prepaid had it not been paid until the last day of the interest
          period, exceeds

               (ii) the interest which would have been recoverable by the Bank
          by placing the amount prepaid on deposit in the London interbank
          market for a period starting on the date on which it was prepaid and
          ending on the last day of the interest period for such portion.

          (h)  The Bank will have no obligation to accept an election for an
     Eurodollar Rate portion if any of the following described events has
     occurred and is continuing:

                                       3
<PAGE>

               (i)  Dollar deposits in the principal amount, and for periods
          equal to the interest period, of an Eurodollar Rate portion are not
          available in the London interbank market; or

               (ii) The Eurodollar Rate does not accurately reflect the cost of
          an Eurodollar Rate portion.

          (i)  If at any time during any applicable interest period the
     Eurodollar Rate shall exceed the Maximum Rate and thereafter the Eurodollar
     Rate shall become less than the Maximum Rate, the rate of interest payable
     shall be the Maximum Rate until the Bank shall have received the amount of
     interest it otherwise would have received if the interest payable had not
     been limited by the Maximum Rate during the period of time the Eurodollar
     Rate exceeded the Maximum Rate.

          (j)  Prior to receipt of the Compliance Certificate to be delivered
     with the Borrower's financial statements for the fiscal quarter ending
     September 30, 1999, the margin over the Libor Rate for the Line of Credit
     shall be _____ percent (____%); thereafter, the "Applicable Libor Margin"
     shall be determined in accordance with the following table:

          ==========================================
            RATIO OF TOTAL
            LIABILITIES TO
             TANGIBLE NET                LIBOR RATE
                WORTH                      MARGIN

          Less than 1.25 to 1.00           0.875%
          ------------------------------------------

          Greater than or equal to          1.00%
          1.25 to 1.00 but less
          than 2.01 to 1.00
          ------------------------------------------

          Greater than or equal to         1.125%
          2.01 to 1.00 but less
          than 2.76 to 1.00
          ------------------------------------------

          Greater than or equal to          1.25%
          2.76 to 1.00
          ==========================================

          Upon delivery of the Compliance Certificate pursuant to subsection
                                                                  ----------
     8.2(g) after the end of each fiscal quarter commencing with such Compliance
     ------
     Certificate delivered for the fiscal quarter ending December 31, 1999, the
     Applicable Libor Margin shall automatically be adjusted to the rate
     corresponding to the Ratio of Total Liabilities to Tangible Net Worth of
     Borrower set forth in the table above, such automatic adjustment to take
     effect prospectively the third Business Day after receipt by the Bank of
     the Compliance Certificate (the "Adjustment Date"). If Borrower fails to
                                      ---------------
     deliver such Compliance Certificate with respect to any fiscal quarter
     which sets forth such ratio within the period of time required by
     subsection 8.2(g), the
     -----------------

                                       4
<PAGE>

          Applicable Libor Margin shall automatically be adjusted to one and one
          quarter percent (1.25%) per annum. The automatic adjustments provided
          for in the preceding sentence shall take effect on the last day that
          the Compliance Certificate was required to be delivered and shall
          remain in effect until subsequently adjusted in accordance herewith
          upon the delivery of such Compliance Certificate.

     Section 2.4  Amendment to Section 4.2 of the Loan Agreement. Effective as
                  ----------------------------------------------
of the date hereof, Section 4.2 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

