<PAGE>
                                                                   EXHIBIT 10.21


                                                                  Execution Copy


                   REVISED FIFTH AMENDMENT TO PARENT GUARANTY

               This Revised Fifth Amendment to Parent Guaranty (the "Revised
Amendment") is entered into as of September 23, 2002, to a certain Second
Amended and Restated Parent Guaranty dated as of August 1, 1999, as amended by a
certain Amendment to Parent Guaranty dated as of September 29, 2000, as amended
by a certain Second Amendment to Parent Guaranty and Waiver dated as of March
13, 2001, as amended by a certain Third Amendment to Parent Guaranty dated as of
April 12, 2001, and as amended by a certain Fourth Amendment to Parent Guaranty
dated as of January 18, 2002 and effective as of September 30, 2001
(collectively, the "Parent Guaranty") issued by Caraustar Industries, Inc., a
North Carolina corporation (the "Guarantor"), in favor of Toronto Dominion
(Texas), Inc., as administrative agent for the Lenders and the Issuing Bank (the
"Administrative Agent") (capitalized terms not otherwise defined herein shall
have the meanings ascribed to such terms in the Parent Guaranty).

                                   WITNESSETH:

               WHEREAS, an affiliate of the Administrative Agent has issued for
the account of Standard Gypsum, L.P., a Delaware limited partnership and the
successor by conversion to Standard Gypsum, L.L.C., a Texas limited liability
company (the "Borrower"), a letter of credit in the aggregate original face
amount of $46,643,014 (the "First Letter of Credit"), pursuant to a
Reimbursement Agreement (the "First Reimbursement Agreement") dated as of May 1,
1999 between the Borrower and the issuer of the Letter of Credit (the "Issuing
Bank"); and

               WHEREAS, the Issuing Bank has also issued for the account of the
Borrower an additional letter of Credit in the aggregate original face amount of
$10,095,891 (the "Second Letter of Credit" and, collectively with the First
Letter of Credit, the "Letter of Credit"), pursuant to a Reimbursement Agreement
(the "Second Reimbursement Agreement" and, collectively with the First
Reimbursement Agreement, the "Reimbursement Agreement") dated as of August 1,
1999 between the Borrower and Issuing Bank; and

               WHEREAS, Toronto Dominion (Texas), Inc. acts as Administrative
Agent for itself and for the benefit of the Issuing Bank in connection with the
transactions contemplated by the Reimbursement Agreement; and

               WHEREAS, the Borrower is a fifty percent (50%) subsidiary of the
Guarantor and the Guarantor, in connection with the transactions contemplated by
the Reimbursement Agreement, has agreed to guarantee fifty percent (50%) of the
obligations and covenants of the Borrower under the Reimbursement Agreement and
the other Loan Documents (the Reimbursement Agreement and the other Loan
Documents as previously executed and as amended, modified or extended from time
to time, the "Guaranteed Agreements"); and

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               WHEREAS, the Guarantor, certain of its subsidiaries, the Lenders
thereunder, and Bank of America, N.A., as administrative agent, are parties to
that certain Credit Agreement dated as of March 29, 2001 (as amended, restated
or otherwise modified from time to time, the "Guarantor Credit Agreement"); and

               WHEREAS, the parties to the Guarantor Credit Agreement have
agreed to amend the provisions thereof and, in connection therewith, to enter
into a Security Agreement (the "Security Agreement") under which the Guarantor
and its subsidiaries party thereto will provide Bank of America, N.A., as
administrative agent, and the Lenders thereunder with a lien on certain of their
assets, and such parties have further agreed that the Administrative Agent is an
intended third party beneficiary, for itself and on behalf of the Issuing Bank,
of such lien and shall share in the distribution of proceeds from any recovery
from such assets in accordance with the provisions of the Security Agreement;
and

               WHEREAS, the parties previously entered into that certain Fifth
Amendment to Parent Guaranty dated as of June 3, 2002 (the "June 2002
Amendment"), which contained certain amendments to the Parent Guaranty and other
agreements among the parties with respect to the Parent Guaranty; and

