Section 000 Historic Lime Flat Plaster Repair Over Wood Lath or Brick
Part I, General
A. The _____________ 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, removal of modern plaster patches, cracks larger than hairline, and apply 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: ______________
1-2 Quality assurance
1. For materials; as noted.
2. For repair determinations, a Historic Plaster Repair Contractor in consensus with the contracting officer (CO) or owners 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.
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 over brick and masonry walls
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
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, with the approval of the CO.
2-3 Gauging Plaster
USG Champion Quality Gauging Plaster or equal
Lime putty that has emley plasticity greater than 400, 98% or better calcium, and a high surface area of 30m2/gram or better. This lime putty that meets this specification is available from Traditional & Sustainable Building, www.traditionalandsustainable.com at 443-822-0983.
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 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, cattle hair, goat hair, hog hair, jute, sisal, manila, or hemp. 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 (TM) and Big Wally's Plaster Magic Conditioner (TM) will be used according to, manufacturer's directions
2-10 Metal Lath, is not for application on sound exposed wood lath or over brick
Galvanized steel expanded (diamond) mesh lath is incompatible with historic structures. This is a rigid building system and is not for use in flexible structures.
The tie wire, shall be 18 ga. galvanized soft annealed wire.
For wood lath to wood framing, stainless steel, ring shank siding nails or stainless steel screws.
PART 3: EXECUTION
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 (TM) are to be used according to manufacture's specifications. This adhesive will reattach historic plaster to brick also. For contact information please call Big Wally's at (802) 254-1330 or e-mail at email@example.com
3-2 Preparation; for plaster repair
A. At modern patches, evaluate their soundness and remove if necessary. These include but are not necessarily limited to,
B. At exposed wood lath, re-secure to existing framing with stainless steel nails or pre-drill holes for deck screw attachment. If brick make sure your surface is sound then plaster over the brick. 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 water the surface is damp; using a mix of water with non-detergent surfactant.
D. Replace missing wood lath with similar materials. In general 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 cause 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 3/8” 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, Do not rake out cracks unless the fibrous binder is rendered. Cutting the fibrous binder weakens the plaster.
D. Surface delaminations, remove as necessary, and replace with non-sanded finish coat material, flush with the surrounding surfaces.
E. 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 000 Historic Lime Plaster Repair
Copyright 2000, Rory Brennan