             4.2  Personal Property Supporting Guaranty. The obligations of
                  -------------------------------------
     Aztec Industries, Inc., Aztec Industries, Inc. - Moss Point, Automatic
     Processing, Incorporated, The Calvert Company, Inc., Gulf Coast
     Galvanizing, Inc., Arkgalv, Inc., Arbor-Crowley, Inc., Aztec Group Company,
     Aztec Holdings, Inc., Aztec Manufacturing Partnership, Ltd., Aztec
     Manufacturing-Waskom Partnership, Ltd., Rig-A-Lite Partnership, Ltd.,
     Atkinson Industries, Inc., Arizona Galvanizing, Inc., Hobson Galvanizing,
     Inc., International Galvanizers Partnership, Ltd., and Drilling Rig
     Electrical Systems Partnership, Ltd. (collectively, the "Guarantors") to
                                                              ----------
     the Bank will be secured by all equipment, fixtures, inventory, accounts,
     receivables and related assets the Guarantors now own or will own in the
     future, as further defined in the security agreement executed by the
     Guarantors; provided that the term "Guarantors" shall include CGIT upon its
                 --------
     execution of a guaranty within ninety (90) days of the acquisition of CGIT
     by the Borrower as provided by Section 1.4 of this Agreement.
                                    -----------

     Section 2.5  Amendment to Section 8.1 of the Loan Agreement. Effective as
                  ----------------------------------------------
of the date hereof, Section 8.1 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

             8.1  Use of Proceeds. To use the proceeds of the Line of Credit
                  ---------------
     only for the general working capital needs of the Borrower and its
     subsidiaries and to finance acquisitions permitted hereby, including,
                                                                ---------
     without limitation, the acquisition of CGIT.

     Section 2.6  Amendment to Section 8.4 of the Loan Agreement. Effective as
                  ----------------------------------------------
of the date hereof, Section 8.4 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

             8.4  Tangible Net Worth. To maintain on a consolidated basis
                  ------------------
     Tangible Net Worth equal to at least Eleven Million Dollars ($11,000,000,
     plus fifty percent (50%) of the Borrower's positive net income for each
     fiscal quarter of the Borrower ending after June 30, 1999 (no reductions to
     be made for any losses). As used herein, the term "Tangible Net Worth"
                                                        ------------------
     means the gross book value of the Borrower's assets (excluding goodwill,
     patents, trademarks, trade names, organization expense, treasury stock,
     unamortized debt discount and expense, deferred research and development
     costs, deferred marketing expenses, and other like intangibles, and monies
     due from affiliates, officers, directors or shareholders of the Borrower)
     less total liabilities, including but not limited to accrued and deferred
     income taxes, and any reserves against assets.

                                       5
<PAGE>

     Section 2.7  Amendment to Section 8.5 of the Loan Agreement. Effective as
                  ----------------------------------------------
of the date hereof, Section 8.5 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

             8.5  Current and Long Term Liabilities to Tangible Net Worth. To
                  -------------------------------------------------------
     maintain on a consolidated basis a ratio of long term debt and Current
     Liabilities to Tangible Net Worth not exceeding 4.50 to 1.00 for the period
     from the date of the Sixth Amendment to this Agreement through February 28,
     2000, 3.00 to 1.00 thereafter through February 28, 2001, or 2.00 to 1.00
     thereafter.

     Section 2.8  Amendment to Section 8.6 of the Loan Agreement. Effective as
                  ----------------------------------------------
of the date hereof, Section 8.6 of the Loan Agreement is hereby amended and
                    -----------
restated to read in its entirety as follows:

             8.6  Cash Flow Ratio. To maintain on a consolidated basis a Cash
                  ---------------
     Flow Ratio of at least 1.6:1.0. As used herein, the term "Cash Flow Ratio"
                                                               ---------------
     means the ratio of Cash Flow to the current portion of long term debt plus
     interest expense. "Cash Flow" is defined as net income from operations
                        ---------
     (before extraordinary or nonrecurring gains or losses), after taxes, plus
     depreciation, amortization and other non-cash charges, plus interest
     expense, minus dividends. This ratio will be calculated at the end of each
     fiscal quarter, using the results of that quarter and each of the 3
     immediately preceding quarters. The current portion of long term debt will
     be measured as of the last day of the fiscal quarter preceding the date of
     calculation.

