Caulked cracks flashing on tilt up concrete after painting

by A Property Manager

Exterior walls made of tilt up concrete. Found some cracks and had them caulked with Sikaflex 1A.

Painted the walls with Sherlastic and the caulk line is flashing through the paint.

Because the caulk was applied during a time of rain and high humidity, I think it had not fully cured.

I wonder if I can fix this problem by

A.) Removing the sherlastic
B.) Letting the caulk fully cure and
C.) Painting over the cured caulk with a primer

What kind of primer should I use? perhaps a shellac based primer? and then re-applying the Sherlastic.

Please advise


Comments for Caulked cracks flashing on tilt up concrete after painting

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May 30, 2015
Avoid Flashing
by: Mike

Flashing is caused by Plasticizers in the Caulk leaching out and coming through the paint.This causes a couple of problems: Shiny areas (especially on Flat paint, and dirt and mildew pick up. Part of the advice given sounded good but is not correct. A simple Elastomeric Caulk will still Flash. Trust Me, I've tried it. You can use a product called "Eslsopatch" made by DAP or their Alex Flex. Both will not Flash the paint. PPG (formerly Glidden) has a product called TopGun 400 which also is non-flashing.

As far as getting rid of an existing problem, Shellack may do the trick, but should not be used as a whole body primer on Exterior surfaces - only spot priming. I would be a little concerned with cracking being an issue, since the caulking is flexible and the primer is not. The same would hold true for an oil-based primer like Coverstain, but that might work as well.

Aug 10, 2013
Curing Compound
by: Curing Compound in India

Curing compounds and surface hardeners are used to seal the surface of fresh concrete and prevent rapid loss of neutralized prior to installing ceramic tile or stone with a mortar.moisture.These consist of liquids containing film-forming polymers and metallic and non-metallic materials.Chemical removal of curing compounds using acids is not recommended because the chemicals must be completely.

Mar 26, 2013
Curing Compound
by: Sakshi Chem Sciences

Amazing post on Curing Compound on the basis of insulated concrete form.Since it is concrete it is vitally important that you know before construction where you want windows and doors placed since cutting through 6 inches of solid concrete and rebar to add a window is a real pain.

Apr 13, 2011
Paint flashing on Tilt up concrete walls
by: Shawn

Hi Steve,

Im going to assume that the Tilt Up had been properly prepped and coated prior to your crack repairs and that this is a re-paint. If not there are recommended procedures to follow when caulking, priming and painting new Tilt Up Concrete. Otherwise all kinds of issues can arise due to PH, the bond breakers and curing oils etc.

With that said I tend to find that a caulked crack flashes when the caulking is different in some way to the surrounding surface. As long as the texture of the caulking and surface are the same then the formulation of caulking is the issue. What I mean by that is the caulking is absorbing, not absorbing or reacting to the coating in a different manner than the painted concrete.

To avoid such a problem I would have used an elastomeric caulking, followed up with a concrete & masonry primer/sealer (one that's recommended for the specific project being done) then an elastomeric coating.

I'm not entirely sure how one would go about removing the Sherlastic as that could prove to be a task and a half. Your caulking should be fully cured though prior to painting.

At this point, since I'm thinking the Sherlastic and caulking has bonded, I would let it go through the summer as is.

Once the walls have had a few months (or seasons) of sunshine apply a concrete & masonry primer/sealer (maybe Sherwin Williams Loxon, ask your dealer) to the entire surface.

By priming all areas you will ensure uniformity with the finished look. You could try spot priming and painting just the filled cracks but I'm sure that your painted sections will then flash.

In the very least spot priming then doing an entire repaint with one (or two) coat/s of Sherlastic is recommended.

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