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Pin Hole Process

Phil

Well Known Member
Making the transition between banging rivets and doing fiberglass work on the -10 is fun. :)

I've got a questions related to the process for filling pinholes. I get the part about mixing with balloons and dragging them across the surface of the glass with a squeegee in an attempt to fill the holes.

Then I get the part about shooting a thin 'indicator' coat of primer on the surface to help locate the remaining holes for the second pass.

Here's where I get hung up on the process.

After the indicator coat has been laid down do I leave the primer on and try to fill the holes through the primer?

Do I sand the primer off and start over? That doesn't seem to make sense because that only opens more pores that you have to deal with in the future.

What do we do with the indicator coat?

Also, I'm not planning on painting the airplane myself. I'm planning on letting a professional (TBD at a later date) paint the airplane. So I don't know what type of primer I should put on the fiberglass sections of the -10. Is paint compatability a concern here?

Also I'd hate to run the engine for 50-60 hours before getting the airframe into the paint shop and have the glass covered with oil residue. So I feel like I need something there...

What gives?

Phil
 
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pin hole process

First, don't short change the filling of the pinholes with epoxy, Nothing holds better. I sanded and filled my cowl twice for pinhole coverage.
After you see you have filled all the holes you can see or feel, then you are ready to shoot it with a high build primer. The indicator coat is also called a guide coat. This is an off the shelf black spray paint that you spray a FOG coat over the cowl. You are not trying to cover the primer here, just spray it so you get dots of paint everwhere but thin enough so you still see the primer below. This is used to level your primer. The process is to wet sand the primer with 320 with a STIFF rubber sanding block till all the guide coat is removed and the finish looks and feels smooth. If you sand through the primer then you must reapply.
If you see any dots when you finish this area is low and if you run through the primer then you have a high spot that needs to be sanded down and of course more primer.

Long explaination but it's a process.
Tad Sargent
 
I would add (to save you money at the paint shop) Use Professional Grade Urethane High build primer on your fiberglass..
Rattle cans are cheaper than a quart of 2K primer and hardener, yes.. but the hours of sanding the rattle can crapola off at the paint shop will get expensive!
Just my 2 cents..
Cheers!
 
Phil,
Micro/epoxy is for shape and contour, not pinholes.

Straight epoxy for pinholes and filling open air bubbles in the sanded micro. Sand it slick without breaking through the epoxy skin.

Epoxy primer for pinhole check and tie coat. After the straight epoxy step you'll have very few pinholes.
(a) You can correct a few scattered pinholes with some cheap 2-part polyester, but sand off every bit except what is down in the actual pinhole.
(b)If you have a lot of pinholes you blew the straight epoxy step....sand off the primer and seal again.

Like John said, shoot a good high build urethane so you (or your painter) have something to block before finish paint.
 
Phil,
The goal is to have all the weave/pinholes filled before primer. That does not usually happen, though.

Squeegeed in epoxy is probably the best method. A lighter alternative is Superfil heated up with a heat gun until it is just about liquid. But epoxy is faster...

You can also squeegee in the first coat of primer, but it will most likely shrink a bit as it dries, so don't get in a big hurry to sand it.

Use only quality catalyzed urethane or epoxy primer/surfacer. Add the suggested reducer to thin the product so it will get down into (instead of "bridging" over) the pits and weave.It's ok to use a little catalyzed spot putty over the fresh primer, but if you have to use a lot, like Dan said, you blew it... Remember that the primer will "imprint" the surface of the part so much of the imprefections that you see should sand out.

I would avoid polyester filler primer if you are not planning to paint before first flight. It does not like water.

Before flight in primer you can also topcoat with (at least) a good wet coat of "sacrificial" filler primer that can be sanded off later leaving a clean surface to paint. Or topcoat with a product like PPG's DP-48LF for added protection.

Regards,

Brad Simmons
Airframes Inc.
Milan, TN
731-686-3610
 
Try this for fiberglass

Check out this product, it works great for fiberglass
They did an article in kit planes the last two months. The stuff for fiberglass is called wonder-fill.
I ordered from them, great products.
I'm not associated with them just a happy customer.
Email
[email protected]
Web- Loehle aircraft.
 
