Pepto pink cowk filling difficulties

rjcthree · #1 03-01-2011, 06:13 PM

I've been working on my cowl, a new pepto cowl. I admit that do to extra blisters for the H2AD my top cowl, I had all sorts of fab the required filling. It was a grand experiment . . .

The lower cowling I went with the West System fill process, resin and micro. The issue is that after 6 coats and wet sanding, I still had visible 'divots' around the supporting hex core, mostly in 'horizontal' surfaces, nothing I would expect a high build primer to fill. Pinholes? Nope, not a one.

I'm going to go with a swipe of polyfiber epoxy filler , wet sand smooth, and a thinned coat of west resin over the top of that, wet sanded, then shoot a high build for wet sanding/guide.

Is this dumb?

Rick 90432

9GT · #2 03-01-2011, 07:40 PM

If your talking about Super Fil, I would not bother. Lots of folks have had problems with it delaminating over in canard land because its so dry and difficult to apply (I have built 1.5 Cozy MKIV's). I would stick with the West System epoxy's mixed with some micro added to suit for minor filling/finishing. Thicken it up stiff for those divot areas,,,otherwise it will run out. It is EZ stuff to apply and sand. Final coat of pure epoxy fills in any leftover pinholes or rogue sandpaper gouges, sand, then high build primer, sand and prime then paint.

Transporter · #3 03-01-2011, 10:09 PM

Instead of thinned epoxy for the final coat, I recommend System 3 Clear Coat. It's available in small or large kits from a number of shops.

Clear Coat is an extremely thin epoxy, designed to penetrate wood (as in wooden boats below the waterline, such as cedar strip canoes, etc.). Flows like water and works great for filling pinholes-just brush it on.

Regarding divots, etc. I'm not sure what sanding technique you're using; if you're not already using a fairing board you can make your own using a flat board (birch plywood is great) and some 3M contact spray to stick the abrasive on. Avoid finger sanding-it almost guarantees low spots. See Dan Horton's tips here for technique:

http://www.vansairforce.com/communit...erglass&page=2

Good luck,
Mike

rjcthree · #4 03-02-2011, 08:23 AM

Yes - superfill is what I WAS going to use. Past tense. I'll stick with West and micro avoid the risk, at least on the cowl. Additionally, after trying a couple test areas, I don't like the way the SF sands, even wet. Less effort, more clogging/mudding, inconsistent material removal rate.

I'm going to stick with the West- like paint, I don't like changing systems midway.

95% of my sanding is done with 3 different sanding blocks, various hardnesses of rubber. For the first cut, I'm using a 180 grit wet, second pass is a 220, then onto an epoxy high build.

The depth of the divots - before I started - is on the order of 0.018" (I cross sectioned one at random and put it on the optical comparitor here at work, so yes, it's really 0.018"). They were 5 iron from the fairway divots. Square feet of them. Not impressed. Having some bagging exp, I think they are using too much vac. The core is pressed to forcefully into the prepreg, and it bunches into the center of the core and cures.
Rick 90432

Transporter · #5 03-02-2011, 11:30 AM

Rick,
Agree with your comment about the cowl...not the best work I've ever seen and mine has the same issues. The West Systems with micro will get you the results you want.

Don't worry about system compatibility when using the System 3 Clear Coat to fill pinholes if you're using West Systems or other quality epoxy. I've used the Clear Coat for several years with no issues in terms of bonding/compatibility. Way preferable in my opinion compared to thinning epoxy for the same task or using a non-epoxy filler. A small kit is about $35 and covers approx. 50 s.f.-money well spent in terms of time saved IMHO.

Good luck with whatever system you choose.
Mike

dsmithlib · #6 03-06-2011, 08:02 PM

Thank you for your posts on this subject. I trimmed all my fairings and have been avoiding the finishing work - I can wait no longer!!

I have the West and micro so will give it a try.

What technique do you use to finish the regular layup parts like intersection fairings?

Thanks again...

Transporter · #7 03-06-2011, 10:17 PM

For general fairing/fiberglass finishing tips, see the post by Dan Horton in the thread I referenced above.

For wheel fairings, see his post at:

http://www.vansairforce.com/communit...light=fairings

Good luck,
Mike

rjcthree · #8 03-07-2011, 07:13 PM

I think there is a difference to finishing the pepto cowl and the pants. Filling the waffle of the core of the cowl is a PITA.

I figured out that my last coat, applied with a foam roller, thinned, lays down a lot like paint. It takes two days to cure, wet sands decently, and seems to to have a few thou of filling power.
Rick 90432