DIY Repair for Loose Plaster Lath
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Loose plaster, like that described on this page, is a problem in walls and ceilings with wood lath. Wood lath plaster will usually be found in houses built before the 1920's, after which time gypsum board was developed for use as plaster lath.
Over many years the nails in wood lath become corroded by the lime in the plaster coats. As a result the lath becomes loose and prone to movement due to vibration from foot traffic, etc. These vibrations cause the scratch coat key to break free from the wood lath. The result is a plaster coat that "floats" over the lath, cracking and crumbling as it moves. A broken plaster key can sometimes be repaired, especially on walls. See the Repairing Broken Plaster Key page for help with this problem.
To stabilize plaster and prevent further cracking, the technique on this page can be used to reattach wood lath on walls and ceilings. This will work nicely to restore the plaster in cases where the key is still generally intact. Ceilings with extremely loose plaster and broken scratch coat key, may be impossible to repair using this method. In those cases it may be better to cover the ceiling with new drywall. See Drywall Ceiling Installation for help.
Reattaching Wood Lath
Locate the wood lath and the studs or joists behind the loose plaster. Use a drill and an eighth inch masonry bit to bore holes at one inch intervals along the ceiling or wall until you locate the framing.
Mark the location of the framing and bore a one eighth inch pilot hole thru the lath strip and into the framing behind. Do this at each stud or joist. Next bore ½in. countersink holes in the plaster coats at each pilot hole. Plaster will dull drill bits in short order so use old bits or masonry bits for drilling and countersinking in the plaster coats. Use a wood bit to bore pilot holes thru the wood lath and into the framing. Use 2 to 3 inch drywall or wood screws and ½in. washers to reattach the wood lath to the framing.
Press the plaster coats back into place before driving the screws. To hold the plaster coat in place on walls use a small piece of plywood (about 2ft. by 6ft.) and a 2x4 brace at regular intervals. Press the plaster as flat as possible before reattaching the lath. Tighten the screws down slowly to avoid sudden movement that could crack the plaster coats. Space the anchor screws at about 8 to 12 inches being sure to hit a lath strip and framing member at each point. Repair the holes using the repair methods on the Drywall Repair Nail Pop page. Repair cracks using this crack repair process.
Use a Tee to Repair Ceilings
To press ceiling plaster back into place and avoid cracking the plaster coats, use a homemade tee and a small piece of plywood to distribute pressure over a large area. Bore the countersink and pilot holes at 8 to 12 inch intervals along the edge of the support. Move the tee a little at a time to finish reattaching all the loose ceiling lath.
