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Fiberglass help

Scott Hersha

Well Known Member
I have a dilemma. My RV6 is in the paint shop and they just started the paint process yesterday. Today they called me to say that my cowling is in terrible shape. There seems to be pin holes everywhere. No surprise to me, because I didn’t fill them. When I took the airplane there for an estimate, I asked them what they wanted on the cowl - and other fiberglass parts. I wanted to make sure what I did was compatible with their paint process and chemicals. They said the cowl looked fine and no need to do anything. That really surprised me, but I thought - great, I hate doing that kind of ****. This is an epoxy cowl that was sort of greenish looking originally. I guess they thought I had filled pin holes, but the honeycomb weave was clearly evident, and I mentioned that to him. Apparently there was some sort of miscommunication. Anyway, they etched and alodined yesterday and primed today. I drove up there and picked up the cowling this afternoon to bring it home and finish it. I told them I had used UV Smooth prime in the past and it worked out OK (20 years ago), so he ordered a gallon ($300). It is now Tuesday night 11 pm, and I was just reading about UV smooth prime online. Poly fiber says you need to wait at least 3 weeks after using smooth prime before priming with your epoxy primer. Needless to say, I won’t be doing that. They want the cowling back on Monday. The shoot color on the rest of the airplane tomorrow, and can do the cowl later, but not 3 weeks later. I’ve sanded and scotchbrited the primed cowl and now need to fill weave. Looking for recommendations on materials to use. I have my epoxy supplies at home with me (west system epoxy and fillers, plus super fill), but wondering if there is another filler that sets up quicker so I can do a couple coats per day. I think the polyester fillers have gotten better, but need a recommendation. I don’t have the ability to spray it on, that’s why smooth prime appealed to me (roller).

Not happy about this…. I’ll attach a couple photos so you can see what I’m dealing with. May need to zoom in.

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I would mix up some West System epoxy with microballoons into a thick cake frosting (or even drier) consistency, then using a single edge razor blade as an applicator (use like a squeegee) to try and fill all of the pinholes. Let it set up completely dry, then lightly sand down any high spots. You should be able to use the blade of the razor to get the micro pushed down into the pinholes. Application of heat (lightly) with a heat gun might help it flow into the holes. You might need to do several passes to get the pin holes filled and smoothed. You can finish off the cowling with a coating of epoxy to seal off the surface before doing a light sanding that won't reopen any of the pin holes.

I did this on my cowling and it went from awful to acceptable. I did use UV Smooth Prime after this and it does need time to out gas before getting top coated.

Check out my Cowling build log pages.
 
An idea

To meet your time table, think about using a high fill (thick) 2K primer with agressive catalyst. Consult you local refinishing supply. Micro balloons, as often discussed here, leave more pinholes to fill after sanding.

My thought is to Squeegee in the Slurry to fill the fill the weave and pin holes. Block sand and then apply more coats with a roller intil guide coat sanding meets your quality criteria.

Consult your pant supplier. My Spies Hecker primer, AKA Axalta, cures pretty fast and will water sand with 320 and 600 grit that looks like a gloss finish before base coat.
 
You're looking at 20 or more hours of work over the next week.

Day 1 - Five coats of squeegied in West Systems epoxy using fast hardener. Apply the "next" coat once the last coat is somewhat tacky.

Store in a warm place overnight.

Day 2 - Block sand. Apply catalyzed spot putty in any remaining pin holes.

Day 3 - Re-sand puttied areas. Spray with your choice of catalyzed high build primer. Maybe one coat followed by another coat a few hours later. You're trying to build thickness and give it time to dry/cure so you can sand it a day later.

Store in a warm place overnight.

Day 4 - Block sand. Apply catalyzed spot putty on any remaining pin holes.

Day 5 - Re-sand puttied areas. Re-spray with high build if necessary.

Store in a warm place.

Day 6 - Block sand again.
 
Pinhole Filler

I had good results filling the pinholes in my cowl and fiberglass parts with Evercoat 440 Pinhole Filler. This was applied after sanding down the 2K high build primer.

It is easy to apply and remove. See this YouTube video.
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You have it primed already, so I would squeegee on a layer of polyester surfacing filler (it is like low viscosity bondo) to fill the pinholes. Sand that back to level, Spray on a couple coats of 2k high-build primer, sand again (repeat if needed) and then take it to the shop. I assume they will do a primer-sealer and the topcoat. That can all be done in 1-2 days. The poly is ready to sand in 30min, primer is ready to sand in 4hrs. Topcoat is 30min-18hrs, so no wait for you really.
 
