Document:

<PAGE>

                                                                   Exhibit 10.35
                                    JOINDER

     Radnor Delaware II, Inc., a Delaware corporation (the "New Credit Party"),
hereby joins in the Fourth Amended and Restated Revolving Credit and Security
Agreement dated as of December 26, 2001 ("Credit Agreement") between WinCup
Holdings, Inc., Radnor Chemical Corporation, Radnor Holdings Corporation,
StyroChem U.S., Ltd., StyroChem Delaware, Inc., WinCup Texas, Ltd., StyroChem
GP, L.L.C., StyroChem LP, L.L.C., WinCup GP, L.L.C. and WinCup LP, L.L.C. (each,
a "Borrower" and jointly and severally, the "Borrowers"), the financial
institutions which are or became parties thereto (collectively, the "Lenders")
and PNC Bank, National Association, as agent of the Lenders (in such capacity,
the "Agent") as a "Borrower" thereunder and agrees to assume in full and become
jointly and severally liable for all of the Obligations (as defined in the
Credit Agreement) of the Borrowers thereunder and under any other agreement
between Borrowers, Agent and Lenders. Without limiting the generality of the
foregoing, in order to secure the prompt payment and performance to Agent and
Lenders of the Obligations, the New Credit Party hereby assigns, pledges and
grants to Agent a continuing security interest in and to all of its Collateral
(as defined in the Credit Agreement), whether now owned or existing or hereafter
acquired or arising and wheresoever located.  The undersigned further agrees to
deliver to Agent each of the documents described on Exhibit A attached hereto.

     IN WITNESS WHEREOF, and intending to be legally bound hereby, the New
Credit Party has duly executed this Joinder as of the 24/th/ day of January,
                                                      ------        --------
2002.

                                   RADNOR DELAWARE II, INC.

                                   By: /s/ Michael T. Kennedy
                                       ------------------------
                                   Name: Michael T. Kennedy
                                   Title:  Chairman

                                       1
<PAGE>

                          ACKNOWLEDGEMENT OF JOINDER

     The undersigned parties to the Credit Agreement hereby acknowledge and
agree to the joinder of Radnor Delaware II, Inc., as a Borrower under the Credit
Agreement.

IN WITNESS WHEREOF, and intending to be legally bound hereby, each of the
undersigned has duly executed this acknowledgement as of the 24/th/ day of
                                                             ------
January, 2002.
-------

                              WINCUP HOLDINGS, INC.

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                  Michael T. Kennedy, President

                              RADNOR CHEMICAL CORPORATION

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                  Michael T. Kennedy, Chairman

                              STYROCHEM U.S., LTD.,
                              By: StyroChem GP, L.L.C.,
                                    its general partner,
                              By: Radnor Chemical Corporation,
                                    its sole member

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                  Michael T. Kennedy, Chairman

                              RADNOR HOLDINGS CORPORATION

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                  Michael T. Kennedy, President

                              STYROCHEM DELAWARE, INC.

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                  Michael T. Kennedy, Chairman

                                       2
<PAGE>

                              WINCUP TEXAS, LTD.
                              By: WinCup GP, L.L.C.,
                                    its general partner,
                              By: WinCup Holdings, Inc.,
                                    its sole member

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                    Michael T. Kennedy, President

                              STYROCHEM GP, L.L.C.
                              By: Radnor Chemical Corporation,
                                    its sole member

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                    Michael T. Kennedy, Chairman

                              STYROCHEM LP, L.L.C.
                              By: Radnor Chemical Corporation,
                                    its sole member

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                    Michael T. Kennedy, Chairman

                              WINCUP GP, L.L.C.
                              By: WinCup Holdings, Inc.,
                                    its sole member

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                    Michael T. Kennedy, President

                              WINCUP LP, L.L.C.
                              By: WinCup Holdings, Inc.,
                                    its sole member

                              By: /s/ Michael T. Kennedy
                                  -------------------------------
                                    Michael T. Kennedy, President

                                       3
<PAGE>

                                    PNC BANK NATIONAL ASSOCIATION, as Lender

                                    By: /s/Janeann Fehrle, VP
                                        ---------------------------
                                    Name: Janeann Fehrle
                                    Title: VP

                                       4
<PAGE>

                                   Exhibit A

     (1) Schedules to the Credit Agreement updated to reflect the joinder of the
New Credit Party, as an additional Borrower thereto.

