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Filler Primer

jswareiv

Well Known Member
In the new video from Van's showing how to fiberglass the front of the canopy (fairing)(great by the way), they mention using an filler primer and rolling it on for the finishing step to fill any remaining small pinholes. They don't mention a brand of filler. Looking around here, is K36 the recommendation? If rolling it on, I'm guessing sand the first coat with 400, then reapply? Recommendations on nap of roller? After all the hours spent fiberglassing and sanding, I would hate to mess it up. Every part of this process has been a learning experience. I appreciate the help, thanks.
 
In the new video from Van's showing how to fiberglass the front of the canopy (fairing)(great by the way), they mention using an filler primer and rolling it on for the finishing step to fill any remaining small pinholes. They don't mention a brand of filler. Looking around here, is K36 the recommendation?

All primer-fillers (aka high-build primer, primer-surfacer, and often primer-sealer) are a base liquid suspending a solid bulk media. Most of the good primer-surfacers these days are acrylic urethane base. The common bulk media is talc or similar.

Years ago, the base was polyester. In the immortal words of Monty Python, "Run away, run away!"

Any solid (or liquid that turns solid) that you can work down into the pinhole will satisfy the basic requirement. We have good builders here who swear by drywall compound, and I don't doubt river mud would work well too. The question is how will the chosen filler (1) react long term with the substrate and the overcoats, and (2) hold up to environmental conditions, mostly a matter of heat and moisture.

Note that in the above, the material is not used as a surface coating. It is not a layer in the stack of primers and paints. Its all sanded off, leaving just the material down in the holes.

I quit using acrylic urethane surfacers for pinhole work some time ago. It's good stuff, but they all cure in the usual manner; the solvent evaporates out, then cross-linking hardens the material. Although it's not difficult to work the primer down into the pinholes (squeegee, roller, old credit card, whatever), I find that as the solvent evaporates, the pinholes tend to re-appear as little depressions in the surface, or re-open. So you let it cure, reapply, sand again, reapply, sand again, etc. I prefer an epoxy wipe, as there is no shrinkage during cure, no long term chemical or environmental issues, and it's a one-shot application.

I do use a lot of high-build primer for its intended purpose, as a final build coat prior to topcoat. Spray a contrasting epoxy primer, then spray a few mils of high build, then block sand to eliminate the last little fine ripples in the surface.
 
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Also consider WLS primer, which can be bought directly, or through Lancair. It is an epoxy based filler primer/surfacer. It all ships from the west coast, so factor shipping costs into the purchase price...
 
Primer Filler

I prefer an epoxy wipe, as there is no shrinkage during cure, no long term chemical or environmental issues, and it's a one-shot application.

I do use a lot of high-build primer for its intended purpose, as a final build coat prior to topcoat. Spray a contrasting epoxy primer, then spray a few mils of high build, then block sand to eliminate the last little fine ripples in the surface.

Dan,

Speak slowly, remember, I'm learning. Here is the video and questions. My canopy looks like the first one and Scott uses some kind of primer filler than he rolls on. Rolling on would be preferable to me, since I really don't want to spray around my canopy, even though I know it is well covered. I want to end up with the same look as what Scott has, ready for paint?

2jepc3t.png


2vkmipj.png
 
Anyone use Smooth Prime on the canopy fairing? Section 5 of the manual mentions it for the cowling.
 
+ 1, for Dan H.

Dan has it right on the button here. Just one comment, we use the West systems epoxy thinned out and spread to fill. you can use their system to do many jobs on you aircraft and other things. In the long run it is a good one to get to know and use all of it's different additives and mixes. Hope this helps, R.E.A. III #80888
 
Thinner for West Epoxy ?

