How to Paint Bare Plaster – A Simple Guide

Updated May 13, 2024 | Posted Dec 5, 2022 | Professional insight, Product Advice | 2 comments

People seldom ask how to paint bare plaster. It is super easy but 90% of ‘do it yourself’ homeowners miss a crucial step, and it can go terribly wrong. Follow my guide and get it right every time.

 

Equipment for painting bare plaster:

 

Step One – Make Sure the Plaster is Dry

When the plasterer is finished, the plaster will be a very dark terracotta colour. There will be a damp smell in the air, and after a few hours, I touch my hand gently to the surface and it feels very cold. I know it is dry when this colour has turned about 6 shades lighter. When all the water has evaporated and the plaster has set, it will feel warm and dry to touch.

To aid the drying process I encourage air-flow and warmth. I open the windows a little. If condensation or water is forming on the inside of the windows, I know they’re not open enough. Or if it feels too cold, I gently warm the room. But I make sure it’s not too hot. Above 21 degrees I may start to see some cracks in the plaster.

This small kitchen ceiling pictured, is in a warm apartment block, and took a few days to dry. To be on the safe side we left it a week before beginning work. The bigger the area of bare plaster, or walls and ceilings together, it will likely take longer to dry.

How to Paint Bare Plaster - A Simple Guide

Step Two – Prepping Your Plaster

The idea of checking over the whole room can feel a bit daunting, so I start with one metre square at a time. I imagine a box 1m high and 1m wide, and check that area. I get into it quite quickly and before I know it, I have covered the room.

I’m looking for lumps, bumps and holes. Using a fine grit (120g or 180g) piece of sandpaper, I gently swipe across the surface, I don’t want to scratch the plaster, so I keep a really light pressure.

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I use a gypsum-based filler on the holes as I want my filled patches to remain a similar texture to the bare plaster itself. Fillers that are flexible, like the ones that are like a light and fluffy mousse, are not really suitable at this stage. If there are cracks on the plaster, I don’t fill them until after the first coat of paint.

Once I have checked over all the bare plaster, and the filler has surpassed its drying time, I whizz round again and sand the filler patches smooth.

 

Step Three – Fixtures and Fittings

With a damp cloth, I clean the plaster off anywhere it should not be, such as on woodwork, or around window frames.

I would opt to have a competent person to remove all the electrical fittings before the plasterer arrives, if not the plasterer may loosen them off, or tape round them to protect them.

However more recently, some plasterers feel it is not within their jurisdiction to touch electrical fittings prior to plastering. I often see sockets and switches covered in plaster, making them look like they have been sunk deeper into the wall. When this happens, I need to gently excavate them and set them back to their original position.

To do this I make sure the electric is off, I gently scrape away the plaster to reveal the fitting plate, I then unscrew the screws enough to loosen the plate and fill behind it. I only fill up to the edge of the back box. This is the little house that is set back into the wall where all the wires are. I do not touch or fill anything inside the box. I do not want to add ‘being electrocuted’ to my bill.

I then wipe over any areas of bare plaster that I have sanded with a damp cloth to remove any loose dust particles and I’m ready paint.

 

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Step Four – Prime the Plaster

This is the most important aspect of painting bare plaster, it’s super easy, and hardly any homeowners do it, and it causes so many problems later down the line.

I must thin my paint according to the instructions on the tin. In the decorating industry, ‘Thinning’ means to dilute the paint by adding something to it. If the tin says clean up in soapy water. I know I can add water to thin that product. If it says clean up in white spirit, I know I can thin it with that spirit. Though the latter is most unlikely for wall paints. If the paint says something like ‘use a primer for bare plaster’ it means that my chosen top coat is not suitable for thinning, and I need to buy an acrylic primer to use as a base.

I thin the paint with water in order for it to penetrate the bare plaster and adhere correctly. This will prevent your paint from peeling further down the line, and create the perfect base for additional coats.

 

It Doesn’t Have to be White

*Hot tip* your first coat doesn’t need to be white. If my topcoat colour is dark, I’ll use a grey thinned matt emulsion to prime the bare plaster. Or order an acrylic primer in grey. This will also save me time having to apply so many coats of the finished colour.