     (2) A copy of the resolution in form and substance reasonably satisfactory
to Agent, of the Board of Directors of the New Credit Party authorizing the
execution, delivery and performance of the joinder, the Credit Agreement and the
granting Liens upon its Collateral, certified by the Secretary or an Assistant
Secretary of the New Credit Party, as of the date of this joinder.

     (3) A copy of the Certificate of Incorporation of the New Credit Party, and
all amendments thereto, certified by the Secretary of State or other appropriate
official of its jurisdiction of incorporation with copies of the By-Laws of the
New Credit Party, certified as accurate and complete by the Secretary or an
Assistant Secretary of the New Credit Party.

     (4) A good standing certificate for the New Credit Party, dated not more
than thirty (30) days prior to the date of this joinder, issued by the Secretary
of State or other appropriate official of the New Credit Party's jurisdiction of
incorporation and each jurisdiction where the conduct of the New Credit Party's
business activities or the ownership of its properties necessitates
qualification.

     (5) Executed legal opinion of Duane, Morris & Heckscher LLP, counsel to the
New Credit Party, in form and substance satisfactory to Agent regarding the due
authorization, enforceability and validity of the joinder and the transactions
contemplated herein.

     (6) Any documents, agreements or instruments necessary, as determined by
Agent, to continue the effectiveness and maintain the priority of the security
interests in all Collateral that was assigned or transferred from Radnor
Delaware, Inc. to another entity.

                                       5<PAGE>

                                                                   EXHIBIT 10.36

                         COMMITMENT TRANSFER SUPPLEMENT

     COMMITMENT TRANSFER SUPPLEMENT, dated as of February 4, 2002, among PNC
Bank, National Association (the "Transferor Lender"), Fleet Capital Corporation,
("Purchasing Lender"), and PNC Bank, National Association, as agent for the
Lenders under the Fourth  Amended and Restated Revolving Credit and Security
Agreement described below (in such capacity, the "Agent").

                              W I T N E S S E T H
                              - - - - - - - - - -

     WHEREAS, this Commitment Transfer Supplement is being executed and
delivered in accordance with Section 15.3 of that certain Fourth Amended and
Restated Revolving Credit and Security Agreement dated as of December 26, 2001
among WinCup Holdings, Inc., Radnor Chemical Corporation, Radnor Holdings
Corporation, Radnor Delaware II, Inc., StyroChem U.S., Ltd., StyroChem Delaware,
Inc., WinCup Texas, Ltd, StyroChem GP II, L.L.C., StyroChem LP, L.L.C., WinCup
GP, L.L.C. and WinCup LP, L.L.C. (each, a "Borrower" and jointly and severally,
the "Borrowers"), PNC Bank, National Association ("PNC"), each of the other
financial institutions named in or which hereafter become a party thereto (PNC
and such other financial institutions, the "Lenders") and PNC, as Agent  (as
same may be amended, supplemented or otherwise modified in accordance with the
terms thereof, the "Credit Agreement");

     WHEREAS, Purchasing Lender wished to become a Lender party to the Credit
Agreement; and

     WHEREAS, the Transferor Lender is selling and assigning to Purchasing
Lender rights, obligations and commitments under the Credit Agreement;

     NOW, THEREFORE, the parties hereto hereby agree as follows:

     1.  All capitalized terms used herein which are not defined shall have the
meanings given to them in the Credit Agreement.

