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Historic Preservation - Technical Procedures

Spectitle:

Removing Biological Growth From Exterior Masonry And Stucco

Procedure code:

0420002R

Source:

Hspg Prepared For Nps - Sero

Division:

Masonry

Section:

Unit Masonry

Last Modified:

02/24/2012

Details:

Removing Biological Growth From Exterior Masonry And Stucco



REMOVING BIOLOGICAL GROWTH FROM EXTERIOR MASONRY AND STUCCO


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on removing biological
         growth such as lichens, algae, mold and mildew from
         masonry and stucco.

    B.   Biological growths such as lichens, algae, moss and fungi
         growing on masonry walls is usually an indication that
         there is excess moisture in or around the masonry.  These
         growths should be removed, as they attract moisture to
         the masonry surface and hold it there, which can lead to
         more serious problems.  Lichens and mosses in particular,
         produce oxalic acid which can damage certain types of
         historic masonry.

    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 MANUFACTURERS

    A.   ProSoCo, Inc.
         P.O. Box 1578
         Kansas City, KS  66117
         913/281-2700

2.02 MATERIALS

    A.   For Removing Mold and Mildew:

         1.   Non-sudsing ammonia or one of the following
              bleaches:

              CAUTION:  DO NOT MIX AMMONIA WITH CHLORINE
              BLEACHES, A POISONOUS GAS WILL RESULT!  DO NOT USE
              BLEACH ON BIRD DROPPINGS.

              Sodium Hypochlorite (NaOCl):

              a.   An unstable salt produced usually in aqueous
                   solution and used as a bleaching and
                   disinfecting agent.

              b.   Other chemical or common names include
                   Bleaching solution*; Household bleach*;
                   Laundry bleach*; Solution of chlorinated
                   soda*.

              c.   Potential Hazards:  CORROSIVE TO FLESH.

              d.   Available from chemical supply house, grocery
                   store or supermarket, hardware store or
                   janitorial supply distributor.

              -OR-

              Hydrogen Peroxide (H202):

              a.   An unstable compound used especially as an
                   oxidizing and bleaching agent, an antiseptic,
                   and a propellant.

              b.   Other chemical or common names include
                   Peroxide of hydrogen*; Solution of hydrogen
                   dioxide*; Superoxol*; (hydrogen peroxide is
                   commonly sold as a 3% solution; Superoxol is a
                   30% solution; Superoxol causes flesh burns; 3%
                   hydrogen peroxide does not).

              c.   Potential Hazards:  TOXIC (when concentrated);
                   CORROSIVE TO FLESH; FLAMMABLE (in high
                   concentration).

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

              -OR-

              Calcium Hypochlorite (CaCl2O2):

              a.   A white powder used especially as a bleaching
                   agent and disinfectant.

              b.   Other chemical or common names include
                   Chlorinated calcium oxide; Bleaching powder*;
                   Calcium oxymuriate*; Chloride of lime*;
                   Chlorinated lime*; Hypochlorite of lime*;
                   Oxymuriate of lime*.

              c.   Potential Hazards:  CORROSIVE TO FLESH;
                   FLAMMABLE (WHEN IN CONTACT WITH ORGANIC
                   SOLVENTS).

              d.   Available from chemical supply house, dry
                   cleaning supply distributor, drugstore or
                   pharmaceutical supply distributor, janitorial
                   supply distributor, swimming pool supply
                   distributor, or water and sanitation supply
                   distributor.

              -OR-

              Chloramine-T:  Chloramine is any of various
              compounds containing nitrogen and chlorine.

         2.   Trisodium Phosphate:

              NOTE:  THIS CHEMICAL IS BANNED IN SOME STATES SUCH
              AS CALIFORNIA.  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.

              a.   Strong base-type powdered cleaning material
                   sold under brand names.

              b.   Other chemical or common names include Sodium
                   Orthophosphate; Tribasic sodium phosphate;
                   Trisodium orthophosphate; TSP*; Phosphate of
                   soda*; (also sold under brand names such as).

              c.   Potential Hazards:  CORROSIVE TO FLESH.

              d.   Available from chemical supply house, grocery
                   store or supermarket or hardware store.