Slicksand

Evercoat Slick Sand. It's a very thick 2k primer that can be rolled on, or squeegeed with a credit card into the holes, can be block sanded about an hour later if reasonably warmed. Sands like primer. I've used it on cowls with no other prep after initial sanding, usually 2 coats will cover all pinholes. one has been in service over 12 years and still looks great. Good luck!
 
What Kyle said. You have to get resin into the pinholes, filler is likely to all out. Apply the resin with a steel scraper and plenty of pressure in long sweeps. It doesn't take very much, you are not looking to build up any depth only to get resin into the pin holes.
 
Thanks everyone for the replies. Yes it has already been shot with the Sherwin-Williams primer that they recommend with their JetGlo paint. I’ve sanded this with 400, and scotch-brited all of it, making it dull to do finishing work. There are numerous areas of weave exposed. The primer they used took care of many of the pinholes. The other fiberglass parts are fine - no pinholes, but this cowl is another story. The problem I have is with the spray part. I have a compressor of course at my hangar, but I’ve given away the three paint guns I had last week, which I really don’t know how to use anyway, and they are not hvlp. As far as 2K primer is concerned - I’ve heard of 2K mentioned numerous times, but have no idea what that means. I assume it has something to do with it being high build. I’ve sprayed in my hangar before using an old tent set up to be a paint booth, and used my airbrush gun with a kind of wide angle tip, and it worked well, but not sure that could be used with 2K primer.

My plan right now, and I mean in about 10 minutes, is to fill the deeper voids with West epoxy and light weight filler, and/or Superfil. I have both and it’s in my heated basement shop. Unless I learn of some easier way, I’ll take the cowl over to a body shop I’ve used recently (car accident) with a beautiful paint booth, and see if I can get them to shoot 2K primer and sand it for me.

I hate to sound so ignorant about this, as this is my 4th (and last) RV build. The other ones were finished and ready for primer and paint before taking them to the painters, but as I said my current painter said to bring it like it is. He didn’t realize what he was looking at. All of my previous RV’s, I used numerous coats of epoxy/filler, and in two cases, UV smooth prime, and they still look beautiful. Of course this finish work was done over an extended period of time and involved an incredible amount of sanding……. I’m getting too old for this….
 
Thanks everyone for the replies. Yes it has already been shot with the Sherwin-Williams primer that they recommend with their JetGlo paint. I’ve sanded this with 400, and scotch-brited all of it, making it dull to do finishing work. There are numerous areas of weave exposed. The primer they used took care of many of the pinholes. The other fiberglass parts are fine - no pinholes, but this cowl is another story. The problem I have is with the spray part. I have a compressor of course at my hangar, but I’ve given away the three paint guns I had last week, which I really don’t know how to use anyway, and they are not hvlp. As far as 2K primer is concerned - I’ve heard of 2K mentioned numerous times, but have no idea what that means. I assume it has something to do with it being high build. I’ve sprayed in my hangar before using an old tent set up to be a paint booth, and used my airbrush gun with a kind of wide angle tip, and it worked well, but not sure that could be used with 2K primer.

My plan right now, and I mean in about 10 minutes, is to fill the deeper voids with West epoxy and light weight filler, and/or Superfil. I have both and it’s in my heated basement shop. Unless I learn of some easier way, I’ll take the cowl over to a body shop I’ve used recently (car accident) with a beautiful paint booth, and see if I can get them to shoot 2K primer and sand it for me.

I hate to sound so ignorant about this, as this is my 4th (and last) RV build. The other ones were finished and ready for primer and paint before taking them to the painters, but as I said my current painter said to bring it like it is. He didn’t realize what he was looking at. All of my previous RV’s, I used numerous coats of epoxy/filler, and in two cases, UV smooth prime, and they still look beautiful. Of course this finish work was done over an extended period of time and involved an incredible amount of sanding……. I’m getting too old for this….

If the recommendation on superfil is to wait 3 weeks, I would NOT use it. Some of these fillers shrink and some shrink a lot and some can take a long time to do so. All of the methods that I use won't help, as you can't spray. I would get some high quality polyester glazing compound. Put on light coats and sand with 180 on blocks. Once it is where you like it, hand it over and the painter and they will either do the final sanding to their spec or can put on a coat or two of 2K primer and block sand it for final spray. Most epoxy primer will cover 220 grit and 2K easily does this. These fillers are much easier to sand than west epoxy and will therefore result in better surface quality. If you have a lot of pin holes, then epoxy might make sense.

