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Removing filler/primer

uk_figs

uk_figs

Well Known Member
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When I built my -7 I sprayed the cowling with a recommended two part filler/primer (gray color in can with a hardener, can't remember the name) to fill pinholes and protect the surface until I painted the plane. A year later the filler is now cracking off in places and does not appear to have either a) adhered well to the underlying fiberglass/resin (I did coat the cowling with raw thinned resin per Vans instructions) or b) filled the underlying pin holes.
I think I sprayed at too cold a temperature and too thick.:mad:
Is there a reasonable way to remove the filler other than sanding back to the fiberglass (I have sanded back one part of the cowl and it took ages :() and is the pin hole filling recommendation these days to squeegee raw resin (versus thinned raw resin).
Also can I prime without making a choice of the type of paint I will eventually use or do they have to match up.
 
You've got some hard work ahead of you!!

You asked: Is there a reasonable way to remove the filler other than sanding back to the fiberglass? Not that I would trust. You obviously have an adhesion problem so remove the old, scuff the cowl with 320 grit, and make sure the new primer adheres. Too thick is not good, also not waiting the appropriate flash time can cause problems too. Most quality products come with data sheets that describe the application, cure, temps, and everything else pertinent.

You asked: Also can I prime without making a choice of the type of paint I will eventually use or do they have to match up. Painting is "a system" and all parts of the system have to work together. Work with one vendor's products from beginning to end for best results. Take the cowl to the paint supplier and let him help you pick out a product.

We're building a 6A from parts that were primered in the 1990's. Tomorrow it's all coming off. I'm not about to risk $1500 worth of paint over unknown, dried out primer.

There are several articles on this website that discourage thinning out WEST with acetone and other chemicals.

Hope this helps.
 
Media blasting

Find an expert in media blasting. The guys who know what they're doing can take that stuff off without hurting anything.
 
Not real hard

Get an electric DA sander and use a coarse paper. The work will go very fast. You may have to hand sand some of the areas around the scoop and inlets.

As I have noted many times, do not do any fiberglass work until everything has been thoroughly cleaned. Even a little contamination will reek havoc.

After you remove the primer and get to bare fiberglass, clean with acetone and then soap and water. Hose off and let air dry.

The time you spend now will save you time later.
 
used palm sander

I used a palm sander with 80 grit and it has still taken a couple of days as I used light pressure so that I would not gouge the fiberglass, now that I am back to the fiberglass I need to fill the pin holes, any better solutions than the raw resin squeegee approach? I will not be painting the plane until the fall.
 
Lots of good advice

Find an expert in media blasting. The guys who know what they're doing can take that stuff off without hurting anything.

That is a good solution but finding such an expert could prove challenging. And if the expert gives your cowl to a trainee, the havoc he could wreak could be significant.

Ergo, the tried and true method of sanding comes back to the forefront. Ignominious it may be, and tiresome on us senior citizens, but it has never let me down.

Darwin?s advice: ?After you remove the primer and get to bare fiberglass, clean with acetone and then soap and water. Hose off and let air dry. The time you spend now will save you time later? hits the nail right on the head.

QUESTION: What?s everyone?s experience with CAB-O-SIL versus MICROLIGHT 410?
 
az_gila said:
...the extra money spent make it sand easier?
Click to expand...

So they say Gil....but it's 2 oz for $10 vs a 1 lb bag of plain micro @$9, and dry micro isn't hard to sand.

Detailed comparison of West 410 and 3M micro is for another time. In the context of this thread, I wouldn't use any additive for surface sealing, just neat epoxy.

BTW, even West makes reference to shelling surfaces with neat epoxy. See the last line here:

http://westsystem.com/ss/fairing/

Are there alternatives? The Azko Nobel pinhole filler is apparently well accepted in industry:

http://www.anac.com/products/DataSheets/28c1.pdf

....and it's probably what Lohle sells as WonderFil. However, it is not going to offer any surface thickness build-up compare to squeeged epoxy, and our poster needs a little surface build after all that sanding to remove mystery primer.
 
