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Pin Holes in Paint


Radial Skybolt Builder: 220.45% completed
Aug 21, 2006
Reaction score
South Jersey
The subject of how to deal with pin holes in paint came up on the Tailwind Yahoo forum.

Here are a few of the comments.

Any other suggestions out there ?

Where I work, we make epoxy fillers, paints and other coatings. Pinholes are a major problem and sometimes cannot be avoided simply because of the material you have. Pinholes can be caused from solvents evaporating too quickly out of the primer, air trapped in the paint from shaking instead of stirring, poor application techniques, etc....whatever the cause, once they have formed under the surface and you sand into them, they become VERY difficult to fill for two main reasons.

First reason is that the bubble is perfectly smooth on the inside, so any filler that gets into the cavity, will pull out very easily. Even with a good squeegee technique, (finger in a rubber cot works well) the filler material tends to pull out of the hole. So far, I have never heard of anybody being able to sand the inside of a pinhole. ;) Another reason they are tough to fill is because many pinholes are only open at the very top where you sanded through, which makes the hole you see only a portion of the size of the actual cavity. When filling this type, there is less of a problem will pull out, but what happens is just the top of the hole gets filled. When you sand it back down, magically the pinhole reappears.

We sell filler to a US carbon fiber bicycle company and this is a major problem for them as well; with as many as 10 to 15% of their bike frames failing inspection after it goes into final paint due to pinholes. They end up sanding the frames down to the carbon and starting over because they say it gives them a higher probability of success. I would tend to agree the best way to get pinholes off is to sand the coating off in those problematic areas and start that spot over.

Loehle sells a product called Wonder-fil. It is applied like paste wax and dries to a white powder. Wipe off the residue and all open pinholes are filled. The Wonder-fil will pull solvents from the next sprayed coat and becomes chemically bonded. I use it on freshly sanded bare composite parts and have found that it fills all of the remaining fabric weave as well asthe pinholes. Awsome product.Edited by: Jerry

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