
<PAGE>
                           OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
            (INCLUDING THE ASSOCIATED COMMON SHARE PURCHASE RIGHTS)
                                       OF
 
                                   CALMAT CO.
                                       BY
                          ALB ACQUISITION CORPORATION
                           A WHOLLY-OWNED SUBSIDIARY
                                       OF
                            VULCAN MATERIALS COMPANY
                                       AT
                          $31.00 NET PER SHARE IN CASH
 
         THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT,
 NEW YORK CITY TIME, ON FRIDAY, JANUARY 1, 1999, UNLESS THE OFFER IS EXTENDED.
 
                                                               November 20, 1998
 
To Our Clients:
 
    Enclosed for your consideration are the Offer to Purchase, dated November
20, 1998 (the "Offer to Purchase"), and the related Letter of Transmittal (which
together constitute the "Offer") relating to the offer by ALB Acquisition
Corporation, a Delaware corporation (the "Purchaser"), and a wholly-owned
subsidiary of Vulcan Materials Company, a New Jersey corporation, to purchase
all outstanding shares of Common Stock, par value $1 per share (the "Shares"),
of CalMat Co., a Delaware corporation (the "Company"), and the associated common
share purchase rights (as described in the Offer to Purchase) (the "Rights"), at
a purchase price of $31.00 per Share, net to the seller in cash, without
interest thereon, upon the terms and subject to the conditions set forth in the
Offer to Purchase and in the related Letter of Transmittal enclosed herewith.
Unless the context otherwise requires, all references to Shares shall include
the associated Rights. Holders of Shares whose certificates for such Shares (the
"Share Certificates") are not immediately available, or who cannot deliver their
Share Certificates and all other required documents to the Depositary on or
prior to the Expiration Date (as defined in the Offer to Purchase), or who
cannot complete the procedures for book-entry transfer on a timely basis, must
tender their Shares according to the guaranteed delivery procedures set forth in
Section 3 of the Offer to Purchase.
 
    WE ARE THE HOLDER OF RECORD OF SHARES HELD BY US FOR YOUR ACCOUNT. A TENDER
OF SUCH SHARES CAN BE MADE ONLY BY US AS THE HOLDER OF RECORD AND PURSUANT TO
YOUR INSTRUCTIONS. THE LETTER OF TRANSMITTAL IS FURNISHED TO YOU FOR YOUR
INFORMATION ONLY AND CANNOT BE USED BY YOU TO TENDER SHARES HELD BY US FOR YOUR
ACCOUNT.
 
    Accordingly, we request instructions as to whether you wish to have us
tender on your behalf any or all Shares held by us for your account pursuant to
the terms and conditions set forth in the Offer.
 
    Please note the following:
 
        1. The tender price is $31.00 per Share net to you in cash without
    interest thereon, upon the terms and subject to the conditions set forth in
    the Offer.
 
        2. The Offer is being made for all outstanding Shares.
<PAGE>
        3. The Offer is conditioned upon, among other things, Shares
    representing at least a majority of the total number of outstanding Shares
    on a fully diluted basis being validly tendered and not properly withdrawn
    prior to the expiration of the Offer. The Offer is also subject to other
    terms and conditions contained in the Offer to Purchase. See the
    Introduction and Sections 1, 14 and 15 of the Offer to Purchase.
 
        4. Tendering stockholders will not be obligated to pay brokerage fees or
    commissions or, except as otherwise provided in Instruction 6 of the Letter
    of Transmittal, stock transfer taxes on the purchase of Shares by the
    Purchaser pursuant to the Offer.
 
        5. The Offer and withdrawal rights will expire at 12:00 midnight, New
    York City time, on Friday, January 1, 1999, unless the Offer is extended.
 
