CF with PC

Just wanted follow-up on a conversation (Forum) with Godzilla regarding problems I had applying CF with his Polycrylic method. I felt it was more difficult to get it to fill than Silkspan.

Brad indicated I needed to put the CF down into filled PC (ZInc Stearate) instead of plain PC. I tried that a couple days ago using PC and talc and wanted to say it is a different animal this way. All of the micro porosity I had before is gone. The filler back-fills the CF and it is much easier to get it smooth after application.

Try it, you'll like it.

FWIW

Stunt1
Hi Curt,

How much Zinc Stearate do you add to a quart can of PC ? I haven't tried this method of finishing yet, but I'm sure getting itchy to give it a try. Just finishing up a replica of my NATS winning F86D Sabre using dope and Polyspan and tissue and I definitely would like a shorter method after all these years of dope finishing. The only part of this finish that scares me is the spraying of the 2 part clear coat, especially since I live and spray in an apartment room building shop. I use an exhaust fan but I've sprayed some Rustoleum in the shop and everything in the room gets sticky, since the enamel takes awhile to dry.

Regards,

Mr. 1969 NATS

Bob Lampione

Hi Bob:

Can't speak for the Zinc Stearate--I have not personally used it--I've continued to use Talc. I use it in dope as well as pc up to the consistency of sour cream. I recall Brad saying he can use it mixed to be like mayonaise. It could be as high as 1:1 by volume approximately.

Never measured it--just add some, shake up and look at it, add more etc.

The clear coat overspray is VERY sticky. Much worse than rusto&*&*m.

And the smell and fumes are not something I would want to try in an apartment.

Even with the HVLP spray guns, it is pretty nasty.

FYI

LAST EDITED ON May-05-04 AT 11:11 AM (CDT)
 
>Hi Bob:
>
>Can't speak for the Zinc Stearate--I have not personally
>used it--I've continued to use Talc. I use it in dope as
>well as pc up to the consistency of sour cream. I recall
>Brad saying he can use it mixed to be like mayonaise. It
>could be as high as 1:1 by volume approximately.

That's it! 1 to 1 is about right.

Works GOOD huh???!!!!

It's the whip poopy. Light too.

>The clear coat overspray is VERY sticky. Much worse than
>rusto&*&*m.
>
>And the smell and fumes are not something I would want to
>try in an apartment.
>
>Even with the HVLP spray guns, it is pretty nasty.

Uh, yes. The better the clear, the more sticky it is... alas...

Don't you have a buddy with a garage? You could always go outside, but I would not recommend it.

Brad,

Craig said that he tried PC on the carbon mat I gave hime and he said it wouldnt brush on. It just ruined the mat. It was like it dissolved it. What gives?

>Brad,
>
>Craig said that he tried PC on the carbon mat I gave hime
>and he said it wouldnt brush on. It just ruined the mat.
>It was like it dissolved it. What gives?

????????
Gremlins?

There seem to be different kinds of carbon veil. The Arts Hobby stuff works fine. The veil I got off the roll from Doug literally falls apart when in contact with water! I hit it with a brush of PC and it turned to a mush that the brush just picked up and pushed around. I guess it had a different kind of bonding agent holding the fibres together. Doug said that it didn't do that with dope. Wierd, huh? Like I said, the Arts Hobby brand was perfect in every way. It has a different, stiffer feel to it.

I made up a balsa 1/16 x 3 x 8 coupon to test PC with the CF veil I purchased from Superior Balsa. No problems with the sizing dissolving, but it looked like it was going to take a ton of filler. Also, the coupon curled up like a potato chip. I think I may understand the perhaps subtle point Brad made in his article that he designs his planes to be compatible with the PC method. Perhaps he always uses planked foam wings? No open bays and no unsupported wood sheeting? When I tried another coupon and used a plastic sheet between it and a weighted platten the finish seemed to be somehow rubbery. I am leaving it out to continue curing.... This seems like an odd chemistry to me. I assume that the water has to evaporate while at the same time the material is cross-linking. If you prevent some of the water from evaporating during the cross-linking period, how are the final characteristics of the finish affected? Never quite as hard? Rubbery?

