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Discussion Starter · #1 ·
Hi everyone. I am using Dynaflex 230 50-year latex caulk on new and existing door casings. I am using Zinser Cover Stain water based primer over the casings and new caulk and am having a problem. As the primer dries, it cracks over the new caulk. As a test, I have allowed the caulk to dry for up to a week so I know the caulk is cured and not continuing to shrink. The cracking gives an alligator skin look just on the new caulk, not the surrounding wood. I notice it more if I thin the primer with water or Floetrol. If the primer is uncut it doesn't seem as bad. But unthinned, and the stuff dries so fast I get nasty brush marks which require sanding before topcoating. Any ideas on this one? Thanks a lot.
 

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This is only from my experience but I noticed that clear caulk does not take primer or paint as well as say white caulk. Also I try to prime all my work then caulk. On trim I imagine you will be painting with a semi-gloss or gloss. They seem to have a better elasticity then a primer or flat paint.
 

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Discussion Starter · #3 ·
Hi. The Dynaflex 230 is a white caulk, not clear. And it is paintable. I always prime before caulking like you mentioned. The only thing I can figure is that the primer doesn't like the Floetrol maybe. Anyone out there thin their primer?
 

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The only time I've had that happen is when the caulk isn't cured (but I would think a week would be sufficient) I also prime before caulking but I doubt thats the cause. Have you tried using un-thinned primer to see if you get better results?
 

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Discussion Starter · #6 ·
Hi, yes I have tried it unthinned as well as thinned. Same result, extensive cracking. Just yesterday, I tried a completely different brand of primer over the same caulking (Dynaflex) and so far so good. The new primer is labeled as a latex acrylic primer, whereas the Zinser is labeled 100% acrylic. I'm thinking that maybe 100% acrylic is harder, or more brittle, than a primer labeled latex/acrylic. I will see how the new primer holds out for a couple days before declaring success....
 

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Priming issues

A couple of things I see here I want to clarify
First.... all caulking is elastomeric. That simply means the material can expand and contract which is the main attribute and need for gaps.
Second.... you should be using oil based primer not water based. This is not needed for drywall but all raw wood and all exterior work should be primed with oil.
You should prime before caulking. Primer is designed to penetrate the fibers of the wood creating a physical bond as it is imbeded into the fibers. A physical bond is stronger than the chemical bond of the paint. Priming first also give the caulk better adhesion.
The good news is that you do not really need the caulk to be primed as the paint will stick to it well unprimed. If the alligator look is showing through sand it or use an exterior paint as they are thicker and can fill in the little cracks better. Oudoor paint can be used indoors but not vice versa.
As a former coatings chemist I can tell you that products which are greener are almost always inferior. If they were not the non green product would be discontinued. Manufacturers are always looking to replace harsher solvent based adhesives with water based adhesives so if you see the harsher solvent based product it is because it is better....almost always.
The two major causes we see in analysis of coatings failures are contractor application errors and choosing the wrong materials. The wrong material are often prompted by going green (water based primer #1) or focusing on looks over the function of the coating system. Paint is far more complicated than people could ever imagine. The manufacturers have endless hours of development invested. Follow their directions and you should be okay for the DIY project. I recommend using one brand for everything. They will work together as they are designed to do so
Pinelle Painting Services is a southern NH northern Ma based painting business. We offer worldwide consultation on coating failure analysis. We are run by two Chemical Engineers who come from the construction and aerospace coatings industries. The consulting is listed as Pinelle Construction Sciences.
Really baffled with a coating problem? Give me a shout it is what we do. [email protected]
 

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I've had this happen a lot on my new residential jobs and the finish coat ALWAYS takes care of this. I know exactly what you're talking about and apparently it's not really a big issue because the finish coat always does it's job.

I've had this happen on all different types of caulking from different companies too. It happens more in the winter time from my experience, could be the dry air and the heat from the torpedo heaters.
 

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right on

As Dorman said watch out for the heaters as they do force the material to dry from the outside in which in most cases isnt a good idea... just thought I would comment... also try 100% acrylic I think waiting a week to coat something you have more time on your hands or you are actually makeing money on the job :)
 
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