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                                                                    EXHIBIT 4.17

                       THIRD AMENDMENT TO CREDIT AGREEMENT

         THIS THIRD AMENDMENT TO CREDIT AGREEMENT (this "Third Amendment"),
dated as of February 20, 2003, is entered into among ELKCORP (formerly known as
Elcor Corporation), a Delaware corporation (the "Borrower"), the lenders listed
on the signature pages hereof (the "Lenders"), BANK ONE, N.A., as Documentation
Agent, WACHOVIA BANK, N.A., as Syndication Agent, and BANK OF AMERICA, N.A., as
Administrative Agent, Swing Line Lender and L/C Issuer.

                                   BACKGROUND

         A.       The Borrower, the Lenders, the Documentation Agent, the
Syndication Agent, the Administrative Agent, the Swing Line lender and the L/C
Issuer are parties to that certain Credit Agreement, dated as of November 30,
2000, as amended by that certain First Amendment to Credit Agreement, dated as
of March 31, 2001, and that certain Second Amendment to Credit Agreement, dated
as of June 5, 2002 (said Credit Agreement, as amended, the "Credit Agreement").
The terms defined in the Credit Agreement and not otherwise defined herein shall
be used herein as defined in the Credit Agreement.

         B.       The Borrower has requested an amendment to the Credit
Agreement.

         C.       The Lenders, the Documentation Agent, the Syndication Agent,
the Administrative Agent, the Swing Line Lender and the L/C Issuer hereby agree
to amend the Credit Agreement, subject to the terms and conditions set forth
herein.

         NOW, THEREFORE, in consideration of the covenants, conditions and
agreements hereafter set forth, and for other good and valuable consideration,
the receipt and adequacy of which are all hereby acknowledged, the Borrower, the
Lenders and the Administrative Agent covenant and agree as follows:

         (a)      AMENDMENT. The definition of "Private Placement Debt" set
forth in Section 1.01 of the Credit Agreement is hereby amended to read as
follows:

                  "Private Placement Debt" means that certain Indebtedness of
         the Borrower (a) in the aggregate principal amount of $120,000,000
         issued on or about June 7, 2002, and (b) in an aggregate principal
         amount of up to $25,000,000 to be issued on or after March 1, 2003.

         2.       REPRESENTATIONS AND WARRANTIES TRUE; NO EVENT OF DEFAULT. By
its execution and delivery hereof, the Borrower represents and warrants that, as
of the date hereof:

         (a)      the representations and warranties contained in the Credit
Agreement and the other Loan Documents are true and correct on and as of the
date hereof as made on and as of such date;

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         (b)      no event has occurred and is continuing which constitutes a
Default or an Event of Default;

         (c)      (i) the Borrower has full power and authority to execute and
deliver this Third Amendment, (ii) this Third Amendment has been duly executed
and delivered by the Borrower, and (iii) this Third Amendment and the Credit
Agreement, as amended hereby, constitute the legal, valid and binding
obligations of the Borrower, enforceable in accordance with their respective
terms, except as enforceability may be limited by applicable debtor relief laws
and by general principles of equity (regardless of whether enforcement is sought
in a proceeding in equity or at law) and except as rights to indemnity may be
limited by federal or state securities laws;

         (d)      neither the execution, delivery and performance of this Third
Amendment or the Credit Agreement, as amended hereby, nor the consummation of
any transactions contemplated herein or therein, will conflict with any Law or
Organization Documents of the Borrower, or any indenture, agreement or other
instrument to which the Borrower or any of its property is subject; and

         (e)      no authorization, approval, consent, or other action by,
notice to, or filing with, any Governmental Authority or other Person (including
the consent of the Board of Directors of the Borrower) is required for the
execution, delivery or performance by the Borrower of this Third Amendment.

         3.       CONDITIONS TO EFFECTIVENESS. This Third Amendment shall be
effective upon satisfaction or completion of the following:

         (a)      the Administrative Agent shall have received counterparts of
this Third Amendment executed by the Required Lenders;

         (b)      the Administrative Agent shall have received counterparts of
this Third Amendment executed by the Borrower and acknowledged by each
Guarantor; and

         (c)      the Administrative Agent shall have received, in form and
substance satisfactory to the Administrative Agent and its counsel, such other
documents, certificates and instruments as the Administrative Agent shall
require.

         4.       REFERENCE TO THE CREDIT AGREEMENT.

         (a)      Upon the effectiveness of this Third Amendment, each reference
in the Credit Agreement to "this Agreement", "hereunder", or words of like
import shall mean and be a reference to the Credit Agreement, as affected and
amended hereby.

         (b)      The Credit Agreement, as amended by the amendments referred to
above, shall remain in full force and effect and is hereby ratified and
confirmed.

         5.       COSTS, EXPENSES AND TAXES. The Borrower agrees to pay on
demand all costs and expenses of the Administrative Agent in connection with the
preparation, reproduction,

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execution and delivery of this Third Amendment and the other instruments and
documents to be delivered hereunder (including the reasonable fees and
out-of-pocket expenses of counsel for the Administrative Agent with respect
thereto).

