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Filling those pesky pinholes

videobobk

videobobk

Well Known Member
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Up to this point, the frustration level on my slow build 9A has been very managable and it has been fun. The wings and tail are painted and most systems are ready to go. A couple of days ago I started on the fiberglass finishing and I am having a bad time getting an acceptable result. Hours of sanding, only to find that way too many 'holes still aren't filled. At this rate, finishing the cowl could become my life's work.

I tried Van's suggested route, trying various "stuff" as filler. What really works?

Bob Kelly, 90854, 24 months into a nearly finished 9A
 
UV Smooth Prime

First let me say that I am NOT a fit & finish expert. I'm not the type to spend days messing around with cosmetics.

I decided to fill the pinholes on my RV-7 cowl a few months ago, and I went with UV Smooth Prime (Spruce sells it). It had come highly recommended by lots of other RV and fast glass builders. It was a repetitive process (brush on, dry, sand, repeat), but it's very easy to use and it works.

I used a foam roller, and I used a foam brush. I think I put on about 4 or 5 coats, sanding most of it off (other than the pinholes, obviously) between coats. It dries pretty quickly. I was able to do the cowl over the course of a weekend.

My cowl isn't 100% filled or painted, so take my "data point" with a big grain of salt. But if and when I finally decide to paint, it will be UV Smooth Prime that I use on the rest of my glass parts when getting it all ready for paint.

)_( Dan
RV-7 N714D
http://www.rvproject.com
 
aah, the 'ol pin hole conundrum. It's not the "stuff" as much as it is the technique and application of whatever stuff you use.

You have to force all the pin holes to show themselves which is really the biggest challenge for getting rid of them. A lot of the time, what can happen is that you will sand the gel coat really thin where a pin hole is lurking just underneath so that when you come back and sand ANY more, you uncover the lurking pinhole.
Other times, pin holes will fill with sanding dust which prevents any filler from getting in there in the first place.

So what you do is to forget about pin holes althogether until ALL of the primary, major filling and/or reshaping is done. In other words, have the part to where you think it should be ready for primer before addressing pin holes.

Now, get out your trusty air nozzle and crank the pressure up to about 125 pounds or so, and then run the tip of that nozzle over the ENTIRE part (every square inch) right on the surface. Any underneath lurking pin holes will be exposed by the air pressure blasting away any thin gelcoat and at the same time, any dust inside pinholes will get blown out as well.

The next step, or trick, is to squeegee on a thin layer of a good polyester filler (I like Evercoat) on the entire part. PRESS HARD as you squish the filler into any hole. Use the edge of your squeegee, not the flat. What can happen is that the air inside the pin hole can act as a compressive barrier to stop the filler from filling the hole. Hard pressure and using the edge of the squeegee helps to overcome that.
When that coat of filler has dried, just sand enough to smooth up the surface. Avoid sanding any further because you could easily sand down even more gelcoat and start the cycle over again.
That's why if you just cover OVER pinholes without filling them, they will still show up as a bubble on that hot sunny day.

Any air pocket (aka "a pin hole not yet exposed") underneath that doesn't get exposed by the high pressure nozzle is probably deep enough to not cause any problems later. However, any air pocket inside the glass does have the potential of showing up later as a bubble under the paint on a hot sunny day.
 
Evercoat makes a filler for filling pin holes. It is thinner than the regular stuff. Vern is right, squeege the stuff over the entire part pressing it into the surface. Wet sand it all off and prime. Fill remaining holes after prime, sand again, and prime a final time. You should have it by then.
 
Reface

I was recommended REFACE by the local Boat builders.
It's a two pot spray putty. Sands easily and filled the pin-holes with one coat.
I live in Australia so I don't know if it is available in the USA.
It is a European product.
If you want to chase it up I could send you a pic of the can.
Pete.
Down Under.
 
I used the smooth prime and the thin Evercoat. I think it is called a glazing filler. It works, but it's work and very dusty. Probably the worst part of building. Certainly the most tedious.

Once I got most of them out with the UV smooth prime, I used Polyfiber white EP 420/430 primer. It is slightly glossy and reveals the pinholes. Then I touched up the remaining holes with the Everite glazing filler. This was followed by a final shot of EP 420/430 and then Aerothane.

Roberta
 
Try building an entire airplane out of fiberglass and you'll know tedious. It took me 2 years to build my Long-EZ and an entire year to fill, sand, and prime. God I love aluminum!
 
Looks like I may finally be on the right track. Thanks for all the tips. Several comments about a thinner filler prompted me to double check the products I was using. It seems that both were stiffer than they should be, probably from age. Basically, I would fill a hole, and as the squeege went past, it was pulling the material partly back out. Things seem to be going better now.

I can't find "Reface" listed from any U.S. source. Sounds good, though. I plan to use a spray glaze for the last, minor holes that are bound to show up.

Bob Kelly, N908BL, "Metal Exercise."
 
After filling all those pesky pin holes with glaze coat I like to spray on a good couple of coats of AWL-QUICK by US Paint. It's the highest building high build primer I have yet to come across. Sands like a dream too. If after that you still have pin holes it's time to get out your trusty .45 and tell those little bastards just how it is. :p :D
 
Pesky pinholes

Vern hit it mostly. The pinholes will be hidden with larger portion under the skin.

As noted get the part fit to final form first. (great alliteration). Then agressively sand with 80 grit paper. If it is gel coated try to get down to the glass. Use the air hose to clean then clean with a brush and soap and water. Rinse, dry with air hose then clean with acetone of lacquer thinner.

Use Rage to fill any big divots. This is where the technique changes from some of the others posted. I now spray on a cover coat of sandable primer from a rattle can. Sand and blow the stuff off again. This will show you where the pin holes are located. From here if the pinholes are signficant squeegee in Evercoat #416. It is called Metal glaze but is all purpose filler. Press hard to force the stuff in the pin holes.

If the pinholes are minor I will prep as before then go with Superfil primer or the UV primer Dan mentioned. In most cases two cycles will do the job. The stuff sands like butter.

The thought is worse than reality!!!

Darwin N. Barrie
Chandler AZ
 
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