Skip to main content

Historic Preservation - Technical Procedures

Spectitle:

Removing Loose Stucco And Patching

Procedure code:

0920010R

Source:

Hspg Prepared For Nps - Sero

Division:

Finishes

Section:

Lath & Plaster

Last Modified:

02/24/2012

Details:

Removing Loose Stucco And Patching



REMOVING LOOSE STUCCO AND PATCHING


PART 1---GENERAL

1.01 SUMMARY

    A.   This procedure includes guidance on patching loose stucco
         by removing deteriorated areas and applying new stucco.

    B.   Historic Structures Precautions:  

         1.   When choosing the type of stucco to be used, the
              Regional Historical Preservation Officer (RHPO)
              should be consulted, to provide chemical analysis
              of the existing stucco and information as to how to
              match for color, structure and texture.

         2.   Contact RHPO for stucco analysis, as well as
              historic practices and technology characteristic of
              the region.

         3.   RHPO will make provisions for analyzing stucco and
              will furnish proportions and detailed material
              specifications.

    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).

1.02 REFERENCES

    A.   American Society for Testing and Materials (ASTM), 100
          Barr Drive, West Conshohocken, PA 19428, (610) 832-9585
          or FAX (610) 832-9555.

         1.   ASTM C207, Type S

         2.   ASTM C150, Type I or II

         3.   ASTM C144

1.03 PROJECT/SITE CONDITIONS

    A.   Environmental Requirements:

         1.   Weather:  Do not proceed with patching under
              adverse weather conditions, or when temperatures
              are below or above manufacturer's recommended
              limitations for installation;  Proceed with the
              work only when forecasted weather conditions are
              favorable for proper cure.  Do not apply or mix
              mortar on outside surfaces with standing water or
              outside during rain.

         2.   Cold Weather, winter construction is not allowed
              without consent of RHPO. Winter construction
              (midwest region) is defined as any time between
              December 1 and March 1 and/or when surface
              temperature of masonry is below 40o F. or air
              temperature is predicted to be below 40o F. within
              48 hours.  All work must be suspended during frosty
              weather unless a heated enclosure is provided.  Do
              not expose curing stucco to freezing temperatures.

         3.   Hot Weather:  The surface temperature of the work,
              not the ambient temperature, should not be higher
              than 100o F.; Mortar mixing should be done only in
              the shade; Cover mortar in hot weather to reduce
              evaporation; Work around the building during the
              day so that the fresh work will be shielded from
              direct sunlight to reduce evaporation rate.  Work
              shall not be done in full sun at temperatures above
              80o F unless shading is provided.  Burlap sacking
              and water misting may be necessary to control
              evaporation.  Keep curing stucco out of the hot sun
              and away from harsh winds.

         4.   All materials must be kept above 40o F.


PART 2---PRODUCTS

2.01 MANUFACTURERS

    A.   Brooklyn Animal Hair Manufacturing Company
         175-185 Beard Street
         Brooklyn, NY  11231
         718/852-3592

2.02 MATERIALS

    A.   Hydrated Lime

    B.   Portland Cement

    C.   Sand

    D.   Cow hair (Brooklyn Animal Hair Manufacturing Company)

    E.   Clean, potable water  

2.03 EQUIPMENT

    A.   Mortar box

    B.   Mixing hoe (with two holes in the blade)

    C.   Masonry bit

    D.   Wire cutters

    E.   Garden hose or spray bottle

    F.   Trowels

    G.   Chisels

    H.   Hammers

    I.   Hawks:  Plywood or steel hawk (mortar board)

    J.   Brushes:

         1.   Natural bristle brushes

         2.   Stiff bristle brushes

         3.   Wire brush

2.04 MIXES

    NOTE:  CONSULT WITH RHPO TO DETERMINE WHICH OF THE FOLLOWING
    MIXES IS APPROPRIATE.  ACTUAL MIX SHOULD BE DETERMINED BY
    ANALYSIS.  IF ORIGINAL MIX IS KNOWN, OR IF PAST PATCHING MIX
    HAS BEEN USED SUCCESSFULLY, USE IT; OR ALTER STANDARD MIX TO
    MATCH ORIGINAL.

    A.   Lime/Sand Stucco Mix:

         1.   Scratch and Brown Coats:  Two coats doubled up to a
              thickness of about 5/8 inch.

              a.   5 parts hydrated lime

              b.   15 parts aggregate (match to original)

              c.   6 lb./cu. yd. hair (1/2- 2 inch length, free
                   of dirt, grease and impurities)

              d.   2-3 parts (max.) Type II portland cement for
                   workability

         2.   Finish Coat:

              a.   1 part hydrated lime

              b.   3 parts aggregate (match to original)

    B.   High Lime Mortar Mix:

         1.   1 bag of hydrated lime

         2.   1 shovelful of white portland cement

         3.   3 cubic feet of sand (matched to original)

         4.   Coarse aggregate matched to original (not to exceed
              15% of total volume of hydrated lime)

         5.   Hair or fiber (for scratch coat) matched to
              original if possible, about 1 pound of hair per 100
              lb. bag of hydrated lime

    C.   Lime/Portland Cement Mortar (More lime makes the mixture
         more "plastic" but more likely to crack from shrinkage;
         more sand or aggregate makes the mixture harder to trowel
         smooth and weakens the mortar).

         1.   1 to 1-1/2 bags hydrated lime

         2.   1 bag portland cement

         3.   5 to 6-1/2 cubic feet of sand

         4.   Coarse aggregate, hair, and fiber as above


PART 3---EXECUTION

3.01 EXAMINATION

    A.   Most stucco damage is caused by water infiltration.

    B.   Sometimes cracks occur due to different expansion rates
         of two surfaces.  These cracks can then allow water
         infiltration.

