<PAGE>
                                                                 Exhibit 4.5.1

                             SUPPLEMENTAL INDENTURE


                  SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated
as of August 3, 2000, among Conspec Marketing and Manufacturing Co., Inc., a
Kansas corporation, and Bristol Investments, Inc., a California corporation,
(each a "Guaranteeing Subsidiary"), each a subsidiary of Dayton Superior
Corporation (or its permitted successor), an Ohio corporation (the "Company"),
the Company, the other Guarantors (as defined in the Indenture referred to
herein) and United States Trust Company of New York, as trustee under the
indenture referred to below (the "Trustee").

                                   WITNESSETH:

                  WHEREAS, the Company has heretofore executed and delivered to
the Trustee an indenture (the "Indenture"), dated as of June 16, 2000 providing
for the issuance of an aggregate principal amount of up to $270.0 million of 13%
Senior Subordinated Notes due 2009 (the "Notes");

                  WHEREAS, the Indenture provides that under certain
circumstances the Guaranteeing Subsidiary shall execute and deliver to the
Trustee a supplemental indenture pursuant to which the Guaranteeing Subsidiary
shall unconditionally guarantee all of the Company's Obligations under the Notes
and the Indenture on the terms and conditions set forth herein (the
"Guarantee"); and

                  WHEREAS, pursuant to Section 9.01 of the Indenture, the
Trustee is authorized to execute and deliver this Supplemental Indenture.

                  NOW THEREFORE, in consideration of the foregoing and for other
good and valuable consideration, the receipt of which is hereby acknowledged,
the Guaranteeing Subsidiary and the Trustee mutually covenant and agree for the
equal and ratable benefit of the Holders of the Notes as follows:

     1. CAPITALIZED TERMS. Capitalized terms used herein without definition
shall have the meanings assigned to them in the Indenture.

     2. AGREEMENT TO GUARANTEE. The Guaranteeing Subsidiary hereby agrees as
follows:

               (a) Along with all Guarantors named in the Indenture, to jointly
          and severally Guarantee to each Holder of a Note authenticated and
          delivered by the Trustee and to the Trustee and its successors and
          assigns, irrespective of the validity and enforceability of the
          Indenture, the Notes or the Obligations of the Company hereunder or
          thereunder, that:

                    (i) the principal of, premium, if any, and interest on the
               Notes will be promptly paid in full when due, whether at
               maturity, by acceleration, redemption or otherwise, and interest
               on the overdue principal of and interest on the Notes, if any, if
               lawful, and all other

                                       1
<PAGE>



               Obligations of the Company to the Holders or the Trustee
               hereunder or thereunder will be promptly paid in full or
               performed, all in accordance with the terms hereof and thereof;
               and

                    (ii) in case of any extension of time of payment or renewal
               of any Notes or any of such other Obligations, that same will be
               promptly paid in full when due or performed in accordance with
               the terms of the extension or renewal, whether at stated
               maturity, by acceleration or otherwise.

               Failing payment when due of any amount so guaranteed or any
               performance so guaranteed for whatever reason, the Guarantors
               shall be jointly and severally obligated to pay the same
               immediately.

          (b) The Obligations hereunder shall be unconditional, irrespective of
     the validity, regularity or enforceability of the Notes or the Indenture,
     the absence of any action to enforce the same, any waiver or consent by any
     Holder of the Notes with respect to any provisions hereof or thereof, the
     recovery of any judgment against the Company, any action to enforce the
     same or any other circumstance which might otherwise constitute a legal or
     equitable discharge or defense of a guarantor.

          (c) The following is hereby waived: diligence, presentment, demand of
     payment, filing of claims with a court in the event of insolvency or
     bankruptcy of the Company, any right to require a proceeding first against
     the Company, protest, notice and all demands whatsoever.

          (d) This Guarantee shall not be discharged except by complete
     performance of the Obligations contained in the Notes and the Indenture or
     pursuant to Section 6 hereof.