         6.       GUARANTOR'S ACKNOWLEDGMENT. By signing below, each Guarantor
(a) acknowledges, consents and agrees to the execution, delivery and performance
by the Borrower of this Third Amendment, (b) acknowledges and agrees that its
obligations in respect of its Guaranty (i) are not released, diminished, waived,
modified, impaired or affected in any manner by this Third Amendment or any of
the provisions contemplated herein, (c) ratifies and confirms its obligations
under its Guaranty, and (d) acknowledges and agrees that it has no claims or
offsets against, or defenses or counterclaims to, its Guaranty.

         7.       EXECUTION IN COUNTERPARTS. This Third Amendment may be
executed in any number of counterparts and by different parties hereto in
separate counterparts, each of which when so executed and delivered shall be
deemed to be an original and all of which when taken together shall constitute
but one and the same instrument. For purposes of this Third Amendment, a
counterpart hereof (or signature page thereto) signed and transmitted by any
Person party hereto to the Administrative Agent (or its counsel) by facsimile
machine, telecopier or electronic mail is to be treated as an original. The
signature of such Person thereon, for purposes hereof, is to be considered as an
original signature, and the counterpart (or signature page thereto) so
transmitted is to be considered to have the same binding effect as an original
signature on an original document.

         8.       GOVERNING LAW; BINDING EFFECT. This Third Amendment shall be
governed by and construed in accordance with the laws of the State of Texas
applicable to agreements made and to be performed entirely within such state,
provided that each party shall retain all rights arising under federal law, and
shall be binding upon the parties hereto and their respective successors and
assigns.

         9.       HEADINGS. Section headings in this Third Amendment are
included herein for convenience of reference only and shall not constitute a
part of this Third Amendment for any other purpose.

         10.      ENTIRE AGREEMENT. THE CREDIT AGREEMENT, AS AMENDED BY THIS
THIRD AMENDMENT, AND THE OTHER LOAN DOCUMENTS REPRESENT THE FINAL AGREEMENT
BETWEEN THE PARTIES AND MAY NOT BE CONTRADICTED BY EVIDENCE OF PRIOR,
CONTEMPORANEOUS, OR SUBSEQUENT ORAL AGREEMENTS BETWEEN THE PARTIES. THERE ARE NO
UNWRITTEN ORAL AGREEMENTS BETWEEN THE PARTIES.

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         IN WITNESS WHEREOF, this Third Amendment is executed as of the date
first set forth above.

                                     ELKCORP

                                     By: ______________________________________
                                          Harold Beattie, Jr.
                                          Senior Vice President, Chief Financial
                                          Officer and Treasurer

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                                     BANK OF AMERICA, N.A., as Administrative
                                     Agent

                                     By: _______________________________________
                                          Name:_________________________________
                                          Title:________________________________

                                     BANK OF AMERICA, N.A., as a Lender, L/C
                                     Issuer and Swing Line Lender

                                     By: _______________________________________
                                          Name:_________________________________
                                          Title:________________________________

                                     BANK ONE, N.A., as a Lender and
                                     Documentation Agent

                                     By: _______________________________________
                                          Name:_________________________________
                                          Title:________________________________

                                     WACHOVIA BANK N.A., as a Lender and
                                     Syndication Agent

                                     By: _______________________________________
                                          Name:_________________________________
                                          Title:________________________________

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                                     THE NORTHERN TRUST COMPANY, as a Lender

                                     By: _______________________________________
                                          Name:_________________________________
                                          Title:________________________________

                                     THE FROST NATIONAL BANK, as a Lender

                                     By: _______________________________________
                                          Name:_________________________________
                                          Title:________________________________

                                     COMERICA BANK-TEXAS, as a Lender

                                     By: _______________________________________
                                          Name:_________________________________
                                          Title:________________________________

                                     COMPASS BANK, as a Lender

                                     By: _______________________________________
                                          Name:_________________________________
                                          Title:________________________________

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ACKNOWLEDGED AND AGREED TO:

ELK PREMIUM BUILDING PRODUCTS, INC.
         (formerly known as Elk Corporation of Dallas)
ELK CORPORATION OF TEXAS
ELK CORPORATION OF AMERICA
ELK CORPORATION OF ARKANSAS
ELK CORPORATION OF ALABAMA
OEL, LTD.

CHROMIUM CORPORATION
CYBERSHIELD OF GEORGIA, INC.
CYBERSHIELD, INC.
CYBERSHIELD INTERNATIONAL, INC.
CYBERSHIELD OF TEXAS, INC.
(formerly known as Chromium Corporation)
ELK TECHNOLOGY GROUP, INC.
ELK TECHNOLOGIES, INC.
ELK PERFORMANCE NONWOVEN FABRICS, INC.
ELK COMPOSITE BUILDING PRODUCTS, INC.

By: _______________________________________
     Harold Beattie, Jr.
     Vice President for All

NELPA, INC.

By: _______________________________________
     Name:_________________________________
     Title:________________________________

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ELK GROUP, L.P.
(formerly known as Elcor Service Limited Partnership)

By: ELK GROUP, INC.
    (formerly known as Elcor Management Corporation),
    Its General Partner

By: _______________________________________
     Harold Beattie, Jr.
     Senior Vice President

ELK GROUP, INC.
(formerly known as Elcor Management Corporation)

By: _______________________________________
     Harold Beattie, Jr.
     Senior Vice President

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