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Why emulsion paint crazes over acrylic caulk?

Listed under Blog, newlife paint, Painting Posted Dec 10 2013

Emulsion paint crazes over acrylic caulk. User error? Maybe. But it can happen, even if you go by the book, and is an issue that, 30 years on, is still quoted as “a new one on us” by paint manufacturers.

Here is some information on caulk, how to use it in general decorating, and for some scientific perspective, paint chemist Keith Harrison at Newlife Paints outlines why standard emulsion may be incompatible with standard acrylic caulk.


caulk with cottonAs a bit of background, caulking is an age old practice for filling joints and cracks. Black jack / bitumen is an old favourite. On wooden boats, I used a fair bit of cotton caulk to fill and seal the joints between carvel planking. Simple science.

Acrylic caulk in a tube is a wonder of modern chemistry, but relatively speaking, it has been around for years. It came out in the USA in the late 60’s and along with latex caulk, is the favoured joint-filling product for decorators. In the late 80’s this UK painter can remember transitioning over from polyfilla pushed into cracks around doors with bleeding fingers, over to a gun applied flexible filler that dried quickly, didn’t crack and was paintable. Painters Mate was a revolutionary step in UK decorating.

In 1992, I remember I saw paint crazing over acrylic caulk. In 2013, the “Oh, I never heard of that before” is still not unheard of from paint company reps.

How to use caulk

If you go by the book, you work in a room at 70 degrees F. You rake out cracks around door frames, remove dust, cut the nozzle a fraction wider than the gap you want to fill, run a thin bead of paintable acrylic caulk in the cracks, smooth off with a pointing tool (ie finger or other method). When cured, you paint over the caulk with the vinyl matt or contract matt emulsion you are using on the walls, and job done – no ugly cracks, nice sharp lines between wall and frame –

or –

what it doesn’t say on the instructions…

you go by the book and the emulsion paint may well craze over the caulk!

30 years later, the UK paint companies, caulk manufacturers and merchants who sell caulk still haven’t communicated to end users, the compatibility issues between the normal caulk and normal wall paint available from every mainstream outlet in the UK. But if you read the take of Newlife Paint’s chemist, Keith Harrison, on what is going on, you will get a good sense of what to look out for. (Cheap will not necessarily make you cheerful.)

Paint chemist’s thoughts on caulk and crazing paint

I’ve had to think a bit about this and researched caulking materials a little.

As you mention, caulk is generally either water-based acrylic or silicone. My (limited) experience is they are both a bit of a problem, hence some manufacturers offer coloured caulking. I would hazard a guess that matt finish acrylic and vinyl may both suffer problems, but that silicone based should likely be the biggest cause of incompatibility, although they may be used less often for this sort of work.

(With decorators caulk in general) I think there are several issues:

1) Surface incompatibility (surface tensions) with water-based paint, for which the silicone is the worst culprit. It can prevent emulsion adhering totally and a generous coat of emulsion, then a second coat may hide this happening – until it cracks and crazes.

2) Flexibility – the caulk is much more flexible than emulsion, so with expansion/contraction from temperature changes again the interface between the paint and that caulk will be stressed and can cause cracking.

3) Impermeability – because the caulk itself is likely to be quite moisture impermeable, the paint over the caulk will not dry and cure as quickly as surrounding areas, and then if given a second coat, the well know “mud like cracking” can occur especially using emulsion with a high filler level. Again, a second coat “hides” what goes on below the surface.

4) the caulking used may be quite a thickness e.g. 3 – 5 mm deep. If so then various substances can continue to dry out of the caulk over a long period of time, certainly weeks or even months. These substance may mostly be water, but other substances such as coalescents (often from the VOC’s in the caulk) could continue even for months, and if so this is very likely to affect a thin coat of paint used over the surface.

In practice, then yes a primer with an eggshell, or even silk finish should make a good difference. These are polymer rich coatings (compared to matt finish), with better adhesion and also more flexibility than a matt coat. This would act as a good primer between matt paint and the caulk itself.

