Exhibit 4.2


                           PENHALL INTERNATIONAL CORP.
                                    as Issuer

                              PENHALL RENTAL CORP.
                                       and
                                 PENHALL COMPANY
                                  as Guarantors

                                       and

                    UNITED STATES TRUST COMPANY OF NEW YORK,
                                   as Trustee

                               -------------------

                          FIRST SUPPLEMENTAL INDENTURE

                           Dated as of August 4, 1998

                                       to

                                    INDENTURE

                           Dated as of August 1, 1998

                                     between

                      PENHALL ACQUISITION CORP., as Issuer

                                       and

                    UNITED STATES TRUST COMPANY OF NEW YORK,
                                   as Trustee

                               -------------------

                               up to $150,000,000

                       12% Senior Notes due 2008, Series A
                       12% Senior Notes due 2008, Series B



                  FIRST SUPPLEMENTAL INDENTURE, dated as of August 4, 1998,
between PENHALL INTERNATIONAL CORP., an Arizona corporation formerly known as
Phoenix Concrete Cutting, Inc. ("Penhall"), PENHALL RENTAL CORP., a California
corporation ("Penhall Corp.") and PENHALL COMPANY, a California corporation
("Penhall Co.") and UNITED STATES TRUST COMPANY OF NEW YORK, as trustee (the
"Trustee").

                  WHEREAS, PENHALL ACQUISITION CORP., an Arizona, corporation
("Penhall Acquisition"), has heretofore executed and delivered to the Trustee an
Indenture dated as of August 1, 1998 (the "Indenture"), providing for the
issuance of up to $150,000,000 aggregate principal amount of Penhall
Acquisition's 12% Senior Notes due 2006, Series A (the "Initial Notes") and
Penhall Acquisition's 12% Senior Notes due 2006, Series B (the "Exchange Notes"
and, together with the Initial Notes, the "Notes"); and

                  WHEREAS, Penhall Acquisition has merged with and into Penhall
and, in connection therewith, Penhall has assumed by operation of law all of
Penhall Acquisition's debts, liabilities, duties and obligations, including
Penhall Acquisition's obligations in respect of the Notes and under the
Indenture; and

                  WHEREAS, Penhall desires by this First Supplemental Indenture,
pursuant to and as contemplated by Sections 5.01, 5.02 and 9.01 of the
Indenture, to expressly assume the covenants, agreements and undertakings of
Penhall Acquisition, in the Indenture and under the Notes; and

                  WHEREAS, each of Penhall Corp. and Penhall Co. is required
pursuant to Section 4.18 of the Indenture to become a party thereto and to
guarantee (the "Guarantees") the obligations of Penhall in respect of the Notes
and under the Indenture as Guarantors; and

                  WHEREAS, the execution and delivery of this First Supplemental
Indenture and the notes evidencing the Initial Notes and the Exchange Notes have
been authorized by a resolution of the Board of Directors of Penhall; and

                  WHEREAS, the execution and delivery of this First Supplemental
Indenture and the Guarantee of the Notes has been authorized by a resolution of
the Board of Directors of each of Penhall Corp. and Penhall Co.; and



                  WHEREAS, all conditions and requirements necessary to make
each of this First Supplemental Indenture and the Notes a valid, binding and
legal instrument in accordance with its terms upon Penhall and the Trustee, and
each of this First Supplemental Indenture and the Guarantees a valid, binding
and legal instrument in accordance with its terms upon each of Penhall Corp. and
Penhall Co. and the Trustee, have been performed and fulfilled by the applicable
parties hereto and the execution and delivery thereof have been in all respects
duly authorized by the applicable parties hereto.

                  NOW, THEREFORE, in consideration of the above premises, each
party agrees, for the benefit of the others and for the equal and ratable
benefit of the Holders of the Notes, as follows:

                                   ARTICLE ONE

                            ASSUMPTION OF OBLIGATIONS

                  SECTION 1.01.  Assumption of Obligations
                                of Penhall Acquisition Co.

                  (a) Penhall hereby expressly and unconditionally assumes each
and every covenant, agreement and undertaking of Penhall Acquisition in the
Indenture as if Penhall had been the original issuer of the Notes, and also
hereby expressly and unconditionally assumes each and every covenant, agreement
and undertaking in each Note outstanding on the date of this First Supplemental
Indenture and any Notes delivered hereafter. Any Notes delivered after the date
of this First Supplemental Indenture, including Notes delivered in substitution
or exchange for any outstanding Notes, as provided in the Indenture, shall be
executed and delivered by Penhall in its own name, with such notations, legends
or endorsements required by law, stock exchange rules or usage, and each Note
shall constitute the obligation of Penhall.