All good tips above Phil - there are almost as many ways to fill pinholes as there are opinions on priming....:)

My only tip is that if you think you know who you want to paint your airplane, talk to them up front about their thoughts on what to use, and how "good" you need to make the surface before turning it over for professional help. Some might rather you left certain steps to them!

Paul
 
... and this is why I like =VAF=.

The posts above are very helpful and probably saved me weeks of heartache.

Dan, Per your emp fairing thread:

Should I be laying down a modest layer of micro across all my parts and then contouring it with a block?

Then at this point is the process:
Use the straight epoxy (to fill pin holes), followed by the high build primer coats (to fill cosmetic scratches, etc), followed by the guide coat (to ensure pinholes are gone). Then sand the guide coat off until reaching the high build coat and stop right there?

What happens if I happen to find some pin holes after the first coat of high build? Can I fill them and then reshoot or do I need to sand that area locally, fill with epoxy, and then reshoot? I'm guessing its okay to try and fill them between layers of the high build primer?

Also, what does tie coat stand for?

Sorry for all the rookie questions, just trying to save myself some work and re-work by understanding the process and getting it right the first time.

Thanks,
Phil
 
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A couple of steps

I would only add a couple of steps to the process.

1) Before doing anything, it is important to clean the glass work. I usually do a good wipe down with acetone. This will remove and mold release (if the part was in a mold) and other surface contaminants. Next scrub the cowl with a soap and water using stiff nylon brush.

2) Many pin holes are actually small pockets or voids in the epoxy used in the layup. The pin hole may be much larger than the visible hole in the surface. For this reason, I always block sand with a fairly course sand paper to "open" the pin holes. From

From there, use the epoxy method to do the initial fill.
 
Should I be laying down a modest layer of micro across all my parts and then contouring it with a block?

Use micro if you need a change in contour. The emp fairing example was a moldless wet layup and could not have a perfect surface contour regardless of how carefully the underlying form was shaped......micro fills all the lows. Ok, now consider a Van's cowl. You may need some micro in a few places (behind the spinner, inlet matching, perhaps a surface depression where the mold was imperfect), but certainly not over the entire surface. Parts made in a carefully shaped and finished production mold just shouldn't need much contouring.

When the shape is good, seal with three (or more) squeegee coats of epoxy, then sand slick without breaking through the epoxy skin. Now you have a sealed part, on contour with a few .001's.

Here's a scratchbuilt part, previously contoured with micro (the white), and in the process of epoxy sealing/pinhole filling:

Skimmed.JPG


The first coat of epoxy was squeegeed hard for pinhole fill. The next two coats were applied with a nappy 3" roller, thus no squeegee marks and less sanding later. The orange peel finish is desired, as it makes a great sanding guide later. Sand only until the shiny specks disappear, and no further, and you won't cut through the epoxy "skin".

From there a lot depends on your paint system choice. For PPG it is DPLF epoxy primer, then do any minor pinhole or flaw correction, then follow quickly with K36 or K38 urethane high build.

I don't use a guide coat over the high build if the part is small enough to hold up to a flat light, or if I can arrange the lighting at a flat angle for a big part. The lighting allows you to see the waves and low spots well enough. Here's the same part as above. I'm block sanding the K36. See the little wave in the surface, right side, just above the third hole? It will need more K36 to fill that wave, blocked flat.

Ripple.JPG


The DPLF epoxy primer is the tie coat. Fresh epoxy primer is sticky, for lack of a better term. It glues the urethane high build to the epoxy coated component surface.
 
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Dan,

Your assistance and willingness to share your experience is greatly appreciated.

There is a another key step missing and that is to 'get started'.

I went out today and spent some time this evening playing with some of the techniques you described. They're not nearly the black magic they appear to be when you're a rookie looking in. After some time playing with fillers and block sanding (wet) with 320 it really started to make some sense.

My cabin top has a great contour but there are voids in the weave that will require filler before worrying about the pin holes. I'm using a West System filler (407) to fill the weave with a squeegee followed by a block sand. Then laying the epoxy layers down on top appears to be the trick. The areas I worked on came out silky smooth and it became obvious that I was headed down the right path.

That -10 cabin top is big and it's going to take quite a bit of filling and sanding. However I think think this process is very predictable (so the time isn't wasted) and it's not too terribly painful.