     2.  Upon receipt by the Agent of four counterparts of this Commitment
Transfer Supplement, to each of which is attached a fully completed Schedule I,
                                                                    ----------
and each of which has been executed by the Transferor Lender and Agent, Agent
will transmit to Transferor Lender and Purchasing Lender a Transfer Effect
Notice, substantially in the form of Schedule II to this Commitment Transfer
                                     -----------
Supplement (a "Transfer Effective Notice").  Such Transfer Effective Notice
shall set forth, inter alia, the date on which the transfer effected by this
                 ----- ----
Commitment Transfer Supplement shall become effective (the "Transfer Effective
Date"), which date unless otherwise noted therein, shall not be earlier than the
first Business Day following the date such Transfer Effective Notice is
received.  From and after the Transfer Effective Date, Purchasing Lender shall
be a Lender party to the Credit Agreement for all purposes thereof.
<PAGE>

     3.  At or before 12:00 Noon (Philadelphia time) on the Transfer Effective
Date Purchasing Lender shall pay to Transferor Lender, in immediately available
funds, an amount equal to the purchase price, as agreed between Transferor
Lender and such Purchasing Lender (the "Purchase Price"), of the portion of the
Advances being purchased by such Purchasing Lender (such Purchasing Lender's
"Purchased Percentage") of the outstanding Advances and other amounts owing to
the Transferor Lender under the Credit Agreement, and the Note(s).  Effective
upon receipt by Transferor Lender of the Purchase Price from a Purchasing
Lender, Transferor Lender hereby irrevocably sells, assigns and transfers to
such Purchasing Lender, without recourse, representation or warranty, and
Purchasing Lender hereby irrevocably purchases, takes and assumes from
Transferor Lender, such Purchasing Lender's Purchased Percentage of the Advances
and other amounts owing to the Transferor Lender under the Credit Agreement and
the Note(s) together with all instruments, documents and collateral security
pertaining thereto.

     4.  Transferor Lender has made arrangements with Purchasing Lender with
respect to (i) the portion, if any, to be paid, and the date or dates for
payment, by Transferor Lender to such Purchasing Lender of any fees heretofore
received by Transferor Lender pursuant to the Credit Agreement prior to the
Transfer Effective Date and (ii) the portion, if any, to be paid, and the date
or dates of payment, by such Purchasing Lender to Transferor Lender of fees or
interest received by such Purchasing Lender pursuant to the Credit Agreement
from and after the Transfer Effective Date.

     5.  (a)  All principal payments that would otherwise be payable from and
after the Transfer Effective Date to or for the account of Transferor Lender
pursuant to the Credit Agreement and the Note(s) shall, instead, be payable to
or for the account of Transferor Lender and Purchasing Lender, as the case may
be, in accordance with their respective interests as reflected in this
Commitment Transfer Supplement.

         (b)  All interest, fees and other amounts that would otherwise accrue
for the account of Transferor Lender from and after the Transfer Effective Date
pursuant to the Credit Agreement and the Note(s) shall, instead, accrue for the
account of, and be payable to, Transferor Lender and Purchasing Lender, as the
case may be, in accordance with their respective interests as reflected in this
Commitment Transfer Supplement. In the event that any amount of interest, fees
or other amounts accruing prior to the Transfer Effective Date was included in
the Purchase Price paid by any Purchasing Lender, Transferor Lender and
Purchasing Lender will make appropriate arrangements for payment by Transferor
Lender to such Purchasing Lender of such amount upon receipt thereof from
Borrowers.

     6.  Concurrently with the execution and delivery hereof, Transferor Lender
will provide to Purchasing Lender conformed copies of the Credit Agreement and
all related documents delivered to Transferor Lender.

     7.  Each of the parties to this Commitment Transfer Supplement agrees that
at any time and from time to time upon the written request of any other party,
it will execute and deliver

                                       2
<PAGE>

such further documents and do such further acts and things as such other party
may reasonably request in order to effect the purposes of this Commitment
Transfer Supplement.

