Can I use emulsion as undercoat?

Undercoats can be expensive to buy and you may be wondering if there is a cheaper alternative that does the same thing. Maybe the thought has crossed your mind to just use regular old emulsion as an undercoat, is this even possible?

The simple answer is yes, you can use emulsion as an undercoat but you probably shouldn’t. Emulsion can be used as a cheaper alternative to a specialist undercoat but has a lot of downsides.

Why Use Emulsion?

So you can use emulsion as an undercoat, but why would you? What are the advantages?

Well, one major advantage is cost. Using your emulsion as an undercoat will save you having to buy another tin of paint so that’s one major plus straight off the bat. The next factor to consider is that emulsion paint tends to be cheaper than undercoat paint.

Another important factor to consider is that if you do use emulsion as your undercoat then it will automatically be the same colour, obviously! This may save you an extra coat of paint down the line, or maybe not, this all depends on the difference in colour between your undercoat and intended finish colour.

And finally, using emulsion as an undercoat can be a great way to use up older paint you have lying around. Let’s admit it, we all tend to have tins of emulsion in the back of the shed or under the stairs that we are probably never going to use. So using them as an undercoat can be a great way to finally use them up and save yourself a bit of brass at the same time. Win-win!

Why use a proper undercoat?

So you have heard my reasons for why emulsion can be used as an undercoat. But what about the other side of the argument I hear you cry, why does a proper undercoat even exist if emulsion works just as well?

To start with an emulsion will not adhere as well to bare wood as an undercoat will. So what this means is that it is more likely to chip off and take all the paint with it. This can lead to bare patches of wood, which is obviously a big downside. The specialist undercoat is designed to have great adhesion and as such is a lot less likely to chip off than emulsion.

The next problem is that emulsion tends to be quite thick, this is great when painting walls as it gives really good coverage. when it comes to undercoating wood though it is not ideal. The thick emulsion can leave lines in your woodwork which will be really hard to remove and will probably end up visible in the finished product. Undercoats tend to be a lot thinner so will not leave unsightly lines in the finish.

What To Use

I recommend using these Zinsser primers below. Which one you pick depends on your situation as they all have relative pros and cons.

Bulls Eye 123 is water-based, B-I-N is shellac based and Cover Stain is solvent based.

Oil Based Vs Water Based

It is always a very good idea to match an oil-based undercoat to an oil-based topcoat and a water-based undercoat to a water-based top coat. This helps to avoid any issues that can arrive from a miss-match of oil-based and water-based paints.

Beyond that potential mix up there are reasons to pick an oil-based paint over a water-based paint and vice versa.

Yellowing is an issue with oil-based white paints. Over time the finish will yellow and there is little you can do about it, I have a full article on the problem here, water-based paints, however, don’t tend to yellow at all.

While yellowing is a definite downside to oil-based paints they do have an advantage in application. They are a lot thicker than water-based paints and this makes it much easier to achieve a really smooth finish which is particularly important with high sheen gloss paints. Ant little lines and bumps in the finish will be noticeable.

But it is not all good for oil-based paints, they are a lot harder to clean up than water-based and also take an age to dry where water-based paints can be dry in hours.

Can You Use Emulsion As Undercoat For Gloss?

You can but whether you should or not depends on a few different factors.

Emulsion will work as a colour covering undercoat and also partially as a sealer. It will not be as effective as specialist primers but it will work.

One of the major downsides though is that emulsion does not sand well. So you will not be able to achieve a really smooth finish like you would with a proper primer.

When painting gloss it is advisable to sand down your primer to remove any high spots as well as brush marks, emulsion won’t stand up well to sanding whereas undercoat will.

Can You Use Emulsion As Undercoat For Satinwood?

Again this will be very similar to the answer for gloss above. You can you emulsion as an undercoat for satinwood but it won’t work as well as a proper undercoat would.

The reasons are similar to gloss, the main problem being you won’t be able to sand the emulsion back so will end up with lumps, bumps and paintbrush marks in your finished paint.

Can You Use Emulsion As Undercoat On Wood?

Yes you can, but emulsion wont have stain blocking properties so any resin or knots in the wood could bleed through into your top coat overtime.

Related Posts

Interesting in emulsion painting? Why not check out the following posts.

• The Best White Matt Emulsion Paint