Polycrylic

Can PC be used as a top coat.Here is why I ask. A fellow club member did some testing and it was fuel proof. Because the test came out so well he brushed PC as a top coat on two new models and they look great. He flew one this weekend and the finish looks OK.I remember many years ago Tom Dixon used polyurethane on a plane and it looked good for a while but it got soft after time. Has any one tried it. I used oil based polyurethane on a combat model a few years ago and it started to suck up oil,but the plane had been in the ground a lot and it had a lot of cracks in the silk.
Ed

Ed, I have six pieces of balsa on which I have tested about every combination of polycrylic and Brodak dope combinations that I could think of. I used PC as base and topped with sanding sealer, then color, then PC as top. No problem. I used PC as base and topped with straight color etc. I have not come up with a combination that showed any seperation of adheasive problems. At this point I have used foam brush to apply top final coat. I am going to try spraying and will let you know results. Latest projest I am applying carbon fiber veil to all wood surfaces with PC. Ablolutely no problem so far. I really like the combination of carbon fiber veil and PC. After second coat of PC, it's ready for sanding sealer and after only two coats of sanding sealer it's ready for color.

Sunshine

>Latest projest I am applying carbon fiber veil
>to all wood surfaces with PC. I really like the
>combination of carbon fiber veil and PC.
>After second coat of PC, it's ready for sanding
>sealer and after only two coats of sanding sealer
>it's ready for color.

Wow. That must provide a really stiff and tough outer shell to the balsa structure.

I love carbon veil, although it seems to me to risk adding some weight. I've been applying it to my ships with Aerogloss (I know, it's retro) and felt maybe I was getting to heavy,

Since reading about PC on this board I'd tried a couple of light coats on my next structure and it toughens up the balsa noticably.

I'd expect a layer of light carbon veil attached on the wood with PC would result in a bullet proof turtle shell around the balsa.

What weight veil are you using and where to do you get it?

What do you expect it adds in weight to your structure?

Cy.

I used PC on my latest, but the final coats are auto paint. While building it, I noticed that if I wiped the PC covered areas with alcohol (the regular rubbing kind), it left the surface sorta sticky until it dried for awhile. As a matter of fact, after putting on the fill coat of PC, alcohol, and zinc stearate, I found that if I rubbed it down with a paper towel soaked in alcohol (after the PC was dry), the surface really became slick smooth. I do not know if this effect would happen after the PC was dry for a few days. I doubt that it would hold up at all on its own, but ask Godzilla. He'll know.

I have a work bench and applied three coats of Water (H2O) Based Polycrylic
for a surface finish. Months later I spilled Power Master fuel, 10% nitro on the
workbench, maybe five minutes passed and a gooey little mess ensued when I wiped it off with a cotton
rag.
I do use it prior to spraying on Rust Oleum paints.

Godzilla said it wasn't fuel proof.

My experiences with water based polyurethanes is similar. I painted a profile 1/2-A with it (Red Devil brand) as the final coat and fuel caused it to go sticky. Polycrylic is, I believe, just a variety of water based polyurethane varnish. I've got a can of Ace Hardware's equivalent product here (can't get the Minwax stuff) and it's great for applying fiberglass cloth to foam. Film will stick to it easily, but not to oil based polyurethane.

Hi Sonny I did not mention your name but your two new planes look great.What I don't understand is all the above mentioned problems with pc as the top coat will also happen with dope.If you have a spill of raw fuel on your plane and let it sit it will get soft very quick. I had a plane sitting upside down on my leg as I worked on the motor and fuel leaked from the tank. When I turned the plane over the finish was soft and some came off on my pants.I now plug the uniflow if I am working on the plane tunned over.I have a almost new repaired plane that is ready for a new top coat and I will top it with PC this week and fly it next weekend at the club meeting and we will find out how well it works short term. The combat plane I mentioned above had a lot of raw fuel on it as it was a upright motor and a open tank.I don't believe any dope finish would have taken that abuse any better than the oil based poly did.I believe Tom Dixon found that it was not a good long term finish but it looked good for over a year.Also repairs were hard to do as the mixing of different products.The new water base pc may solve some of these problems.ANYONE please feel free to give us your comments about pc. Sonny and I will be watching his new planes real close to see how it works.His planes really do shine and these are hand painted.
Ed

LAST EDITED ON Apr-19-04 AT 08:00 AM (CDT)
 
I have been using Poly for the last six months, but never as a top cote. Basically, I have been using Nitrate to attach the silkspan on solid surfaces, I do my filler coats with dope. After I have filled the silkspan I brush on two thin coats of Poly as a base for paint. After the Poly dries, the finish prior to painting is super hard and has proven to be durable. I have found that Rustoleum doesn't stick to dope very well, but it adheres to the Polycrylic perfectly.

I have never seen any paint other than auto clear-cote that can stand up to raw fuel sitting on it for extended periods of time. However, I have done some test with the Poly and even raw fuel being wiped over it seemed to soften the finish. I’m very interested to see how Sonny’s planes hold up over an extended period of time. So far so good, they are beautiful!

I have only tried Min Wax Polycrylic.

Some brands of water-based polyurethane(Min Wax Polycrylic, Olympia) are NOT fuel proof. Even just exhaust spray will make them turn soft and sticky after awhile.

Other brands were relatively fuel proof- Varathane and Carver-Tripp. Haven't been able to find them locally lately though.

Buyer beware, and test the blasted stuff first.

That said, if you have some fuel proof polycrylic it sure makes a easy to use, safe final finish.

Yeah, just the oily exhaust turns Red Devil water based poly into goo.

Oil based polyurethane is, on the other hand, quite fuel proof. I found a couple of spray cans of the stuff cheap at Ace, and used it on my latest plane, and it's holding up nicely. But it isn't as friendly to use as the water based stuff, though since it is in a spray can it is fairly easy to apply and there was no brush to clean. Supposedly yellows with age, not a problem on this particular plane, since the underlying paint was yellow rattlecan lacquer (the local version of Krylon).

One unpleasant discovery I made a while back.. Malaysian brush-on oil based polyurethane melts foam. ^#^%&*^&6#@$%^$%^&^&!!!!