Paint cracking over caulk – what are the solutions?

Updated Feb 7, 2024 | Posted Aug 9, 2018 | Professional insight, Miscellaneous, Product Advice | 37 comments

The cracking of caulk has been a common topic on The Decorators Forum UK over the last few years, and decorators are always on the hunt for a caulk that ‘doesn’t crack’. After a hell of a lot of research and some personal experiments, I thought I would share my findings after getting to the bottom of this problem.  You may also want to check out my Compatibility Test, which will help when choosing the brands of caulk use.

 

What causes the paint cracking Over Caulk?

 

A lot of painters presume that the cracking is down to the caulk they are using, but in actual fact, it’s not just down to the caulk itself, but paint plays a big role in the problem!

Because of the newer chemical makeup of paints, some have lost a lot of their elasticity. Contract and vinyl matt emulsion are particularly brittle and cracking over caulk when using this type of paint is common.  Caulk has always had anything from a 4-15% shrinkage rate while drying and the general formula in caulks haven’t changed much over the years, yet the paint has.

 

Drying times:

One thing which can amplify the problem is caulk not being fully dry before you paint over it with emulsion. Even though the surface may seem dry, even if it has been left overnight, it may still have some shrinking to do. Therefore, when painting over it, the paint film dries and then shortly after, the caulk continues shrinking, pulling the paint film apart and leaving cracks on the surface. This is why you don’t have a problem when using soft sheen/vinyl silk/masonry & glosses etc, as they are flexible and they move with the caulk, so doesn’t split.

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Temperature

Another reason for paint cracking with emulsion-based paints can be down to the paint being applied on a substrate with a too low a temperature. Emulsion based paints need a minimum temperature for good film development. This temperature is approximately +7°C. If you are painting during winter with an emulsion paint, the surface temperature of the sealant may be too low. So, even if the inside air-temperature is high enough (above +7°C) the surface temperature of the sealant could be too low and result the caulk taking longer to completely dry (even if it seemed touch dry). This would result in the cracking of the paint-film.

 

Thicker application:

With the shrinkage rate of caulk and drying times, the thicker the bead of caulk, the longer it is going to fully dry and the more it’s going to shrink back. So, if you’re searching for a solution to paint cracking over caulk, you may want to start by applying thinner beads of caulk.

 

Some Caulk is More Prone to Cracking

 

A lot of decorators are on the hunt for a new caulk as cracking is becoming a frustratingly common problem. This has prompted the manufacturers to use it as a selling point.

These ‘anti crack’ slogans written on new products by all these manufacturers are all well and good… until you read the small print. On every datasheet I have looked at, on a lot of different “anti-crack” caulks you notice a bit about the ‘limitations’ of the product. They all say things like;

“Some paints (especially certain vinyl matts) have very little movement in the dry film which could cause cracking”

“Painting over with highly filled water based paints can cause cracks in the paint film”

“Painting over with highly filled emulsion paint can cause cracks in the paint surface.”

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There are lots of other round about ways of saying the same thing. “highly filled paints” they are referring to are pretty much all the contract/vinyl matts you get on the market with modern formulas.

 

How to solve this problem?

 

So, after scrolling through all the information I could find on caulk, newer make up of paints and a good year trying different caulks in different conditions with different paints, this is my advice:

Use a thinner bead of caulk and leave it to dry longer. This is not always possible (especially following some carpenters). I have also tried and tested ‘priming’ the caulk with anything that would act as a barrier (gardz, Primer Sealer Stain Block, Cover Stain, or I have been successful in using acrylic primer after a few tests) prior to using emulsion. This is quite a pain but still a solution.

If you have already experienced the issue and now want to save it, I’d suggest applying a coat of Zinsser Peel Stop over your cracked paintwork. This will sort the issue and allow you to repaint your caulk. Available online here.

Some caulks are less susceptible to cracking and crazing than others. The best I’ve found is Dunlop Flexible Acrylic Filler, which has never let me down. You can apply a medium sized bead, leave it an hour at room temperature, then paint over without issue.

Dunlop Caulk being tested, ready to review

Another method which I discovered while spraying, is finish the woodwork first and paint onto the walls (thus covering all the caulk with undercoat, gloss, satin etc.) Then tape off the woodwork (or some may say trim) and complete the emulsion after. This way you create a barrier between emulsion and caulk, preventing the emulsion from cracking.

This is frowned upon by some decorators because you need to use tape, but I tested this theory in a couple empty rental properties I was decorating with brush and roller. I was shocked at how much it sped me up. It left crisp straight lines (that I am more than capable of doing by hand) with no effort. Being able to whop in the skirting boards without caring about getting a line, and same for the emulsion really sped me up, and…. there was no crazing.