Where possible allow a good cure time before painting over caulking even before priming.

I asked Keith about siliconised acrylic caulk.

…siliconised may well mean they have chosen a water carried dispersion as an additive only to assist with the flexibility, without the problems of a “normal” silicone – that’s those that smell of vinegar (acetic acid) when they cure.

And I asked him for a bit more info about the Soudal Acryrub caulk, and any technical clues as to why it has worked well for me in the past. (Not the B&Q version, but the product recommended to me and supplied by UK Sealants.)

I know Soudal fairly well, and would rate them as very technically competent. They likely spent considerable time designing their caulk specifically for this purpose, hence the good result. I’ve checked their MSDS and their volatile level in Acryrub is very low – ideal for this purpose, so when using a deep fill there will be little in the product to continue to evaporate out after normal curing time, and cause problems.

The answer probably lies with using a caulk specially designed for this purpose, not a general purpose “flexible filler/caulk” that can do lots of uses, and just includes “can be overpainted” as an extra. There are lots of cheap fillers and caulks on the market, but I would say Soudal is well priced and tends to have products well designed for their end use.

Background to the question of crazing caulk

Decorators may say there was no issue back in the day and it is a problem arising since the 2010 paint reformulations when they removed VOCs from paint for the betterment of mankind. (Sounds like they should have removed VOCs from acrylic caulk first?)

1992, I can recall being phoned up to go to a new executive home and suggest why the paint had crazed around every single door frame and along the tops of all skirtings. It had been caulked with “Painters mate” and walls painted with a good trade vinyl matt emulsion. The cause of the 1/4″ wide band of crazing? We didn’t have a clue and the paint rep sure wasn’t letting on either!

Forward to 2010, the same crazing issue is still being reported by decorators. It had been a reported glitch for years, but was always “a new one on us” when you asked paint companies’ tech support.

2011 I asked Dulux tech support for a step by step on how to caulk. They said they didn’t have anything to do with the Dulux Decorator Centre branded caulk that was crazing, but they kindly stated their proposed approach – room temperature, bead size, drying time etc. It still failed.


The likely universal solution for emulsion painting straight over caulk without pre-priming it, is to use a high spec acrylic caulk that is very low in VOCs, that cures quickly and can be overpainted. These products are about, but they aren’t 20p for a dozen tubes.

Alternatively, if you are going to stick with cheap caulk, spend your time pre-priming caulk with oil base undercoat. This is an approach that seems to work every time, but makes cheap caulk very expensive in terms of labour costs.

High acrylic content emulsion seems to be more reliable than vinyl matt over acrylic caulk. (I only have anecdotal proof of that!)

A paint company tech support recommended acrylic eggshell, which Keith referred to and explained the technical reasoning as to why it would likely be a compatible primer. Acrylic eggshell will dry a lot quicker than oil based undercoat too.

An alternative is to use flexible filler like Toupret’s Elafib. Or the scrim tape and overfill. Not as convenient as a bead of caulk.

I am sure there are some brand product suggestions out there to help advance / minimise this issue. Any thoughts welcome, especially from painters in the USA. What do you use, is this a problem for you?

Further reding

For an overview, This Old House has an easy read article on all things caulk.

And this is The Environmentally Responsible Construction and Renovation Handbook from Canada with more info on caulks and their use in a home environment

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26 comments to “Why emulsion paint crazes over acrylic caulk?”

  1. Alan Iles

    Great article and well tackled. However, I would like to just add something if I may.

    Now, I know many decorators have problems with overpainting caulk, some seem to find crazing happens with just a few brands, and some find it happens with almost all available brands. Personally, I have found crazing occasionally with one or two.

    The worst crazing always happens when rather than filling just the gap (for this example lets use the gap between a skirting board and wall) but over filling the gap and smoothing off with a finger and leaving caulk on the top edge of the skirting and a few mm up the wall. I see many instances of this where there should be a nice straight right angle at the top of a, non-rounded, skirting to the wall but instead so much caulk has been used the right angle has been reduced to a radius.

