Painting Caulk – a Full Guide

Updated Sep 1, 2023 | Posted Aug 27, 2023 | Professional insight, Product Advice | 0 comments

When decorating a room, caulk is used to fill fine cracks around the edge of door frames, skirting boards, windows, and other bits of trim. Painting caulk never used to be an issue until about 10 years ago. Now, due to changes in some caulk products (mostly down to cost cutting on the part of the manufacturers), and changes to paint, you can experience issues unless you’re conscious of a few things.

As a Professional Painter and Decorator, I spend a few hours every week working with decorator’s caulk, and I’ve used just about every brand available. In this blog I’m going to talk through the issues you can experience when painting over caulk, how to fix problems when they arise, how to avoid problems altogether, and the best caulk products available. I hope you find it useful.

 

The Problems you Can Experience when Painting Caulk

 

Caulk is supposed to be easy. A lot easier than messing around with powder filler anyway. You squeeze it onto a crack with an application gun, smooth it off, then paint over it. However, sometimes it doesn’t go to plan.

The most common failure is crazing (your paint film splits over the top of caulk, which then looks like mud cracking). This is due to the flexibility of your caulk. If your caulk hasn’t properly cured when you paint, then it may still be contracting, even after your paint has dried. Most emulsion paints are quite brittle, so it can’t contract with the caulk, and the paint cracks.

Even if your caulk has cured, you can still experience crazing. The moisture from your paint is enough to trigger expansion of a caulk bead, which again, causes surface tension in the paint and leads to crazing.

The other failure you can experience is the discolouration of paint. This happens mostly with cheap caulk. Something from the caulk bleeds into the paint and causes it to discolour.

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How to Avoid Problems When Painting Over Caulk

 

If you already have issues with caulk failing, then scroll ahead to the next section and I’ll tell you how to fix it. But first, I wanted to touch on the steps you can take to avoid problems all together. The easiest way is to use a good quality caulk (again, scroll ahead to the section on the best caulk products).

However, there are other steps you can take when painting caulk to avoid problems. The first is to only apply small beads of caulk at a time. My dad always used to say, “less is more”, and he was right. Don’t use more than you need to, because smaller beads are less likely to expand or contract and cause issues.

Another tip is to leave your caulk to fully cure before painting it. This way, you know it has contracted as much as it’s going to, so there is less chance of it crazing. There is also less chance of your paint discolouring.

One last tip, prime your caulk before painting it. Acrylic primer undercoat, or even regular undercoat will do the job, although it is slow drying and can leave brush marks. You need to adhere to recoat times when it comes to painting over caulk. That said, undercoat is still an option.

If you are caulking around woodwork and you’re painting it anyway, one solution is to undercoat your woodwork and cut slightly onto your wall, covering all the caulk. Simply emulsion your walls afterwards and you should avoid issues.

The other product you can prime caulk with is Zinsser Cover Stain in a spray can. This is a quick drying oil-based paint that will not expand the caulk, blocks any discolouration, and acts as a barrier coat between your finishing paint and caulk. It’s a quick and easy solution.

Fixing Problems That Have Already Happened

 

If you already have crazing on your painted caulk, then there is an easy fix.

I used to use a barrier coat of an oil-based product, and then fine fill to get rid of the cracks, but there is a much easier way. Get yourself a small tin of Zinsser Peel Stop.

Peel Stop will act as a barrier coat, and it also fixes crazing. It’s a clear stabilising solution that is easy to use and fills the crack for you. It goes a long way, so don’t buy a big tin. Just fly round your crazed caulk and apply a couple of coats, allow plenty of time to dry, then paint over as normal.

If your caulk has discoloured, then all you need is a stain block, and then touch your paint up. Revert to the Zinsser Cover Stain Spray Can in the above section.

 

The Best Caulk Products

You can avoid issues when painting caulk if you choose a decent caulk to begin with. I recommend HB42 caulk, which is something a lot of other Decorators agree with. It’s easy to use, doesn’t cost a ridiculous amount of money and you shouldn’t experience any type of problem when painting it. No cracking or crazing, and certainly no discolouration.

HB42 is how caulk used to be. When you could use it inside or out, didn’t need to prime, and knew you wouldn’t have any issues. It feels thick too, which means it’s easy to apply it neatly without smearing it.

More Tips for Applying Caulk

 

I thought I’d run through another few tips for applying caulk. The first is to never caulk to bare plaster. If you do this, then over time the caulk will come away and peel. You will need to dig it all out and start again. Always mist coat your walls, and prime bare timber before applying caulk.

Another tip is if you have an excessive amount of caulking to do, then have a tub of water and a cloth handy. Always keep your finger clean and wet. This will make application easier and your work neater, especially on a warm day.

Oh, you can’t really sand decorators caulk, so don’t fill cracks proud with the intention of getting it neat by abrading it once dry. If for whatever reason you’re struggling to get the caulk neat to begin with, then try applying it with a different nozzle with a smaller hole, or get more water on the caulk to make it easier to use.

Last one, don’t be afraid to use caulk outside. Just double check the spec that comes with the product you’re using to make sure it’s up to the job. As long as the caulk has enough flexibility to cope with the Great British Weather, you’re good to go.

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Final Thoughts

 

Hopefully this blog has given you all the information you need without overcomplicating things or scaring you. You can experience problems when painting over caulk, and if you found this blog on the net, then you’ve probably already experienced them firsthand.

Don’t panic too much though, caulk is paintable. After all, what it’s for. Caulk is a flexible filler used to combat cracks when decorating and can easily be painted. Just follow the advice on this blog and you can’t go wrong.

Painting Caulk – by Mike Gregory

What Other Decorators Have to Say About Painting Over Caulk

It’s sad that painting caulk has become a talking point really. Even a lot of Decorators have problems with it now, so I can only imagine how hard it is for DIYers. You used to be able to use caulk as a fine surface filler on emulsion, paint over it with one coat of contracts matt, and it would look mint. No flashing, no crazing, no adhesion issues. So, what happened? We’re paying a lot more for caulk now and we’re having to prime it before we can paint.

The best thing to do is use a good quality caulk and dosh over it with your woodwork paint before painting your walls. You can’t touch it with emulsion.

Phil Dawe

Just use a good quality caulk and don’t overdo it. Thin beads are all you need. Any substantial cracks need to be filled first with two-pack or expanding foam.

Lee Thornton

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I’ve never had a problem to be honest. I always do my caulking the day before I paint, and I don’t use it to fill huge gaps. I’ve never bothered priming it with anything. The other thing is to avoid cheap caulk.

John Tate

Updated Sep 1, 2023 | Posted Aug 27, 2023 | 0 comments

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