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How to Stabilize Loose and Damaged Plaster
Traditional plaster is usually repairable as long as it keeps its grip on the supporting lath. When it does loose its grip and begins to sag or pull away from the lath, repair work is usually a waste of time because cracks are quick to reappear. The only other alternatives are a replastering job or removing and replacing the plaster with drywall - both very costly items.

It's not possible, even for the professional to reattach the plaster to the lath, but it is possible to stabilize loose plaster by pulling it back against the lath with drywall screws equipped with thin metal washers. Using this technique repairing large cracks, holes and sagging plaster is a doable project for the average homeowner. Here's how to do it.

Stabilizing Loose Plaster

A plaster wall is actually composed of two or more coats of plaster. The first coat of plaster is troweled against the lath so it is pushed through the small spaces between the lath. Gravity causes the plaster to sag and droop behind the lath. When this base coat hardens it is keyed tightly to the lath. The following coats adhere to the base coat to form the rock hard plaster wall.

When the plaster keys behind the wall break away, the plaster no longer has a grip on the lath. The plaster can then move or droop away from the wall. As long as the plaster can flex and move, repair work is temporary at best. This loose plaster is also potentially dangerous since it can fall off the ceiling or wall.

If the plaster flexes when you push on it, you have an area of plaster that has lost its key. Here's how to refasten it to the lath using plaster washers.

Determine how wide of an area is loose. Push on the plaster and mark the boundaries of the area the moves with chalk. Next, locate the wall studs or ceiling joists. Drive a 2-in. drywall screw equipped with a spring steel plaster washer through the plaster and into the stud or joist where the boundary lines cross the studs. Place additional screws and plaster washers at 8-in. to 10-in. intervals along the studs or joists.

Drive additional 1 1/2-in. drywall screws equipped with plaster washers through the plaster and into the lath around the perimeter of the repair. Then install washers and screws working toward the center. Place these in 8-in. to 10-in. centers.

Tighten the screws with a screw gun or variable-speed drill equipped with a Phillips screwdriver bit. Drive the screws in and tighten them just enough to pull the plaster snug against the lath. You'll see the perforated metal washer flattens out against the plaster.

The screws will bite into the lath, but make sure you drive some screws into the wall studs or ceiling joists. To pull a sagging ceiling back into contact with the lath, it is necessary to get as many screws as possible into the ceiling joists.

If you use a drywall screw gun, experiment with the screw depth setting. You want to set the depth so the screw will come up tight and flatten the washer. The screw gun can break off the screw head or strip the driver slot when it tries to sink the screw head into the metal washer if the depth setting is too deep.

If tightening the screws does not flatten the washers, you have missed the stud or joist or the screw could have gone between two pieces of lath. Remove the screw and washer, move it about a inch in either direction and try again.

Plaster washers are no more difficult to finish than drywall screws, their heads are just larger. Apply drywall joint compound over each washer with a 6-in. broad knife. If the blade strikes the screw head or washer tighten the screw to recess it more. When the compound is dry (usually overnight) apply a second coat. After a final sanding, the surface is ready for primer and finishing.

Repair a Hole or Large Crack in Plaster

The plaster keys usually break and loses their grip on the lath around large cracks and holes in plaster. This is the main reason that cracks soon open up after they have been spackled. For any repair to last, the plaster must be pulled back tight against the lath and stabilized so it can't move.

The easiest method to do this is to drive drywall screws equipped with plaster washers along both sides of the crack or around the perimeter of the hole. Space these washers 6-in. to 8-in. apart, but be sure that some are driven into the wall studs or ceiling joists.

You can tell when the plaster is tight against the lath when it doesn't move when you push on it. Fill small cracks and holes with spackle. Use drywall compound and fiberglass mesh tape to patch larger cracks or holes.

Written by the editors of HouseNet
Copyright HouseNet, Inc.

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