Having a problem with blisters in the paint again. Does anyone have a good tip for repairing these blisters short of cutting them out and doing a spot paint repair?

I seem to have this problem with this when doing high-build primer and chart tape panel lines over glassed airframes. It seems to be the primer blistering up from the glass cloth in dark color areas when exposed to the hot sun for any extended time...like 8-10 minutes. Granted, it was 103F in the shade here in Charlotte today, but this has happened before when it was only 85-90F on a different plane.

I'm hesitant to glass and paint another plane if I'm going to continue to have this result, which sucks since I really enjoy the detailing. I've done one using the Polycrylic and glass cloth method and this one was with WestSystems epoxy and glass cloth. After finishing the glassing, a light coat of automotive primer was applied,sanded, low spots identified, spot puttied, sanded, repeated as req, then final sanded with 380 grit. Chart tape applied, Primer built up, sanded, tape removed, color coats(Krylon, rustoleum, valspar rattle can stuff etc), weathering and a final clear coat of KlassKote satin. The blisters have always been under the primer...paints and primers compatability don't seem to be the problem. More of an issue with getting the primer to bond with the glassing medium. I have always wiped down the surfaces after sanding with denatured alchohol and allowed them to drywell before begining to prime to ensure a clean surface.

Where am I messing this up?

Blister on the base of the "t" looking character and a larger one just to the right of it; also just to the left of the base of the "7" looking character at the wing root/wing walk.

Thanks

First let me say that I have no idea if this is true or not, but I have always "heard" that you should not use alcohol to wipe the plane down with before paint. Supposedly I can leave some sort of residue. Again, I have zero fact to back that up, but I have never used alcohol, and I have never had my primer bubble.
That being said, my next one will bubble....[:@]

What high build primer are you using? Sounds like the primer is the problem, I would switch.

I have seen many paint blisters in my day, and they are always caused by the same thing. Air trapped in the paint somewhere, usually pin holes in the primer from being applied too thick. Thin coates, dry well between coates. Be sure to wipe down with wax and grease remover and tack cloth before you spray.

Another obvious thing, make sure the paint and primer are compatible</p>

Frets24,

My guess is, your issue begins with the resin application.

Look for the largest blister and cut it away and remove the material. The tell, will be the color of the inside. Simply put, that blister ain't sticking!

58 years of model building and 40 years of using Automotive paint products and I've never had a blister on anything I've ever painted.

Also, once a model is glassed using quality resin and cloth, ANY chemical can be used as a cleaning agent, as long as it doesn't attack the surface resin.

I use and will continue to use only Polyester resins. In fact, I went on line looking today. One gallon with hardener for 33.00. This IS professional stuff, not consumer grade. And it ain't West.

Most blisters are caused by either some type of contamination or are the result of what is called "gassing".

First, when you wipe the surface down prior to applying your primer, are you wiping it dry also? If not, you might consider starting. If you don't wipe it dry with a clean cloth, you're taking a chance that whatever contamination may be on the surface is just being rubbed around and not totally removed.

As for gassing, basically that's when something in the resin or another coating layer isn't completely cured to a point where you are ready to apply the next coat. In other words it can trap solvents and since paint dries from the outside in, when that outer layers dry up they trap solvents and as the temp goes up, it wants to evaporate. Since high build primers are designed to provide some build and fill imperfections in a surface, it's easy to put it on thick and try to recoat before it's ready. Same applies to resin.

There are/could be other things going on with yours but these two items are where I would start. Thin layers, wipe dry and time to cure between different coatings.

Hope you get it worked out.

Once upon a time, it was said to use dishwashing detergent, and thoroughly wash any fiberglass parts, to remove whatever "release" agent the manufacturer had used. I have always done that, and had no problems.

Les

In some cases you wouldn't want the paint to dry completely between coats. Depends on the paint you're spraying.

Agreed. Didn't say to let it dry completely between coats. I said to let it get "completely cured to a point where you are ready to apply the next coat." and "time to cure between different coatings.".