          (e) If any Holder or the Trustee is required by any court or otherwise
     to return to the Company, the Guarantors, or any custodian, Trustee,
     liquidator or other similar official acting in relation to either the
     Company or the Guarantors, any amount paid by either to the Trustee or such
     Holder, this Guarantee, to the extent theretofore discharged, shall be
     reinstated in full force and effect.

          (f) The Guaranteeing Subsidiary shall not be entitled to any right of
     subrogation in relation to the Holders in respect of any Obligations
     guaranteed hereby until payment in full of all Obligations guaranteed
     hereby.

          (g) As between the Guarantors, on the one hand, and the Holders and
     the Trustee, on the other hand, (x) the maturity of the Obligations
     guaranteed hereby may be accelerated as provided in Article 6 of the
     Indenture for the purposes of this Guarantee, notwithstanding any stay,
     injunction or other prohibition preventing such acceleration in respect of
     the Obligations guaranteed hereby, and (y) in the event of any declaration
     of acceleration of such Obligations

                                       2

<PAGE>


     as provided in Article 6 of the Indenture, such Obligations (whether or not
     due and payable) shall forthwith become due and payable by the Guarantors
     for the purpose of this Guarantee.

          (h) The Guarantors shall have the right to seek contribution from any
     non-paying Guarantor so long as the exercise of such right does not impair
     the rights of the Holders under the Guarantee.

          (i) Pursuant to Section 11.03 of the Indenture, the Obligations of a
     Guaranteeing Subsidiary shall be limited to such a maximum amount as after
     giving effect to any maximum amount and any other contingent and fixed
     liabilities that are relevant under any applicable Bankruptcy or fraudulent
     conveyance laws (including, without limitation, all Senior Debt of such
     Guarantor), and after giving effect to any collections from, rights to
     receive contribution from or payments made by or on behalf of any other
     Guarantor in respect of the Obligations of such other Guarantor under
     Article 11 of the Indenture, shall result in the Obligations of such
     Guarantor under its Guarantee not constituting a fraudulent transfer or
     conveyance.

     3. SUBORDINATION. The Obligations of the Guaranteeing Subsidiary under its
Guarantee pursuant to this Supplemental Indenture shall be junior and
subordinated to the Senior Debt of the Guaranteeing Subsidiary on the same basis
as the Notes are junior and subordinated to the Senior Debt of the Company. For
the purposes of the foregoing sentence, the Trustee and the Holders shall have
the right to receive and/or retain payments by the Guaranteeing Subsidiary only
at such time as they may receive and/or retain payments in respect of the Notes
pursuant to the Indenture, including Article 10 thereof.

     4. EXECUTION AND DELIVERY. Each Guaranteeing Subsidiary agrees that the
Guarantees shall remain in full force and effect notwithstanding any failure to
endorse on each Note a notation of such Guarantee.

     5. GUARANTEEING SUBSIDIARY MAY CONSOLIDATE, ETC. ON CERTAIN TERMS.

               (a) The Guaranteeing Subsidiary may not consolidate with or merge
          with or into (whether or not such Guarantor is the surviving Person)
          another corporation, Person or entity whether or not affiliated with
          such Guarantor unless:

                    (i) subject to Section 11.05 of the Indenture, the Person
               formed by or surviving any such consolidation or merger (if other
               than a Guarantor or the Company) shall be a corporation organized
               and validly existing under the laws of the United States or any
               state thereof or the District of Columbia, and unconditionally
               assumes all the Obligations of such Guarantor, pursuant to a
               supplemental indenture in form and substance reasonably
               satisfactory to the Trustee, under the Notes, the Indenture and
               the Guarantee on the terms set forth herein or therein;

                    (ii) immediately after giving effect to such transaction, no
               Default or Event of Default exists; and



                                       3
<PAGE>


                    (iii) the Company would be permitted, immediately after
               giving effect to such transaction, to incur at least $1.00 of
               additional Indebtedness (other than Permitted Indebtedness)
               pursuant to Section 4.09 of the Indenture.

