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Historic Preservation - Technical Procedures

Spectitle:

Removing Lime Mortar Deposits From Brick Masonry

Procedure code:

0421113R

Source:

Developed For Hspg (Nps - Sero)

Division:

Masonry

Section:

Brick Unit Masonry

Last Modified:

02/24/2012

Details:

Removing Lime Mortar Deposits From Brick Masonry



REMOVING LIME MORTAR DEPOSITS FROM BRICK MASONRY


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing lime mortar
         deposits from both clay and calcium silicate bricks using
         hydrochloric acid and water.  

    B.   Material composition and method of manufacture are the
         major differences between clay and (sand-lime) calcium
         silicate bricks.

         1.   Clay bricks are composed mainly of sand and clay -
              moulded, dried and burned into shapes.  Some
              characteristics include the following:

              a.   Compact texture

              b.   Generally free of cracks, lime, stones and
                   pebbles

              c.   Uniformly burnt

         2.   Calcium silicate bricks are composed of a sand-lime
              mixture compressed into precise, uniform shapes.
              Some characteristics include the following:

              a.   Smooth, fine textured and light in color

              b.   Steamed, not burned

    C.   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 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.   Hydrochloric Acid (30-35%):

         1.   A strong corrosive irritating acid.

         2.   Other chemical or common names include Chlorhydric
              acid; Hydrogen chloride; Muriatic acid* (generally
              available in 18 degree and 20 degree Baume
              solutions); Marine acid*; Spirit of salt*; Spirit
              of sea salt*.

         3.   Potential Hazards:  TOXIC, CORROSIVE TO FLESH;
              CORROSIVE TO CONCRETE, STEEL, WOOD OR GLASS,
              FLAMMABLE.

         4.   Available from chemical supply house, drugstore or
              pharmaceutical supply distributor, or hardware
              store.

    B.   Clean, potable water

    C.   Drying Materials:  Clean natural fiber rags

2.02 EQUIPMENT

    A.   Garden hose and nozzle

    B.   Stiff bristle brushes (non-metallic)

    C.   Wood or plastic scraper


PART 3---EXECUTION

3.01 PREPARATION

    A.   Protection:

         1.   Provide adequate wash solutions (i.e. water, soap
              and towels) before starting the job.

         2.   Whenever acid is used, the surface should be
              thoroughly rinsed with water as soon as its action
              has been adequate.  Otherwise it will continue
              etching the masonry even though the stain is gone.

3.02 ERECTION, INSTALLATION, APPLICATION

    NOTE:  DO NOT TRY MORE THAN ONE TREATMENT ON A GIVEN AREA
    UNLESS THE CHEMICALS USED FROM PRIOR TREATMENT HAVE BEEN
    WASHED AWAY.

    A.   Stone and Clay Bricks:

         1.   If possible, remove large pieces of mortar deposits
              using a wood or plastic scraper.

         2.   Wash down the affected area with a diluted solution
              of hydrochloric acid (1:10 by volume).

         3.   Thoroughly rinse the surface with clean, clear
              water and allow to dry.

    B.   Calcium Silicate Bricks (or sand-lime bricks):  CAUTION:
         THIS TREATMENT SHOULD BE USED CAUTIOUSLY, AS ACID MAY
         DAMAGE THE SURFACE OF SOME CALCIUM SILICATE BRICKS.

         1.   Lightly abrade the surface using a brick of the
              same color.

         2.   Wash down the affected area with a solution of
              hydrochloric acid (1:20 by volume).

         3.   Thoroughly rinse the surface with clean, clear
              water.

                         END OF SECTION