    This then means of course the paint has to sit on top of say 5mm or more of caulk rather than just 1 or 2mm had just the crack been filled.

    When I come across caulk that has been used to excess and i’m to redecorate, I take great pleasure in removing the old and replacing with a lot less new, and the client gets a nice sharp line between skirtings/architraves and walls, and I need not bother too much about crazing.

    A more expensive alternative for larger gaps which will not craze is Repair Care Dry Seal MP, which is a quick drying putty replacement that stays flexible, and so is more than suitable for use on interiors.

  2. Avatar photo Andy Crichton

    Thanks for the extra info, Al, good spot. The builders thumb syndrome I believe it is called 🙂

    Repair Care is certainly a product that has been referred to, it’s the nuclear option, no bad thing.

    For me the other big news in that info from Keith was the VOC content of caulk causing issues with extended curing times. Funny, with the all the emphasis on low VOC paint, trade caulk is still killing us slowly, along with a lot of paint films!

  3. Charles Budd

    This is a brilliant subject for a blog, and very well-handled – there were quite a few details I didn’t know about (VOC content as you say, Andy).

    Al’s comment above is right on the money too – I’ve been guilty of over-caulking, and one of the guys who worked with me used massive beads! I’ve been using Repair Care Dry Seal indoors for months now, as it’s just so reliable, albeit expensive; but probably cheaper than the extra work needed to deal with possible crazing issues.

    There are dozens of different sealant products out there, and decorators are often used to only a handful at most. Are there cheaper, more generic alternatives to Repair Care? I’m now trying Hippo Pro 3 which is an adhesive, sealant, filler . It’s slow drying – 24 hours to fully skim over, and 3-4 days to cure completely – but can be overpainted after about an hour or two if not too thick and conditions allow. It also comes in clear – which means it could be a great alternative to using silicone to seal around kickboards or splashbacks for example – as it’s overpaintable but still waterproof. It seems as though the price won’t be far off Dry Seal though, sadly! It also claims ‘no VOCs’

  4. Ron Taylor

    Speaking to Ben Sturges of Paints & Interiors recently and his observations were that most chalk and vinyl matt emulsions aren’t compatible with acrylic caulks and will crack over them. Using a product like Den Braven Anti-Crack Sealant definitely reduces the problem, but isn’t always foolproof.
    The higher the acrylic content in paints the less issues you tend to get. This is bourne out by the fact that 100% acrylic paints like Mythic’s higher sheens and Eico products don’t crack. But Mythic’s Ceiling Paint does due to less acrylic and more vinyl being present.
    Where it does become bizarre is when caulk is sealed with something prior to painting and the sealer coat won’t crack but the paint applied on top of it does. Dulux Diamond Matt and Satinwood are terrible for this. I caulked and primed an entire room with Cover Stain once and left it for 7 days. I sprayed the trim with Diamond Satin and it cracked everywhere caulk had been applied under the primer. After re caulking over the crazing, applying no primer and spraying Johnstone’s Acrylic Satin there was no issue at all.
    That says there is a lot more acrylic present in the Johnstone’s product than the Dulux ones.
    The higher the acrylic content the higher the manufacturing cost. So a lot of so called ‘acrylic’ products are often bulked out with vinyl and cheaper ingredients to lower this cost.
    I have totally given up on vinyl matt and chalk emulsions (I’m saying matt because soft sheens and silk vinyls don’t suffer the cracking issues) in favour of products I know won’t give me a problem. They are more expensive, yes, but not as expensive as re caulking, priming and touching up entire rooms can be should problems arise.

  5. Charles Budd

    That makes a lot of sense Ron. I’d have initially thought that an expensive paint like Dulux Diamond Matt with a very high solid content would be better, but it even cracks over Den Braven. Never had problems with any of the Little Greene paints I’ve been using this year.