     8.  By executing and delivering this Commitment Transfer Supplement,
Transferor Lender and Purchasing Lender confirm to and agree with each other and
Agent and Lenders as follows:  (i) other than the representation and warranty
that it is the legal and beneficial owner of the interest being assigned hereby
free and clear of any adverse claim, Transferor Lender makes no representation
or warranty and assumes no responsibility with respect to any statements,
warranties or representations made in or in connection with the Credit Agreement
or the execution, legality, validity, enforceability, genuineness, sufficiency
or value of the Credit Agreement, the Note(s) or any other instrument or
document furnished pursuant thereto;  (ii) Transferor Lender makes no
representation or warranty and assumes no responsibility with respect to the
financial condition of Borrowers or the performance or observance by Borrowers
of any of their Obligations under the Credit Agreement, the Note(s) or any other
instrument or document furnished pursuant hereto;  (iii)  Purchasing Lender
confirms that it has received a copy of the Credit Agreement, together with
copies of such financial statements and such other documents and information as
it has deemed appropriate to make its own credit analysis and decision to enter
into this Commitment Transfer Supplement; (iv) Purchasing Lender will,
independently and without reliance upon Agent, Transferor Lender or any other
Lenders and based on such documents and information as it shall deem appropriate
at the time, continue to make its own credit decisions in taking or not taking
action under the Credit Agreement;  (v)  Purchasing Lender appoints and
authorizes Agent to take such action as agent on its behalf and to exercise such
powers under the Credit Agreement as are delegated to the Agent by the terms
thereof;  (vi) Purchasing Lender agrees that it will perform all of its
respective obligations as set forth in the Credit Agreement to be performed by
each as a Lender; and (vii) Purchasing Lender represents and warrants to
Transferor Lender, Lenders, Agent and Borrower that it is either (x) entitled to
the benefits of an  income tax treaty with the United States of America that
provides for an exemption from the United States withholding tax on interest and
other payments made by Borrowers under the Credit Agreement and Other Documents
or (y) is engaged in trade or business within the United States of America.

     9.  Schedule I hereto sets forth the revised Commitment Percentages of
         ----------
Transferor Lender and the Commitment Percentage of Purchasing Lender as well as
administrative information with respect to Purchasing Lender.

     10.  This Commitment Transfer Supplement shall be governed by, and
construed in accordance with, the laws of the Commonwealth of Pennsylvania.

                        [Signatures Begin on Next Page]

                                       3
<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Commitment Transfer
Supplement to be executed by their respective duly authorized officers on the
date set forth above.

                                               PNC BANK, NATIONAL ASSOCIATION
                                               as Transferor Lender

                                               By:  /S/ JANEANN FEHRLE, VP
                                                  ------------------------------
                                                  Janeann Fehrle, Vice President

                                               FLEET CAPITAL CORPORATION
                                               As Purchasing Lender

                                               By:   /S/ DAVID FIORITO
                                                  ------------------------------
                                               Name:  David Fiorito
                                                    ----------------------------
                                               Title: SVP
                                                     ---------------------------

                                               PNC BANK, NATIONAL ASSOCIATION
                                               as Agent

                                               By:   /S/ JANEANN FEHRLE, VP
                                                  ------------------------------
                                                  Janeann Fehrle, Vice President

Consented to:

WINCUP HOLDINGS, INC.

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

RADNOR CHEMICAL CORPORATION

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

                             Signature Page 1 of 3
<PAGE>

STYROCHEM U.S., LTD.
By: StyroChem GP, LLC, its General Partner
 By: Radnor Chemical Corporation, its Sole Member

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

RADNOR HOLDINGS CORPORATION

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

RADNOR DELAWARE II, INC.

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

STYROCHEM DELAWARE, INC.

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

WINCUP TEXAS, LTD.
By: WinCup GP, LLC, its General Partner
 By: WinCup Holdings, Inc., its Sole Member

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

STYROCHEM GP, L.L.C.
By: Radnor Chemical Corporation, its Sole Member

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

                             Signature Page 2 of 3
<PAGE>

STYROCHEM LP, L.L.C.
By: Radnor Chemical Corporation, its Sole Member

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

WINCUP GP, L.L.C.
By: WinCup Holdings, Inc. its Sole Member

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

WINCUP LP, L.L.C.
By: WinCup Holdings, Inc. its Sole Member

By:  /S/ R. RADCLIFFE HASTINGS
     ----------------------------------------------------
     R. Radcliffe Hastings, Sr. Vice President, Treasurer