         3.   Powdered detergent such as "Tide" or approved
              equal.

    B.   Proprietary cleaner such as "Limestone Restorer"
         (ProSoCo, Inc.), or approved equal.

    C.   Clean, potable water

2.03 EQUIPMENT

    A.   Garden hose and nozzle

    B.   Rubber or polyethylene bucket (DO NOT USE A METAL BUCKET
         AS IT MAY REACT WITH THE CHEMICAL CLEANER AND PRODUCE
         TOXIC FUMES)

    C.   Glass or ceramic mixing bowl

    D.   Knife blade

    E.   Stiff, natural bristle brushes (non-metallic)

    F.   Tampico brush, roller or low pressure (50 psi maximum)
         spray such as pneumatic garden sprayer

    G.   Rubber gloves

    H.   Safety glasses


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Determine the source of excessive moisture, i.e. leaky
         downspout, standing water, roof overhang, vegetation,
         etc., and make any necessary repairs before continuing
         with this task.

    B.   Determine the type of stain, i.e. algae and lichens, or
         mold and mildew.

3.02 PREPARATION

    A.   Protection:  

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

         2.   Do not spray in the immediate vicinity of
              unprotected people and animals.

3.03 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.   Removing Lichens and Algae (ONLY):

         1.   Remove as much plant growth as possible using a
              knife blade and stiff bristle brush.

         2.   Water rinse the surface to remove most of the plant
              material.

              a.   If the substrate is sound and dense, use low
                   to medium water pressure (100-400 psi).

              b.   If the masonry is softer, use standard water
                   pressure from the spigot.

         3.   Allow water to soak plant growth for approximately
              30 minutes.

         4.   Gently scrub the surface with a stiff, natural
              bristle brush.

         5.   Thoroughly rinse the surface again with clean,
              clear water at low pressure from a garden hose.  

         NOTE:  DO NOT USE ANY CHEMICALS WITHOUT FIRST CONSULTING
         WITH RHPO.

    B.   Removing Mold and Mildew (ONLY):

         CAUTION:  DO NOT MIX AMMONIA WITH CHLORINE BLEACHES, A
         POISONOUS GAS WILL RESULT!

         1.   Mix the following:

              3 oz. (2/3 cup) trisodium phosphate (TSP) cleaner
              1 oz. (1/3 cup) powdered detergent (i.e. Tide)
              1 qt. 5% sodium hypochlorite bleach (laundry
              bleach)
              3 qts. warm water

              -OR-

              1 part ammonia with 3 parts water

         2.   Apply the solution to the affected area and scrub
              with a medium-hard natural bristle brush.  Keep the
              surface saturated until the stain is bleached,

              CAUTION:  BE SURE TO WEAR RUBBER GLOVES AND SAFETY
              GLASSES WHEN APPLYING THE SOLUTION.

         3.   Thoroughly rinse the surface with clean, clear
              water from a garden hose and allow to dry.

         4.   Repeat the process as necessary to achieve the
              desired level of cleanliness.

    -OR-

    C.   For treating any of the above (lichens, algae, mold or
         mildew), try using a proprietary cleaner such as
         Limestone Restorer (ProSoCo, Inc.), or approved equal.

         1.   Add 1 part Limestone Restorer to 3 parts water and
              mix in a rubber or polyethylene bucket.

         2.   Apply a flood coat of this mixture to the masonry
              using a low pressure spray (approximately 50 psi).

              CAUTION:  DO NOT USE A HIGH PRESSURE SPRAY WHEN
              APPLYING THIS SOLUTION AS THIS MAY CAUSE THE
              SOLUTION TO BE DRIVEN DEEPER INTO THE PORES OF THE
              MASONRY, MAKING REMOVAL OF THE SOLUTION DIFFICULT.


              a.   Begin spraying at the top of the vertical
                   surface and move across horizontally.  Allow
                   100mm rundown.

              b.   Continue the next horizontal pass across the
                   previous run down.

              c.   Allow the solution to remain on the surface
                   approximately 5-30 minutes depending upon the
                   thickness of the growth.

              d.   Gently scrub the surface with a stiff, natural
                   bristle brush.

              e.   Thoroughly rinse the treated area using
                   pressure-applied water (approximately 400 to
                   1500 psi) with a 40-60 degree fan spray or
                   garden hose with nozzle adjusted to a tight
                   stream.  Rinse from the bottom of the treated
                   area to the top.

              f.   Allow the surface to dry a minimum of 24
                   hours.

                         END OF SECTION