Since I have a whole quart can, I guess the next test is to load some of it with filler and see how that lays down. I have been using a foam brush with no apparent problems. Would like to try this method on a profile fuselage but still worried about warping.

LAST EDITED ON May-05-04 AT 11:54 PM (CDT)
 
Brad's directions work. Apply the PC, let it get tack free, and weight it down on a piece of teflon or other non-stick surface for 24 hours. After it really hardens, it will be very straight. Brad said that subsequent coats would not cause a warp. I used very light balsa on my flaps, and each subsequent coat still seemed to cause slight curving along the length. Not a twist, but a gentle curve. It would be less so if I coated both sides at the same time. I ended up with VERY straight, stiff flaps using the PC and carbon.

I used the PC on the open bays also. This proved to be somewhat strange, but it worked. DO NOT DO WHAT I DID! DO NOT APPLY THE POLYSPAN WITH PC! USE BALSARITE AND IRON IT ON! I got it worked out, but it took a long time to blend it into the surrounding surface the way I did it. I worked on that wing for two weeks (literally)! That was just too much work. This is supposed to be the fast way.

Also, I found myself doing all the fill work with the PC, resulting in an absolutely perfect surface. I think others don't worry so much about that, and use the primer coat to do a lot of the fill. This also added a lot of time. I did discover one interesting thing about PC in the process, assuming you are trying to completely fill and create a slick surface. After you get it pretty well filled with PC and filler (I used ZS, but Brad has found a MUCH better alternative), sand it smooth. Then, take a paper towel soaked in rubbing alcohol and briskly rub down the surface (don't rub excessively hard). The alcohol slightly softens the surface, and the surface gets really slick. You can easily see any flaws.

What I hate is trying to use CF on any even slightly compound curves, such as I found on my cowling. Not good. Recommend you use silkspan or something else. Polyspan is NOT good on compound curves, either.

Unfortunately, the clear coat didn't turn out quite as good as I'd hoped (my first try), but the primer and base color coats proved to be the easiest I have ever sprayed. When it comes to the clear coat, be warned. The first time ask for help. You can do it, but it won't be perfect. Before I do another one, I will definitely watch someone else do it right.

Also, the PC on Polyspan on open bays does seem rubbery. BUT, you can re-shrink it with heat right up until you apply the primer. Kinda neat. After the paint, it's not going anywhere. Just make sure there are no sags, wrinkles, etc., before you spray the primer. Now, I'm not talking about major loose stuff. I don't know, and doubt, if you could shrink that out. But if things get a little slack along the way, just re-shrink it a little. This proved to be an excellent way to do that final check for, and repair of, even very slight warps. I did some final tweaking on this, and the wing is perfectly straight. BE SURE TO ALLOW FOR PRESSURE VENTING ON ALL OPEN-BAY SURFACES!. The wing takes care of itself, with the leadout opening. The elevators, stab, and rudder had to have small vent holes in inconspicuous places. I figured this out when I first tried to re-shrink the stab, and the air inside expanded, causing the polyspan to balloon up somewhat, preventing proper shrinkage. After I worked out the vent holes, re-shrinking worked as planned. These vents are always advisable, due to heating when the plane is in the sun. We've had that discussion here before.

I ran into an issue on the elevators. They seemed really flexible after the polyspan and PC, so I overcoated them with a layer of CF. Now they are like iron! Harder to fill from there, but it worked. On the bear, the elevators are pretty lightly built, and the rubbery nature of the pc scared me. It might have been fine after the auto paint was applied, but I decided to not take a chance. Didn't really add any appreciable weight, and the plane balanced perfectly without any nose or tail weight.

for compound surfaces, woven .5 or .75oz glass cloth will work well.

Getting the correct binder on the veil is critical to the application. I have used the Arts Hobby stuff and the binder is non-affected by dope, acetone, water, epoxy, etc. Because of this, it can only be used on simple form surfaces (non compound curves) Even the slightest compound will force you to cut it or apply gores and it will be very difficult to get it to lay down. Especially with the PC since it has a relatively low "tack" before it sits for a while.

