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                                                                    Exhibit 3.1b

                            CERTIFICATE OF AMENDMENT

                                       OF

                          CERTIFICATE OF INCORPORATION

                                       OF

                               UNIFRAX CORPORATION

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

                        Under Section 242 of the General
                    Corporation Law of the State of Delaware


         UNIFRAX CORPORATION, a corporation organized and existing under and by
virtue of the General Corporation Law of the State of Delaware (the "Company"),
DOES HEREBY CERTIFY:

         1.  The Certificate of Incorporation of the Company shall be amended to
create a class of preferred stock having rights and preferences superior to the
rights and preferences of the common stock. To effect such amendment, Article
FOURTH of the Certificate of Incorporation shall be deleted in its entirety and
the following inserted in lieu thereof:

         FOURTH: The total number of shares of all classes of stock that the
         Company shall have authority to issue is 50,000, of which 40,000
         shares of the par value of $.01 each shall be common stock and 10,000
         shares of the par value of $.01 each shall be preferred stock. The
         relative rights, preferences and limitations of the shares of each
         class are as follows:

                  (a)    VOTING. Except as otherwise provided by applicable law,
                  the voting power for the election of directors and for all
                  other purposes shall be vested in the holders of the common
                  stock and the holders of the preferred stock. The holders of
                  the common


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                  stock and the preferred stock shall each have one vote per
                  share. There shall be no cumulative voting.

                  (b)      Dividends.
                           ----------

                           (i) Each holder of the preferred stock shall be
                  entitled to receive, when and as declared by the board of
                  directors and from the assets of the Company available for
                  the payment of dividends under applicable law, a semi-annual
                  cumulative dividend (collectively "Preferred Dividends") at
                  the rate of 6% per annum on the amount of $1,500 (the
                  "Preferred Liquidation Value") for each share of the
                  preferred stock held by such holder. The Preferred Dividends,
                  to the extent so declared by the board of directors, shall be
                  payable in cash on June 30 of each year with respect to the
                  six-month period ending on June 30 of such year and on
                  December 31 of each year with respect to the six-month period
                  ending on December 31 of such year (individually a "Six-Month
                  Period" and collectively "Six-Month Periods") to holders of
                  record of the shares of the preferred stock on the first day
                  of June and December, respectively. The Preferred Dividends
                  shall accrue on each share of the preferred stock from and
                  including the date of the original issuance of such share
                  (without regard to any transfer of such share on the stock
                  records of the Company) to and including the date on which
                  (A) such share is redeemed by the Company, whether pursuant
                  to paragraph (c) of this Article or otherwise, (B) such share
                  is converted to common stock pursuant to paragraph (e) of
                  this Article or (C) a distribution is made with respect to
                  such share pursuant to paragraph (d) of this Article.

                           (ii) Subject to subparagraph (b)(iii) of this
                  Article, the Company shall incur no liability to any holder
                  of the preferred stock in connection with the failure of the
                  Company to declare or pay any Preferred Dividends.

                           (iii) If the Preferred Dividends shall have been
                  paid with respect to all prior Six-Month Periods, the board
                  of directors may, but shall not be required to, declare and
                  pay dividends on the common stock, such dividends to be
                  payable in an equal amount per share of common stock from the
                  assets of the Company available for the payment of dividends
                  under applicable law; provided, however, that no such
                  dividends shall be declared and paid on the common stock of
                  the Company unless all Preferred


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                  Dividends shall have been paid on each share of the preferred
                  stock with respect to all prior Six-Month Periods.


                  (c)      Redemption.
                           ----------

                           (i) The Company may, at its option and at any time
                  and from time to time after the issuance of any shares of the
                  preferred stock, redeem all, but not less than all, of the
                  outstanding shares of preferred stock. Notice of any
                  redemption by the Company of preferred stock specifying the
                  time and place of redemption, the redemption price and any
                  conditions to be satisfied prior to such redemption shall be
                  mailed by certified mail, return receipt requested, to each
                  holder of record of shares of the preferred stock, at the
                  address for such holder shown on the Company's records, not
                  more than sixty, and not less than seven, days prior to the
                  date on which such redemption is to be effective. Upon
                  mailing any such notice of redemption, the Company shall,
                  subject to the satisfaction of all conditions set forth in
                  such notice, become obligated to redeem at the time of
                  redemption specified in such notice all outstanding shares of
                  preferred stock.