  6. Fresh Fresh

    Only just seen this post – very interesting. I have switched to Tembe Hippo Pro 3 now which is a filler / adhesive and sealant in one. Some may balk at it being £9 a tube but it works and makes more sense having adhesive properties too as it stops shrinkage

  7. Charles Budd

    I’ve also tried Tembe Hippo Pro and although paint didn’t crack on it, paint doesn’t adhere to it as well as to caulk – it definitely needs 2 coats. Useful to have, particularly when using Dulux which has a tendency to craze on anything it seems! Although Repair Care Dryseal is a bit more expensive, I prefer it to Hippo Pro as although it has similar adhesive & sealant properties, it dries quicker.

  8. Fresh Fresh

    Surely it’s a minimum of two coats anyway Mr Budd 😉 – I’ve been happy with it’s performance up to now on a range of paint brands. Il give Dryseal a go too as have used a lot on exteriors and it’s a great product

  9. Charles Budd

    Ha ha! Yes, of course it’s a minimum of 2 coats, I was merely commenting that the first coat doesn’t cover the sealant completely like it does with caulk.

  10. Noel

    Glad it’s not just me! This is the single biggest headache I have at work. Seriously. I’ve let caulk dry for hours, days and weeks. No difference. It crazes. B&Q used to sell “Cerafix” made by Henkel up until 3 or 4 years ago? This was their “cheap” own-brand caulk (blue tube). It dried grey but never mattered because was always painted and it NEVER crazed. The Soudal stuff they sell now crazes with everything Matt water-based. Same with No Nonsene, Painter’s Mate, Geo Cell, Dow, Vallance…. …I must have tried every caulk going. Evo-Stick (white/orange tube) worked for a while. But one day “BANG”. Crazing everywhere… Must be the paint? Must be me? No, they must have changed the recipe. It used to say “suitable for Exterior and Interior”. Now it just says Interior only. And guess what? It crazes.

    Zinsser 1-2-3 and BIN work as Primers over caulk and stops crazing. I was sure I’d used Dulux Trade Super Grip Primer before too but first job of the year CRAZING everywhere. Polyfilla Caulk (the expensive dark blue tube) + Super Grip + Fired Earth and Dulux retail emulsion = CRAZE CENTRAL.

  11. Avatar photo Andy Crichton

    It is a pain but you have the answer pretty much there – a non vinyl primer coat (BIN< oil undercoat even) and good acrylic paint. The Soudal at B&Q is a retail version, the Soudal Acryrub from UK Sealants isn't the same, admittedly I havent used v matt over it though, just steer clear.

  12. Noel

    Forgot to say. Never thought of using Repair Care. But £12 a tube and it’s seriously messy stuff (or is that just me?) so I don’t think I’ll go down that route. But will use it for deep cracks if foam is unsuitable. Good tip, thanks.

    Also, as Ron said. The Primer (Super Grip) did not craze but the Matt applied over the Super Grip did.

  13. Charles Budd

    Repair Care Dry Seal is a bit trickier to use than caulk – it’s a lot thicker – so a geared gun helps massively, and it’s harder to spread. But once you get the hang of it, it’s brilliant. I now use it to seal between glass and glazing bars on interiors – I know it’ll dry within 2 hours, it’ll stick really well, it’s a sealant so even when the paint fails it seals – no brainer really, even at £12 a tube!

    A quick tip – using a silicone spreader helps spreading it and getting really neat profiles. I have a Yato set which is getting a bit ragged now, I’ll order another set tonight while I think of it! 🙂

  14. Noel

    Yes, I have one of the recommended Palu spreader tools for Dry Seal (Repair Care). Still get into a right old mess though! I wonder if some warm soapy water would help? Must get a geared gun though. You mentioned using it for sealing interior glazing gaps. Do you use it for the same gaps on exterior glazing bars too? Or something else?

    Sorry to go slightly off-topic but why is the nozzle so small? To match the thickness of the existing putty I have to cut 80% of the nozzle off. Not a huge deal but don’t quite understand why they don’t have a wider nozzle.