Good quality poly fillers can shrink a bit, but the amount of it is not noticeable outside of very high end work, especially with thin coats on flat surfaces. Auto shops routinely only give it a day and the paint comes out just as good as factory cars, which means good, not museum quality, where you are looking to read fine print in the reflection off the clear coat.

a tip for others is to leave the cowl in the sun for a couple of days. The stuff takes a long time to fully cure and the UV is an excellent accelerator. Many times the paint will be very flat and after a few months, the FG weave starts to become visible due to the curing. Much bigger issue with polyester than epoxy, but still there.
 
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Thank you for the tips Larry. The superfil is a Poly Fiber epoxy product and doesn’t need the 3 week cure. The product that needs that is called UV SmoothPrime - also a PolyFiber product. It is a waterborne urethane and needs the 3 weeks or more to allow the water to evaporate out (outgasses, I guess). In the past when I used this product, it ended up being a few months before I could get the plane to the paint shop, so it was fully cured, and the smooth prime protected the fiberglass from UV damage.
What I’m doing will work, it’s just taking a whole lot more effort than I thought it would. I might take the advice from above and use a quality polyester filler at the end if I have areas that are not quite right. Evercoat Rage seems like a good one. Evercoat Slick Sand is a good product too from what I read, but I don’t want to cover the whole cowl with it. I’d rather use West epoxy, even though it takes longer before sanding is is more difficult to sand - at least until I get it close.
Thanks for all the help and advice gentlemen. By Sun N Fun it will be a distant memory. Can’t wait!
 
UV Smoothprime

Just a point of clarification. Poly Fiber UV Smoothprime, at least as I read the directions and spec sheet, requires ONE week of cure before over-coating with epoxy primer, not three.

I've had one bad experience with the old UV Smoothprime (cross-linked) about 14 years ago. I think I put an epoxy sealer over it just a day or two after application, and it failed in huge blisters. So do follow the directions.


I have a dilemma. My RV6 is in the paint shop and they just started the paint process yesterday. Today they called me to say that my cowling is in terrible shape. There seems to be pin holes everywhere. No surprise to me, because I didn’t fill them. When I took the airplane there for an estimate, I asked them what they wanted on the cowl - and other fiberglass parts. I wanted to make sure what I did was compatible with their paint process and chemicals. They said the cowl looked fine and no need to do anything. That really surprised me, but I thought - great, I hate doing that kind of ****. This is an epoxy cowl that was sort of greenish looking originally. I guess they thought I had filled pin holes, but the honeycomb weave was clearly evident, and I mentioned that to him. Apparently there was some sort of miscommunication. Anyway, they etched and alodined yesterday and primed today. I drove up there and picked up the cowling this afternoon to bring it home and finish it. I told them I had used UV Smooth prime in the past and it worked out OK (20 years ago), so he ordered a gallon ($300). It is now Tuesday night 11 pm, and I was just reading about UV smooth prime online. Poly fiber says you need to wait at least 3 weeks after using smooth prime before priming with your epoxy primer. Needless to say, I won’t be doing that. They want the cowling back on Monday. The shoot color on the rest of the airplane tomorrow, and can do the cowl later, but not 3 weeks later. I’ve sanded and scotchbrited the primed cowl and now need to fill weave. Looking for recommendations on materials to use. I have my epoxy supplies at home with me (west system epoxy and fillers, plus super fill), but wondering if there is another filler that sets up quicker so I can do a couple coats per day. I think the polyester fillers have gotten better, but need a recommendation. I don’t have the ability to spray it on, that’s why smooth prime appealed to me (roller).

Not happy about this…. I’ll attach a couple photos so you can see what I’m dealing with. May need to zoom in.

View attachment 36582

View attachment 36583

View attachment 36584
 
My experience with pushing West Systems

Even using the slow 206a hardener and very dry slurries, a box with a small space heater on low will get the part to 140F and hold it there. For me, that’s been the magic temp to push a cure to allow two applications per day without anything happening like warp age to the base part. You must let it come down to room temp before washing the blush or sanding though, or it gets gooey. YMMV.
 
Honeycomb

Maybe I missed it but no one addressed the honeycomb.
That's pretty important.
It should have a few layers of fiberglass over it.
I prefer the micro then epoxy method for finishing.
Micro can be mixed really dry by adding 10% denatured alcohol. You have to work fast because it gets even drier as the alcohol evaporates. The extra dry micro is easy to sand optically flat. After micro, a couple coats of neat epoxy seals most pinholes. That wet sands pretty easy. Follow with two brushed coats of unthinned 2K primer. Cure and wet sand.
The micro, epoxy and 2K all cure overnight so no long cure times or worry about compatibility.
Any remaining pin holes are easily filled with glazing compound.
 