    C.   When identifying the source of infiltration, examine:

         1.   Flashing:  Check for holes, splits, or general
              corrosion.  Replace if required.  Copper, lead-
              coated copper, terne metal and terne-coated
              stainless steel are the best; aluminum is
              questionable.  To prevent corrosion due to galvanic
              action, flashing metal should be compatible with
              other metals, such as gutters and downspouts or
              other flashing, used on the building.

         2.   Drip edges:  A discontinuity formed into the
              underside of a window sill or wall component to
              force drops of water to fall free of the face of
              the building rather than move farther toward the
              interior.  Check to see that they are free from
              paint or dirt build-up.

         3.   Gutters:  Check to see that gutters are clear of
              debris (rust, tar patches) and have no open joints.

         4.   Walls outside of kitchens, bathrooms and chimney
              flues:  Look for damaged stucco caused by water
              vapor migration.  Remedy by altering water vapor
              transmission:

              a.   Apply a vapor barrier paint on the interior
                   walls.

              b.   Caulk joints along interior window trim and
                   baseboards.

              c.   Properly vent bathrooms and kitchens.

              d.   On a chimney, line the flue with a non-porous
                   liner like stainless steel.

         5.   Termination of stucco at ground level:  Stucco
              should terminate at least 4 inches above the
              ground.

         6.   Site Grading:  Make sure the ground slopes away
              from the stucco wall.

         7.   Joints between parapet walls and roofs:  Look for
              deteriorated and improperly installed flashing.

         8.   Plumbing:  Repair any leaks.

    D.   Determine the extent of the damage:

         1.   Check for spongy areas by pushing against the
              stucco with your hand:  any areas that move back
              and forth while making a squishy sound will need to
              be removed.

         2.   Tap the stucco with a hammer handle:  a succession
              of sounds indicates loose stucco; Areas that do not
              move and make only one solid sound indicate good
              stucco.

3.02 ERECTION, INSTALLATION, APPLICATION

    A.   Removing Damaged Stucco:

         1.   Make cuts through the stucco around the damaged
              area either with a cold chisel or by drilling a
              series of holes with a masonry bit.


         2.   If possible, cut back the coats of old mortar in
              square layers; Undercut the area to provide a firm
              bonding for the patch.  Cut to the lath; Pry off
              the old stucco with a broad flat tool like a nail
              puller.

         3.   Clean out all dust, dirt, and loose material with a
              wire brush.

         4.   Nail back to the sheathing any loose wood or metal
              lath under the old stucco.

         5.   Repair any small areas of lath that were damaged by
              nailing wire lath in place.

         6.   Replace any rusted corner beads with new corner
              beads.

    B.   Hand-Mixing the Mortar:

         1.   Place 1/2 the sand required for one bag of cement
              in one end of the mortar box; Spread the cement
              over the sand.

         2.   Lay the balance of the sand over the cement.

         3.   Place the amount of coarse aggregate or hair
              required for a bag of cement over the top of the
              sand.

         4.   Repeat as necessary until all of the required
              material is in the box.

         5.   Using a hoe, start at one end of the box and pull
              the hoe toward you in short choppy strokes until
              all of the materials are thoroughly mixed.

         6.   Pour the water into the box, and pull the dry
              material into the water using short choppy strokes;
              Continue to add water as needed to bring the mix to
              a soft, plastic mass.

         7.   Chop the hoe through the wet material until all the
              dry material has been wetted and pulled to the end
              of the box.

         8.   Change direction, and pull the mortar to the other
              end of the box.

         9.   Well combined materials will produce a uniform
              mortar color.

    C.   Applying Stucco Patch Using a Three-coat System:

         1.   Dampen wood lath by spraying lightly with a garden
              hose set for fine spray or use a spray bottle; A
              better method is to wet the lath with water
              containing photographer's wetting agent, i.e. Kodak
              Photo-Flo.

         2.   Apply first coat of stucco (scratch coat) 3/8 to
              1/2 inch thick, matching the thickness of the
              original scratch coat.

         3.   Cross-hatch the first coat of mortar with a trowel
              or piece of wire lath to provide good keys for the
              second coat.

         4.   Cure for 18 to 24 hours.

         5.   Moisten the surface with water before applying the
              second coat.

         6.   Apply the second coat (brown coat) 3/8 to 1/2 inch
              thick, matching the thickness of the original
              scratch coat.

         7.   Finish the second coat with a wood float that has a
              small nail driven through it (only the nail tip
              protrudes) to provide good keys for the finish
              coat.

         8.   Cure coat for several days; Sprinkle it with water
              occasionally so that direct sun or dry weather does
              not cause it to dry too rapidly and crack.

         9.   Moisten the surface with water right before
              applying the top coat so that the first two coats
              do not draw water out of the fresh stucco.

         10.  Apply the top coat (finish coat) to a thickness of
              at least 1/8 inch, to be flush with surface.

         11.  Wait 1-3 hours, then wire brush, float or trowel
              top coat using mild pressure to duplicate existing
              finish appearance.

3.04 ADJUSTING/CLEANING

    A.   Wipe all excess mortar as the work progresses.  Dry brush
         at the end of each day's work.  After stucco is
         thoroughly set and cured, clean new masonry surfaces,
         walls, sills, overhangs, etc., of all loose stucco, and
         dirt.  Patch all nail holes, cracks, etc., after which
         wash down all masonry walls, leaving them clean and neat.

                             END OF SECTION