Cracked emulsion, also known as ‘crazing’, can be absolutely heartbreaking in a newly decorated room, but it’s quite a common defect. I thought I’d put a quick guide together on the possible causes and explain how to repair it. Don’t worry too much because there is often a quick fix.
Why Does Matt Emulsion Crack?
The most common cause of cracking and crazing of emulsion is when you apply a brittle paint such as retail matt emulsion or contract matt over a flexible paint such as silk. As you’re applying your paint, the moisture from your brittle emulsion causes the flexible paint to expand. It only contracts again after your brittle paint has dried. Because your new paint can’t cope with the flexibility, you get hundreds of little cracks on your finished wall or ceiling.
It isn’t always silk paint that causes the defect. I’ve seen it when painting over wallpaper paste, PVA and even mid-sheen emulsion. It’s the same thing; the material on your wall is flexible and you’re using a brittle paint to try and cover it.
How to repair cracked emulsion
There is a product on the market that will fix cracking and crazing emulsion in short order. The first thing you need to do is sand over your affected areas using aluminium oxide. Then remove as much dust as possible.
Then get yourself a tin of Zinsser Peel Stop and apply two coats over your cracked emulsion. This will do two things: It will fill most of the little cracks, meaning you don’t need to fill extensively. The second thing it will do is create a barrier coat between the flexible paint on the wall or ceiling, and the new paint you apply afterwards.
You MUST stick to the recommended recoat times on any product you use over cracked emulsion. That includes both the Peel Stop and the new emulsion you apply. The reason for this, is you need to avoid excess surface tension wherever you can.
After you’ve applied both coats of Zinsser Peel Stop, apply a coat of new emulsion. Use a good quality trade vinyl matt like Johnstone’s Trade Covaplus or, if you’re looking for a premium emulsion, try Johnstone’s Perfect Matt. A good quality emulsion paint like this is less likely to crack. Click here to see online prices.
If any cracks are still visible, they can be filled at this point. Then sand and spot prime your filler with the emulsion you’re using as a topcoat. You’re now ready to apply your last coat of emulsion, leaving you with blemish-free surfaces.
What Causes Flaky Emulsion
If your emulsion is cracking and flaking off, then it’s failing for a different reason. This is usually down to poor adhesion, which can happen because of cheap emulsion, the wrong type of emulsion, or the wrong primer being used on bare plaster.
A lot of people I know wrongly use contract matt to prime plaster before using more expensive emulsion products over the top. This occasionally causes issues with adhesion. Contract matt is a very cheap emulsion with little polymer binder, resulting in a chalky surface once you’ve applied it. Paint such as durable matt just won’t stick to it, meaning cracking and flaking can occur.
Equally, if you were to apply neat emulsion onto bare plaster with no primer at all, you will also encounter adhesion issues, leading to peeling paint.
Either way, the fix is the same. You must remove all unsound paint; it doesn’t matter what paint products you use, if the paint underneath is close to failing, then it will keep failing after you’ve applied new emulsion, and the problem comes back. I have used steam strippers in the past to get back to bare walls.
Then Zinsser Peel Stop is the way forward. It stabilises any chalky emulsion, and it sticks down the edges of flaky paint.
Allow everything to dry, fill any imperfections, and then apply two coats of emulsion to finish.
Final Thoughts on How to Repair Cracked Emulsion
It’s nice when there’s a relatively quick fix to a problem. Repairing cracked emulsion is straightforward enough. For me, it’s still a pain, but emulsion doesn’t crack too often and luckily because I’m in the trade, I can normally spot potential problems before they arise.
However, I do still get caught out from time to time. It might put an extra half a day or so onto a job, plus the added materials needed. I often work to a price, and repairing cracked emulsion that I wasn’t expecting eats into my profit margin. That said, I’d rather spend the extra time than rush the job.
How to Repair Cracked Emulsion – by Mike Gregory