Repairing Plaster: It's Easy If You Follow These
Types of Plaster Problems
- Cracks Due to Settling of Walls/Foundation
- Gouges, Scrapes, Nail Holes, Wear and Tear
- Water Damage Around Windows, Doors, Plumbing
Tools and Material You Will Need
- plaster: for large repairs, rough and finish plaster
- small pointed trowel, large square trowel, putty knife
- two one-gallon plastic paint pails and paint stirrers
- spray bottle, two sponges, dry cleaning rags
Cracks Due to Settling of
The cracks are usually narrow. You will need to chisel out a wider area, tapering to the crack, so the plaster will hold.
This should be about two inches wider than the crack at the surface.
Gouges, Scrapes, Nail Holes, Wear and
Sometimes you will need to make the damaged area bigger so that the hole or gouge is tapered to help the plaster hold.
Water Damage Around Windows, Doors,
First, you must remove all loose and powder-like plaster around the damaged area. The main reason that plaster
repairs fail is because folks are afraid to remove enough of the bad plaster. It is often necessary that the plaster that must
be removed is four to ten times the size of the visual damage. You must remove any of the bad plaster until you get to
hard, good plaster. Brush away all dust, dirt, and plaster "crumbs." The edges of the damaged area shoud be tapered at
Plaster, when mixed with water, will set up in 20 minutes. You need to apply plaster in layers of about 1/4 inch.
Intermediate layers need to be "scratched" with the tip of your trowel before it sets up so you have a cross-hatch pattern about
an inch square. It is recommended you start out with a small amount and mix only about 1/2 of what you think you
need. Don't try to mix enough to fix the entire area at one time.
If the plaster is too dry, it can "flash set" near 20 minutes since mixing it will get rock-hard and unusable. When it
is mixed correctly, it won't have any lumps and it will be thicker than mayonnaise and thinner than peanut butter.
First, get all your materials and tools set up near where you'll be working. In one of the plastic pails, fill it with water.
You might want to get a small cup to help measure the water.
When you have everything ready, take one sponge, wet it, wring out all the water, and set it aside. Take another
sponge, wet it, and with it "sopping" wet, wet the entire area you are repairing. Now mix your plaster.
Applying the Plaster
If the area where you are going to apply the plaster has dried, use your spray bottle to "mist" the area to dampen. Use
the larger, square trowel, flat side up and handle down, to carry some plaster. Use the small, pointed trowel to cut off
some plaster. Start from the center and apply about 1/4 inch thick. Spread it out even but don't worry if it is smooth. Don't
play with it get it on the wall fast. After about 10 minutes, you are almost out of time. Get all of it in place. Then take the
tip of your trowel and scratch across all the plaster you applied, making a one inch pattern of squares by scratching
diagonally in both directions.
Use the moist sponge you set aside to "feather" the plaster near the edges. Scrape off plaster on your tools and put
them in the bucket with water. If you have any plaster left over, throw it out and wash your plaster bucket.
Sit Down and Relax
If this is your first try, you probably have a mess on the floor and your patch looks worse than when you started. Not
to worry. Clean up your mess and get ready for the next round. Normally, there are many, small steps used to repair plaster.
If you've got a hole where there is no lathing (wood or metal for a backing to attach the plaster) you can make a
backing with some cardboard or paper bag stuffed in the hole. The idea is to keep the plaster from leaking in the hole.
Pay attention to the drying time mentioned on the plaster mix container. It depends on which type of material you
bought. In cooler weather, it takes longer to set up hard enough to apply the next coat.
Building up the Plaster
Plaster is amazing, in that you can build it up in small amounts until you finally get it done and it will be as strong as
if applied all at once. The trick is to moisten the previous layer with water, and each layer (except the finish coat)
is scratched to provide good bonding.
With each layer, you want to make the area smaller, and filled a little more, until eventually the entire repair is
Finish Coat of Plaster
The final coat should be under 1/4 inch. Mix this slightly more wet. Cover the area quickly, getting it slightly over
level. Next, clean and wet your trowel, then work across the area to smooth it out. If it is not just right, don't fool with it too
long; use your moist sponge and remove some plaster so you can try again after it has set up.
Adding Texture to Match the Wall or
This is a little tricky. You can use plaster or other texturing materials. Try to make it match the adjoining area. Use a
moist sponge to feather the edges. One trick is to wear cotton gloves, and after applying some plaster or texture materials,
wet your gloves and, like "finger painting," play with the area to get a match. If the surrounding area has a sand finish, you
can buy "sand texture" to add to your primer paint just for the patch.
Most plaster repairs can be primer coated and painted within 24 to 48 hours. If the patched area shows signs of
water damage, the chemical used in plaster will bleed through when painted. Shellac is often used as a primer for plaster
that has water damage. You might have better luck with a product like Porter's® Stay-Kill®. It is an excellent, oil based,
primer that dries fast and works well with latex paint. Other brands have a similar product which works well, too.
Tips on Painting Plaster . . . If you are using an oil base primer or paint, you must wait 24 to 48 hours, minimum, to
let the plaster dry completely. With latex paint, it is best to let plaster dry overnight or longer. If the plaster is around a
window or door, or near plumbing, consider an oil base primer or latex enamel to protect the new plaster from water damage.
Reprinted with permission,