                           (ii) The redemption price for each share of
                  preferred stock to be redeemed pursuant to this Article shall
                  be equal to the Preferred Liquidation Value of such share,
                  plus an amount equal to all Preferred Dividends that are
                  unpaid on such share with respect to any prior Six-Month
                  Period.

                           (iii) On or before the date set for the redemption
                  of the preferred stock pursuant to this Article, each holder
                  of shares of the preferred stock shall surrender all
                  certificates for such shares to the Company at the then
                  principal place of business of the Company and, upon doing
                  so, shall be entitled to receive payment of the redemption
                  price. All certificates surrendered for redemption shall be
                  duly endorsed, or shall be accompanied by separate stock
                  transfer powers duly endorsed, for transfer to the Company.

                  (d)      Liquidation, Dissolution or Winding Up.
                           ----------------------------------------

                           (i) In the event of any liquidation, dissolution or
                  winding up of the Company or any similar distribution of its
                  assets to its stockholders, whether voluntary or involuntary,
                  the holders of the preferred stock shall be entitled, before
                  any payment or other


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                  distribution is made to the holders of the common stock of
                  the Company in connection with such liquidation, dissolution
                  or winding up, to be paid from the assets of the Company
                  legally available therefor, an amount in cash equal to the
                  Preferred Liquidation Value for each share of the preferred
                  stock, plus an amount equal to all Preferred Dividends that
                  are unpaid on such share with respect to any prior Six-Month
                  Period as of the date of such payment.

                           (ii) To the extent the assets of the Company legally
                  available for distribution in the event of a liquidation,
                  dissolution or winding up of the Company are insufficient to
                  pay in full the Preferred Liquidation Value, plus an amount
                  equal to all Preferred Dividends that are unpaid with respect
                  to any prior Six-Month Period as of the date of such payment,
                  for all shares of the preferred stock, the Company shall pay
                  to the holders of the preferred stock a pro rata amount of
                  (A) the Preferred Liquidation Value plus (B) such Preferred
                  Dividends.

                           (iii) After the payment to the holders of the
                  preferred stock of the Preferred Liquidation Value, plus an
                  amount equal to all Preferred Dividends that are unpaid with
                  respect to any prior Six- Month Period as of the date of such
                  payment, the holders of the common stock shall be entitled,
                  to the exclusion of the holders of the preferred stock, to
                  receive, equally on a share for share basis, all of the
                  remaining assets of the Company available for distribution to
                  its stockholders.

                           (iv) The sale or other transfer of all or
                  substantially all of the assets of the Company to, or the
                  merger or consolidation of the Company into or with, any
                  other entity shall not be deemed a liquidation, dissolution
                  or winding up of the Company for the purposes of this
                  paragraph (d).

                  (e)      Conversion Rights.
                           ------------------

                           (i) Subject to subparagraph (e)(iii) of this
                  Article, shares of the preferred stock shall be convertible
                  into fully paid and non-assessable shares of the common stock
                  at the rate of one share of the common stock for each share
                  of the preferred stock. A holder of any shares of the
                  preferred stock may convert such shares to shares of the
                  common stock upon (A) giving notice in writing to the board
                  of directors of the election to so convert and (B)


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                  surrendering all certificates for such shares to the board of
                  directors duly endorsed, or accompanied by separate stock
                  powers duly endorsed, for transfer to the Company. If the
                  Company redeems any shares of the preferred stock, whether
                  pursuant to this Article or otherwise, such right of
                  conversion shall terminate, as to the shares so redeemed,
                  upon payment of the redemption price. In the event of the
                  liquidation, dissolution or winding up of the Company, such
                  right of conversion shall terminate at the close of business
                  on the tenth business day prior to the date set for the first
                  distribution to the holders of the preferred stock.