     Section 2.9    Amendment to Section 8.11 of the Loan Agreement. Effective
                    -----------------------------------------------
as of the date hereof, Section 8.1l of the Loan Agreement is hereby amended and
                       ------------
restated to read in its entirety as follows:

             8.11 Treasury Stock. Not to purchase, redeem, or otherwise acquire
                  --------------
     for value any of its shares, or create any sinking fund in relation
     thereto.

     Section 2.10   Amendment to Section 8.22 of the Loan Agreement. Effective
                    -----------------------------------------------
as of the date hereof, clause (c) of Section 8.22 of the Loan Agreement is
                                     ------------
hereby amended and restated to read in its entirety as follows:

                    (c)  enter into any consolidation, merger, pool, joint
                    venture, syndicate, or other combination or purchase or
                    acquire all or substantially all the assets of another
                    business, except for such transaction if (i) the Borrower or
                    applicable Guarantor is the surviving entity; (ii) no
                    default exists hereunder or would result therefrom and
                    before, and after giving effect to, the proposed
                    acquisition, the representations and warranties set forth
                    herein shall be true and correct; and (iii) Borrower
                    delivers to the Bank an Environmental Questionnaire and
                    Disclosure Statement in form and disclosing such information
                    as is acceptable to the Bank relating to the assets or
                    entity to be acquired prior to the acquisition.

     Section 2.11   Amendment to Article 8 of the Loan Agreement. Effective as
                    --------------------------------------------
of the date hereof, Article 8 of the Loan Agreement is hereby amended by adding
                    ---------
thereto new Sections 8.24 to read in its entirety as follows:
            -------------

                                       6
<PAGE>

          8.24      Funded Debt to EBITDA. To maintain on a consolidated basis
                    ---------------------
     at the end of each of the Borrower's fiscal quarters ending after the date
     of the Sixth Amendment to this Agreement a ratio of Funded Debt to EBITDA
     for the four consecutive fiscal quarters then ended not exceeding 3.00 to
     1.00. As used herein, the term "Funded Debt" means all debt of the Borrower
                                     -----------
     and its Subsidiaries for borrowed money (including capital lease
     obligations) and the term "EBITDA" means: (i) net income from operations
                                ------
     (before extraordinary or non-recurring gains or losses); plus (ii) any
                                                              ----
     provision for income or franchise taxes deducted in determining net income;
     plus (iii) interest expense deducted in determining net income; plus (iv)
     ----                                                            ----
     depreciation and amortization expense deducted in determining net income;
     plus (v) other non cash charges deducted in determining net income.
     ----

                                   ARTICLE 3

                             Conditions Precedent
                             --------------------

     Section 3.1    Items to be Delivered By Borrower. Prior to or
                    ---------------------------------
simultaneously with execution and delivery of this Amendment, the Borrower shall
deliver, or cause to be delivered, to the Bank the following:

          1         Officer's Certificates. Due certification by the corporate
                    ----------------------
     secretary (or other duly authorized officer acceptable to the Bank) of the
     Borrower and each other Pledging Party (or the general partner of any
     Pledging Party) (a) attaching a copy of resolutions duly adopted by its
     board of directors approving the terms and conditions contained in this
     Amendment, (b) certifying that the certificate of incorporation, bylaws,
     certificate of limited partnership, and other constituent documents of the
     Borrower, such other Pledging Party, or its general partner (as applicable)
     as previously certified to the Bank remain in full force and effect without
     amendment, and (c) including a certification of incumbency of all officers
     who are authorized to act in respect of the corporate resolutions
     referenced above, including the name, office, and signature of each such
     officer.

