Non-dope sealer for polyspan?

I will be using polyspan (which can be adhered with water-based glue)on the open bay wing areas of the plane I am building. Is there a sealer I can use on the polyspan other than dope? I am striving for as solvent-free a finish as possible. The plan is to use thinned Titebond II and silkspan for the balsa sheeted areas as per Jim Thomerson, water-thinned spackling compound for a filler coat ala Tom Dixon, water-based acrylics for color, and water-based urethane for the final clear coat. The plane will be diesel powered. (Go figure.)

Well,

You can try the Minwax Polycrylic water base clear as base coat, but I don't know how it might sand over any open bays though. I believe it should work very well over straight balsa though. If you do use it, it gets very hard and is hard to sand. Be very careful that you don't sand through the polyspan on an open bay. The only way to fix it is with a patch of silkspan or another piece of polyspan. I have used a good bit of polyspan. You need to be very careful when attaching it to and shrinking it around compound curves on wingtips. It can be done with perseverance however!

I have been experimenting with water based polyurethane (Varathane Diamond Finish) over Polyspan for about a year now. It's a little too early to comment on the longevity of the finish but it does go on virtually odour-free. I used the satin finish (not gloss) as the base coat and found that it sanded out marvelously. You do have to watch out when sanding over wing ribs and so forth because it is very easy to sand right through. It's rather weird stuff - you open a can of clear and there's this milky looking liquid and a lot of solids on the bottom that you have to stir up before using. Something like old fashioned shellac. Once stirred up it works like a charm. I've even made grain filler by mixing talc into it. I also use it to put 1/2 oz. glass cloth on over sheeted areas. A lot quicker, easier, lighter and a ton less messy than epoxy. It loves humid weather, the water vapour in the air makes it cure and it never blushes. It seems to function like a low shrink dope and does tighten up the Polyspan somewhat. I'm just now starting to use the coloured stuff. Although the range of colours is limited the price is pretty good. Try it out and see what you think.

>I have been experimenting with water
>based polyurethane (Varathane Diamond Finish)
>over Polyspan for about a
>year now. It's a
>little too early to comment

Dave;

How are you applying it (brush or spray) and what is the weight added from the finish? I am also curious as to how many coats it takes of color for good coverage.

Bob,

I've been putting on the clear filler coats by brush. It probably takes more coats to fill than dope because it's very thin - once mixed up it flows pretty much like water. But then I don't really know since I've never used dope on Polyspan. The clear seems to be very light weight. I think the colours are a different matter. First, they're very thick, and the label warns against thinning. After a little initial work spraying unthinned I sent an email to Flecto customer service explaining why I would want to thin the the product and was told that thinning with water (I used distilled) was acceptable, more than that and the gloss starts to go. I suspect that for our purposes, if putting a clear coat over it, we could thin more than 20%. I've done only a small amount with the colours (cowl for a Magnum)up to now. That consisted of making a light gray blocking coat by mixing a small amount of black with white and after that was dry, spraying it black. My spray gun is very basic so you don't need megabuck equipment to handle this stuff. I sprayed the cowl without thinning (followed the label) and it took a lot of pressure. In future I will thin it considerably. Fortunately I have a bunch of reproduction black ladder-back chairs that need refinishing. By the time I'm finished with them I should have all tricks to handling this stuff completely worked out.