EXHIBIT 10 (i)
                                NSC CORPORATION

                              FOURTH AMENDMENT TO
                           REVOLVING CREDIT AGREEMENT

THIS FOURTH AMENDMENT TO REVOLVING CREDIT AGREEMENT (this "Fourth Amendment") is
made and entered  into as of the 22nd day of  December,  1997,  by and among NSC
CORPORATION,  a Delaware corporation (the "Parent"),  its Subsidiaries listed on
the signature pages hereto (the "Subsidiaries", the Parent and such Subsidiaries
collectively  referred  to  herein  as the  "Borrowers"  and  individually  as a
"Borrower"),  each of which Borrowers  having its principal place of business at
49  Danton  Drive,  Methuen,  Massachusetts,  01844,  BANKBOSTON,  N.A.  ("BKB",
formerly  known as The  First  National  Bank of  Boston),  a  national  banking
association  having its  principal  place of  business  at 100  Federal  Street,
Boston,  Massachusetts 02110, FLEET NATIONAL BANK ("Fleet"),  a national banking
association  formerly  known  as  Fleet  Bank of  Massachusetts,  N.A.  with its
principal place of business at One Federal Street,  Boston,  Massachusetts 02111
(the "Banks"), and BKB, as Agent for the Banks (the "Agent").

WHEREAS, the Borrowers,  the Banks and the Agent entered into a Revolving Credit
Agreement  dated as of May 4, 1993 and amended as of  December  2, 1993,  May 1,
1996 and May 9,  1997  (the  "Credit  Agreement")  pursuant  to which  the Banks
extended credit to the Borrowers on the terms set forth therein:

WHEREAS, the Banks, the Borrowers, and the Agent have agreed to amend the Credit
Agreement as hereinafter set forth:

NOW, THEREFORE,  for good and valuable consideration the receipt and sufficiency
of which is hereby acknowledged, the parties hereto agree as follows:

I.  AMENDMENT TO THE CREDIT AGREEMENT

A.  Amendment to ss.8.6 of the Credit Agreement.

Section 8.6 of the Credit  Agreement  is hereby  deleted in its entirety and the
following substituted in place thereof:

"ss.8.6  Restricted  Distributions  and Redemptions.  None of the Borrowers will
declare and pay any Distributions other than (a) Distributions payable solely in
common stock of the Borrowers,  (b)  Distributions  by the  Subsidiaries  to the
Parent, and (c) annual Distributions by the Parent to its shareholders, provided
that after giving effect to such Distribution described in clause (c), the ratio
of (i) EBITDA,  as at the end of each fiscal quarter  immediately  prior to such
Distribution  commencing with the fiscal quarter ending March 31, 1998,  (x)on a
cumulative  quarterly basis for the fiscal quarter ending March 31, 1998 through
the fiscal quarter ending  September 30, 1998, and (y) thereafter,  for the four
fiscal quarters ending on such date, to (ii)Consolidated  Total Debt Service for
such period shall not be less than 1.10:1,  and provided further that no Default
of Event of Default shall exist or be created by the making of any  Distribution
pursuant to this ss.8.6. In addition,  the Borrowers shall not redeem,  convert,
retire  or  otherwise  acquire  shares  of any  class  of  capital  stock of the
Borrowers in aggregate  amount in excess of $500,000 in any year.  The Borrowers
shall not  effect or  permit  any  change in or  amendment  to any  document  or
instrument pertaining to the terms of the Borrower's capital stock."


B.  Amendment to ss.9.1 of the Credit Agreement.

Section 9.1 of the Credit  Agreement  is hereby  deleted in its entirety and the
following substituted in place thereof:

"ss.9.1  Debt  Service  Coverage  Ratio.  As at the end of each  fiscal  quarter
commencing  with the fiscal  quarter  ending March 31, 1998, (i) on a cumulative
quarterly  basis for the fiscal quarter ending March 31, 1998 through the fiscal
quarter  ending  September 30, 1998,  and (ii)  thereafter,  for the four fiscal
quarters  ending on such  date,  the ratio of  (a)EBITDA  for such  period  less
Capital  Expenditure and income tax expenses for such period to (b) Consolidated
Total Debt Service for such period shall not be less than 1.50:1."

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C.  Amendment to ss.9.3 fo the Credit Agreement.

Section 9.3 of the Credit  Agreement  is hereby  deleted in its entirety and the
following substituted in place thereof:

"ss.9.3 Interest Coverage Ratio. As at the end of each fiscal quarter commencing
with the fiscal  quarter  ending March 31, 1998,  (i) on a cumulative  quarterly
basis for the fiscal  quarter  ending March 31, 1998 through the fiscal  quarter
ending  September 30, 1998, and (ii)  thereafter,  for the four fiscal  quarters
ending on such date, the ratio of (a)EBITDA for such period to (b)  Consolidated
Total Interest Expense for such period shall not be less than 4:1."