On the other hand, if you have some mat with binder that breaks down with the material being used, (water, epoxy, dope, etc.) it can be layed down smooth on the compound surfaces. But you have found the down side to light weight veil--without the binder, the veil falls apart very readily and cannot be handled like regular tissue or cloth.

What is your source for the material that breaks down with water?

Anyone have a source for veil with binder that breaks down with lacquer (dope) products?

FWIW

It was given to me by a friend. He got it from a now-defunct hobby shop in a big roll. It is definitely more plyable than the Arts Hobby stuff - both good and bad, it seems, depending on your needs. Doug Moon has used it with dope with no problems.

You can iron the CF before you lay it down. Heating it slightly with an iron will soften it to go around corners. The stuff I gave Craig came from Aerospace Composites, I think. I love it with dope and it goes around cowls and everything with ease.

It kicks butt with dope so does Poly Span.

I am to scared to put water based maerials on balsa. The warp factor is just to great.

LAST EDITED ON May-06-04 AT 07:31 PM (CDT)
 
>>I am to scared to put water based maerials on balsa. The
>warp factor is just to great.

Well, then live with the stink... it's one or the other.

The stink isnt what bothers me the most. Accept these days I do worry about it with baby and all. Dope gasses for days and the fumes do linger for a while. But I dont finish my planes in the house like you do so I can use stinkier stuff. I think I am going to move my doping to the shed out back. It is the drying time of PC and the cost of dope that I dont like, oh and putting water based materials on balsa. I never liked doing that with SS either. You work your ##### off to build it straight and light. Then watch your plane warp all to heck and HOPE it comes back all the way. 99% of the time it doesnt and there is always some twisting or massaging that has to be done. When I went away from SS and anything that had water in the application keeping things straight became easier. Dope costs so much more than it used to. I bought a gallon of SIG off the shelf for 25$ several years ago. Now it is more than 50 or darn close. PC is cheap comparitively. I put on CF with dope and sand it out in the same building session. PC needs over night dry time. I hate that. Adds way to much time to the finishing. And you know how I cant stand long finishes. This is all my opinion. I have seen your plane and it looks great and should have a killer finish on it. I am not knocking it as a way to do the finish. I just have my reservations that is all. Why am I even making this reply? I dont know. Maybe it is because I am bored and the baby absolutely will not go to sleep. Anyway if the carbon molding works out like it is so far filling and dope and tissue or PS or PC or CFV will be a thing of the past on the wing. Hope it works out.

Yes, the PC has to dry overnight, but it is equal to several coats of dope, so it's about even. The water on balsa issue bothers me too, and it caused me some concern. If you use a lot of CA on the wing like I do (and shouldn't), it can be a problem on sheeted surfaces. There has been discussion here concerning molding parts which are made from sheets joined edge to edge with CA, and how, if you let the wood soak too long, the joint will turn loose. This happened to me in a couple of places using PC. I was able to get to it to fix it without a problem, but it was of concern. While the PC was wet, the sheeting began to expand and buckle some, and that caused a couple of places to come loose from the ribs near the center section. This was before I covered the open bays, so, after the PC dried and the sheeting settled back down, I was able to get to the joints and re-glue. Subsequent coats of PC didn't cause the problem. Next time, I plan to use different glue on the sheeting.

How did we ever manage to finish a plane with PC in the first place?

IF you are buckling the wood on the first coat, you are soaking the thing. Use a paper towel instead of a brush and lightly wet the wood to seal. Better yet, use the filler mix of zinc stearate and you won't have the penetration problems.

I have never noticed that ANY finishing method on punk balsa will stay straight. I always jig my planes for drying.

Yeah, I didn't know about the "rub it on with a paper towel" trick when I started mine. I just brushed it on. It survived, but next time I will definitely use the wipe-on method for the first coat. I did MANY things wrong. But it survived. This stuff is really forgiving overall, and it is light.