Capt Jim

My Feedback: (168)

I am testing this new process where you glass your balsa sheeted model using Minwax Polycrylic in place of the typical epoxy or polyester resin. I have sealed the test balsa sheets with sanding sealer, then laid on the .75 oz fiberglass cloth, and then applied the polyester resin to one test sheet and Minwax Polycrylic to the other, saturating the cloth, and then scraping the excess of with a credit card like tool. The Minwax Polycrylic is much easier and more convenient to use. It is thinner, penetrates the glass and balsa better, levels out better, and of course requires no mixing because it is a one part product...and it cleans up with water. I like it a lot so far. My question is this...what is the trade off...if any...in using the Polycrylic in place of the typical polyester resin, and how could I go about testing these test panels to determine which is really better. So far, the Polycrylic gets my vote on ease of application, clean-up, and leveling for great surface appearance. The sanding sealer is used to help prevent the water in the Polycrylic from soaking the wood and creating warps.
Thanks for your suggestions.
Jim

Campy

My Feedback: (1)

The use of poly instead of resin has some disadvantages and advantages.

As you have already found out, it is a lot easier to use, soap/water clean up, easier sanding, etc.

The glass done with a water base polyurethane has ABOUT 60% of the strength of a resin glassing job, however, it weighs only ABOUT 1/2 as much.

It is substantially easier to sand. In fact, you do need to be careful that you do not sand through since the sanding is that much easier.

You have no fumes, and if you have any allergies/reactions to resin you don't have to worry about that aspect.

The final finish for painting is just as good as a resin glassing job.

If you check through some of the newer posts you will see how I suggest applying/doing the glassing job.

There is also a link to an article by Roy Vallencourt (Top Gun competitor) on using latex to paint with. Latex will also help keep the final weight of the plane down.

Hope this helps.

Capt Jim

My Feedback: (168)

Hi CAMPY. Thanks very much for the comments. I am rushing to finish my P-47 for this years Top Gun, and the poly' just makes things so much faster and easier. I have a couple of test panels done with each and I have been experimenting by banging them with tools only to find that they both dent quite similarly. They both hold up just fine under the beating. Since the plane is totally wrapped in f/g cloth, and the strength really comes from the glass cloth rather than from the resin, I am making myself comfortable with the bonding power of the polycrylic by testing its resistance to peeling away from the balsa. I find that it holds very well...certainly well enough for our applications. I wouldnt build a boat with it though. heh heh. I havent selected my primer or paint yet, but I must do that very soon. One of my friends locally is a writer for RCM magazine, (Art Johnson) and he did an article on Klass Kote paints, and he thinks highly of them...as does Dave Platt. However, I do like the ease of cleanup on the latex stuff, and so I may just opt to use it. I bought a used plane done in latex house paint from Home Depot and although it holds up fairly well under gasoline spills, some of the color will come off when rubbed...as when cleaning the plane at the end of the flying day. I suppose there must be a non-gloss clear coat that would look good on a warbird and further protect the paint.
Thanks for all.
Jim

3dd

My Feedback: (6)

satin finish minwax polycrylic is great for flat ,just use a little 000 steel wool on it after it cures and wax

Capt Jim

My Feedback: (168)

Does the Minwax Polycrylic allow itself to be sprayed, or must it be applied with a brush or roller?
Jim

branded

My Feedback: (9)

I have used both methods throughout the years and settled on one I think is the best. I apply the cloth with epoxy resin and later fill the weave with the poly.....

I find that the poly will warp certain sheeted surfaces (distorts the sheeting) if used as the first coat to apply the glass. Using the epoxy resin seals the balsa adequately to prevent the warping.

The second thing I've found to be a nuisance with applying glass with poly is that it's not a tacky as the epoxy resin and the weight of the wet glass pulls away from the sheeted surface when doing large curved areas such as fuselages.

I use poly (with some microbaloons stirred in) to fill the weave after applying all the glass, allowing it to cure, trimming it and lightly cleaning up the seams around edges, etc.

The poly is much easier to sand than epoxy.