Thank you for the tips Larry. The superfil is a Poly Fiber epoxy product and doesn’t need the 3 week cure. The product that needs that is called UV SmoothPrime - also a PolyFiber product. It is a waterborne urethane and needs the 3 weeks or more to allow the water to evaporate out (outgasses, I guess). In the past when I used this product, it ended up being a few months before I could get the plane to the paint shop, so it was fully cured, and the smooth prime protected the fiberglass from UV damage.
What I’m doing will work, it’s just taking a whole lot more effort than I thought it would. I might take the advice from above and use a quality polyester filler at the end if I have areas that are not quite right. Evercoat Rage seems like a good one. Evercoat Slick Sand is a good product too from what I read, but I don’t want to cover the whole cowl with it. I’d rather use West epoxy, even though it takes longer before sanding is is more difficult to sand - at least until I get it close.
Thanks for all the help and advice gentlemen. By Sun N Fun it will be a distant memory. Can’t wait!

I use the rage product and can endorse that it is high quality. There are several different versions of Rage with different qualities. For this type of work, you want the thinner version, as it is easier to spread thinly over large areas and will give a bit of self levelling. I believe it is the extreme you want, but be sure to check.
 
Scott has a fitted cowl with some primer and pinholes. It needs simple surface finishing, not contour change. No micro, and certainly no bondo.

The pinholes require a wipe application of a low vicosity liquid or paste. Wiping an epoxy resin into an epoxy/glass cowl is bulletproof, but there are other choices, like Akzo Nobel 28C1 or even drywall compound, both of which are fast solutions. Building epoxy thickness requires less high build primer in the next step, but the key here is to get something down in the pinholes.

An epoxy primer seals whatever filled the pinholes, makes any final corrections obvious, and provides the tie bond to the epoxy/glass cowl. It flashes off in 30 minutes or so, and can then be sprayed or rolled with a compatible urethane high build primer. PPG DPLF followed by K36 is a good example of a compatible pairing. Block sand and apply more high build until satisfactory. Done.
 
Drywall compound

Would do the lightweight drywall compound to fill the pin holes
Squeegee it on with a plastic spreader and sand it off with a 120 sanding sponge.
Sands off fast and easy. Then hit with a high build epoxy primer. Wet sand 220 or 320. Smooth as glass and fast. The drywall compound works well to fill the holes.
 
Lots of good help here. What I did and am still doing is a combination of a few different solutions recommended here. Since the cowl was already primed with Sherwin-Williams JetGlo primer, I had to deal with something that was already started. I sanded the primed cowl with 220 paper and then scotchbrite pads to make the surface rough enough to accommodate the next step. The scotchbrite dips into the depressions from the honeycomb weave a little. This exposed several areas of original underlying epoxy cowl structure from my overly aggressive sanding. I applied neat West epoxy to these areas, and a few other areas where the underlying cowl structure was too coarse. Sanded these areas with 400 wet or dry (wet). Then applied a layer of epoxy with West 410 filler to try to cover the weave still evident. This was pretty hard to sand. There were still a few areas of depressed weave, so today I added a skim coat of SuperFill to several areas. I will sand this one down tomorrow, and then move to step 3 - the last step for me. I will apply one or two layers of 2K Evercoat Slick Sand. I’ll sand that after it sets up, and lay down another layer, and then sand to 400. It’s pretty smooth right now, but the Slick Sand will make everything even and finish it off. My painter will prime again with the SW primer before paint.
I could have done all this during the two months that I waited for the delayed paint shop opening, had I known and realized that the paint shop manager didn’t know what he was getting in to when he told me the cowling was fine - just bring it in and we’ll fix what needs to be done. I think this was his first RV. They typically paint Cessnas, and my judgement on their quality was based on the Cessnas they had recently done. They don’t have to do much body work on Cessna strip and paint jobs other than paint stripping. On mine, they were supposed to shoot the base color today, but had body work to do on some of my canopy fairings that looked great, but once shot with primer showed scratches from the too aggressive 80 grit that I started sanding with and didn’t get out with the finer layers. I couldn’t see it just looking at the layers of epoxy that I used, but it tells me they are concerned with doing a good job. I have two buddies that are waiting in the wings to get theirs painted (RV7 & RV10), and want to see how mine turns out. The beautiful thing is, it is close to home so I can visit the progress and put it all back together myself. They will weigh the airplane and balance the controls (not sure how they are going to do that), before they let it out of their shop.
 
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