I hope this has helped.

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FAQs

 

Will emulsion paint over caulk?

Yes, providing you use a good quality caulk and a trade vinyl or durable emulsion, you will be fine painting straight over caulk. If in doubt, you can always prime caulk with Zinsser Cover Stain first. This will avoid problems with crazing.

 

How do you fix cracked caulking?

If it’s the caulk that’s cracked, your best course of action is to remove it and then re-caulk. If your paint is cracking over caulk, then you should prime the cracked paint with Zinsser Peel Stop and paint again.

 

What happens if you don’t paint over caulk?

Caulk is designed to be painted. If you don’t paint it, then it may discolour over time, or dirt might stick to it, but it’ll be structurally sound. There are several acrylic sealants that can either be left or painted. I’d suggest opting for one of these.

What do Other Decorators Think?

Paint cracking over caulk never used to be an issue. Manufacturers have been playing around with formulas to try and save money and stay competitive, which is a real pain. It makes our lives as decorators more difficult. We’re now faffing around with different products to try and find a combination that works.

Stick with Dunlop caulk. It’s a pain to use, but you won’t get any cracking or crazing. Stay away from contract matt emulsion too.

Tim Marks

I’ve seen loads of people complaining about paint cracking on caulk, but I’ve never had an issue. Just don’t lather it on and leave it 24 hours before painting. If you’re caulking woodwork up, why not undercoat before painting your walls? It might avoid having problems.

Chris Baker

Use a spray can of Zinsser Cover Stain and prime any caulk before you paint. It acts as a barrier and solves the problem. It only takes 5 minutes to fly round a room with aerosol.

Phil Dawe

Updated Feb 7, 2024 | Posted Aug 9, 2018 | 37 comments

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37 Comments

  1. Stephen george

    Geocel has been the best for me with no problems. Use it right and wont over caulk. Stick to the guide lines.

    Reply
    • Billy warren

      Hi guys just gonna put this out there on the cracking caulk thin the emo down would like some feed back on this Billy Warren painter and decorator 37 years

      Reply
      • Allan Robinson

        That actually makes sense, as I was doing 2 bedrooms and a hall. The two bedrooms had been skimmed with plaster. I had no cracking, as I mist coated first. In the hsl I had slight cracking in a couple of places, where I had gone straight on with a vinyl matt.
        I’ve recently tried the soudal from toolstation for only 98p per tube. I couldn’t believe how good it was for the money. Gives good results, if given time to thoroughly cure. A definite go to for me, if on a budget.

        Reply
  2. Rob

    Very helpful thanks mate 👍

    Reply
  3. Adam Featherstone

    I personally think a major factor is 1) the amount of caulk people apply, 2) how soon people paint it.
    The method I’ve found is to, Apply the bead of caulk, wet my finger and push the caulk it place, I then wipe it over with a wet sponge, I’l then go back over the caulk with my finger and push more firmly this removes a load of excess caulk that you would think was there or needed to removed, I’l then qucik wipe over with the sponge to smooth the area out, yes this take longer than normal but not that much longer.
    I always try to plan the job so the caulk has either overnight to dry to, or as normal I’l caulk up and then say start painting the ceiling, filling the walls and wood work etc.
    I’ve used 3/4 different brands of caulk and using the above method I’ve not has any issues.

    I also think it’s what paint you are using, the standard vinyls UK paints tend to craze but imported paints don’t tend to craze but more often they are vinyls.

    A trick that works is to either go over the caulk with gardz or coverstain,
    Another paint that helps stop this if used as a primer for it, is dulux trade diamond eggshell.

    Reply
    • Cait Whitson

      Adam we do the same thing. Always have. We seldom have an issue. Our clients allow us to lead them on product too so we recommend a durable matt 9 out of 10 and they are less likely to crack due to the high acrylic content. Anything alkyd based (water based or solvent borne) will also seal the caulk off and stop it cracking if for any reason you’ve to do a deep or wide caulk area.
      I only remember one project having an issue and it was as Phil mentions, a very cold humid winter.

      Reply
    • Zelda Sonnekus

      Hi Adam, thank you for your explanation, could you please let us know what brands you used, as we are struggling to find what Geocel recommended. Anyone used Dunlop at all?

      Reply
  4. Praful Varsani

    Wurth – acrylic sealant. Best I’ve used and still using for 15 years, never cracked or crazed

    Reply
  5. James cantlon

    Give it all a coat of zinsser and it never cracks whatever caulk you use

    Reply
    • JRSL

      It’s a process that is often overlooked – spotting caulk is a must to stop crazing and although added labour – solves this problem. We finish woodwork first and tape off to finish spotted emulsion afterworlds. Pain in the ass but that’s what seperates the pros from the corner cutters

      Reply
    • Owen

      What time blur or red?