Assuming the back of the tin says ‘thin first coat 30%’ I use the lines on the side of my scuttle to add the correct amount of water, I then pour the paint in to top it up, so if I need 10 litres, I pour water to the 3l mark, and then top with paint to the 10l mark. Stirring as I go. I have a drill with a whisk cyklone stirrer, but you can use a normal stir stick if that’s all you have.

diluting emulsion to paint bare plaster

Once I have my mix, commonly known as a ‘mist coat’ because of the misty appearance the paint adopts when going on the wall. I want to keep rolling this onto the wall until it looks more solid. This is how I feed the plaster with paint; it will be very thirsty. When the once bare plaster looks as though it cannot handle any more paint, I move to the next section.

Once I have covered the entire area and it has dried, I use a flexible filler to fill the cracks. Once this has dried, I sand it smooth and apply two full top coats of emulsion to finish the wall. If the paint feels sticky to roll, I add a splash of water into the first top coat. I gently sand the surface between applying each coat of paint. This is how I achieve a professional finish painting bare plaster.

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FAQs

 

What is the best primer for fresh plaster?

This depends entirely on what product you are using as a topcoat. A lot of Decorators wrongly use cheap contract matt as a primer for bare plaster, but this can lead to problems. My advice would be to buy the paint you are using to finish your walls or ceiling, and then read the instructions. Most manufacturers of vinyl and durable matt paints now recommend applying that product directly to the plaster. All you do is dilute the first coat. However, this can be slightly different in some cases. Brands like Tikkurila and Farrow and Ball for example specify their own primer.

Is one mist coat enough?

One mist coat is fine. All you’re doing is sealing the plaster to aid adhesion.

 

What kind of paint can go straight onto plaster?

There are specialist “bare plaster paints”. But the truth is that most emulsion paint products can be applied to bare plaster if you dilute the first coat. You should look at the instructions of the product you’re using to make an informed decision.

 

Can a mist coat be too watery?

A very watery mist coat will still seal the plaster, but it tends to run and over-hydrate the plaster.

 

Why is my mist coat not sticking to plaster?

This might be down to a couple of things. There might be dust on the walls, creating a barrier. Your plaster might be too polished, in which case you might need to abrade it, or go with a different primer. It might just be that you’re using the wrong paint entirely.

 

How many coats of paint on bare plaster?

If you’re using a good-quality trade paint, then two coats are usually fine. If you need to carry out excessive prep after the mist coat, or the paint you’re using is low quality, then you will probably need to apply three coats.

 

How long after a mist coat can I paint?

Just look at the “recoat time” for the product you used as a mist coat. It’s usually 4 hours, but it differs from product to product.

 

What ratio should a mist coat be?

This differs from product to product so always check the instructions (you sometimes need to find the Technical Data Sheet for the product online). The normal ratio is either 10% or 20% water.

 

Should I add PVA to mist coat?

NO! PVA on bare plaster is a myth and it can cause adhesion issues or crazing. Keep it away from your paint.

 

Is a mist coat meant to be patchy?

Yep, don’t worry about how your mist coat looks. All you’re doing is sealing the bare plaster ready for your topcoat.

 

Is Matt or silk better for mist coat?

Never use silk for mist coating. In fact, avoid silk all together. It’s horrible paint.

Updated May 13, 2024 | Posted Dec 5, 2022 | 2 comments

About the Author

About the Author

Mike Cupit has been in the decorating industry since 2002 and has mostly worked as a Trade Decorator in the domestic sector (peoples’ homes). Self-proclaimed “product geek”, Mike has a passion for paint and decorating tools. Mike now spends most of his time testing paint products and tools, comparing them to similar products on the market, and blogging about the industry in general.

2 Comments

  1. Richard

    Dulux supermatt white 1 thinned,
    l full or probably thinned slightly, nice non chalky finish it saves a coat this way.
    Touched up a dream other trades mess up walls etc
    Goes for miles the spreading rate 18sm2

    Reply
  2. Chris

    Can you use something like a sealer or primer product like Zinsser? These have adhesion properties?

    Reply

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