          2         Amendment Documents. Each agreement, certificate, document,
                    -------------------
     or instrument required by the Bank to be executed or delivered by the
     Borrower or any other Pledging Party in connection with this Amendment (the
     "Amendment Documents"), duly executed or delivered by the parties thereto.
      -------------------

     Section 3.2    Other Conditions. The effectiveness of this Amendment is
                    ----------------
subject to the satisfaction of each of the additional following conditions
precedent:

         1          Continued Effect of Representations and Warranties.  All
                    --------------------------------------------------
   representations and warranties contained in any loan document (including,
  without limitation, the Loan Agreement, as amended hereby; all of such loan
documents are referred to collectively herein as the "Loan Documents") shall be
                                                      --------------
true, correct, and complete in all material respects (as determined by the Bank
in its sole discretion) except as disclosed otherwise to the Bank in writing and
as acceptable to the Bank or representations specifically relating to a prior
date

                                       7
<PAGE>

or no longer relevant due to the occurrence of an event or circumstances
specifically permitted hereunder or by any other Loan Document;

          2    Absence of Default. No default or event of default shall have
               ------------------
     occurred and be continuing (after giving effect to this Amendment);

          3    Corporate Proceedings. All corporate proceedings taken in
               ---------------------
     connection with the transactions contemplated by this Amendment and all
     other agreements, documents, and instruments executed and/or delivered
     pursuant hereto, and all legal matters incident thereto, shall be
     satisfactory to the Bank and its legal counsel; and

          4    Additional Information. The Bank shall have received such
               ----------------------
     additional agreements, certificates, documents, instruments, and
     information as the Bank or its legal counsel, Jenkens & Gilchrist, a
     Professional Corporation, may reasonably request to effect the transactions
     contemplated hereby.

                                   ARTICLE 4

                         Representations and Warranties
                         ------------------------------

     Section 4.1    Representations and Warranties. The Borrower hereby
                    ------------------------------
represents and warrants to the Bank that, as of the date of and after giving
effect to this Amendment: (a) the execution, delivery, and performance of this
Amendment and any and all other Amendment Documents executed and/or delivered in
connection herewith have been authorized by all requisite corporate action on
the part of the Borrower and will not violate the Borrower's certificate of
incorporation or bylaws; (b) all representations and warranties set forth in the
Loan Agreement and in the Loan Documents are true and correct in all material
respects as if made again on and as of such date (except as disclosed otherwise
to the Bank in writing and as acceptable to the Bank or representations
specifically relating to a prior date or no longer relevant due to the
occurrence of an event or circumstances specifically permitted hereunder or by
any other Loan Document); (c) no default or event of default has occurred and is
continuing; and (d) the Loan Agreement and the other Loan Documents (as amended
by this Amendment) are and remain legal, valid, binding, and enforceable
obligations of the Borrower.

                                   ARTICLE 5

                                 Miscellaneous
                                 -------------

     Section 5.1    Governing Law. THIS AMENDMENT, AND ALL DOCUMENTS AND
                    -------------
INSTRUMENTS EXECUTED IN CONNECTION HEREWITH, SHALL BE GOVERNED BY AND CONSTRUED
ACCORDING TO THE LAWS OF THE STATE OF TEXAS, PROVIDED THAT TO THE EXTENT FEDERAL
                                             --------
LAW WOULD ALLOW A HIGHER RATE OF INTEREST THAN WOULD BE ALLOWED BY THE LAWS OF
THE STATE OF TEXAS, THEN WITH RESPECT TO THE PROVISIONS OF ANY LAW WHICH
PURPORTS TO LIMIT THE AMOUNT OF INTEREST THAT MAY BE CONTRACTED FOR, CHARGED OR
RECEIVED IN CONNECTION WITH ANY OF THE OBLIGATIONS, SUCH FEDERAL LAW SHALL
APPLY.

                                       8
<PAGE>

     Section 5.2    Agreement Remains in Effect; No Waiver. Except as expressly
                    --------------------------------------
provided herein, all terms and provisions of the Loan Agreement and the other
Loan Documents shall remain unchanged and in full force and effect and are
hereby ratified and confirmed. No delay or omission by the Bank in exercising
any power, right, or remedy shall impair such power, right, or remedy or be
construed as a waiver thereof or an acquiescence therein, and no single or
partial exercise of any such power, right, or remedy shall preclude other or
further exercise thereof or the exercise of any other power, right, or remedy
under the Loan Agreement, the Loan Documents, or otherwise.