SST

My Feedback: (2)

You can buy it in spray cans at Home Depot/Lowes-type places

Capt Jim

My Feedback: (168)

Quote from branded..."I find that the poly will warp certain sheeted surfaces (distorts the sheeting) if used as the first coat to apply the glass."
Have you tried, and had any success with, using a sanding sealer as the first coat on the raw balsa, in order to protect the balsa from warping due to the water content in the poly?
I tried it with minwax sanding sealer but my results were inconclusive. I applied a very light coat of sealer, but the piece did "cup" a little, but it was 3/32 soft balsa sheet, unsupported by any framing or ribs. I am still hopeful that sealing the wood first eliminates that problem, and that framed up pieces such as wings etc will have enough internal strength to resist any warping....and of course the poly is much more user friendly than the resins, making me want to stick with it. I may have to try another test piece to become more comfortable with it.
Thanks for your comments.
Jim

DamonTX

Jim, I've been doing some testing of my own this week before finishing my TF Arrow. I've got two identical test pieces, coated with sealer and covered with 3/4 oz. cloth. I used the MinWax water based poly on one and Zpoxy Finishing Resin on the other.

So far, I've only got the cloth laid and haven't begun to fill the weave. Since the poly is so much thinner than the resin, its apparent I've got a lot more work ahead of me to fill the weave on the poly part.

I'm tending to agree with branded that maybe the first coat should be done with resin and the weave should be filled with the poly (adding balloons to help with the consistency). This way when I do the final sanding, I'm sanding mostly poly instead of resin. Looks like I'm gonna have to make a third piece for my little experiment.

branded....have you ever tried using poly with balloons mixed in when laying the cloth?
Damon

branded

My Feedback: (9)

Damon, as I said in my post. I've never really had much luck keeping the cloth on the surface when using WBP. If you add microballoons to it it probably would be less effective keeping the glass down.

I only do the last two to three coats of WBP mixed with microballoons. When you mix micro baloons into the WBP you contantly have to mix it in the cup, bowl, or whatever you're going to use otherwise all the balloons float to the top.

Capt Jim

My Feedback: (168)

Damon...did the water based poly' create any warp in your test piece? I found that after the first application of poly' the weave was very very minimal. I'll have to lay on an additional layer to see what it takes to get it even smoother. I am also thinking that if I use a high-build primer...that will do a lot more more to fill the weave and then there is the finish paint. I hate to add unnecessary layers and just create more weight but I just do not know how the succeeding primer and paint will fill it in. This is so experimental, but good experience. Please do keep me up on how your tests turn out.
Jim

DamonTX

branded... sorry I overlooked what you said about applying the first layer. I'll take your advice about not adding microballoons when laying the cloth.

Jim...my test pieces are solid blocks with rounded and cornered edges so I can get a good feel of how things will work. Since they are solid there was no warping. I think I was under the false impression that if I applied sanding sealer then there wouldn't be any warping to deal with. So, my main concern was stopping the balsa from soaking up the resin or poly.
I'm thinking there's no way to create an entirely smooth surface with the resin or poly alone and we'll have to rely some on several layers of primer.

I think it was Caffeenman's website (not sure) but I read that you should expect to do up to 8 coats of primer sanding between each coat. I did do this on a glassed test piece last week and it turned out great after painting.
Damon

Campy

My Feedback: (1)

If you apply 1 coat of a sanding sealer before putting on the fiberglass, I don't think you will have any warping problems. I use the sanding sealer first, and on 1/16" sheeting (Topflite P-40 wing) I had 1 very minor warp. I am still not sure if it was a warp or a low spot I missed.

Do not use the micro balloons or any type of filler when applying the cloth - it will greatly reduce the adhesion. Also, do not thin the poly when applying the initial coat, use it full strength. When you spray the poly later on, I add 1 1/2 caps of FloTrol per quart of UNDILUTED poly. Due to the thiness of the poly, I suggest thinning about 10% with water and see how it sprays, then go from there.

FWIW - I have had my best results spraying latex AND water base poly at 25 - 30 psi.