                           (ii) Upon any conversion of shares of the preferred
                  stock into shares of the common stock pursuant to this
                  Article, a holder of the preferred stock shall continue to be
                  entitled to receive, when and as declared by the board of
                  directors and from the assets of the Company available for
                  the payment of dividends under applicable law, all Preferred
                  Dividends that are unpaid as of the date of such conversion
                  with respect to any prior Six-Month Period on the shares of
                  the preferred stock so converted; provided, however, that no
                  other payment shall be made in connection with such
                  conversion.

                           (iii) The number of shares of the common stock into
                  which each share of the preferred stock is convertible
                  pursuant to subparagraph (e)(i) of this Article shall be
                  subject to adjustment from time to time as follows:

                           (A) If the Company shall (1) declare a dividend on
                  the common stock payable in shares of the common stock, (2)
                  subdivide the outstanding shares of the common stock, (3)
                  combine the outstanding shares of the common stock into a
                  smaller number of shares, or (4) issue by reclassification of
                  the common stock any shares of the Company, each holder of
                  the preferred stock shall thereafter be entitled upon a
                  conversion pursuant to this paragraph (e) to receive for each
                  share of the preferred stock the number of shares of the
                  common stock of the Company the he, she or it would have
                  owned or been entitled to receive after the occurrence of any
                  event described in clauses (1), (2), (3) and (4) of this
                  sentence had such share been converted immediately prior to
                  the occurrence of such event. Such adjustment shall become
                  effective immediately after the close of business on the
                  record date for such dividend or the date upon which any
                  subdivision, combination or reclassification shall become
                  effective.


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                           (B) If the Company shall (1) consolidate or merge
                  into or with another entity or (2) sell or otherwise transfer
                  all or substantially all of its assets, each share of the
                  preferred stock then outstanding shall thereafter be
                  convertible pursuant to this paragraph (e) into the kind and
                  amount of securities, cash and other assets received by a
                  holder of the number of shares of common stock into which
                  such share could have been converted immediately prior to the
                  occurrence of any event described in clauses (1) and (2) of
                  this sentence, and shall have no other conversion rights.

                           (C) Whenever any adjustment is required in the
                  shares of common stock into which each share of the preferred
                  stock is convertible pursuant to subparagraphs (e)(iii)(A)
                  and (e)(iii)(B) of this Article, the Company shall maintain,
                  at its principal place of business, a statement describing in
                  reasonable detail such adjustment and the method of
                  calculation used in calculating such adjustment.

                           (D) The Company shall at all times reserve and keep
                  available out of the authorized but unissued shares of the
                  common stock the full number of shares of the common stock
                  into which all shares of the preferred stock from time to
                  time outstanding are convertible pursuant to this paragraph
                  (e). Notwithstanding the immediately preceding sentence,
                  shares of the common stock held in the treasury of the
                  Company may, in the discretion of the Company, be reissued in
                  connection with any such conversion of shares of the
                  preferred stock pursuant to this paragraph (e).

                           (E) Shares of the preferred stock converted into
                  common stock shall have the status of authorized but unissued
                  shares of preferred stock and such shares may be reissued by
                  the Company as shares of preferred stock.


                  2.  The Board of Directors of the Company duly adopted a
resolution setting forth the amendment to the Certificate of Incorporation of
the Company being adopted in this Certificate, declaring its advisability and
calling a special meeting of the stockholders of the Company entitled to vote in
respect thereof for the consideration of such amendment. Such


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amendment has been duly adopted by the unanimous written consent of the
stockholders of the Company in accordance with Sections 228 and 242(b) of the
General Corporation Law of the State of Delaware.

                  IN WITNESS WHEREOF, the Company has caused this Certificate to
be signed by William P. Kelly, its president, and Mark D. Roos, its secretary,
on the 21st day of April, 1997.


                                            UNIFRAX CORPORATION



                                            By   /s/William P. Kelly
                                              ---------------------------------
                                                   William P. Kelly, President
ATTEST:


By  /s/Mark D. Roos
    -------------------------
      Mark D. Roos, Secretary