14 May Need to Know: Painting Plaster Walls
If you have newly-plastered walls in your home, then there are a few things you need to know before you start painting them.
1. Seal it
New plaster needs to be sealed to make it less absorbent and to help the top coat adhere better. A common way to seal it is with watered-down emulsion, also known as a mist coat. The plaster sucks up the water and becomes less absorbent. After the mist coat is applied, you’ll be able to see where you need to fill more easily than you would with bare plaster.
2. Use watered-down emulsion
Watered-down emulsion is messy to work with because it drips much more than standard emulsion. Be careful to wipe, use a roller, or brush-out drips right away in order to avoid a bad finish. The paint dries quickly because the plaster is absorbent. If your topcoat is white, it’s best to use watered-down white emulsion for the mist coat. Otherwise, you’ll end up having to do more coats of topcoat than you need to.
3. The trouble with white topcoat
Using a white topcoat on new plaster means that it can take multiple patches of topcoat to cover. To save time and paint, use a stain block or a base coat emulsion on these patches. There are products specifically designed for new plaster (they need to be diluted with 20% water for the first coat) and problem walls. It seals the plaster and also fills hairline cracks, which sometimes appear in newly plastered walls and ceilings. This can especially happen if the walls and ceilings are lath and plaster.
4. Specialist paints
Paints designed to be applied directly to bare plaster are available in do-it-yourself stores. They’re more expensive than watering down cheap emulsion, but they’re much nicer to use because they don’t drip everywhere. Remember that it can be harder to get a good finish with them, though.
Watered-down emulsion produces what’s known as a ‘soft’ edge on new plaster, whereas bare plaster paints often produce a ‘harder’ edge that can adversely affect the finish. It is advisable to water down the first coat if you don’t mind making a mess. Painting plaster before it’s fully dry can cause the paint to peel, but some bare plaster paints allow the plaster to continue breathing and drying after the paint’s applied.
5. Dealing with damp
Sometimes patches of new plaster don’t dry out because of damp. Often the best solution is to remove the plaster back to the brickwork and hire a professional plasterer to do a waterproof render before re-plastering. This should stop any moisture in the brickwork coming back through the plaster. The cause of the damp should also be addressed by a professional at that time.
There are many quick fixes, such as applying damp paint/seal to the damp patches and then painting, or tiling or cladding the wall. However, you’re covering the damp rather than dealing with it and it may come through again once the damp paint/seal starts to fail.