               WHEREAS, notwithstanding the fact that the June 2002 Amendment
was executed by the parties and deemed closed as of June 3, 2002, the June 2002
Amendment contained certain conditions to effectiveness that have not been
satisfied and, accordingly, the June 2002 Amendment has not become effective
except to the extent provided therein; and

               WHEREAS, the Guarantor has requested that the Administrative
Agent, the Lenders and the Issuing Bank agree to amend certain provisions of the
Parent Guaranty, and the Administrative Agent, for itself and on behalf of the
Lenders and the Issuing Bank, has agreed to such amendments on the terms and
conditions set forth herein, and the parties intend for this Revised Amendment
to amend, restate and replace in its entirety the June 2002 Amendment, and the
June 2002 Amendment shall have no further force and effect; and

               NOW, THEREFORE, in consideration of the foregoing premises and
other good and valuable consideration, the receipt and sufficiency of which are
acknowledged, the parties hereby agree that, as of the Effective Date (as
defined below), the June 2002 Amendment is amended, restated and replaced in its
entirety as set forth herein, and further agree as follows:

        1.     Amendment and Restatement of Section 18(a) of the Parent
Guaranty.

                      (a)    Section 18 of the Parent Guaranty is hereby amended
and restated by deleting the existing Section 18(a)(i) in its entirety and by
substituting the following therefor:

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                      "(i) At all times after the Fourth Amendment Effective
               Date (as defined in the Credit Agreement dated as of March 29,
               2001 among the Guarantor, certain of its subsidiaries, the
               Lenders thereunder, and Bank of America, N.A., as Administrative
               Agent (as in effect on the Effective Date of the Revised Fifth
               Amendment to this Guaranty, the "Guarantor Credit Agreement")),
               the Guarantor and the other Credit Parties (as defined in the
               Guarantor Credit Agreement) shall not permit Tangible Net Worth
               to be less than the TNW Floor (as defined below) plus, as of the
               end of each fiscal quarter, commencing with the end of the first
               fiscal quarter ending after the Fourth Amendment Effective Date,
               (i) 50% of Net Income (to the extent positive) for the fiscal
               quarter then ended (or, with respect to the fiscal quarter in
               which the JS Industrial Packaging Group Acquisition (as defined
               below) occurs, for the portion of the fiscal quarter occurring
               after the date such acquisition is consummated), such increases
               to be cumulative, and (ii) 100% of the net cash proceeds of
               equity issuances during the fiscal quarter then ended (or, with
               respect to the fiscal quarter in which the JS Industrial
               Packaging Group Acquisition occurs, for the portion of the fiscal
               quarter occurring after the date such acquisition is
               consummated), such increases to be cumulative.

               "For purposes hereof, "TNW Floor" shall mean (A) initially,
               $108,900,000 and (B) upon the consummation of the JS Industrial
               Packaging Group Acquisition, 90% of actual Tangible Net Worth as
               of the date of such consummation (and after giving effect
               thereof), as calculated in good faith by the Guarantor and as
               certified in writing to Bank of America, N.A., as administrative
               agent under the Guarantor Credit Agreement, on the date of such
               consummation by a responsible officer of the Guarantor. "JS
               Industrial Packaging Group Acquisition" shall mean the
               Guarantor's acquisition from Jefferson Smurfit Corporation (U.S.)
               of the business referred to as the "JS Industrial Packaging
               Group" for an aggregate consideration of approximately
               $90,000,000 (plus approximately $5,000,000 of transaction
               costs)."

                      (b)    Section 18 of the Parent Guaranty is hereby further
amended and restated by deleting the existing table contained in Section
18(a)(ii) in its entirety and by substituting the following therefor:

<TABLE>
<CAPTION>
               ----------------------------------------------------------------------
                                                                  Maximum Total
                               Period                            Leverage Ratio
               ----------------------------------------------------------------------
<S>                                                              <C>
               fiscal quarter ending March 31, 2001                   72.5%
               ----------------------------------------------------------------------
               fiscal quarter ending June 30, 2001                    72.5%
               ----------------------------------------------------------------------
               fiscal quarter ending September 30, 2001               72.5%
               ----------------------------------------------------------------------
               fiscal quarter ending December 31, 2001                72.5%
               ----------------------------------------------------------------------
               fiscal quarter ending March 31, 2002                   70.0%
               ----------------------------------------------------------------------
</TABLE>