Raw epoxy it is

Thanks for the tips and the link to the west systems user guides, wish I had thought to check their site when I did the fiberglass the first time. I still have some of the microlight 410 and need to smooth the canopy fairing a little better before paint so the fairing guide was a good read.
 
Pin holes

Maybe changing the subject slightly, but I fail to see why guys are sweating all the pinholes before the priming process. I had a former life as a paint and body guy, and we used a lacquer based filler made by Nitro-Stan for filling small pinholes after priming just before topcoating with acrylic enamel or lacquer. Fast forward 25yrs and primers are all epoxy/urethane base with elastomeric hardners. They fill better, dry faster and are much easier to sand.

The auto body world still uses polyester body fillers that have very little problems with pinholes, such as a high quality filler like Rage gold preimum. Although Vans recomends that you don't use any polyester filler on the tips, etc and instead go with the West system epoxy filler for bonding and fairing. I have just finished the empenage and used the West system for filling, and Sherwin-Williams for the priming. The epoxy still has a ton of pinholes after the initial sand out with 80 grit. I then apply the etch primer followed by their recomended 2K-urethane primer-surfacer P30A. After a final wet sand, any pin holes can then be filled with a primium glazing putty like, Evercoat (METAL GLAZE polyester finishing and blending putty #416).

The SW rep says any topcoat can be used over this finishing putty, and that all the top reputable shops in the Houston area use this system for their topcoats, even large fleets like FedEx using their Genesis urethane paint system.

So back to my original question. Why sweat the pinholes in the epoxy. It seems to me that a person is just creating extra work for himself trying to get rid of them, and after all that's what the primer is for.
 
Lacquer based products

Mark:

I too used RAGE, Evercoat, and SW Genesis to finish several Classic Chevys & my 9A and I have not had an issue with pinhole pops even though the paint is three years old.

I also agree that Evercoat is a much better product than lacquer based Nitro-Stan. Twenty years ago I painted a Triumph TR3 for a friend who filled many holes with a lacquer based filler. The end result was a disaster. Folks who choose to use body supplies to fill pinholes should avoid lacquer based products. Evercoat is first rate and has never let me down.

On the 6A we?re building now, the original builder covered lacquer based filler with lacquer based primer. This past weekend, we systematically removed both products. Adhesion is a major consideration when painting and anything I can do to promote adhesion is worth considering. I also do not want to risk softening any product that lies below the primer such as lacquer based products.

The main message I try to convey to people who are considering painting their own cars or airplanes is to carefully study the products they intend to use. Work with one vendor all the way thru and read the prints that vendors circulate.
 
Rage gold

I think it was rage gold that I actually used, it was gray with a separate hardener, and I was following recommendations from others on this site.
With it now sanded back to the fiberglass you can see that it did not fill all the pin holes particularly in the areas of the cowling that are a honeycomb sandwich. As I said in the earlier post I may have sprayed it too thick and in too cold an environment and I remember the mixing was also not that easy as it seemed that you did not use much hardener for a spray gun volume of filler.
I did sand the epoxy coating with 80 grit prior to the application of the filler but it obviously did not stick well in some areas.
I seems to me that this is an area like fiberglass where it takes a few tries to learn how to do it right and you have to be sensitive to the mixing ratios, environmental conditions etc for it to turn out correctly.
Another element of the education process:)
 
Barry,

That's good to know that you have had good results so far using the Rage Gold filler. I think the reason Vans says to use the West system is that the tips and fairings are epoxy based fiberglass. But I could be wrong. Anyway, I agree to stay away from lacquer based primers and fillers, especially when topcoating with urethane. BTW I saw a beautifully restored 55 Chevy two door the other day at the gas pump. He was on the way to the car show.

Classic!!
 
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