How to Prep Walls Before Painting

As a Professional Decorator, it’s fair to say I have done a lot of prep over the years. I thought I’d sit down and write a quick blog on how to prep walls before painting. I’ll take you through the different methods I use for various situations and recommend products as I go.

 

Should You Sand Previously Painted Walls Before Painting?

 

In short, yes, you should sand walls before painting. This is for a couple of reasons; Firstly, it helps smooth out imperfections that would otherwise show through your finished paint work.

The other reason is adhesion; You need your new paint to stick to the old paint. This isn’t always an issue, but it can be if you’re painting over eggshell, silk, or contract matt.

If your walls are in good nick, you might just need to surface fill any blemishes, lightly abrade the whole wall, then just give it a quick dust off, and you’re ready to paint. Axus sandpaper is probably the best, but any will do.

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How to Prep Newly Plastered Walls

 

Newly plastered walls are a little bit different. A lot of people make the mistake of sanding new plaster before painting it. However, this can coat the wall with a thin layer of dust, which causes adhesion issues and results in paint peeling further down the line.

Instead, inspect the walls and scrape off any plaster snots (lumps of plaster that have fallen off the trowel onto the wall). Then apply a ‘mist coat’ to prime the walls. The product you use as a mist coat will be named on the instructions of the product you are using as a topcoat. Normally your mist coat is a diluted coat of the same product as your topcoat, but some brands (like Farrow and Ball and Tikkurila) specify a different primer, so always check.

Once mist coated, allow to dry, do any filling and sanding as required, then crack on and paint your walls.

 

How to Prep Walls That Are in a Bad State

 

Depending on how bad your walls are, you may need to surface fill and sand your entire wall. If it still isn’t smooth enough to paint, then installing lining paper may be an option. Or you could skim the walls yourself using roll-on filler, which is surprisingly easy to do with the right materials.

 

Surface Filling

There are plenty of fillers you can use as part of your prep before painting walls. Powder filler (the type you mix yourself) is generally easier to sand smooth after you’ve applied it. Go for an interior filler too, as some of the multipurpose products contain cement which can flash through your paint.

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My suggestion would be Gyprock Easifill, which is easy to use, readily available, and reasonably priced. Click here to see online prices.

Simply add some water to a tub or bucket, then add the filler, and mix until you reach a smooth consistency. Then apply a thin coat over all the imperfections on your wall using a filling knife.

You should open any cracks with the edge of a scraper before filling so the filler can penetrate.

Once dry, simply sand smooth, dust off, and paint your wall. Your first coat of paint over filler should be diluted to aid adhesion.

Occasionally you may notice the odd imperfection after you’ve applied your first coat of paint. No need to panic, just fill any bits, sand, spot prime with paint, then apply your topcoat.

filler on a prepped wall ready to paint

Skimming Walls with Roll-On Filler

This way of prepping your walls before painting is going to cost you a little more, and it is more physical. But it’s easy enough to achieve a good finish and it’s a lot cheaper than hiring a plasterer. I’ve been using a new product called Dalapro Roll Nova. You just apply it with a paint roller and then smooth it off with a filling blade. Once dry you just give it a quick sand, dust it off, then you’re ready to paint.

Click here for full instructions on how to do it.

a skimmed wall which can now be painted

Lining the Walls Before Painting

You will still need to fill most of the imperfections on a wall before lining, so it isn’t a quick fix. However, lining your walls can be a great way to combat reoccurring cracks and movement on your wall, so your paint finish will last longer.

I like using 1400 grade lining paper, which can be bought online by clicking here. You can apply it horizontally or vertically, and you’ll find it easier to use than normal wallpaper. Click here for insight on the best wallpapering tools.

My favourite paste is Beeline, but any ready mixed paste is generally fine. Avoid flake (paste you mix yourself) because it isn’t as strong, and your lining paper can bubble when you’re painting it.

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How to Prep Walls That Were Previously Wallpapered Before Painting

 

You should take a few additional steps when prepping a previously wallpapered wall before painting, simply because your paint can react with leftover paste.

Some people vigorously wash the walls down with a cleaning agent called Zinsser DIF. This is great if you can get all the paste off the wall, but there is an easier way.

I allow everything to dry properly, sand the wall smooth, then apply a coat of Zinsser Gardz. This acts as a barrier coat, stopping your paint from touching your paste and reacting with it. Zinsser Gardz is thin, easy to apply, clear, and goes for miles. Click here to see online prices.

 

Final Thoughts

 

Prepping walls before you paint isn’t complicated. I’m lucky in that I have dust free sanding equipment which makes things cleaner, quicker, and safer. Without it, you will make a mess unless you take steps to cut down on dust. I’d also recommend wearing a mask.

Other than that, it’s quite straightforward. Happy decorating.

How to Prep Walls Before Painting – by Mike Gregory

Posted Dec 27, 2023 | 0 comments

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