No, you should never skim over damp plaster. Trapping moisture will ruin the new skim coat, causing it to bubble, crack, and flake. It can also encourage toxic mold growth and salt contamination behind the wall. Always identify and fix the source of the moisture first.
If you need to skim over plaster that was applied the previous day, follow these steps: Check Moisture Levels – The plaster should be firm but not overly damp. Apply a PVA Coat – Mix PVA with water (1:3 ratio) and roll it onto the surface. Let it dry slightly until tacky.
Plastering over a damp wall without carrying out damp proofing will not solve the root cause of the problem, and could lead to damp patches reappearing. Moisture can become trapped within the masonry, leading to issues such as cracking, blistering and salt contamination.
Apply each layer of plaster 15-30 minutes after the previous layer. If there is not enough time to finish the project in one day, it is important to apply a thin layer of water over the plaster before applying the next layer. If a new layer is applied to plaster that is already fully dry, it will not bond.
Common Visual Clues to Bad Plastering
Wide, uneven or randomly placed cracks are a clear indicator. Cracks at the edges or corners may mean the plaster did not bond to the wall properly. Another clue is uneven surfaces. Walls might look wavy, bumpy or have noticeable dips.
Fill in holes and cracks
A joint compound or filler can work here. Fill them in to sit flush with your wall. Don't worry about putting too much filler on; you'll be sanding it down once dried. You can also purchase skim repair fillers which you roll on with a roller, which could work for larger areas.
Cost: Skimming is usually cheaper because it needs fewer materials and less labour.
Common mistakes in this step are not cleaning the surface properly, not removing dust or old paint, and ignoring cracks and holes. Before you start on a plastering job, you have to make sure that the surfaces you're working on are thoroughly clean. This is to make sure that the plaster adheres properly to the surface.
The Disadvantages of Skim Coating: What to Consider
Direct warm air at small damp patches to lift off surface moisture and condensation. Run a dehumidifier to remove excess moisture and address the issue of moist air. Improve ventilation by opening windows so that you have plenty of fresh air.
If you have damp damage then you need to hack off all the render back to the bricks and re-render with waterproof solution mixed in with mortar. Yes it's a builder job." "Hi, you will need a builder or plasterer for this one. Hack off all the plaster and treat with a slurry mix then re-plaster."
Always skim in two plaster coats. Plaster coat ONE is roughing on and plaster coat TWO is laying down. Roughing on plaster coat should be about 3mm thick, even and relatively flat. Plastering trowelling lines will be blended into the laying down plaster coat which will be up to 2mm thick.
Yes, you can use drywall mud (joint compound) on plaster, but only for patching, skimming, or cosmetic repairs. Because plaster is dense and less porous than drywall, proper preparation—like using a bonding agent and a setting-type mud—is essential to prevent peeling or cracking.
For most beginners, a medium-sized firm steel trowel is a good all-round skimming trowel choice. It is large enough to cover ground, but not so big that it feels unwieldy.
Lath and plaster was a skilled craft and a time-consuming technique and the advent of cheaper, mass produced, pre-manufactured plasterboard meant lath and plaster largely fell out of favour by the 1930s and 1940s. Plasterboard was simply faster and less expensive to install.
Don't rush – a quick finish is a poor finish.
One of the worst things you can do for your plaster is rush the job. Plastering requires proper preparation of the surface and time to dry. Rushing through the steps will end in disaster for your finish.
Yes, you can skim coat over old plaster. It is one of the best ways to breathe new life into an uneven, cracked, or dated wall. The most important rule to know is that the skim coat will only be as strong as the plaster underneath it.
People choose plaster over drywall for its superior durability, better soundproofing, and smoother, more polished aesthetic. While drywall is quicker and cheaper to install, plaster provides a premium, hard-surface finish that is highly resistant to dents and is ideal for curved walls.
Skim coating can last for about a decade. But they will need constant repair and renovation. Although the task is a tedious one with a lot of time required, if done without a single error the restoration can make the walls look all good as new again.
Covering bad plaster walls comes down to your budget and the severity of the damage. For minor cracks, apply a joint compound. If the walls are severely crumbling or heavily textured, the most durable solutions are skim coating, hanging 1/4” drywall, or installing textured wallpaper.
Eco-conscious designers now use materials like bamboo, natural clay, and wool insulation. These options offer smooth walls and low embodied energy. Clay plaster is also great for interior walls, providing a clean look without chemicals or VOCs.
If your walls in your house are ugly or dull because of plaster that is past its prime or not to your taste, you can cover the plaster with drywall. It's as simple as just putting the drywall sheets right over old plaster. By using some sheets you can cover up old imperfections without a lot of complications.