Although drywall has become the choice material over the last several decades for interior wall construction, many older homes (built prior to 1950 or so) will have plaster walls throughout.
A plaster mixture (usually gypsum, lime, or cement) is wet when first mixed, allowing it to be spread out as a putty over wall framework (usually a wooden lath), until it cures or hardens.
When wet plaster is spread out over a lath, it fills in the small spaces between each strip of wood, creating keys that will keep the wall secured in place once it dries.
Over time, the plaster can become dislodged from the lath, resulting in cracks or “loose spots” where the wall is noticeably separated from the framework. Check out our complete review of the best spray foam insulations to fill all those cracks.
This article will go over how to repair these damaged areas - from chips and small cracks, to large holes and entire sections of wall the need replacing.
Cracks, chips, and other small repairs
Cracks are quite common in plaster, and often result when work has been done to the wall (i.e. hammering in nails, cutting holes for a new electrical box, etc.)
Usually, a visible crack will also indicate that that section of the wall has become dislodged from the lath behind it. Press firmly along the length of the crack to feel for ‘soft areas’ where the wall can easily be pressed up and down. Any soft areas will have to be re-attached to the lath, and we’ll discuss how to do this shortly.
If there doesn’t appear to be any soft spots, the crack itself can be simply fixed with a good 5 or 6-in-1 tool (like this one from Hyde Tools), some spackle or joint compound, and a putty knife.
First, use the 6-in-1 tool to scrape out the crack - you want to widen it out slightly, just enough for spackle to fill in to and get a good grab. After you widen the crack, scrape over the length of the crack to clean it up. Then, use a damp sponge or rag to clean the area. Next, use a putty knife to add spackle or joint compound and fill in the crack until it’s flush with the wall. You may need to do a few layers for a quality job, and allow each layer to dry before adding another.
Here’s an excellent video on how to fill in cracks like a pro.
Spackle can also be used to fill in chips and small holes, such as screw holes that were used to mount a picture or TV. Use your 6-in-1 or a utility knife to clean out the hole (you may want to use a vacuum to suck any dust out), scrape/wipe the area clean, and fill in with spackle until flush.
Re-attaching the wall to the lath
Repairing sections of wall that have become unattached from the lath requires a different technique.
Identify any ‘soft spots’ that are able to be easily pressed up and down - these areas of wall will need to be re-attached to the lath behind it. What you’ll do is drill holes throughout the damaged area, and insert a liquid adhesive that will re-bond the plaster to the wood lath.
First, use a masonry bit to drill holes throughout the entire ‘soft area’. If there are soft spots on either side of a crack, you’ll need to drill holes on both sides. Take care to ONLY DRILL THROUGH THE PLASTER - stop when you get to the lath.
You may end up drilling dozens of holes, depending on the size of the area that needs re-attaching. You should aim to hit every other lath - you don’t need to hit each one. Also, don’t worry about spots where you shoot between the wood strips, simply mark these holes with a pencil, indicating not to insert adhesive there.
Once you drill out the entire area that needs repairing, use a damp cloth and scraper to clean off the area, and vacuum out the holes to get rid of any dust.
Next, you need to condition the lath before inserting the adhesive. Use a spray bottle to spray the conditioner (like this one from Big Wally’s Plaster Magic) through each hole. Once the conditioner is applied, you can use a caulk gun to insert the adhesive that will re-bond the plaster to the lath. You don’t need to apply tons of adhesive to each hole - simply add enough to where it starts oozing out of the hole.
Once the adhesive has been applied, you’ll need to immediately clamp the area using drywall screws and plastic rings. When putting the screws in, you do not need to get them too tight. Simply screw them in until you feel the wall come into contact with the lath - you should see some of the adhesive ooze out from behind the wall as it’s tightened down to the framework.
Check out this link for a complete Big Wally’s repair package that includes conditioner, adhesive, and plastic ring clamps.
Wipe away any adhesive that’s dripped down onto the walls, and allow to dry. Once fully dried, you can remove the screws and plastic rings, and use joint compound to finish the area.
Here’s a great video on this whole process.
Repairing/patching large holes
If you need to patch or repair a large hole or entire section of wall, you can either mix and spread new plaster, or cut out a piece of ¼” drywall to use as a patch (the thickness of the drywall of course will depend on the thickness of the plaster).
If you’re going to mix and spread new plaster, you’ll need a few tools such as good plaster hawk, mixers, and putty knives. Also, getting the right consistency in the mixture is crucial - here is a good video on how to do this.
You’ll also need to make sure that the framework is in good enough condition to hold the wall - often when a section of plaster wall is damaged, the lath framework behind it is damaged as well.
When spreading the plaster, you’ll want to do two separate coats to get it good and flush with the surrounding wall. Add the first layer, but before it fully dries, roughen it up with a trowel to ensure that the second layer has something to ‘grab on to’. Here’s an excellent video on how to do a great job.
To finish the section, use two or three very thin layers of joint compound.
If you’re going to use drywall to patch the area, you can simply screw it into the lath framework, then use joint compound to fill in the gap between the patch and the wall. You can also use several layers of joint compound over the drywall patch to finish the area.