Can you use matt emulsion as undercoat on walls?

You are decorating the house and have decided to go for a change of colour on the walls, but you worry about how many coats of paint it will take to properly cover the wall. After all, you are going for quite a drastic colour change. Maybe you have pondered using a specialist undercoat, but that stuff can add quite a chunk to your decorating bill, and is it really needed? There is that tub of emulsion you have lying around under the stairs, won’t that just do the job, can you use matt emulsion as an undercoat on walls? Let’s have a look!

Can you use matt emulsion as undercoat on walls?

Yes, you can. In fact, this is an excellent way to save money, especially when transforming walls from light to dark colours or vice versa. Matt emulsion works great as an undercoat and allows pretty much any paint to be applied on top of it.

Why use matt emulsion?

It is a great way to save money when decorating. Buying specialist undercoat paints can get expensive fast, and there is really no need for it.

Most homes already have a tin of matt emulsion lying around either under the stairs, in the loft or hiding out in the shed. So why not simply use that as your undercoat, it is the same type of paint anyway.

Colour Changing

Using matt emulsion as an undercoat is particularly effective when the colour on the walls is going through a large change, think maybe a black to magnolia for a dramatic example.

Rather than spending lots of money on coloured emulsions, it can be a lot cheaper to just get a large tub of a white emulsion. A white emulsion is nearly always the cheapest emulsion available and you can get a great deal on larger tubs.

Choosing the perfect wall colour
Choosing the perfect wall colour

You can then paint with this to get the walls nearer to the final colour of your choosing. So when it comes time to add your fancy coloured emulsion you may only need to use a single coat, saving you a lot of money potentially.

This is obviously also true in reverse when going from a light coloured wall to a dark wall. However darker paints do tend to cover better than lighter ones, so you might not need to do as much painting to get a decent finish.

Painting Fresh Plaster

Again you don’t need a specialist paint here and you can just go ahead and use emulsion as your undercoat.

What you do want to do however is something called a mist coat. This is where you water down your emulsion for your first coat. New plaster is very absorbant so will soak up anything that goes on it.

This is why we water down our first coat, this allows the paint to go further and also dry slower. (if the paint drys out too quick because all of the moisture has been sucked out of it by the plaster it can leave a poor finish)

Once the mist coat has dried it acts as a sealer, preventing the next coat from soaking into the plaster as much.

To find out what ratio of paint to water to use read our article on mist coat ratios.

Second Coat On
Different mist coat ratios

Where an undercoat is needed

So all that is well and good, but there are certain circumstances where a splash of undercoat would be very useful.

Stain blocking

If your walls are stained with tricky, repeat offending marks then a stain-blocking primer would be really useful. Some of the worst offenders for these kinds of stains are the following:

  • Nicotine
  • Water Stains
  • Pen/Crayon

A primer such as Zinsser B-I-N or Bulls Eye would work really well here, but they are not cheap. You could however use them as a spot primer just to cover the stains. This obviously won’t work if your entire room has been dyed yellow with nicotine and you will obviously need to cover the whole place!

If you are new to all the different Zinsser primers I have an article called which Zinnser primer to use, I highly recommend you give it a read.

Flaking Surface

When flaking, peeling or chalking is an issue you would be well advised to use a special sealer. Zinsser again comes to the rescue with an excellent product. Zinsser peel stop is a clear, flexible bridging sealer, for surfaces where peeling, flaking, dusting or chalking is a problem. Forms a tough acrylic film that stays flexible and helps prevent peeling by letting moisture escape. For interior and exterior use.

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Sam Wood

Wood by name, wood by nature. I am a fully qualified, time-served, award-winning joiner with an NVQ Level 3 in Carpentry and Joinery as well as an HNC in Construction. Beyond my joinery qualifications, I have also earned a degree in building surveying. I believe these qualifications make me perfectly positioned to provide expert advice on many different areas of DIY as well as share all of the tips I have picked up in over a decade working on building sites!

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