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Historic Preservation - Technical Procedures

Spectitle:

Removing Stains And Efflorescence From Architectural Scagliola

Procedure code:

0920009R

Source:

Interior's Handbook For Historic Buildings - Jeff Greene

Division:

Finishes

Section:

Lath & Plaster

Last Modified:

02/24/2012

Details:

Removing Stains And Efflorescence From Architectural Scagliola



REMOVING STAINS AND EFFLORESCENCE FROM ARCHITECTURAL SCAGLIOLA


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing metallic
         stains and efflorescence from architectural scagliola by
         mechanical surface removal or poulticing.
 
         1.   A poultice is usually made by adding a solvent or
              chemical cleaning agent to water and blended with
              an inert filler to make a smooth paste.  The paste
              is then applied over the stain using a trowel or
              spatula.

         2.   The liquid portion of the paste migrates into the
              stone where it dissolves some of the staining
              material.  Then the liquid gradually moves back
              beyond the stone surface and into the poultice,
              from which it evaporates, leaving its burden of
              dissolved staining material in the poultice.

         3.   When the poultice has dried, it is scraped and
              brushed away.

    B.   Stains may be caused by the presence of water, either on
         the face of the scag or at the rear.  Water can contain
         dirt and contaminants which can stain the surface.  These
         contaminants can also migrate into the scag if the
         surface finish is deteriorated.  Moisture within the scag
         can then cause internal metal components to oxidize,
         which can lead to metallic staining on the surface.

    C.   Excessive amounts of water present in the scag can result
         in the migration of mineral salts from adjacent masonry
         or from the scagliola to migrate to the surface, evident
         as a white powder - efflorescence.

    D.   For general information on scagliola, including its
         characteristics, uses and problems, see 09200-05-S.

    E.   See 01100-07-S for general project guidelines to be
         reviewed along with this procedure.  These guidelines
         cover the following sections:

         1.   Safety Precautions

         2.   Historic Structures Precautions

         3.   Submittals

         4.   Quality Assurance

         5.   Delivery, Storage and Handling

         6.   Project/Site Conditions

         7.   Sequencing and Scheduling

         8.   General Protection (Surface and Surrounding)

         These guidelines should be reviewed prior to performing
         this procedure and should be followed, when applicable,
         along with recommendations from the Regional Historic
         Preservation Officer (RHPO).


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   The Procter & Gamble Co.
         P.O. Box 599
         Cincinnati, OH  45202
         513/983-1100

2.02 MATERIALS

    A.   Neutral pH detergent, such as "Orvus" (Procter & Gamble),
         or approved equal.

    B.   White absorbent material (molding plaster, untreated
         white flour, white tissue, paper towels, powdered chalk,
         talc, fullers earth or laundry whiting).

    C.   Mineral water

    D.   Plastic sheeting

    E.   Clean dry towels for blotting the area after treatment

2.02 EQUIPMENT

    A.   Sanding blocks and paper

    B.   Glass or ceramic container for mixing the solution

    C.   Wooden utensil for stirring the ingredients

    D.   Wood or plastic spatula

    E.   Masking tape


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Verification of Conditions:

         1.   Determine the source of the staining.  Is there
              evidence of moisture, leaks, etc.?

         2.   Determine which type of scagliola it is - true scag
              or marezzo.  THIS WILL REQUIRE A CONSERVATOR'S
              EXPERTISE.  The biggest difference lies in how each
              is manufactured, applied and finished.  Marezzo is
              made in reverse order from the way true scag is
              produced and is generally a less labor-intensive
              process.  Recognizing the difference between the
              two can aid in better understanding the problem or
              failure.  The typical polish used for each type is
              also significant, as some polishes have proven to
              be detrimental to the material.

3.02 PREPARATION

    A.   Surface Preparation: ALWAYS test cleaning methods in an
         inconspicuous area to determine the effects of cleaning
         on the material and whether this procedure is suitable
         for use in this situation.

3.03 ERECTION, INSTALLATION, APPLICATION

    A.   For surface staining, the recommended procedure is to
         mechanically remove the surface layer of the scagliola to
         a clean surface layer below.  See 09200-07-R for guidance
         on polishing the new scagliola surface.

    B.   For penetrating stains: Try poulticing with a neutral
         detergent.  NOTE: NEVER USE ALKALINE CLEANERS OR
         POULTICE-TYPE PAINT REMOVERS ON SCAGLIOLA.  THESE MAY
         LEAD TO DISINTEGRATION OF THE GYPSUM AND CAN PRODUCE
         EFFLORESCENCE.

         1.   Thoroughly rinse the area to be treated with
              mineral water.

         2.   Mix the liquid solution to be used in a glass or
              ceramic bowl.

         3.   Thoroughly moisten the stained surface with this
              liquid.  Be sure to dampen well beyond the stain.

         4.   Mix the remaining liquid with the white absorbent
              material to form a paste the consistency of oatmeal
              or cake icing.  (Approximately one pound of paste
              is needed for every square foot of surface area to
              be treated).

         5.   Using a wooden or plastic spatula, apply the paste
              to the stained surface in layers no more than 1/4
              inch thick.  The poultice should extend well beyond
              the stain to prevent forcing the stain into
              previously clean stone.

         6.   Check the coating for air pockets or voids.

         7.   Cover the poultice with plastic sheeting and seal
              with masking tape.

         8.   Let set for 48 hours (unless otherwise specified).

         9.   After set period, dampen the poultice with mineral
              water.

         10.  Remove the poultice with a wooden or plastic
              spatula to avoid scratching the surface.

         11.  Again, thoroughly rinse the cleaned area with
              mineral water, blot with clean towels and allow the
              surface to dry.

         12.  Once the surface has dried completely, check for
              remaining residue and repeat the treatment if
              necessary.

                         END OF SECTION