The Best Primer for Interior Walls

 As a Decorator, I often get asked about the best primer for interior walls. Unfortunately, it isn’t a “one product fits all” type of answer. So, with that in mind, I thought I’d put pen to paper and write a simple guide. Hopefully, this will help make things clearer.

The Best Primer for Bare Plaster

The first coat on bare plaster is known as a “mist coat”. Old school Decorators still use contract matt as a mist coat, however this is more of an old-fashioned practice and may not be the best solution. It all depends on what you’re using as a topcoat. Although you can still use contract matt, the normal procedure is to use a very diluted coat of whatever you’re using as a finish. This is true of most vinyl or durable matt emulsion paints. However, some products have a specific primer (Farrow and Ball or Tikkurila for example). Click here to see a range of contract matt options.

The best bit of advice I can give you is check the manufacturer’s instructions. These are normally on the back of the tin, however sometimes you may need to look at a data sheet online. Another important thing is to make sure you really dilute your first coat!! It is important that moisture from the paint is drawn into the plaster, taking some of the paint product with it. This then seals (primes) the plaster and offers good adhesion going forward.

The Best Primer for Painting Over Wallpaper

Painting over vinyl wallpaper is something I try to avoid as a Decorator, however if you’re on a budget and the wallpaper is stable, it can be done. A lot of the time you can just paint over with a standard emulsion, but I’m normally weary. Emulsion may not adhere very well to smooth vinyl, so I like to use an oil-based adhesion primer before I crack the emulsion out. This is because oil will not penetrate the wallpaper like water can, so you avoid potential issues with bubbles, or seams opening. Using an oil-based primer also acts as a barrier between wallpaper and the additional coats of paint.

You could use Zinsser Cover Stain, or even oil-based undercoat. But the best primer for wallpaper is a product called Zinsser Wallpaper Cover up.

Zinsser Wallpaper Cover Up is an oil-based paint primer that will not only handle adhesion in its stride, but it’ll also act as a barrier coat. It does stink as you apply the paint, but it does a job. It also prevents potential bubbling in the paper. I’d highly recommend this primer. Available online here.

The Best Primer for Walls Which Were Previously Wallpapered

If you strip wallpaper from a wall or ceiling and you’re going to coat it with emulsion, you first need a primer to seal in any left-over paste residue. For me, it must be Zinsser gardz. This is a clear alkaline primer / stabilizer which is designed to act as a barrier coat between any nasties on a wall and your paint products. It is important to adhere to the specified drying times when it comes to gardz, as it carries on contracting after it is touch dry. Available online here.

Best Primer for Plasterboard

Again, bare plasterboard should be primed using Zinsser gardz, but this time it isn’t to act as a barrier coat. Plasterboard is very porous and although adhesion between plasterboard and emulsion products should not be an issue, a coat of gardz to seal the substrate will prevent dragging. You’ll find it’s much easier to achieve a great finish if you prime your boards before emulsioning.

Best Primer for Walls That are to be Wallpapered

A lot of Decorators I know prime walls with “size” before wallpapering. “size” is an old-fashioned term which basically means diluted wallpaper paste. This may be an old-fashioned approach, but it still works well. It seals your walls and aids adhesion.

I prefer to use Beeline Primer Sealer, which is a specialist product, designed for this very job. It does everything size does and more. It allows some “slip”, making the wallpaper easier to hang. It also sets harder than size, meaning you can prime your walls, then give everything a good sand down before applying your wallpaper. Availalbe online here.

The Best Tools to Use to Prime Bare Plaster

Regardless of what product you use to prime your walls, material tends to drag slightly when working over bare plaster, so using a brush and roller that holds and distributes plenty of material will help massively.

I recommend looking at the Purdy Colossus Roller for this type of job. It’s a great roller to apply your finish coats too, but it’s perfect for applying any material that drags. It’s long-pile, so holds loads of paint, but allows you to lay it off evenly. You will need to de-lint it before you start work, but other than that, it’s perfect. Click here to see online prices.

As for the brush, it’s Purdy again for me. The Purdy monarch Elite XL is one of the best all-round paintbrushes on the market. It’s thick stock holds loads of material, and it holds its shape well, so it’s perfect for priming walls. Click here to see online prices.

FAQs

What is difference between undercoat and primer?

Funnily enough, modern products like Zinsser BIN Aqua and Bedec Prime-All have started blurring the lines between undercoat and primer. But generally speaking, a primer handles adhesion or seals a surface. Undercoat is about building up a paint film, or handling opacity.

Do I need to prime over old paint on a wall?

Walls that have been painted previously do not need to be primed again, unless the previous paint is oil-based (which is very rare). You’re generally ok to apply two coats of new emulsion.

Do you sand after priming walls?

Yes!! A lot of people make the mistake of sanding walls before priming them, but this can lead to more problems. You create a dust film, which can prevent your primer from adhering.

A better method is to prime your walls, allow to dry, and then sand.

Do I need to wash walls before priming?

Walls need to be clean and dust free before priming, but I wouldn’t worry too much unless they’re visibly dirty. Clean any mould, or dust down if needed, but leave the marigolds and soapy water for when you’re washing the dishes.

Final Thoughts

I hope this blog has given you the insight needed to choose the best primer for your interior walls. It isn’t difficult, but if you get your primer wrong, then any additional coats of paint can fail.

I see it often in the trade. I’ll apply a coat of emulsion on a re-dec, and the original paint will start to bubble. Or worse still, come off in sheets! More times than not, these problems are caused by the lack of an appropriate primer when the room was first decorated.