      Reply
    • Sunny m

      Zinsser 123 (Blue can) or BIN (red can)?

      Reply
    • BIll Braggins

      complete bollo>< ! I tried the zinser trick and it made it worse!

      Reply
  6. Cait Whitson

    Great piece Phil.

    Reply
  7. Andy Foster

    I find i see it more with Contract Matts. Probably due to the fact theres no give in the paint.
    Ive gone over troublesome areas with softsheen then matt on top in the past.

    Reply
  8. Gary Melville

    Having had this problem for years I have now switched to the Dunlop flexible acrylic filler. So far seems to work for me…

    Reply
  9. Chris Mckenna

    I find using acrylic primer undercoat for a quick coat over the caulk prior to paint works but can be time consuming aswell

    Reply
  10. paul

    Dulux own caulk brand is notorious for cracking/crazing its the worse caulk on the market bar none !

    Reply
  11. Alan Kelly

    Great article Mike, Interesting about not having as much of a problem when using acrylic paints.

    Reply
  12. Matt

    One of my decorator’s has used a tiny bit too much caulk and painted too soon.

    So, now that fine lines have appeared, what’s the answer? Red Zinsser, Undercoat or rake out and start again? RSVP soon. Cheers:)))

    Reply
  13. Lesley

    I’m a lady decorator, I paint the ceilings, then the trim, when it’s dry I mask up with low tac tape and then paint the walls, take the tape off before the emulsion drys and hey presto, it’s cut in and finished much quicker. Ant bleed through I just touch up at the end.

    Reply
  14. Mike

    Thanks for the useful info guys. Had the paint crack on some coving I caulked up.

    Reply
  15. Dave

    Hi guys
    Massive problem for me on every job couldn’t stop the cracking
    Then pure accident I put stain block on let the stain block dry then as I always only use acrylic durable matt on top of the stain block 100% perfect
    Hope this helps
    Be lucky

    Reply
  16. Mia Watson

    Great advice
    Will try the zinnsser over the top.
    Also leave my woodwork till last but I might have a go the opposite way round..see how that goes 👍

    Reply
  17. Sunny M

    Which Zinsser? (blue can or red can) Is used over caulk before you emulsion?

    Reply
    • Mike Cupit

      Either really. Some decorators spray thicker caulk beads with BIN aerosol before emulsioning, however Bullseye 123 will also work. As will acrylic undercoat

      Reply
      • Sunny M

        Zinsser bullseye 123 (blue) is water based. Zinsser BIN (red) is shellac based. Both do the same thing for caulk?

        Reply
  18. Dodgy dan

    Would using a silicone sealant instead of decorators caulk stop cracking? The silicone could be primed with Zinsser bullseye before the emulsion goes on

    Reply
    • Mike Cupit

      I wouldn’t say so personally. You are encouraging a different set of problems

      Reply
  19. Dave

    Hi guys (complete novice here) caulking cracked so re caulked on top of old and cracking is worse, do I have to scrape off residue and re caulk, or apply Zinsser 123 to the cracked caulk and This will cover the cracking, if I have to scrape out old cracked caulk and re caulk do I apply Zinsser 123 as caulk is drying or completely dried, tia.

    Reply
  20. James

    Three words; Acrylic gap filler. Bin caulk, look for any acrylic filler/sealant and you won’t have any cracking issues. No need to prime, use massive amounts if you want, doesn’t shrink, doesn’t crack after painting and drys quick! Trust me

    Reply
    • Harry Hope

      Thanks, acrylic it is from now on.

      Reply
    • Carrie.

      This has happened all over my house. The caulk has pulled the paint away down to the plaster and needs complete redecoration. Should I cut out all caulk and reapply? Then how do I deal with the uneven surface where quite a few layers of paint have been pulled away? Thank you!

      Reply
  21. Carrie.

    This has happened all over my house. The caulk has pulled the paint away down to the plaster and needs complete redecoration. Should I cut out all caulk and reapply? Then how do I deal with the uneven surface where quite a few layers of paint have been pulled away? Thank you!

    Reply
  22. Shelly

    We have the cracking problem. I think we painted too soon. Can we paint a second coat to cover the cracks or will this not work?

    Reply
    • Alan

      It’s a pain in the arse but I found that using red zinsser over the top of caulk is the only thing that works.

      Reply
  23. Wil

    Thank you – very helpful

    Reply

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