D.  Amendment to ss.9.4 of the Credit Agreement.

Section 9.4 of the Credit  Agreement  is hereby  deleted in its entirety and the
following substituted in place thereof:

"ss.9.4 Profitable  Operations.  The Borrowers will not permit  Consolidated Net
Income to be less than $0 (a) in three of the four fiscal quarters of any fiscal
year, or (b) for any fiscal year;  provided,  however, the Borrowers may incur a
Consolidated  Net Deficit of no more that $27,000,000 for the fiscal year ending
December  31,  1997 of which  amount  $25,000,000  shall be  related  to special
charges."

E.  Amendment to ss.9.6 of the Credit Agreement.

Section 9.6 of the Credit  Agreement  is hereby  deleted in its entirety and the
following substituted in place thereof:

'ss.9.6 Consolidated Net Worth.  As at the end of any fiscal quarter  commencing
with the fiscal quarter ending December 31, 1997,  Consolidated  Net Worth shall
not be less than $28,800,000.'


II. PROVISIONS RELATING TO THIS FOURTH AMENDMENT

A.  Definitions.

Capitalized  terms used herein without  definition have the meanings ascribed to
them in the Credit Agreement.

B.  Ratification, etc.

Except as expressly amended or waived hereby,  the Credit  Agreement,  the other
Loan Documents and all documents, instruments and agreements related thereto are
hereby  ratified and confirmed in all respects and shall  continue in full force
and effect.  This Fourth  Amendment and the Credit  Agreement shall hereafter be
read and  construed  together as a single  document,  and all  references in the
Credit Agreement or any related  agreement or instrument to the Credit Agreement
shall refer to the Credit Agreement as amended by this Fourth Amendment.

C.  GOVERNING LAW.

THIS FOURTH  AMENDMENT  SHALL BE GOVERNED BY AND  CONSTRUED IN  ACCORDANCE  WITH
THE LAWS OF THE  COMMONWEALTH  OF  MASSACHUSETTS  AND  SHALL  TAKE  EFFECT  AS A
SEALED INSTRUMENT IN ACCORDANCE WITH SUCH LAWS.

D.  Counterparts.

This  Fourth  Amendment  may be executed  in any number of  counterparts  and by
different  parties  hereto  on  separate  counterparts,  each of  which  when so
executed and delivered shall be an original, but all of which counterparts taken
together  shall be deemed to constitute  one and the same  instrument.  Complete
sets of counterparts shall be lodged with the Banks.

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E.  Effectiveness.

This Fourth  Amendment shall become  effective upon the  satisfaction of each of
the following:

This Fourth  Amendment  shall have been executed and delivered by the respective
parties hereto; and The Agent shall have received an amendment fee of $25,000 to
be  shared  pro  rata  among  the  Banks in  accordance  with  their  respective
Commitment Percentages.

F.  Entire Agreement.

THE CREDIT  AGREEMENT  AND THE  SECURITY  DOCUMENTS  AS  AMENDED BY THIS  FOURTH
AMENDMENT  REPRESENTS  THE FINAL  AGREEMENT  BETWEEN  THE PARTIES AND MAY NOT BE
CONTRADICTED  BY  EVIDENCE  OF  PRIOR,   CONTEMPORANEOUS,   OR  SUBSEQUENT  ORAL
AGREEMENTS OF THE PARTIES.  THERE ARE NO UNWRITTEN ORAL  AGREEMENTS  BETWEEN THE
PARTIES.

IN WITNESS  WHEREOF,  the undersigned  have duly executed this Fourth  amendment
under seal as of the date first set forth above.

THE BORROWERS:

NSC CORPORATION
By:    Efstathios A. Kouninis
Title:  Vice President of Finance

NATIONAL SERVICE CLEANING CORP.
By:  Efstathios A. Kouninis
Title:  Vice President

NATIONAL SURFACE CLEANING INC.
By:    Ron Biebel
Title:  Vice President

OLSHAN DEMOLISHING MANAGEMENT, INC.
By:  Efstathios A. Kouninis
Title:  Vice President

NSC SPECIALTY COATINGS, INC.
By:  Efstathios A. Kouninis
Title:  Vice President

NSC ENERGY SERVICES, INC.
By:  Efstathios A. Kouninis
Title:   Vice President



THE BANKS:

BANKBOSTON, N.A.
(formerly known as The First National
Bank of Boston)
By:
Title:

FLEET NATIONAL BANK
By:
Title:

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