                             Signature Page 3 of 3
<PAGE>

                 SCHEDULE I TO COMMITMENT TRANSFER SUPPLEMENT

LIST OF OFFICES, ADDRESSES FOR NOTICES AND COMMITMENT AMOUNTS
-------------------------------------------------------------

<TABLE>
<S>                                        <C>                                 <C>
PNC Bank, National Association             Revised Commitment Amount                $  20,000,000

                                           Revised Commitment Percentage            57.142857143%

Fleet Capital Corporation                  Commitment Amount                        $  15,000,000

                                           Commitment Percentage                    42.857142857%
</TABLE>

Addresses for Notices for Fleet Capital
---------------------------------------
Corporation
-----------

Attention:
Telephone:
Telecopier:
<PAGE>

                SCHEDULE II TO COMMITMENT TRANSFER SUPPLEMENT

                      [Form of Transfer Effective Notice]

To: _________________, as Transferor Lender and _________________, as Purchasing
Lender:

          The undersigned, as Agent under the Fourth Amended and Restated
Revolving Credit and Security Agreement dated as of December 26, 2001 between
WinCup Holdings, Inc., Radnor Chemical Corporation, Radnor Holdings Corporation,
Radnor Delaware II, Inc., StyroChem U.S., Ltd., StyroChem Delaware, Inc., Wincup
Texas, Ltd., StyroChem GP, L.L.C., StyroChem LP, L.L.C., WinCup GP, L.L.C. and
WinCup LP, L.L.C. (each, a "Borrower" and jointly and severally, the
"Borrowers"), PNC Bank, National Association ("PNC"), each of the other
financial institutions named in or which hereafter become a party thereto (PNC
and such other financial institutions, the "Lenders") and PNC as agent for the
Lenders, acknowledges receipt of four (4) executed counterparts of a completed
Commitment Transfer Supplement in the form attached hereto. [Note: Attach copy
of Commitment Transfer Supplement.] Terms defined in such Commitment Transfer
Supplement are used herein as therein defined.

          Pursuant to such Commitment Transfer Supplement, you are advised that
the Transfer Effective Date will be [Insert date of Transfer Effective Notice].

                                                 PNC BANK, NATIONAL ASSOCIATION,
                                                 as Agent

                                                 By:
                                                    ----------------------------
                                                 Title:
                                                       -------------------------

ACCEPTED FOR RECORDATION
 IN REGISTER:
<PAGE>

                           Transfer Effective Notice

To:  PNC Bank, National Association, as Transferor Lender and Fleet Capital
Corporation, as Purchasing Lender:

          The undersigned, as Agent under the Fourth Amended and Restated
Revolving Credit and Security Agreement dated as of December 26, 2001 between
WinCup Holdings, Inc., Radnor Chemical Corporation, Radnor Holdings Corporation,
Radnor Delaware II, Inc., StyroChem U.S., Ltd., StyroChem Delaware, Inc., Wincup
Texas, Ltd., StyroChem GP, L.L.C., StyroChem LP, L.L.C., WinCup GP, L.L.C. and
WinCup LP, L.L.C. (each, a "Borrower" and jointly and severally, the
"Borrowers"), PNC Bank, National Association ("PNC"), each of the other
financial institutions named in or which hereafter become a party thereto (PNC
and such other financial institutions, the "Lenders") and PNC as agent for the
Lenders, acknowledges receipt of four (4) executed counterparts of a completed
Commitment Transfer Supplement in the form attached hereto.  Terms defined in
such Commitment Transfer Supplement are used herein as therein defined.

          Pursuant to such Commitment Transfer Supplement, you are advised that
the Transfer Effective Date will be February 4, 2002.

                                               PNC BANK, NATIONAL ASSOCIATION,
                                               as Agent

                                               By: /s/  Janeann Fehrle, VP
                                                  ------------------------------
                                                  Janeann Fehrle, Vice President

ACCEPTED FOR RECORDATION
 IN REGISTER:

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