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Historic Preservation - Technical Procedures

Spectitle:
Removing Dirt From Terra Cotta Surfaces

Procedure code:
0421404P

Source:
Developed For Hspg (Nps - Sero)

Division:
Masonry

Section:
Terra Cotta Unit Masonry

Last Modified:
02/24/2012

Details:
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.


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing superficial
         and loosely attached dirt from glazed and unglazed terra
         cotta surfaces.

    B.   Avoid overcleaning; aim for achieving 85% clean; most
         damage to masonry occurs when attempting to clean the
         last 15%.

    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

         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).

    E.   For general information on the characteristics, uses and
         problems associated with terra cotta, see 04214-03-S.


PART 2---PRODUCTS

2.01 MANUFACTURERS

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

2.02 MATERIALS

    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
              dichloride.

         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
              supply distributor.

    B.   Neutral pH (non-ionic) liquid soap such as "Joy" (Procter
         & Gamble), or approved equal.

    C.   Clean, potable water

2.03 EQUIPMENT

    A.   Plastic pot scours or stiff bristle brushes (non-metallic)


PART 3---EXECUTION

3.01 ERECTION/INSTALLATION/APPLICATION

    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).

         -OR-

         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
                   discoloration.

              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
              attached dirt.

         NOTE:  ABRASIVE POWDERS AND POWDER-BASED DETERGENTS
         SHOULD NOT BE USED.

                         END OF SECTION