          (b) In case of any such consolidation, merger, sale or conveyance and
     upon the assumption by the successor Person, by supplemental indenture,
     executed and delivered to the Trustee and satisfactory in form to the
     Trustee, of the Guarantee endorsed upon the Notes and the due and punctual
     performance of all of the covenants and conditions of the Indenture to be
     performed by the Guarantor, such successor Person shall succeed to and be
     substituted for the Guarantor with the same effect as if it had been named
     herein as a Guarantor. Such successor Person thereupon may cause to be
     signed any or all of the Guarantees to be endorsed upon all of the Notes
     issuable hereunder which theretofore shall not have been signed by the
     Company and delivered to the Trustee. All the Guarantees so issued shall in
     all respects have the same legal rank and benefit under the Indenture as
     the Guarantees theretofore and thereafter issued in accordance with the
     terms of the Indenture as though all of such Guarantees had been issued at
     the date of the execution hereof.

          (c) Except as set forth in Articles 4 and 5 of the Indenture, and
     notwithstanding clause (a)(iii) above, nothing contained in the Indenture
     or in any of the Notes shall prevent any consolidation or merger of a
     Guarantor with or into the Company or another Guarantor, or shall prevent
     any sale or conveyance of the property of a Guarantor as an entirety or
     substantially as an entirety to the Company or another Guarantor.

     6. RELEASES. In the event of a sale or other disposition of all of the
assets of any Guarantor, by way of merger, consolidation or otherwise, or a sale
or other disposition of all to the capital stock of any Guarantor, then such
Guarantor (in the event of a sale or other disposition, by way of merger,
consolidation or otherwise, of all of the capital stock of such Guarantor) or
the corporation acquiring the property (in the event of a sale or other
disposition of all or substantially all of the assets of such Guarantor) will be
released and relieved of any Obligations under its Guarantee; provided that the
Net Cash Proceeds of such sale or other disposition are applied in accordance
with the applicable provisions of the Indenture, including without limitation
Section 4.10 of the Indenture. Upon delivery by the Company to the Trustee of an
Officers' Certificate and an Opinion of Counsel to the effect that such sale or
other disposition was made by the Company in accordance with the applicable
provisions of the Indenture, including without limitation Section 4.10 of the
Indenture, the Trustee shall execute any documents reasonably required in order
to evidence the release of any Guarantor from its Obligations under its
Guarantee.

     Any Guarantor not released from its Obligations under its Guarantee shall
remain liable for the full amount of principal of and interest on the Notes and
for the other Obligations of any Guarantor under the Indenture as provided in
Article 11 of the Indenture.



                                       4
<PAGE>

     7. NO RECOURSE AGAINST OTHERS. No past, present or future director,
officer, employee, incorporator, stockholder or agent of the Guaranteeing
Subsidiary, as such, shall have any liability for any Obligations of the Company
or any Guaranteeing Subsidiary under the Notes, any Guarantees, the Indenture or
this Supplemental Indenture or for any claim based on, in respect of, or by
reason of, such Obligations or their creation. Each Holder of the Notes by
accepting a Note waives and releases all such liability. The waiver and release
are part of the consideration for issuance of the Notes. Such waiver may not be
effective to waive liabilities under the federal securities laws and it is the
view of the Commission that such a waiver is against public policy.

     8. NEW YORK LAW TO GOVERN. THE INTERNAL LAW OF THE STATE OF NEW YORK SHALL
GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE WITHOUT GIVING EFFECT
TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT THE APPLICATION
OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

     9. COUNTERPARTS. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

     10. EFFECT OF HEADINGS. The Section headings herein are for convenience
only and shall not affect the construction hereof.

     11. THE TRUSTEE. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Guaranteeing Subsidiary and the Company.



                                       5
<PAGE>






                  IN WITNESS WHEREOF, the parties hereto have caused this
Supplemental Indenture to be duly executed and attested, all as of the date
first above written.

                            Dayton Superior Corporation, as Issuer



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



                            Conspec Marketing and Manufacturing Co., Inc., as
                            Guaranteeing Subsidiary



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



                            Bristol Investments, Inc., as Guaranteeing
                            Subsidiary


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



                            UNITED STATES TRUST COMPANY OF
                             NEW YORK, as Trustee



                            By:
                               ---------------------------------------------
                               Name:  Cynthia Chaney
                               Title: Assistant Vice President