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Historic Preservation - Technical Procedures
Removing Dirt From Terra Cotta Surfaces
Developed For Hspg (Nps - Sero)
Terra Cotta Unit Masonry
Removing Dirt From Terra Cotta Surfaces
REMOVING DIRT FROM TERRA COTTA SURFACES
THE CLEANING OR REMOVAL OF STAINS FROM MASONRY MAY INVOLVE THE
USE OF LIQUIDS, DETERGENTS OR SOLVENTS WHICH MAY RUN OFF ON
ADJACENT MATERIAL, DISCOLOR THE MASONRY OR DRIVE THE STAINS DEEPER
INTO POROUS MATERIALS. USE THE PRODUCTS AND TECHNIQUES DESCRIBED
HERE ONLY FOR THE COMBINATIONS OF DIRT/STAIN AND MASONRY SPECIFIED.
A. This procedure includes guidance on removing superficial
and loosely attached dirt from glazed and unglazed terra
B. Avoid overcleaning; aim for achieving 85% clean; most
damage to masonry occurs when attempting to clean the
C. Avoid harsh cleaning methods such as mechanical cleaning,
acid-based cleaning and alkali-based cleaning.
D. 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).
E. For general information on the characteristics, uses and
problems associated with terra cotta, see 04214-03-S.
A. The Procter & Gamble Co.
P.O. Box 599
Cincinnati, OH 45202
NOTE: Chemical products are sometimes sold under a common
name. This usually means that the substance is not as pure as
the same chemical sold under its chemical name. The grade of
purity of common name substances, however, is usually adequate
for stain removal work, and these products should be purchased
when available, as they tend to be less expensive. Common
names are indicated below by an asterisk (*).
A. Methylene Chloride: (For small areas ONLY)
NOTE: THIS CHEMICAL IS BANNED IN SOME STATES.
REGULATORY INFORMATION AS WELL AS ALTERNATIVE OR
EQUIVALENT CHEMICALS MAY BE REQUESTED FROM THE
ENVIRONMENTAL PROTECTION AGENCY (EPA) REGIONAL OFFICE
AND/OR THE STATE OFFICE OF ENVIRONMENTAL QUALITY.
1. Other chemical or common names include
Dichloromethane; Methylene bichloride; Methylene
2. Potential hazards: TOXIC.
3. Available from chemical supply house, dry cleaning
supply distributor, paint store, photographic
supply distributor (not camera shop), or printer's
B. Neutral pH (non-ionic) liquid soap such as "Joy" (Procter
& Gamble), or approved equal.
C. Clean, potable water
A. Plastic pot scours or stiff bristle brushes (non-metallic)
A. Removing Dirt from Glazed Terra Cotta Surfaces:
1. For removing superficial and loosely-attached dirt:
Wash the surface with clean water or use a water-rinsable
neutral pH liquid soap, such as "Joy", or approved
equal (plastic pot scourers may also be helpful).
2. For SMALL areas of dirt more difficult to remove:
a. Thoroughly wet the surface to be cleaned.
b. Apply an emulsion of methylene chloride. Use
an amount adequate to fully cover the affected
area. Avoid excessive application to minimize
c. Rinse thoroughly with clean, clear water and
allow to dry.
d. Repeat as necessary to sufficiently remove
loosely attached dirt.
NOTE: SOILING UNDER OR WITHIN A GLAZE CANNOT BE REMOVED
WITHOUT DAMAGE TO THE GLAZE.
B. Removing Dirt from Un-glazed Terra Cotta Surfaces: There
is not a satisfactory method of removing all the dirt
from heavily soiled surfaces without removing part of the
surface in the process. The safest systems involve
leaving a percentage of the dirt intact.
1. Spray the surface with hot water.
2. Using hot water and a neutral pH, non-toxic, non-ionic
liquid soap such as "Joy", or approved equal,
gently scrub the soiled surface with the compact
bristle heads of the stencil brush type or a
plastic pot scourer.
3. Rinse with clean, clear water and allow to dry.
4. Repeat as necessary to sufficiently remove loosely
NOTE: ABRASIVE POWDERS AND POWDER-BASED DETERGENTS
SHOULD NOT BE USED.
END OF SECTION