Removing Stains And Efflorescence From Architectural Scagliola
- Procedure code:
- Interior's Handbook For Historic Buildings - Jeff Greene
- Lath & Plaster
- Last Modified:
REMOVING STAINS AND EFFLORESCENCE FROM ARCHITECTURAL SCAGLIOLA
New York Landmarks Conservancy. "Restoring Scagliola to Glory", Common Bond, Vol.18, No.1 and 2, Fall-Winter 2003.
A. This procedure includes guidance on removing metallic
stains and efflorescence from architectural scagliola by
mechanical surface removal or poulticing.
NOTE: THIS PROCEDURE SHOULD ONLY BE PERFORMED BY AN
EXPERIENCED ARCHITECTURAL CONSERVATOR.
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
2. The liquid portion of the paste migrates into the
scagliola where it dissolves some of the staining
material. Then the liquid gradually moves back
beyond the 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
B. Stains may be caused by the presence of water, either on
the face of the scagliola or at the rear. Water can contain
dirt and contaminants which can stain the surface. These
contaminants can also migrate into the scagliola if the
surface finish is deteriorated. Moisture within the scagliola
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 scagliola 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
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).
2.01 MANUFACTURERS AND REFERENCE SOURCES
A. Manufacturer: The Procter & Gamble Co.
B. Reference Source: American Institute for Conservation
A. Neutral pH detergent, such as "Orvus" (Procter & Gamble),
or approved equal; check internet for retail/wholesale sources.
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
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
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 scagliola
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 scagliola 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.
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
1. Thoroughly rinse the area to be treated with
2. Mix the liquid solution to be used in a glass or
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
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 scagliola.
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
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
END OF SECTION