I thought I’d write a very quick blog on how to paint over filler, which, I’m sure you’ll agree, is a riveting subject. There are a few scenarios to cover, so unless you find the topic as fascinating as I do, feel free to skip ahead and pick out the information you need.
Painting over filler isn’t difficult, but you do need to put a little bit of thought into it. As a Professional Decorator, I can tell you that prep, and following the correct system, are two very important factors in any decorating job.
Painting Over Filler on Walls
Whether you’ve filled hairline cracks, minor defects, or something more substantial, painting over filler on internal walls is something you need to do on pretty much every job. If you just cover everything with neat emulsion, then it may bubble and flake over time.
The first thing you need to do is allow the filler to properly cure before sanding. This is because some fillers contain cement which needs to cure, otherwise the alkaline burns through your paint.
Once cured and sanded, you should treat filler on interior walls like you would bare plaster. Dust everything off (paint won’t adhere to dust) and then have a look at the instructions on the paint you’re using for the topcoat.
Most vinyl and durable matt emulsion paints come with instructions that tell you to dilute the first coat by x% to prime bare plaster. Sometimes you’re asked to use a specific primer. Follow these instructions and you won’t go far wrong. The only time I deviate is when I’ve surface-filled large areas; in which case, I follow the process in the next section.
Painting Over Large Patches of Filler on Interior Walls
I know I said you should treat filler on interior walls like you would bare plaster, and that is correct in most cases, but if you have large patches of filler, then it’s slightly different. Some Decorators still just dust off, dilute their first coat of emulsion, and crack on. But this has caused problems for me in the past.
Filler is usually very dusty, and emulsion won’t stick to large dusty surfaces. I find it safer to use a stabilising solution like Zinsser Gardz first.
Zinsser Gardz is a clear material which is reasonably priced and easy to use. You apply one coat onto the filler and then paint as you would normally. The video below was filmed as a question for other Decorators on social media. Around half said they’d use Gardz, and the other half said they’d dilute the first coat of emulsion. I maintain that Gardz is by far the better choice.
When should you use Zinsser Gardz to prime filler
Stabilising filler is always a good idea before painting over.
How to Paint Over Masonry Filler
There are slightly different approaches you can take when painting over masonry filler. If you are using a hard cement-based filler like Toupret Rock Solid filler, then after the proper cure time, you should sand and then treat it like bare masonry. Follow the instructions on the masonry paint you’re using regarding bare surfaces, but you’d normally just dilute the first coat.
However, if there’s any hint that the filler isn’t as stable as the masonry around it, or the filler is powdery, then you should use a stabiliser. The best stabilising solution for exterior masonry in my opinion is Zinsser Peel Stop.
Zinsser Peel Stop is fantastic for exterior work. It prevents peeling paint on masonry and wood. I use it as my chosen primer when I’m working outside, and it’s great on filler.
How to Stop Filler Showing Through Paint
I thought I’d include a little section on how to stop filler showing through paint, simply because it’s a very common problem. The issue occurs for one of two reasons:
Texture
Sometimes the filler is a slightly different texture to the walls. In this case, your best course of action might be to use a different filler, sand the walls flat, or try to create a uniform texture when painting.
Flashing
Sometimes you see the filler through paint because your filler contains cement, which is alkaline and burns through your paint. This happens a lot with multi-purpose fillers like Polyfilla and Tetrion. The quick fix is to allow the filler to cure properly before painting over.
Final Thoughts
I told you it was a riveting topic! I hope the advice on this page has helped. I see some DIYers breaking out the PVA to use as a primer, or even contract matt. Either of these products can cause issues.
Just follow the advice on this page and you won’t go far wrong.
FAQs
Do I need to prime filler before painting?
Yes, you should treat filler like bare plaster; so, apply a primer before your topcoat. This is to ensure good adhesion and an even finish.
Why does paint crack over filler?
This is most likely an adhesion issue between paint and filler, which can either be caused by dust, or the surface not being properly primed
How long to wait for filler to dry before painting?
This depends on which filler you’re using and the ingredients in that filler. Always check the box or online and always adhere to the advice given. Painting filler too soon may result in flashing, or peeling paint.
Can I paint over filler without sanding?
No, you may encounter adhesion issues if you paint filler without sanding.
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