It's all good.

Do tell! At that price I would be very interested in doing a polyesther resin job. I've seen your posts in the past highlighting your experience with that medium and have not pursued it only because of a prohibitive pricefor what I've been able to find. Like upwards of $80.00 foe a gallon and an additional $15.00 for hardener.

Only question I still have on that medium is; How's the clean up?

Frets24,

What clean up?

I have a box of surgical gloves, blue is nice, but you can now buy violet, that's nice also.

I mix only what I need for the task. So, small mixing cups get tossed. Clean brush in acetone, or use through-away.

I have a vented area and fan, vacuum as I sand when I sand and where a mask.

I will never change my winning game.

Hey! I'm not vague!

Here's the source.

http://www.fiberglasssite.com/servle...Resin-1/Detail

Not sold at that link, but you can also use a product made by "Mason." Sold in QTs for 26.00 with hardener. Will last forever! Hafta Google that.

I'll probably buy a Qt. of Mason's because I've used it many times before.

Guys are probably "sick" of seeing these photos but, this model has the Mason product. Resin and cloth. Finished in automotive two part paints, a little Gold Leaf, and Dupont two part clear.

Charles

The primer is obviously not adhering to the resin properly. Here are a few possible causes in order of likely hood.


The two chemical bases are not compatable. Alot of high build primers are polyester based. If you add MEKP to the primer as a hardener it is polyester and cannot be used over epoxy.

The epoxy was not fully cured adn was still gassing when the primer was applied. I usually wait a week before sanding and priming and never let the part see a temp less then 65 degrees during cure. The mix ratio could have been off, West Systems is one of the more ratio critical epoxies out there. You must always mix by weight.

Surface contamination. Epoxy surfaces should be wiped down with acetone before painting or having something else epoxied to them. Never handle with bare hands. Skin oils are disasterous contaminates.



The really bad news is that it really can't be fixed at this point. your options are to strip it and start over, the paint should peel off in sheets so it won't take long. Live with it or each time a blister forms, mix up some epoxy and inject the blister. You will have to squeeze any excess out then put down a square of chromite tape, some release film, some bagging film and then apply vacuum. This will apply enough pressure to glue the blister back down to the epoxy surface.

Thanks for all the replies, guys.

I don't think that there is any problem with the compatability of the paints and primers as I have been using these same and wide array of paints over and under each other for many years on all sorts of planes and other projects with no problems other than the occasional laquer over enamel too heavy, too soon.[X(] It has only been on the RC projects where I've been moving into greater detailing and the creation of relieved panel lines using the chart tape and the much thicker builds of primer used to accomplish that.

I have cut away one of the blisters and it is definitely the primer separating from the resin. I have noted however, that it only seems to occur in areas where there has been a high build of primer....namely, just as in the photo above, near a panel line or especially in the middle of a smaller panel section.

I'm leaning toward the explanation that the primer is not being allowed to dry/cure enough between coats. On the two recent problem projects I have used "Dupli-Color" filler/high build formula automotive primer and "Dupli-Color" sandable automotive primer as well as Rustoleum "ultimate finish" laquer type primer.

Application has been as follows after glassing, assuming the temps and humidity are favorable;

1. give the glassing medium of choice a good rub down with 380 grit. from now on I don't handle the parts with out surgical gloves or a towel and I'm very mindful of drops of sweat.
2. wipe down with denatured alchohol or acetone immediately before 1st primer to remove all of my skin oils and sweat from the surface. Wipe down with a fresh, clean cloth.
3. light coat of regular primer grey with a light coat of brown on top.
4. light sand to reveal surface dips-all brown and most of grey removed removed except in low spots.
5. putty the deeper dips and allow primer to fill the shallower stuff.
6. continue grey/brown coats and putty 3-5 times til satisfied with surface. 380 and 400 grits. at this point there is only primer or putty in the low spots and the rest of the surface is back down to/not through the resin.