I thought it was rocket surgery or brain science, but it's only plastic and some form of media to hold it all together. Pretty easy stuff.

Thanks for the info. I'm sure I'll have more questions but I'm certainly headed down a predictable path and it doesn't appear that I'm creating a bunch of extra work for myself.

Thanks again for your contribution to the group.

Phil
 
Use of Peel Ply

Phil,
Micro/epoxy is for shape and contour, not pinholes.

Straight epoxy for pinholes and filling open air bubbles in the sanded micro. Sand it slick without breaking through the epoxy skin.

Epoxy primer for pinhole check and tie coat. After the straight epoxy step you'll have very few pinholes.
.....

Can I use Peel Ply when using straight epoxy to fill pin holes in order to make sanding easier between coats or will this pull the epoxy from the pin holes and defeat the purpose?
 
Can I use Peel Ply when using straight epoxy to fill pin holes in order to make sanding easier between coats or will this pull the epoxy from the pin holes and defeat the purpose?

"....sanding between coats"? Do not allow full cure between epoxy coats. Simply let the previous get tacky enough that it will not scrape away, and then squeegee on another coat.

I don't see much merit in peel ply for this particular task, but give it a try if you like. FWIW, you won't pull epoxy out of pinholes with it.

As noted in previous post I do experiment with technique and material. Lately I've been applying the first coat with a squeegee and rolling to remove lines, then rolling on a 2nd and 3rd coat. The mild "orange peel" cured finish is easy to sand without breaking through because you can see how much you've cut.....see the intake scoop in the post above.
 
"....sanding between coats"? Do not allow full cure between epoxy coats. Simply let the previous get tacky enough that it will not scrape away, and then squeegee on another coat.

I don't see much merit in peel ply for this particular task, but give it a try if you like. FWIW, you won't pull epoxy out of pinholes with it.

As noted in previous post I do experiment with technique and material. Lately I've been applying the first coat with a squeegee and rolling to remove lines, then rolling on a 2nd and 3rd coat. The mild "orange peel" cured finish is easy to sand without breaking through because you can see how much you've cut.....see the intake scoop in the post above.

Okay, I assumed that each coat was allowed to dry and what you outlined now makes sense. However, on your final coat that you will let cure, would it make sense to use peel ply to give you a more uniform finish and reduce sanding?
 
...would it make sense to use peel ply to give you a more uniform finish and reduce sanding?

Can't let it go, eh? ;)

Peel ply is best used over new layups. Without peel ply the surface will clearly show weave.

With peel ply the surface will be filed to the top of the fibers, but no more.

Finishing is a bit different. The goal is to seal the surface (with all its pinholes, fuzzy glass fibers, and voids in the micro) under an epoxy shell..... not a thick shell, but not zero. You want to build enough thickness to allow sanding some of it off without breaking back into the glass. Peel ply won't leave much surface epoxy, and any touchup sanding will just open new pinholes.

 
Can't let it go, eh? ;)

Good one! Yes, I do like peel ply, however i'm a newbie when it comes to glass so I don't always know when NOT to use it. As usual, your illustrations enlighten us!

I'm getting ready to do the layups on my windshield and I thought I would try removing the pinholes before tackling some of the other parts, especially the cowl.

I appreciate your time and effort in answering our questions. Even the dumb ones!!:D
 
So, filling the pin holes is important to keep liquids out if you're not planning to paint right away, right? If this is the case, is there a really need to apply primer? I'd rather leave that work to the painter a year or two after flying. Does the same go for the windshield fairing?

Thanks
 
So, filling the pin holes is important to keep liquids out if you're not planning to paint right away, right? If this is the case, is there a really need to apply primer?

An epoxy shell will seal out everything.

I would shoot a good two-part primer for several reasons.

First, you can't really judge the quality of your finish work until you spray it one dull color. Previously invisible flaws will become hugely apparent, and you will marvel or cuss depending on your nature.

Second, you need UV protection.

Third, unpainted glasswork is ugly enough to frighten small children.
 
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For the first epoxy coat I found a sponge with a ?wax on wax off? type motion works really well. I then squeegee off the excess and use only the squeegee for all additional coats.

Dan,
Can you recommend any particular high build primer filler?
 
Dan, Can you recommend any particular high build primer filler?

