Historic Plaster Repair Specifications

Section 09200   Historic Lime Flat Plaster Repair

Part I, General

A. The (Name Your Site) is a significant historic structure. All work shall be completed in such a way as to protect existing architectural features from damage   and to retain as much historic fabric as possible, with a minimum of loss.

B. The work of this section consists of evaluating the condition and then patching and repairing areas of removed or damaged plaster, the removal of modern plaster patches, repairing cracks larger than hairline, and applying a scratch, float, or setting coat, where required, to restore and preserve wall and ceiling areas to a physically and historically compatible finish.

C. The scope of work includes the following areas: (Add The Areas Here)

1-2 Quality assurance

A. Standards:

1. For materials; as noted.

2. For repair determinations, a Historic Plaster Repair Contractor in consensus with the contracting officer (CO) or owner’s representative will determine the extent of repair.

B. Materials: as stated or by approval of the CO

C. Qualifications of Historic Plaster Repair Contractor: Must be experienced in all phases of historic plaster repair, specifically lime based plasters, the preservation and reproduction thereof. The contractor must have six years and/or four projects of similar historical significance. They should have had training at a nationally recognized hands-on training program in historic plaster repair that stresses the stabilization of historic plaster with conservation adhesives.

1-3 Submittals, prior to commencement of work:

A. Submit written repair procedures to CO

B. Execute two sample panels of replacement plasters to be used as standards for the patching material.

C. Submit documentation of adhesive reattachment plaster projects.

D. This section may be waved in any or all of its parts by the CO as warranted.

1-4 Job conditions

A. Protect and cover all adjacent architectural features and work completed by other trades.

B. Determine what substrates to which plaster materials are to be applied are sound and free from defects affecting proper application of the lime plaster. Report defective surfaces to the CO.

C. Insure that a minimum temperature of 65 degrees F is maintained for an adequate period prior to, during and after application of plaster and that heating and/or ventilation is properly regulated to insure correct curing of the lime plaster.

1-5 Product Handling

Follow manufacturers directions, and store materials where directed on site to prevent damage.

PART II: Materials

2-1 Basecoat Plasters (course stuff), for application on wood lath or masonry

Mix lime putty, 1:3, with sand, for the scratch coat, well haired

Mix lime putty, 1:2.0-2.5, with sand, for the float coat, haired

OR: formulate according to mortar analysis or volumetric test

2-2 Finish coat Plasters or small area, crack repair

Mix lime putty, 1:1, with graded sand, for the finish coat,


Mix lime putty, 3:1, with gauging plaster


Mix according to the mortar analysis or volumetric test

2-3 Gauging Plaster

USG Champion Quality Gauging Plaster or equal

2-4 Lime

Lime putty that has emley plasticity greater than 400, 98% or better calcium, and a high surface area of 30m2/gram or better. Lime putty matching these specifications is available from Traditional & Sustainable Building, www.traditionalandsustainable.com at 443-822-0983,

2-5 Sand

Sand shall be well graded, masons, and shall be clean and free of dirt, and organic substances. Or match the existing historic sand as determined by the CO and/or the mortar analysis.

2-6 Fiber for Scratch and Float coats

The allowable fibers are as determined by mortar analysis or as follows in order of priority, hemp, goat hair, cattle hair, hog hair, jute, sisal, or manila. The fiber should be 1″ to 1/2″, in length. It shall be added in the proportion of 1/2 pound of fiber to 2.25 cubic feet of course stuff.

2-7 Water shall be clean, fresh, potable, and free from organic substances.

2-8 Bonding agents will not to be used without specific permission of the CO.

2-9 Adhesive, for the reattachment and stabilization of loose plasters, use Big Wally’s Plaster Magic Adhesive and Big Wally’s Plaster Magic Conditioner will be used according to, manufacturer’s directions

2-10 Metal Lath, not for application on sound exposed wood lath or over sound masonry

Galvanized steel expanded (diamond) mesh lath if needed.

The tie wire shall be 18 ga. galvanized soft annealed wire.

2-11 Fasteners

For wood lath to wood framing, stainless steel, ring shank siding nails.

For metal lath to wood framing, galvanized or stainless steel bugle head deck         screws and galvanized metal plaster washers.


3-0 Evaluation of plaster condition

The Historic Plaster Repair Contractor shall conduct an evaluation and in   conjunction with the CO formulate a plan for the plaster repair on these surfaces.

3-1 Adhesive reattachment- Big Wally’s Plaster Magic Adhesives are to be used according to manufacture’s specifications. For contact information please call Big Wally’s Adhesives, Inc., 802-254-1330, or e-mail, info@plastermagic.com .

3-2 Preparation; for plaster repair

A. At modern patches, evaluate their soundness and remove if necessary.

B. At exposed wood lath, re-secure to existing framing with stainless steel nails or pre-drill holes for deck screw attachment. Clean out keys and vacuum clean. Attach perimeter of sound plaster with an approved conservation adhesive, (see, 3-1), allow to coalesce as necessary. Rake perimeter of hole, to cut it back, for  replacement plaster to tuck in behind the existing plaster.

C.  Dampen wood lath until the surface is damp; using Big Wally’s Plaster Magic Conditioner.

D. Replace missing wood lath with similar materials. It is not appropriate to mix wood and metal lath.

E.  At existing sound plaster bases/ delaminating top coats: Determine, in consultation with the CO, which delaminations are to be saved and which are to be removed. Reattach the ones that are to be saved with the conservation adhesive and remove the others.

F. The cracks are not to be raked out.  This cuts the fiber binder that is still bridging the crack. This raking would weaken the plaster stability. If the fibrous binder is rendered by the width of the crack it is permissible to rake out the crack after stabilization with adhesives.

3-3 Application of plaster

A. Large area repair, adhere the perimeter of the opening and fill with two to three layers of the lime/sand/hair basecoat plaster, no more than 5/16″ per coat, and a finish coat, flush with the surrounding surfaces.

B. Small area repair, two inches or larger, fill with large area material, smaller, fill  with crack fill material, flush with the surrounding surfaces.

C. Crack fill rake out crack , (only if fibrous binder is rendered, if crack fiber is intact do not rake out) to approximately 1/2″ depth and fill with non sanded finish coat material, flush with the surrounding surfaces. If crack is not open then topping with a thin layer of ready mix joint compound after stabilization is appropriate.

D. Surface delaminations, remove as necessary, and replace with non-sanded finish coat material, flush with the surrounding surfaces.

E. Skim surface for cosmetic effect with joint compound, either ready mix or setting type.

F. Moldings, remove old repairs, evaluate conditions in conjunction with CO and decide on course of repair. Repair to follow crack repair specifications keeping true to profile.

End Section 09200 Historic Lime Plaster Repair