Tip: Stewart paint / Stits micro filler 😢

Everywhere I used Stits filler material the Stewart paint is rough like pinholes or degassing. Everything was primed ( sealed ? ) with Stewart one component primer. I used Stits filler hoping it would adhere to aluminum better than 105 and micro balloons.

Not an expert, just passing on an observation.

Larry, what grit sandpaper was used over the filler? Then was it resanded, or shot wet-on-wet for primer and top coat? There is something called sand scratch swelling over some body fillers and I have usually had to put on the primer and sand with fine paper after to get all the surface even and smooth.

Sanding Stits filler

Bill,
I used 320 wet for all blocking and feathering. The waterborne Stewart primer is prone to pinholes if sprayed too wet and rather porous if applied drier and thin .

If I get any fact based insight on Stits vs West micro and Stewart waterborne I will update the post.

Larry DeCamp said:

Bill,
I used 320 wet for all blocking and feathering. The waterborne Stewart primer is prone to pinholes if sprayed too wet and rather porous if applied drier and thin .

If I get any fact based insight on Stits vs West micro and Stewart waterborne I will update the post.

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SuperFil is bisphenol-A epoxy and microballoons, just like epoxy and microballoons mixed at home. Although there are certain convenience aspects, it's a expensive way to use dry micro.

Cured and sanded micro should be sealed before primer. Remember, it is mostly hollow glass (or phenolic, if dark red) spheres, which are cut open by sanding. In addition, a certain amount of air is entrained while mixing, and the air bubbles also form pinhole voids when exposed by sanding.

There are primer-surfacer-sealer products (look up PPG K36 and K38 for example), which are urethane primers with a high filler content (usually talc). Most users have found it takes more than a few rounds of spraying and sanding to get a pinhole free surface. Since micro is commonly used to surface fiberglass, and the fiberglass also needs sealing, I use a skim coat of plain mixed epoxy, sand without breaking through, then shoot epoxy primer , then the primer-surfacer wet-on-wet for blocking. Search the archives.

Epoxy skimmed micro over glass, custom air intake:



Skimmed cowl exit panel:



Sanded without cutting through the epoxy seal coat, first coat of epoxy primer:

Thanks Dan !

I had read all the pinhole filler horror stories. Unfortunately I had some early success with solvent based high build primers and the Steward water based single component. I will be diligent and seal EVERYTHING well henceforth.
Thanks again for part numbers.....Larry

I had a few parts where pinholes popped up when I sprayed Eko prime. I thought that I had them all filled but we all know how that goes! When I primed my gear fairings, I was greeted with thousands of tiny pinholes! I took a credit card and worked the wet primer back and forth over and into the pin holes. You have to be persistent and and just keep working the primer back and forth. I had good success doing this and the primer dries fast and can be sanded quickly. Sand it smooth with 220 grit and a soft sanding block then spray another coat to check that you got all the pinholes filled. Sands easy and quick!