  15. Charles Budd

    It is a bit messy and time consuming, but practice helps a lot!

    I use Dry Seal for interior and exterior glazing gaps and beads. I just know I can trust it.

    In the summer when doing exteriors I often have two tubes on the go with different nozzle hole sizes – one for doing large beads when I’m replacing putty, and one for smaller gap filling jobs. I find the nozzle sizes fine.

  16. Sarah

    Completely baffled, probably due to being a novice. I have used caulk in a corner of a room, run my finger down to get a neat finish. Painted on top and have the crackled effect. What would be the best thing to do sand off newly applied paint, prime and repaint?

  17. Avatar photo Andy Crichton

    hi Sarah, it is a common fault usually from applying a standard vinyl matt or contract matt emulsion over acrylic caulk, maybe compounded by applying the paint before the caulk has set. The solution is to now coat it with for example, an oil based undercoat, and when that has dried overpaint with the emulsion paint. Hope that helps.

    (Tell the caulk maker you are baffled and I would bet they will say the same!)

  18. jason

    What’s the best tool for raking out caulk a putty blade ,or utility blade, or blunt screwdriver.

  19. Rob Allbright

    Great article’ I’ve been scratching my head for yrs with this problem’ something I have with the so called more “fashionable paints” as opposed to the traditional trade brands’ thanks for this and I to think this problem has become more visible in recent years, great blog.

  20. Peter Broadey

    I have been decorating for years using decorators cork and have not found any difference with expensive or cheep cork they all crack and shrink. The last job I did I used Evostick decorators cork to fill the cracks on a ceiling. I hooked out the crack to about 3mm fillies the crack with cork and filling knife and used a small brush with water to remove excess. When dry the shrinkage was massive so I refilled over the top repeating the process. It still shrank and cracked. I repeated the process a third and fourth time before it was reasonable for my customer. Evostick is not a cheap alternative and is the brand sold by the only local builders merchant. This is before any paint has been applied. I know that it will make no difference even with undercoat and gloss paint, over a couple of weeks it cracks.

  21. Andy Etheridge

    White smooth masonry paint applied with a half inch fitch over the caulk after being left for a couple of hours. Or If it is the skirting then undercoat up over the dried caulk and cut the emulsion in the next day before you gloss. Most painters apply the caulk far to thick anyway, which just makes the problem worse, as the incompatability is greater.

  22. Cullen

    Used caulk all over hairline cracks on wall put emulsion on top and can see where cracks where!

  23. Avatar photo Andy Crichton

    Caulk dries smooth, so it is a different texture to painted emulsion. For cracks, either use a more compatible powder filler like Toupret TX 110, or on more severe movement cracks, look into the flexible Elafib (old name) Toupret system with option for lightweight scrim.

  24. Dave Jones

    I’ve found this problem every time I have painted over caulking with vinyl matt emulsion. I’ve used loads of different makes of caulking and it always ends up the same. If you don’t fill the crazing/cracks afterwards, especially up against the skirting then the cracks fill with dust which makes the joint look horrible and dirty in no time. Recently I’ve started to coat the caulk with pva glue mixed into some water. This goes off quite quickly if you use warm water so you can paint over it quite quickly. This has stopped any crazing for me where I have tried it so far.

  25. Bobo

    The problem is the differential properties of the sealant and the overpaint. Acrylic sealant dries to a flexible impermeable state, but ordinary emulsion dries fairly hard and dry and semi-porous.
    The trick is to match the properties of the two. Acrylic sealant requires acrylic overpaint. If you must use standard emulsion then prime the sealant areas with acrylic eggshell and then apply standard emulsion when dry. The acrylic eggshell remains slightly flexible, but binds more securely to sealant and the later coats of emulsion and so there is less chance of crazing.Thin coats are best. Thick coats will always crack more readily.

  26. Avatar photo Andy Crichton

    Nice explanation, thanks

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