     Section 5.3    Survival of Representations and Warranties. All
                    ------------------------------------------
representations and warranties made in this Amendment or any other Loan Document
shall survive the execution and delivery of this Amendment and the other Loan
Documents, and no investigation by the Bank or any closing shall affect the
representations and warranties or the right of the Bank to rely upon them.

     Section 5.4    Reference to Loan Agreement and Loan Documents. Each of the
                    ----------------------------------------------
Loan Documents, including the Loan Agreement, the Amendment Documents, and any
and all other agreements, documents, or instruments now or hereafter executed
and/or delivered pursuant to the terms hereof or pursuant to the terms of the
Loan Agreement, as amended hereby, are hereby amended so that any reference in
the Loan Documents to the Loan Agreement shall mean a reference to the Loan
Agreement as amended hereby, and the term "loan documents" as used in the Loan
Agreement and as used in any of the other Loan Documents includes, without
limitation, the Amendment Documents.

     Section 5.5    Severability. Any provision of this Amendment held by a
                    ------------
court of competent jurisdiction to be invalid or unenforceable shall not impair
or invalidate the remainder of this Amendment and the effect thereof shall be
confined to the provision so held to be invalid or unenforceable.

     Section 5.6    Successors and Assigns. This Amendment is binding upon and
                    ----------------------
shall inure to the benefit of the Borrower, the Bank, and their respective
successors in interest and assigns. The Borrower may not assign any right,
power, duty, or obligation hereunder without the prior written consent of the
Bank.

     Section 5.7    Headings. The headings, captions, and arrangements used in
                    --------
this Amendment are for convenience only and shall not affect the interpretation
of this Amendment.

     Section 5.8    Expenses of the Bank. As provided in the Loan Agreement, the
                    --------------------
Borrower agrees to pay on demand all reasonable, third party out-of-pocket costs
and expenses incurred by the Bank in connection with the preparation,
negotiation, and execution of this Amendment, the Amendment Documents, or the
other Loan Documents executed pursuant hereto and any and all amendments,
modifications, and supplements thereto, including, without limitation, the
reasonable fees of the Bank's legal counsel, and all reasonable costs and
expenses incurred by the Bank in connection with the enforcement or preservation
of any rights under the Loan Agreement, as amended hereby, or any other Loan
Document, including, without limitation, the reasonable costs and fees of the
Bank's legal counsel.

                                       9
<PAGE>

     Section 5.9    Counterparts. This Amendment may be executed simultaneously
                    ------------
in one or more multiple originals, each of which shall be deemed an original,
but all of which together shall constitute one and the same agreement.

     THIS AMENDMENT, TOGETHER WITH THE LOAN AGREEMENT AND THE OTHER
     LOAN DOCUMENTS AS WRITTEN, REPRESENT 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.

     IN WITNESS WHEREOF, the Borrower and the Bank have caused this Amendment to
be executed and delivered by their duly authorized officers effective as of the
date first written above.

                                   BORROWER:
                                   --------

                                   AZTEC MANUFACTURING CO.

                                   By: /s/ DANA PERRY
                                       ----------------------------------------
                                   Name: DANA PERRY
                                         --------------------------------------
                                   Title: V.P. FINANCE
                                          -------------------------------------

                                   BANK:
                                   ----

                                   BANK OF AMERICA, N.A. (successor by
                                   merger to Bank of America, Texas, N.A.)

                                   By: /s/ VINCE LIBERIO
                                       ----------------------------------------
                                   Name: VINCE LIBERIO
                                         --------------------------------------
                                   Title: SENIOR V.P.
                                          -------------------------------------

                                       10

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