I'm not a professional, so I haven't tried a variety. I did have a peel problem back in the dark ages, with a then-popular high build sprayed directly over sanded glass/EZpoxy. About two years later it came unstuck.

Now I use one manufacturer's system and never vary. PPG, Sherwin Williams, and the rest spend a lot of money to know what is compatible. I suspect they are all pretty good, and I suggest using whatever brand is best supported in your area. Here in Montgomery the PPG store is excellent, so it's DPLF epoxy primer and K36 or K38 high build.
 
If you go way back to an earlier thread you'll recall a mention of experiments with System Three ClearCoat, a 2-1 epoxy with a mixed viscosity not much more than water. Its intended purpose is waterproofing wood, as it is thin enough to soak in. I started buying it to seal wood wings and got thinking it should seal glasswork too.

About 60 hours on the RV-8 now. My cowl was modified to use swappable exit panels so I could play with a cooling experiment. Time to shrink the exit area for the third time; CHT's are still too cool. Here's the new panel:

Exit%20%233%20Layup.JPG


Panel%20Sealed.JPG


The above is a single application of ClearCoat, worked into the surface with a squeegee, then rolled. No effort was made to scrape off excess epoxy; the well-wetted surface was rolled with a nappy 3" dry roller to simply even things out and eliminate drag marks. The cured result looks like orange peel, which creates a very good sanding guide so you don't break back through into the glass. Block sand just until the speckles are gone, and no more.

Spraying epoxy primer and K36 didn't turn up a single pinhole...none, nada, zip:

Panel%20Primed.JPG


I'd still do 3 coats of West to seal (1) over honeycomb, like the cowls, or (2) if the surface contour still needed a little work and some sanding thickness is desired, (3) if there were any significant pits and holes. However, for sealing slick, hard, well-contoured glass, this has become my new favorite.
 
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For those less interested in sanding than in painting, enter the lessons of the racing world.

Paint-on-a-roll.

Lighter than a full paint job, easier to apply and get to look good; tested to over 200mph on race cars; and easy to strip and replace if you want to change your paint job.

Note that it's still a good idea to get the pinholes filled first...

:D
 
Great thread

I've read it several times and now I'm ready to start filling the pinholes on my -8 cowling. Before reading this information I was planning to let the paint shop do this work. Thanks to the generous sharing of information by VAF members, I've learned a lot and will save some $$ in the process.
Question: (1.) If I squeege three coats of raw epoxy - how long should I wait between coats ? I'm assuming that I'll have to mix a new batch of epoxy for each coat and use a new foam roller pad each time.
(2.) The front of the cowling (vertical surface) that forms the opening for the prop, just behind the spinner, seems to be slightly concave (perhaps .01 in.) . Should I fill this area with micro/epoxy mixture or try to level it w/ a few coats of epoxy before moving on to the main body of the cowl.
Thanks
Steve
 
,Question: (1.) If I squeege three coats of raw epoxy - how long should I wait between coats ? I'm assuming that I'll have to mix a new batch of epoxy for each coat and use a new foam roller pad each time.

Apply the next coat while the previous is still tacky, but firm enough to not disturb with the squeegee.

(2.) The front of the cowling (vertical surface) that forms the opening for the prop, just behind the spinner, seems to be slightly concave (perhaps .01 in.) . Should I fill this area with micro/epoxy mixture or try to level it w/ a few coats of epoxy before moving on to the main body of the cowl.

Use micro. Remember, the idea is to not sand through the new epoxy skin, so a 0.010" fill with epoxy would require about 0.012" of buildup. Anyway, if you look and feel real close you'll probably find a few more spots which can use a bit of micro to get perfect contour. Keep looking and feeling with the flat of your hand.
 
Rust Defender

When Bobby Potts painted my -7A he primed with Rust Defender which is available from Aircraft Spruce. It serves as a primer as well as pinhole filler. The result was fantastic although admittedly he is a professional. Does anybody else have any experience with Rust Defender?
 
epoxy brand?

I am about to begin filling pin holes on my pink cowl and learned a lot from this thread...thanks all for the suggestions on methods.

Question as to what type of epoxy is "best". I have been mostly using West System 105, and just started using Aeropoxy for my plenum. Which would be better for the cowl...or does it even matter?
 