7a. On many past projects this is where a light primer/finish sanding followed by color coat and fuel proofing would be applied with no subsequent problems with regard to paint. The projects which have presented problems have the following difference:

7b. forego finish sanding for now and apply chart tape
8. med/heavy application of high build filler primer over tape lines
9. 1-2 hours hit it again or as soon as it won't cause the previous layer to orange peel or run.
10. 3-4 more heavy coats as quickly as I can get them on without souring the underlying coats.
11. next day it's usually dry enough to wet sand. by the time the sanding is complete the top, clear layer of the chart tape has been more or less removed and the wood grain is becoming visible in the areas where there is a large expanse between the tape lines. most of the primer has been removed again, except at the chart tape.
12. dry everything off, wipe it down, hit it with the air hose and hang it up by wires.
13. when I'm sure water contamination is no longer a factor I hit everything with a couple light coats of regular primer and some finish sanding. 400 and 600 grit.
14. last coat of dark grey primer, just enough to be uniform and cover.
15. 3-4 hours later fish sand wet @ 800 grit followed by a few light coats and a couple medium coats of "10 minute dry time" silver as the base for the rest of the color coats.

14 and 15 are the same as 7a and have been fine in the past.
It's the addition of 7b-13 that I know are the problem. I think maybe I'm not giving the high build primer enough time to fully "off gas" and cure before I'm locking the still wet solvents in with the quick dry color coat. Then even 3-5 weeks later some areas blister in the sun.

Or is there something else that may be in the proceedure on top of insufficient time between heavy prime coats as well as insufficient time for the primer overall?

What do ya'll think?

Thanks again.

Yes I've seen your pics quite a few times, Avaiojet.
Still like 'em. They're part of why I'd like to try the poyesther resin. My wife is British so she really likes your plane a lot!

If I'm not able to find the right products, would you mind if I PM'd you sometime in the future when I'm at that point on the next build?

[X(]Yikes!!![X(]

After chasing a couple blisters on the P-51 last summer it seems to have survived the heat so far this year with no more occurences. Hopefully the KI-61 will follow the same.

I was going to inject these from below with some slo-cure CA then clamp them with some blocks. Luckily these blisters are above the area of the split flaps so I can work from the underside. The one that I cut I'll spot repair differently.
Last go 'round I had some luck wth cutting the blister away, sealing the edges with CA then spot puttying and repaintng the repair to blend. It's just a tedious way to have to chase blisters for the rest of the summer. Either that or put it away and maiden next year or only take it out on cloudy days

Hadn't thought of vac bagging it. That's a great idea for any that may come up in areas that I can't get to the underside of, Thanks!

Frets24,

Certainly you can contact me at any time, I'll be glad to help. That's why I'm here.

"Modelers helping modelers." There isn't enough of that!

BTW, I restored British sports car for 40 years, well, others also, both as a professional and a collecter. I had a Morgan +4 for over 30 years. Loved it so much I restored it and kept it. They tagged me, "Morgan." Last car I did the metal restoration on was a 356 Convertible D. The car went to Germany.

PM or E me anytime!

Charles

After reading your application description, you have one of two problems. First is the pinholesI stated in my first post. When you spray primer on thick it tends to form pinholes. Apply another coat over the pinholes and you have trapped air. Your blisters form in heat, so I would still suspect this.
Another possible problem is gassing off. If the primer is not two part urethane, an application of several thick coats will take a few days to cure. One part paints dry by solvent evaporation whick slows considerably when the primer skins over. The primer drys from the outside in, which is very slow on thick coats.

Best of luck
Scott

Pylonracr,

Yep, That's what I'm leaning toward as well. I hadn't thought of the pin hole angle, but it's certainly a possibility on the smaller "pimples". I will do my high build primer in lighter coats and allow a day between each coat on the current project. Hopefully I won't have this issue again.

thanks for your reply and insight.