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<TABLE>
<S>                                                              <C>
               fiscal quarter ending June 30, 2002                    70.0%
               ----------------------------------------------------------------------
               fiscal quarter ending September 30, 2002               70.0%
               ----------------------------------------------------------------------
               fiscal quarter ending December 31, 2002                70.0%
               ----------------------------------------------------------------------
               fiscal quarter ending March 31, 2003                   70.0%
               ----------------------------------------------------------------------
               fiscal quarter ending June 30, 2003                    70.0%
               ----------------------------------------------------------------------
               fiscal quarter ending September 30, 2003               67.5%
               ----------------------------------------------------------------------
               fiscal quarter ending December 31, 2003 and            65.0%
               each fiscal quarter ending thereafter
               ----------------------------------------------------------------------
</TABLE>


                      (c)    Section 18 of the Parent Guaranty is hereby further
amended and restated by deleting the existing Section 18(a)(iii) in its entirety
and by substituting the following therefor:

                      "(iii) Guarantor shall maintain a Fixed Charge Coverage
               Ratio, measured as of the end of each fiscal quarter ending on or
               after September 30, 2002, of 1.50 to 1.00.

               For purposes of the foregoing financial covenant, "Fixed Charge
               Coverage Ratio" shall mean the ratio of the Guarantor's EBITDA
               minus Capital Expenditures (each as defined in the Guarantor
               Credit Agreement) to the sum of the Guarantor's Interest Expense
               plus Cash Taxes plus Dividends plus Scheduled Debt Payments (each
               as defined in the Guarantor Credit Agreement), in each case for
               the period of four (4) consecutive fiscal quarters ending on such
               day."

        2.     Amendment and Restatement of Section 18(b) of the Parent
Guaranty. Section 18 of the Parent Guaranty is hereby amended and restated by
deleting the existing Section 18(b) in its entirety and by substituting the
following therefor:

                      "(b) The Guarantor agrees that it shall pay a fee in favor
               of the Administrative Agent for the benefit of the Issuing Bank,
               commencing on the effective date of the Revised Fifth Amendment
               to this Guaranty, payable at the times and in the manner provided
               for the payment of Letter of Credit fees pursuant to Section 2.3
               of the Reimbursement Agreement, on fifty percent (50%) of the
               remaining face amount of the Letter of Credit, at a rate equal to
               the higher of (i) the "Applicable Percentage" for "Offshore Rate
               Loans," subject to the quarterly increases set forth in the
               definition of "Applicable Percentage", as each such term is
               defined in the Guarantor Credit Agreement, or (ii) the interest
               rate per annum equal to the per annum Letter of Credit fee that
               would be paid by Guarantor if its long-term senior unsecured debt
               alone were the basis for the application of the Pricing Grid
               contained in Section 2.3(a) of the Reimbursement

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               Agreement, less, in either case, the rate set forth for the
               Letter of Credit fees in the Reimbursement Agreement."

        3.     Representations and Warranties. The Guarantor hereby represents
and warrants in favor of the Administrative Agent on behalf of the Lenders and
Issuing Bank that:

                      (i)    each representation and warranty set forth in the
               Parent Guaranty is hereby restated and affirmed as true and
               correct on the date hereof;

                      (ii)   the Guarantor has the corporate power and authority
               (a) to enter into this Revised Amendment, and (b) to do all acts
               and things as are required or contemplated hereunder to be done,
               observed and performed by it;

                      (iii)  this Revised Amendment has been duly authorized,
               validly executed and delivered by the Guarantor and the Parent
               Guaranty, as amended by this Revised Amendment, constitutes the
               legal, valid and binding obligation of the Guarantor, enforceable
               against it and in accordance with its terms; and

                      (iv)   the execution and delivery of this Revised
               Amendment and performance by the Guarantor of its obligations
               under the Parent Guaranty, as amended hereby, do not and will not
               require the consent or approval of any regulatory authority or
               governmental authority or agency having jurisdiction over the
               Guarantor which has not already been obtained and will not be in
               contravention of or in conflict with the Certificate of
               Incorporation or Bylaws of the Guarantor or the provisions of any
               Applicable Law or any material indenture, agreement or other
               instrument to which the Guarantor is party or by which its assets
               or properties are bound or affected.

