
<PAGE>   1
                                                                EXHIBIT 10.9



[BANK OF AMERICA LOGO]


                                                                February 5, 1993



CalMat Co.
P.O. Box 2950
3200 San Fernando Road
Los Angeles, CA 90065
Attention:  Frederick T. Sauer
            Vice President & Treasurer

                 Re:  Credit Agreement dated as of June 30, 1992, as amended

Gentlemen:

         We refer to the Credit Agreement dated as of June 30, 1992, as
amended, (the "Credit Agreement") among CalMat Co. (the "Borrower"), the banks
parties thereto (the "Lenders"), and Bank of America National Trust and Savings
Association, as agent (the "Agent").  Capitalized terms not otherwise defined
herein shall have the meanings specified in the Credit Agreement.

         You notified the Agent that the Borrower will be in default under
Sections 6.6B and 6.6D of the Credit Agreement.  The Borrower has requested the
Lenders and the Agent, and the Lenders and Agent are willing, on the terms and
conditions set forth below, to waive the foregoing defaults and to also
temporarily modify Section 6.1(v) of the Credit Agreement.

         1.      Subject to paragraph 4 hereof, the Lenders and the Agent agree
to waive, through and including March 30, 1993, any default under Sections 6.6B
and 6.6D of the Credit Agreement for the period ending December 31, 1992, and
further agree to temporarily modify Section 6.1(v) of the Credit Agreement
through and including March 30, 1993 by increasing the limit on the aggregate
principal amount of Indebtedness which has any scheduled payment on or prior to
the Maturity Date from $42,500,000 to $47,500,000.

         2.      As an inducement to the Agent and the Lenders to grant these
waivers and make this modification, the Company hereby represents and warrants
that:  (a) except as waived







      Bank of America National Trust and Savings Association
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CalMat Co.
February 5, 1993
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herein, the representations and warranties set forth in Section 4 of the
Agreement are true and correct in all respects on and as of the date hereof as
though made on and as of the date hereof; (b) except as waived herein, no
Potential Event of Default or Event of Default exists; (c) no default or event
of default exists under the Credit Agreement dated as of August 1, 1988, as
amended, among the Borrower, the banks listed therein and Morgan Guaranty Trust
Company of New York, as agent (the "Morgan Agreement"); and (d) no default or
event of default exists under the Credit Agreement dated as of August 20, 1991,
as amended, among the Borrower, the lenders listed therein and The First
National Bank of Chicago, as agent (the "First Chicago Agreement").  The
effectiveness of these waivers and modification is expressly conditioned upon
the foregoing being true and correct.

         3.      If a default or event of default exists under the Morgan
Agreement or the First Chicago Agreement, the effectiveness of these waivers
and modification is expressly further conditioned upon the Agent receiving
evidence satisfactory to it that any such default or event of default
thereunder has been cured or waived through at least March 30, 1993.

         4.      If a default or event of default occurs under the Morgan
Agreement or the First Chicago Agreement after the date hereof, the waivers and
modification made hereunder shall thereupon expire.  The Company agrees to give
immediate notice to Agent of any such default or event of default.

         5.      The waivers and modification set forth in this letter are
specific in time and in intent and do not constitute, nor should they be
construed as constituting, a waiver or modification of any other term of, or
right, power or privilege under, the Loan Documents or under any agreement,
contract, indenture, document or instrument mentioned in the Loan Documents.
Such waivers and modification do not preclude any or further exercise of any
other right, power or privilege under any Loan Document or under any agreement,
contract, indenture, document or instrument mentioned therein, including
without limitation the taking of any action based upon an Event of Default
occurring under Section 7.4 of the Credit Agreement, whether or not based upon
a default under any provisions similar

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CalMat Co.
February 5, 1993
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to those waived or modified herein which are contained in other agreements
relating to Indebtedness or Contingent Obligations.

         6.      Upon the expiration of these waivers and modification, the
Lenders and Agent may exercise any of their rights, remedies, powers or
privileges under the Credit Agreement with respect to the defaults waived
herein or the section modified hereby, including without limitation, declaring
an Event of Default based upon such defaults and/or based upon the Borrower's
failure to thereafter be in compliance with Section 6.1(v) as it existed prior
to the modification set forth herein.

         If the foregoing accurately sets forth our agreement please sign and
return a copy of this letter where indicated below.


                                           Very truly yours,


                                           BANK OF AMERICA NATIONAL
                                           TRUST AND SAVINGS ASSOCIATION,
                                           as Agent


                                           By:     /s/ Jouni Korhonen   
                                                  ----------------------
                                                  Jouni Korhonen
                                                  Vice President


                                           BANK OF AMERICA NATIONAL
                                           TRUST AND SAVINGS ASSOCIATION,
                                           as a Bank


                                           By:     /s/ Valerie Milner   
                                                  ----------------------
                                                  Valerie Milner
                                                  Vice President

(Signatures continue)


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CalMat Co.
February 5, 1993
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                                           THE VALLEY NATIONAL BANK OF ARIZONA


                                           By:    /s/ John Abbott       
                                                  ----------------------
                                           Name:      JOHN ABBOTT       
                                                  ----------------------
                                           Title:     VICE PRESIDENT    
                                                  ----------------------


                                           CHEMICAL BANK


                                           By:    /s/ Alan J. Cyron            
                                                  ----------------------
                                           Name:      ALAN J. CYRON            
                                                  ----------------------
                                           Title:     MANAGING DIRECTOR     
                                                  ----------------------


                                           THE CHASE MANHATTAN BANK, N.A.


                                           By:     /s/ Alexander S. Rapetski II
                                                  --------------------------
                                           Name:   ALEXANDER S. RAPETSKI II
                                                  --------------------------
                                           Title:      VICE PRESIDENT       
                                                  --------------------------



AGREED AND ACCEPTED:

CALMAT CO.


By:  /s/ Ronald C. Hadfield
     ----------------------
Ronald C. Hadfield, Exec VP/Fin & Admin
Date:                     
       -------------------

By:  /s/ Frederick T. Sauer
     ----------------------
Frederick T. Sauer, VP & Treasurer


