<PAGE>   1
                                  EXHIBIT 10.4

                                  AMENDMENT TO
                   ZARING HOMES, INC. RETIREMENT BENEFIT PLAN


         The Zaring Homes, Inc. Retirement Benefit Plan (the "Plan") is hereby
amended, effective as of January 1, 1996, in the following respect:

         A new paragraph reading as follows shall be added immediately after the
first paragraph under "401(k) Provisions, Item 11.1" which is contained in Part
I of the Plan:

                           Notwithstanding any other provision of the Plan to
                  the contrary, no Employee who is a Key Employee (as defined in
                  Section 10.2(b) of the Plan) for any Plan Year based on his
                  pay, officer status, and/or ownership interest in the Employer
                  prior to the start of such Plan Year (or prior to the first
                  Entry Date which otherwise applies to him if such Entry Date
                  occurs in such Plan Year), or who otherwise is reasonably
                  determined by the Plan Administrator (based on his rate of
                  pay, officer status, and/or ownership interest in the Employer
                  prior to the first day of such Plan Year (or prior to such
                  Entry Date)) will be a Key Employee for such Plan Year if he
                  remains employed by the Employer throughout such Plan Year
                  (without such rate of pay, officer status, and/or ownership
                  interest changing), shall be in any event ineligible to elect
                  to have Elective Contributions or Matching Contributions made
                  on his behalf for such Plan Year.


         IN WITNESS WHEREOF, the Plan sponsor has caused its name to be
subscribed to this Plan amendment.

                                  AMENDMENT TO
                   ZARING HOMES, INC. RETIREMENT BENEFIT PLAN

         The Zaring Homes, Inc. Retirement Benefit Plan (the "Plan") is hereby
amended, effective as of May 8, 1997, in the following respects:

         1. The name of the Plan is amended to be "Zaring National Corporation
Retirement Benefit Plan."

         2. Section 1.12 of the Plan is amended in its entirety to read as
follows:

                  1.12. The term "Employee" shall mean Zaring National
         Corporation (or any corporate successor thereto) and Zaring Homes, Inc.
         (or any corporate successor thereto); except that Zaring Homes, Inc.
         (or any corporate successor thereto) shall be part of the Employer only
         while at least 80% of the total voting power of its stock is owned by
         Zaring National Corporation (or any corporate successor thereto).
         Notwithstanding the foregoing, any reference contained in this Plan to
         the Employer which concerns the administrator or the administration of
         the Plan, the appointment or removal of the Trustee or the amendment or
         termination of the Plan shall be deemed to refer just to Zaring
         National Corporation (or any corporate successor thereto).

         IN WITNESS WHEREOF, both the current sponsor of the Plan and the Plan's
prior sponsor have caused their names to be subscribed to this Plan amendment,
effective as of May 8, 1997.