        4.     Conditions Precedent to Effectiveness. This Revised Amendment
shall be deemed effective as of the date (the "Effective Date") upon which each
of the following terms and conditions has been satisfied:

               (a)    The Administrative Agent shall have received duly executed
        counterparts of this Revised Amendment signed by the Guarantor;

               (b)    The continued truth and accuracy of the representations
        and warranties contained in Section 3 hereof (including giving effect to
        the JS Industrial Packaging Group Acquisition, but only if consummated
        on or prior to such date) with the same effect as if made on such date;

<PAGE>

               (c)    The Administrative Agent shall have received a fee of
        0.25% on the maximum principal amount guarantied under this Guaranty,
        which fee shall be fully earned when due and non-refundable when paid
        (it being understood and agreed that such fee shall be in addition to
        the amendment fee previously paid to the Administrative Agent for the
        consent of the Administrative Agent, the Lenders and the Issuing Bank to
        the June 2002 Amendment, which prior fee was paid at the closing of the
        June 2002 Amendment and is fully earned and non-refundable);

               (d)    The Security Agreement shall have been executed and the
        Guarantor shall have delivered to Bank of America, N.A., as collateral
        agent (the "Collateral Agent"), all such other documents as the
        Collateral Agent may reasonably require, including without limitation,
        an opinion of counsel;

               (e)    The Guarantor's requisite senior lenders shall have agreed
        to provisions amending the Guarantor Credit Agreement, substantially
        identical to the change in this Revised Amendment to Section 18(a) of
        the Guaranty (and other senior lenders to the Guarantor similarly
        situated shall also have agreed to a substantially identical amendment),
        and such amendment shall have become effective; and

               (f)    The Administrative Agent shall have received any other
        documents it may reasonably request, certified by an appropriate
        governmental official or officer of the Guarantor if so requested.

        5.     No Other Amendments or Waivers.

               (a)    Except for the amendments expressly set forth and referred
        to in Sections 1 and 2, the Guaranty shall remain unchanged and in full
        force and effect and is hereby in all respects ratified and affirmed.

               (b)    The Guarantor hereby acknowledges and agrees that any
        amendment or other change after the Effective Date of this Revised
        Amendment to the Guarantor Credit Agreement shall not affect the fee
        payable by the Guarantor pursuant to Section 18(b) of the Parent
        Guaranty (as amended by this Revised Amendment) unless the
        Administrative Agent has consented to such amendment in writing and a
        corresponding amendment to the Parent Guaranty is executed by the
        Guarantor and the Administrative Agent.

        6.     Counterparts. This Revised Amendment may be executed in multiple
counterparts, each of which shall be deemed to be an original and all of which,
taken together, shall constitute one and the same agreement. In proving this
Revised Amendment in any judicial proceeding, it shall not be necessary to
produce or account for more than one such counterpart signed by the party
against whom such enforcement is

<PAGE>

sought. Any signatures delivered by a party by facsimile transmission shall be
deemed an original signature hereto.

        7.     Governing Law. This Revised Amendment shall be deemed to be made
pursuant to the internal laws of the State of New York with respect to
agreements made and to be performed wholly in the State of New York, and shall
be construed, interpreted, performed and enforced in accordance therewith.

        8.     Loan Document. This Revised Amendment shall be deemed to be a
Loan Document for all purposes.


             [The remainder of the page is intentionally left blank]

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               IN WITNESS WHEREOF, the parties hereto have executed this Revised
Amendment or caused it to be executed under seal by their duly authorized
officers, effective as of the day and year first written above.

GUARANTOR:              CARAUSTAR INDUSTRIES, INC.

                                By: /s/ Henry L. Thrash, III
                                    ______________________________________

                                Its: Vice President Planning & Development
                                     and Chief Financial Officer
                                    ______________________________________

ADMINISTRATIVE
AGENT:                  TORONTO DOMINION (TEXAS), INC.

                                By: /s/ Carol Brandt
                                    ______________________________________

                                Its: Vice President
                                    ______________________________________




                   REVISED FIFTH AMENDMENT TO PARENT GUARANTY