Exhibit 10.1

Execution Copy – March 16, 2006
AGREEMENT
     This Agreement dated March 16, 2006, between Lafarge North America Inc., a
Maryland corporation (“Lafarge N.A.”) formerly known as Lafarge Corporation,
Kilmer Van Nostrand Co. Limited, an Ontario corporation (“Kilmer”) and Kilmer
LCW Limited, an Ontario subsidiary corporation of Kilmer (“LCW”):
     WHEREAS, on December 29, 2000, Lafarge N.A. issued a certain Warrant to
Purchase Lafarge Corporation Common Stock in favor of Kilmer, pursuant to which,
subject to the terms and conditions set forth therein, the Holder of the warrant
from December 29, 2005 through December 29, 2015 is entitled to receive
4,400,000 shares of the Common Stock of Lafarge N.A., upon the proper exercise
of the warrant, including payment of the exercise price of U.S. $29.00 per share
(the “Warrant”);
     WHEREAS, Kilmer transferred the Warrant to LCW as of August 22, 2001;
     WHEREAS, on February 21, 2006, Lafarge S.A., a société anonyme organized
under the laws of France, and the majority stockholder of Lafarge N.A.,
commenced a tender offer through its wholly-owned subsidiary Efalar Inc., a
Delaware corporation, for the shares of Common Stock of Lafarge N.A. that it
does not already own (the “Tender Offer”);
     WHEREAS, Kilmer and LCW have requested and Lafarge N.A. deems it advisable
and has agreed to amend the terms of the Warrant to abridge the warrant exercise
notice period provided in the Warrant in order to permit the Holder, should the
Holder deem it appropriate in its absolute discretion, to effect a conditional
tender to the Tender Offer, as it may be amended, or to any other tender offer
or other transaction involving the Common Stock of Lafarge N.A. that may
hereafter be implemented by any person, and Kilmer and LCW have agreed to waive
the notice of any going private transaction or change of control transaction
required, to the extent applicable, by the last paragraph of Section 1.1 of the
Warrant in respect of the Tender Offer.
     NOW, THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged by the parties hereto, Lafarge
N.A., Kilmer and LCW agree as follows:

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Execution Copy – March 16, 2006
     1. Section 3.2 of the Warrant is hereby amended inserting “(a)” prior to
the first full sentence thereof and by adding new subsections (b), (c) and
(d) as follows:
(b) At the option of the Holder and without limitation to the Holder’s ability
to exercise the Warrant in accordance with Section 3.2(a), notwithstanding
Section 3.2(a), in the event of a tender offer for Common Stock of the Company
or other transaction requiring the tender or surrender of Common Stock in order
to participate (an “Offer”), the Holder may exercise the Warrant without regard
to the thirty (30) day notice period applicable to the Notice of Exercise
provided in Section 3.2(a) at any time prior to the acceptance of shares of
Common Stock for payment pursuant to the Offer (the “Acceptance”). The Exercise
Notice delivered as provided in this Section 3.2(b) shall be in the form
attached as Attachment B hereto. Such Notice of Exercise shall be revocable by
the Holder at any time prior to the Acceptance.
(c) In the event that the Holder exercises the Warrant in accordance with
Section 3.2(b), notwithstanding Section 3.3, the Company shall instruct and use
its best efforts to cause its transfer agent to issue and deliver to the Person
or Persons entitled to receive the same a certificate or certificates for the
number of shares of Common Stock issuable upon such exercise such that the
Holder may tender in accordance with the requirements of the Offer.
(d) In the event that (i) an Offer expires without an Acceptance of the shares
tendered in connection with the Exercise Notice or (ii) the Notice of Exercise
delivered pursuant to Section 3.2(b) is revoked no later than two New York Stock
Exchange trading days prior to an Acceptance, such Notice of Exercise shall be
null and void and without any further effect and this Warrant shall continue to
be outstanding and unexercised by the Holder thereof and no exercise price shall
have been due in respect thereof (and any advance payment of exercise price
shall be returned to the Holder).

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Execution Copy – March 16, 2006
2. Kilmer and LCW hereby waive the requirement that the Holder receive prior
notice as specified in the last paragraph of Section 1.1 of the Warrant in
respect of the Tender Offer to the extent applicable.
3. Except as provided herein, the terms and conditions of the Warrant have not
been amended, modified or waived and remain in full force and effect. Initially
capitalized terms used herein without definition shall have the same definitions
assigned to them in the Warrant.
[Signature page follows]

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Execution Copy – March 16, 2006
     IN WITNESS WHEREOF, each of the undersigned has caused this Agreement to be
executed and delivered by a duly authorized person on the date first written
above.

            LAFARGE NORTH AMERICA INC.
      By:   /s/ Eric C. Olsen         Name:           Title:           KILMER
VAN NOSTRAND CO. LIMITED
      By:   /s/ Lawrence M. Tanenbaum         Name:           Title:          
KILMER LCW LIMITED
      By:   /s/ Lawrence M. Tanenbaum         Name:           Title:        

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ATTACHMENT B
CONDITIONAL NOTICE OF EXERCISE

To:   LAFARGE NORTH AMERICA INC. (the “Company”)

     The undersigned hereby elects to exercise the right to purchase set forth
within and represented by the Warrant attached hereto
                                        shares of Common Stock of the Company as
provided for therein, which exercise is to be effective as of the date that,
pursuant to the offer made by                                          [name of
offeror] for Common Stock of the Company pursuant to
                                        [title of document implementing the
Offer] (the “Offer”), such shares of Common Stock have been accepted for payment
(the “Acceptance”, and the date thereof, the “Exercise Date”) and agrees to
tender no later than the first business day immediately following such Exercise
Date (unless the Acceptance occurs prior to 11:00 a.m. Maryland time, in which
case such purchase price shall be paid on such Exercise Date) payment of the
full purchase price for such shares in the form of a wire transfer in
immediately available funds, or by such other means as may be agreed by the
Company and the Holder, in the aggregate amount of $                      U.S.
Dollars. If said number of shares shall not be all the shares purchasable under
the within Warrant, a new Warrant Certificate is to be issued in the name of
said undersigned for the balance remaining of the shares purchasable thereunder
less any fraction of a share paid in cash. Please issue a certificate or
certificates for such shares of Common Stock in the name of, and pay any cash
for any fractional share to                     .
     In the event that the Offer expires without an Acceptance, this Notice of
Exercise shall be null and void and without any further effect and the Warrant
attached hereto shall continue to be outstanding and unexercised by the Holder
thereof.
     This Conditional Notice of Exercise shall be revocable by the Holder by
notice in writing to the Company (including by facsimile transmission) addressed
to its General Counsel at any time prior to two New York Stock Exchange trading
days prior to an acceptance of shares of Common Stock for payment pursuant to
the Offer.
     The undersigned certifies that he/she is not a U.S. person and the warrant
being exercised hereby is not being exercised on behalf of a U.S. person as such
term is defined within Regulation 902(k) promulgated under the Securities Act of
1933, as amended.
Dated:                     , 20     

             
By:
      Signature:    
 
           
 
  Print Name:        

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