                  (b) Promptly following the execution and delivery of this
First Supplemental Indenture, the Trustee shall, upon the written order of
Penhall in the form of an Officers' Certificate of Penhall, authenticate and
deliver Initial Notes substantially in the form of Exhibit A to the Indenture in
exchange for the outstanding Initial Notes.




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                  SECTION 1.02.  Assumption of Obligations
                                 of the Guarantors.

                  Each of Penhall Corp. and Penhall Co. hereby expressly and
unconditionally assume each and every covenant, agreement and undertaking of a
Guarantor under the Indenture and also hereby expressly and unconditionally
assume each and every covenant, agreement and undertaking relating to the
Guarantors in each Note outstanding on the date of this First Supplemental
Indenture.

                                   ARTICLE TWO

                            MISCELLANEOUS PROVISIONS

                  SECTION 2.01.  Terms Defined.

                  For all purposes of this First Supplemental Indenture, except
as otherwise defined or unless the context otherwise requires, terms used in
capitalized form in this First Supplemental Indenture and defined in the
Indenture have the meanings specified in the Indenture.

                  SECTION 2.02.  Indenture.

                  Except as amended hereby, the Indenture, the Notes and the
Guarantees are in all respects ratified and confirmed and all the terms shall
remain in full force and effect.

                  SECTION 2.03.  Governing Law.

                  THIS FIRST SUPPLEMENTAL INDENTURE, THE NOTES AND THE
GUARANTEES SHALL BE GOVERNED BY AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE
STATE OF NEW YORK BUT WITHOUT GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICT
OF LAWS. EACH OF THE PARTIES HERETO AGREES TO SUBMIT TO THE JURISDICTION OF THE
COURTS OF THE STATE OF NEW YORK IN ANY ACTION OR PROCEEDING ARISING OUT OF OR
RELATING TO THIS SUPPLEMENTAL INDENTURE, THE NOTES OR THE GUARANTEES.

                  SECTION 2.04.  Successors.

                  All agreements of Penhall, Penhall Corp. and Penhall Co. in
this First Supplemental Indenture, the Notes and the Guarantees shall bind their
respective successors. All agree-



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ments of the Trustee in this First Supplemental Indenture shall bind its
successors.

                  SECTION 2.05.  Duplicate Originals.

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

                  SECTION 2.06.  Trustee Disclaimer.

                  The Trustee accepts the amendment of the Indenture effected by
this First Supplemental Indenture and agrees to execute the trust created by the
Indenture as hereby amended, but only upon the terms and conditions set forth in
the Indenture, including the terms and provisions defining and limiting the
liabilities and responsibilities of the Trustee, which terms and provisions
shall in like manner define and limit its liabilities and responsibilities in
the performance of the trust created by the Indenture as hereby amended and,
without limiting the generality of the foregoing, the Trustee shall not be
responsible in any manner whatsoever for or with respect to any of the recitals
or statements contained herein, all of which recitals or statements are made
solely by Penhall, Penhall Corp. and Penhall Co., or for or with respect to (i)
the validity of the terms of this First Supplemental Indenture or any of the
terms or provisions hereof, (ii) the proper authorization hereof by Penhall,
Penhall Corp. and Penhall Co. by corporate action or otherwise, (iii) the due
execution hereof by Penhall, Penhall Corp. and Penhall Co. or (iv) the
consequences (direct or indirect and whether deliberate or inadvertent) of any
amendment herein provided for, and the Trustee makes no representation with
respect to any such matters.

                            [Signature Page Follows]




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                                   SIGNATURES

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

                                    PENHALL INTERNATIONAL CORP.,
                                      as Issuer

                                    By:  /s/  Martin W. Houge
                                       ----------------------------------------
                                       Name:  Martin W. Houge
                                       Title: Vice President - Finance

                                    PENHALL RENTAL CORP.,
                                      as Guarantor

                                    By:  /s/  Martin W. Houge
                                       ----------------------------------------
                                       Name:  Martin W. Houge
                                       Title: Vice President - Finance

                                    PENHALL COMPANY,
                                      as Guarantor

                                    By:  /s/  Martin W. Houge
                                       ----------------------------------------
                                       Name:  Martin W. Houge
                                       Title: Vice President - Finance

                                    UNITED STATES TRUST COMPANY
                                      OF NEW YORK, as Trustee
 
                                    By:  /s/  Christine C. Collins
                                       ----------------------------------------
                                       Name:  Christine C. Collins
                                       Title: Assistant Vice President