Matt cracking and crazing over silk emulsion is common problem that gets brought up on Decorators Forum UK. So much so I thought I would write an article about it to help fellow decorators should they encounter the issue.
What Causes Matt to Crack and Craze?
The cause of this is down to the substrate being a ‘reactive’ surface. Now by this I mean that when it gets wet it can soften and expand. It isn’t just silk that it happens with, it happens with surfaces that have old paste residue, thick PVA, or even cleaning products.
The cause of a matt paint cracking and crazing over silk or a similar surface is; as the matt paint is applied over the top, it softens the silk causing it to expand, then the matt dries on the surface first, then the silk underneath dries and contracts causing it to pull the matt apart (crazing). Like the pictures underneath. This doesn’t happen EVERY time you paint matt over silk, so if it hasn’t happened to you then you are one of the lucky ones, but it all depends on how reactive the substrate is. This could be down to quality/how thick the silk is as to how much it expands.
If something you have painted has done this, there are a few solutions to prevent or solve the problem. I personally use Zinsser Peel stop. (click here to see online prices). It is specifically designed amongst other things to seal cracking & Crazing (see pic below). I never use this as a prevention, but only for a cure.
This is because crazing over silk doesn’t always happen, so I take my chances to prevent unnecessary extra work. There are a few other suggestions that pop up on the forum to resolve this like ‘Use soft sheen as first coat’ or ‘oil undercoat’ but I see this as a more costly resolution. However, uing a barrier coat is a solution. You’re simply blocking moisture from coming into contact with the silk, thus preventing it from expanding.
While spending months scrolling the internet researching this problem, I decided to carry out an experiment myself on 3 different jobs painting matt over silk.
I’d read somewhere that rubbing down the silk could cause it to be more reactive, so on each job I rubbed 1 wall down before coating the first coat of matt. On each job the 1 wall I rubbed down crazed and the others were fine apart from one, but was nowhere near as bad as the one wall I rubbed down. So personally I’d suggest if you are painting over silk, get the first coat of matt on it first then rub it down, as it clearly softens the silk more by doing so. Click here to see online prices.
Matt Cracking and Crazing Over Silk – A decorator
What do Other Professional Decorators Think?
I have never used peel stop, but there is a similar product made by Zinsser called Gardz. I apply a quick coat of it on the silk walls before I paint over it with any matt product. The only issue is, you’ve got to wait 3 hours before you can paint over it or it’ll craze anyway. I think I’ll give the Zinsser Peelstop a go on my next job.
Thought I was going “crazy” yesterday or whenever it was when everyone was saying that it was perfectly fine to go over silk with matt. I suppose most of the time you probably can get away with it without having any issues, but I’ve slipped up a couple of times now.
I think Zinsser gardz is probably your best way forward. You can use it to prime silk before applying matt, or you can use it after the matt has already crazed. It seems to get into all the little cracks and fills them, as well as becoming a barrier between additional coats and the silk.
If you seal the crazing with the Gardz or peel stop after it has happened, you won’t need to fill any of the cracks. All you need to do is apply topcoats of emulsion. Just make sure you give it enough time to dry properly. I think recoat is 2 hours, but I’d give it at least half a day to settle down.
Some great advice in this blog. The issue of matt crazing over silk or wallpaper adhesive isn’t one you come across very often, but when you do, you need to know how to deal with it. You should always try to apply thin coats of paint when going over silk. Then if it does start to craze, just apply one big coat of Zinsser Gardz or Peelstop and you’re good to go
Matt cracking and crazing over silk can be a nightmare at times. I went for years as a decorator without it happening, but it’s happened three times in the last six months. Zinsser Peel Stop has worked as a fix, but it’s still a faff.
Now I coat the walls with Zinsser Bullseye before I start now. It acts as a barrier coat to protect the silk from expanding.