RobertA,
What do you use to thin West Epoxy with ? Doesn't an evaporating solvent pose the same pinhole outgas recurrence as solvent borne high fill primer Re : Dan Hortons comments. Not flaming, looking to learn cause I need a better way on my current project..Larry
 
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Dan A,
What do you use to thin West Epoxy with ? Doesn't an evaporating solvent pose the same pinhole outgas recurrence as solvent borne high fill primer Re : Dan Hortons comments. Not flaming, looking to learn cause I need a better way on my current project..Larry

Epoxy can be thinned with lacquer thinner or acetone. I wouldn't do that in a structural situation without tech data from the manufacturer. As a pinhole filler, it shouldn't be a problem as long as you keep the amount of thinner to a relatively small amount (<10% for sure).

That said, I've found that as a pinhole filler, you can squeegee in normal epoxy - no need to thin it.
 
That said, I've found that as a pinhole filler, you can squeegee in normal epoxy - no need to thin it.

Thinner - - EEEEk:eek:

+1, I took a micro mix with fast hardener and used a hard rubber, sharp edged squeege, raked both directions to fill the holes. Let harden, only light sanding needed.

Then did the same with neat resin, slow hardener, and got all off that I could to seal but not have to spend any time resanding. Scuffed with red scotchbrite and primed.

The hard way is to lay on the resin thick and have to sand it back to smooth. Using a squeege avoids that. Some use a thin steel one, but that did not work for me with the small area and contours of the transition on the canopy.
 
Carl,
I'll bet I know your Dogwood neighbor... he loves that Smooth Prime... but I agree with you...
Smooth prime is simple, and usually trouble free for inexperienced users, but it's not the most efficient product out there...

Tell Bill that Brad said hello ;-)

Brad Simmons
Airframes Inc.
Milan, TN
731-686-3610
 
Smooth Prime Follow up

After conflicting opinions, I decided to stick with Van's recommendation and use Smooth Prime to protect the canopy fairing as was happy with the results. Being water based was a bonus too.

I just rolled it on thick (3-4 coats) with a mini paint roller, let harden overnight, and sanded smooth with 400 grit sand paper the next morning.

It's probably not ready for that Oshkosh winning paint scheme. But, I plan to fly for a couple years unpainted, anyway. So, my goal was simply to cover the scuffed aluminum and protect the canopy fairing from UV.

Here's a pic.

mcQAcQ5.jpg
 
Nicely Done

I am going to be using my West Systems epoxy to correct a cowling mistake and will try to thin it down and use it this weekend.

If I ever manage to figure out this picture thingee on here I will post the results.

Dave
 
What is an "epoxy wipe"?

Hi Dan.

Three years ago you wrote:

"I prefer an epoxy wipe, as there is no shrinkage during cure, no long term
chemical or environmental issues, and it's a one-shot application."

I don't know what an "epoxy wipe" means.

I built my RV-12 canopy fairing with West Systems and am now looking for a "filler primer" to blend the side edge into the metal. Van's suggest PolyFiber UV Smooth Prime but there are mixed opinions about that here.

Also, I'm looking for a primer for the whole fiberglass fairing for UV protection and a gray primer look until I have it painted. Would you recommend specific products? There are so many out there, it is hard for a newbie to pick.

thanks,
Patrick
 
Hi Dan.

Three years ago you wrote:
"I prefer an epoxy wipe, as there is no shrinkage during cure, no long term
chemical or environmental issues, and it's a one-shot application."
I don't know what an "epoxy wipe" means.
I built my RV-12 canopy fairing with West Systems and am now looking for a "filler primer" to blend the side edge into the metal. Van's suggest PolyFiber UV Smooth Prime but there are mixed opinions about that here.
Also, I'm looking for a primer for the whole fiberglass fairing for UV protection and a gray primer look until I have it painted. Would you recommend specific products? There are so many out there, it is hard for a newbie to pick.

A epoxy wipe is just what it sounds like. Use a squeegee or an old key card or similar. Slop some mixed epoxy on the surface, then wipe back and forth as desired, with the goal of squeezing it down into pinholes, divots and flaws. Then use the squeegee to remove the excess epoxy. Just blade it off the edge.

If desired, allow it to cure to the point where it can't be moved, and add another coat, same procedure. How many coats depends on the contour quality of the underlying glass work. Moldless foam core composite might take several, while one good coat is might be enough for a Vans wheel pant.

