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How to Paint New Plaster

As I have been asked this question quite a lot recently I thought I would give this piece of advice for this month - how to prepare and emulsion new plaster surfaces.

The first thing to do is to make sure the plaster has thoroughly dried out, without any damp areas before applying coatings over it.

This could cause the paint to lift later. Although emulsion paints in theory are breathable and can be used over slightly damp surfaces, it is always a safer option to allow the plaster to dry out completely before painting over it.

Next the preparation - if the plasterer has done a 1st rate job (not always the case) there will be virtually no preparation, maybe just a bit of rubbing down to remove any plaster splashes from surrounding woodwork etc. or maybe running your hand over the surface to remove any slight surface dust. More often there will be a bit of preparation: -

If there are trowel marks on the surface or small lumps and bumps, go over the whole surface with a large flat bladed scraper and gently knock these off. DO NOT whatever you do rub the surface over with sand paper, no matter how fine the grade it is, as this will leave fine scratches all over which will show through when you start painting.

Also do not do any filling just yet as this will need to be rubbed down, again causing surface scratches around the filling.

Small hairline cracks can be ignored, as the emulsion paint will fill these.

Larger cracks will need to be filled after the sealer coat has been applied. Again run your hand over the whole surface to remove any dust that will impair paint adhesion.

Next the plaster is going to need a sealer coat applied, as new plaster is very porous. The traditional method of doing this is to thin out your 1st coat of emulsion by about 30 to 40% with clean water, making a sealer coat. This will penetrate deeply into the surface stopping any flaking off later on in years to come. No need to use white emulsion as the sealer coat (white is a hard colour to cover believe it or not) just thin out the emulsion paint chosen as the finish colour, unless you have a load of white emulsion you want to get rid of!!

Another way to seal the plaster prior to painting is to apply a readymade sealer, Dulux make one specifically for new surfaces. I personally use acrylic stabilising solution, really made for stabilising chalky surfaces, but also excellent for sealing bare or new plaster. I know lots of people (tradesmen included) use thinned out P.V.A glue (i.e. Unibond) for this but I personally do not, as it does not penetrate well, it dries on contact and resoftens when painted over, which can cause lifting of the paint later on.

Use a brush to apply sealers as they force the liquids into the surface rather than just laying them on the surface like rollers do.

Now the plaster is sealed you can do any making good either with powder fillers or mastics.

The surface can now be painted, either with a roller, brush or pad, but do not just open your new tin of emulsion paint and start painting, thin the paint out, the surface is still going to be porous, so thin it out by about 10% When this has dried apply your last coat again thinned out but slightly less this time.

Never use emulsion paint straight out of the can; emulsion should always be thinned out slightly before use, two thinned coats are better than one thick coat!

That is the rule with emulsion!

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