The plaster must be primed before it is painted to achieve a long-lasting finish.
New plaster sets as a very porous surface which means that when paint is applied to it, the paint's moisture is sucked straight out. It drys so quickly, the paint has no chance to anchor itself to the wall, it has no "roots" and will soon begin to peel and flake away, ruining the finish. So in order to paint on plaster it is vital to prime the surface first.
Instructions
When and Apply a Water-Based Primer
1. You will need to dilute your water-based paint for use as your primer.
Priming plaster you intend to finish with a water-based paint such as matte or emulsion requires you to seal the surface with a diluted version of your chosen paint. Mix your chosen matte or emulsion paint in a container with water by using a stick to stir the substances together. Quantities of four parts paint to one part water should be used. This dilution will be thinner then the paint is and will allow for the porous plaster to suck the mix into its holes, sealing them off.
2. Apply the mix to the walls using a roller or paint brush. Sometimes it is possible to hear the plaster taking in the mixed paint. If you are worried the dilution is not being absorbed into the plaster, the mix can be further diluted by adding more water up to a point of one part paint to one part water; this makes the mix thinner and easier for the plaster to suck in, which is what results in a good seal.
3. Painting a second coat of the sealant onto the wall may be required.
When and Apply an Oil-Based Primer
4. Priming a surface for an oil-based paint like egg shell or gloss requires the use of an alkaline resistant sealant. Using a mix of water and PVA solution is ideal in these circumstances. Stir together water with PVA adhesive in quantities on one part water to four parts PVA adhesive.
5. Paint the solution onto the plaster with a roller or paint brush; the mix will be sucked into the plaster's pores and will withstand the application of the oil-based paint.
6. The plastered wall is now ready for painting.
Apply a second coat of the mix if needed.
Priming Plaster For Wallpaper
7. Plaster must be sealed before wallpaper can be fixed.
Wallpapering over plaster also requires the surfaces to be sealed. Purchase a product called "size" from your local home improvement store.
8. Mix the size with water as advised on the label.
9. Apply it to the wall with a roller or paint brush then wait for it to dry before papering.
10. Diluting wallpaper paste with water can be used as a substitute for size.
Tags: paint brush, part water, , roller paint brush, with water