        6. Payment for Shares purchased pursuant to the Offer will in all cases
    be made only after timely receipt by First Chicago Trust Company of New York
    (the "Depositary") of (a) Share Certificates or timely confirmation of the
    book-entry transfer of such Shares into the account maintained by the
    Depositary at The Depository Trust Company (the "Book-Entry Transfer
    Facility"), pursuant to the procedures set forth in Section 3 of the Offer
    to Purchase, (b) the Letter of Transmittal (or a facsimile thereof),
    properly completed and duly executed, with any required signature guarantees
    or an Agent's Message (as defined in the Offer to Purchase), in connection
    with a book-entry delivery, and (c) any other documents required by the
    Letter of Transmittal. Accordingly, payment may not be made to all tendering
    stockholders at the same time depending upon when certificates for or
    confirmations of book-entry transfer of such Shares into the Depositary's
    account at the Book-Entry Transfer Facility are actually received by the
    Depositary.
 
    If you wish to have us tender any or all of the Shares held by us for your
account, please so instruct us by completing, executing, detaching and returning
to us the instruction form set forth on the back page of this letter. If you
authorize the tender of your Shares, all such Shares will be tendered unless
otherwise specified on the back page of this letter. An envelope to return your
instructions to us is enclosed. Your instructions should be forwarded to us in
ample time to permit us to submit a tender on your behalf prior to the
expiration of the Offer.
 
    The Offer is not being made to (nor will tenders be accepted from or on
behalf of) holders of Shares residing in any jurisdiction in which the making of
the Offer or the acceptance thereof would not be in compliance with the
securities, blue sky or other laws of such jurisdiction. However, the Purchaser
may, in its discretion, take such action as it may deem necessary to make the
Offer in any jurisdiction and extend the Offer to holders of Shares in such
jurisdiction.
 
    In any jurisdiction where the securities, blue sky or other laws require the
Offer to be made by a licensed broker or dealer, the Offer is being made on
behalf of the Purchaser by Goldman, Sachs & Co., the Dealer Managers for the
Offer, or one or more registered brokers or dealers that are licensed under the
laws of such jurisdiction.
 
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<PAGE>
          INSTRUCTIONS WITH RESPECT TO THE OFFER TO PURCHASE FOR CASH
                     ALL OUTSTANDING SHARES OF COMMON STOCK
            (INCLUDING THE ASSOCIATED COMMON SHARE PURCHASE RIGHTS)
                                       OF
                                   CALMAT CO.
                                       BY
                          ALB ACQUISITION CORPORATION
                           A WHOLLY-OWNED SUBSIDIARY
                                       OF
                            VULCAN MATERIALS COMPANY
 
    The undersigned acknowledge(s) receipt of your letter and the enclosed Offer
to Purchase, dated November 20, 1998 (the "Offer to Purchase"), and the related
Letter of Transmittal (which together constitute the "Offer") in connection with
the offer by ALB Acquisition Corporation, a Delaware corporation (the
"Purchaser"), and a wholly-owned subsidiary of Vulcan Materials Company, a New
Jersey corporation, to purchase all outstanding shares of Common Stock, par
value $1 per share (the "Shares"), of CalMat Co., a Delaware corporation, and
the associated common share purchase rights (as described in the Offer to
Purchase) (the "Rights"), at a purchase price of $31.00 per Share, net to the
seller in cash, without interest thereon, upon the terms and subject to the
conditions set forth in the Offer to Purchase.
 
    This will instruct you to tender to the Purchaser the number of Shares
indicated below (or if no number is indicated below, all Shares) which are held
by you for the account of the undersigned, upon the terms and subject to the
conditions set forth in the Offer.
Number of Shares to Be Tendered: ____________ Shares*
 
--------------------------------------------------------------------------------
 
                                   SIGN BELOW
 
Account Number: _________________________ Signature(s) _________________________
 
Dated: ______________________, 1998
 
________________________________________________________________________________
                          Please type or print name(s)
 
________________________________________________________________________________
                     Please type or print address(es) heres
 
________________________________________________________________________________
                         Area Code and Telephone Number
 
________________________________________________________________________________
              Taxpayer Identification or Social Security Number(s)
 
*   Unless otherwise indicated, it will be assumed that you instruct us to
    tender all Shares held by us for your account.
 
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