Do not thin the epoxy. If you want a low viscosity epoxy, buy a low viscosity epoxy. This is 2018. Ad hoc chemistry is dumb.

Some years ago I started using a cheap paint roller to finish the job. It leaves a nice orange peel finish when cured, which makes a great sanding guide. That's a big plus, because you'll want to sand it smooth, but you absolutely don't want to sand through into the underlying fiberglass. Doing so tends to open new pinholes. Perfect would be an epoxy skin a few mils thick.

The standard "cover it until I get to the paint shop" is two coats of any good epoxy primer. I use PPG DPLF, but recommend you make a friend at your local auto paint supply house. If they are friendly and helpful, go with whatever brand they represent...they know it well.

See this thread; first example is a step by step.

http://www.vansairforce.com/community/showthread.php?t=22931
 
For minor pinhole filling, I found a finishing filler from the local auto-paint jobber worked extremely well. It is a polyester product, but is being sanded off anyway. It is a lower-viscosity filler that can be squeegeed on and cures fast.

I then used a 2k DTM (direct to metal) High-build primer. That primer is an epoxy hybrid that has the anti-corrosion properties of epoxy in a filler format. Pure urethane filler/primers are not recommended for bare metal and are supposed to be applied over an epoxy primer. In traditional auto body work it is: bare metal, epoxy primer, body filler/repair, high-build primer, block sand, primer-sealer, topcoat system.

Since my windscreen fairing interfaces with a metal surface the 2k DTM was the most appropriate. For all fiberglass surfaces, the dtm is not required, but works fine.
 
You can slightly warm the West epoxy. A few degrees will help. Use slow hardener...

Several years ago, I finished a sailboat wooden tiller that way. I heated it to 140 F and took it out of the oven and let it cool for a couple of minutes so the epoxy wouldn't harden on the surface. Then I painted it with West and slow hardener. As the tiller cooled, the epoxy was drawn into the pores.

The process worked quite well. It took three or four coats of epoxy applied that way before it quit soaking up epoxy. For you boaters, I then put on several coats of exterior varnish - that tiller looked good. But it was too slippery. Don't imagine that would be a problem with a cowl.

Perhaps bagging the inside of the cowl, warming it with a hair dryer or small space heater - being careful to keep the exterior temps under say 150 F - and applying the epoxy would work. Once the epoxy is on, shut off the heater and remove the bag. By then the pinholes should be filled (the fiberglass isn't wood), as the epoxy is drawn in slightly.

Dave
 
A water-viscosity epoxy as a seal coat...

I was asked to fabricate and install larger tire clearance blisters in a set of Falco gear doors. First task was to fabricate a form defining the shape of the desired blisters. Easy enough; ordinary 2" pink foam from the big box store, a little micro, and one wet coat of System Three Clear Coat.

Gear%20Door%20Bubble2%20800w.jpg


When cured, sand it slick without breaking through the skin.

Gear%20Door%20Bubble3%20800w.jpg


It was the waxed twice and sprayed with PVA. Two plies of 9oz 8-harness were laid up over this form, cured, and popped off. Another squirt of PVA, another layup, and I have two blisters with excellent shape.

Next task was cutting the old small blisters out of the gear doors. The new blisters were bonded into place, and two more plies of 9oz were laid over the assembly, followed by sanding to fair it all together. One coat of micro for fine contour, finish sand, then bring out the epoxy coat to seal it all. End result is a 4 ply blister on a honeycomb door panel, nice and light because there isn't a whole lot of filler on it:

Larrys%20Inner%20Gear%20Door%20800w.jpg


The sealed doors were sanded slick, just like the pink foam form. I don't remember if I shot them with PPG K-36 or not. I would have if they had shown some very fine ripples or waves when looking across the surface at a low angle. That's the purpose of filler-primer...flattening any surface contour flaw by block sanding. However, if all the work up to that point was done with an eye toward not creating waves in the first place, it's possible to go directly to epoxy primer and finish coats.
 
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