Unanswered question

Question unanswered: Pinholes after first coat of high build. I had some fill /build up issues (my cowl required some mods for the H2AD) iin a couple places, and I did not epoxy over. I shot the SW spectraprime high build (a 3k). Big bummer, in that it's a forest of small pinholes in those sections.

I'm wet sanding down, but the few other pinholes and that ugly set of areas I was going back to west epoxy. Issues there?

Rick 90432

ps - wet sanding in the rain - sounds dumb, but it works, lol
 
It doesn't matter which brand of epoxy you use. Pick based on which one sands easiest.

No problem starting over if you sand off all the high-build.

Shell the inside of the cowl just like the outside, then shoot it with a single stage 2-part white paint.
 
I epoxied the inside of the cowling

as a practice project prior to moving to the outside.
I used advice found in this thread and others as a guide and found all the information helpful.
First, I sanded out the rough spots and sharp edges and scuffed sanded all of the rest. Then I cleaned the inside thouroughly w/ soap and water and gave it a final cleaning w/ acetone. After that, I mixed the epoxy w/o diluting it and brushed it all over the inside. I then used a squegee to work it into any low spots. I was surprised at the amount of epoxy I was able to remove and work out of the cowling by the squegee process. Overall, I think it was a good learning experience that will help me w/ the exterior of the cowling. I plan to scuff sand the interior, prime and topcoat. Have not figured out what color yet.
My friend has a -6 w/ no finish on the inside of his cowling. It looks like oil had permeated the fiberglass weave - he can never get it clean and it always looks messy.
Steve
 
Good for you Steve.

You'll like it sealed and painted some light color inside...leaks show instantly, it is easy to keep clean, reflective heat barrier foil sticks really well, and it improves lighting if you like to peek in the oil door and up the outlet for preflight.

Cowl%20Interior%20Sealed.JPG


Cowl%20Interior%20Painted.JPG


After quite a few hours:

Cowl%20Insulation2.jpg
 
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Ommmmmmm.... Ommmmmm.... Read, review, try, fail, fix, (back to VAF) read some more, try again. I'm closing in on it :). The clear candy shell is key, and those epoxy squeegee coats as thin as humanly possible it seems. This pass at the re-read, I need to go dig up a foam roller to see about dealing with the squeegee lines at application time, instead of spending 'extra' time wet sanding. Thanks Dan!
 
Scott, I'm slow sometimes....I just realized you've been talking about wet sanding the epoxy shell pinhole coats. You should be able to sand dry, in the 120~180 grit range. If it's clogging the paper, you may have amine blush or it's not fully cured. Both are avoided by making the shop warmer and humidity lower.

"Non-sanding primer" (like PPG DPLF) has to be wet sanded, because it is sorta gummy no matter what. Luckily you don't have to sand it unless you let it cure more than a week before topcoat.

High build primer-sealers (like K36 or K38) can be block-sanded wet or dry. I like to block with 320 wet, but I'd do it dry in February ;)

Following the squeegee with a nappy roller is just a trick to eliminate ridges and lines. The resulting orange peel surface is a nice sanding guide so you don't sand through. I've not tried a foam roller. I've been buying the cheapest nappy ones and chopping them to a 3" length on the bandsaw.
 
Thanks Dan.
Another piece of genius from "the Horton": Yesterday, I was ready to shoot a little K36 but it was actually sleeting and snowing outside, if you can believe that! I have a little spray booth setup in my shop with an exhaust fan out a window. I have dedicated central a/c and heat, so I heated up the shop to about 77deg and engaged the Horton: I opened the attic door for air inlet (just outside the booth), and cranked up the exhaust fan. It worked GREAT! My total heat loss was about 5deg over about 20min. Simply amazing.
After the shoot session with parts moved inside to dry, I needed to fully flush the shop so I opened my usual direct fresh air source with the same exhaust and lost 15deg in 3min.
 
pin hole fill

Try using Evercoat Polyester Glazing Compound. A glass airplane builder assist guy turned me on to this stuff, it works great.

jjet
 
This thread has been a god-send. I am just finishing up my canopy interior (with Aerosport Overhead Console). The lessons and tricks here have been beyond in-valuable. My donation to VAF was worth this thread alone. I have never worked with fiberglass before and I would have been lost with out it.

WP_000859.jpg
 
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