CadFlyer

My Feedback: (16)

I have Cub that I want to cover (again). The last time I used Fabric Store "Dress Lining" with Nitrate Dope and it worked really well. However, this time I will use the same fabric but I want to try the Minwax Polycrylic instead of dope. I have a couple questions about this procedure I need help with:

1. Do I apply the PC directly to the wood as to prep it before applying the fabric?

2. After I apply the PC ontop of the fabric to seal it, prime and paint it can I go back over the entire plane with a coat of PC to seal the paint? I will be using (OD Green) PPG Omni Automotive Acrylic Enamel.

3. Can I use PC in the open bay areas of the the wing as well?

4. Should the fabric be wet before applying?

Thanks for all the help,
Cadflyer

Campy

My Feedback: (1)

CadFlyer

My Feedback: (16)

Thanks Campy......... I do have one more question: Should the PC be sprayed on or brushed on with a foam brush???
Thanks,

frugalflyer

I must first confess that I have no experience as to what you intend to do. However I have several years experience in the use of Water Based Polyurethane to cover with fiber glass and to fuel proof over paint. My urgent advice is DO NOT USE THE BRAND, MINWAX POLYCRILIC.
Several winters go I used this brand, to fuel proof over paint of three winter build projects. They looked good until I took them out for the first time. The clear coat had turned goo - ey. My finger stuck to the surface and so did grass clipings. This even happened on a glider and so I know it is not a fuel related problem. I believe the minwax re- absorbed moisture from our humid atmosphere. What a mess. I scraped most of the chewing gum like stuff off with a razor blade and got the last off with soft scrub.
Since then I've been warning all of this problem and have heard from several modellers who have had a similar experience.
I now use 'Varathane' brand WBPU with none of the above problems. Some of my models are now several years old and are still looking good. I am sure that there are other brands of WBPU that will also do the job. but STAY CLEAR of MINWAX.

CadFlyer

My Feedback: (16)

Wow! That is first I have heard of this. Thanks for the tip. However I was only intending to use the Minwax in place of dope. Since I am using Automotive Acrylic Enamel I do not see the need to apply minwax over the paint. How would the Varathane do in place of dope? I was just going to dope the fabric down with the PC or Varathane.
Thanks

dabigboy

Hmmm that's interesting about the PC, I'm planning on using that stuff to seal decals and the paint for ABS parts on my Extra. I've read of several people having good success with the stuff. How long did you let it dry? I get the impression each coat has to dry a LONG time (like over a week) to really seal.

-Matt Bailey

edtded fro tyops............

frugalflyer

My unfortunate experience with Varathane was about three years ago. Maybe Minwax has solved this problem since then. I doubt that they have, as only last month I received an email from another Ohio modeller relating an identical Minwax problem.
On my we site http://geocities.com/wisebrit I have a short how to lay fiber glass with WBPU. I would think one could lay any cloth that way with wbpu as long as it is able to penetrate, though I have not tried it. For open bays, I guess if you fix to the structure first, with wbpu,and let it dry, then you would be able go over them OK.
Re the question on how long I let the minwax dry - Many many weeks.
I built 2 power planes and one glider over the winter months. Painted them with Rustoleum and after a week or so drying painted over with a single coat of Minwax Polycrilic. After completion they set up fine and looked real good hanging in my basement waiting for the spring thaw. On lifting down for the first flight my fingers stuck to the surface so did grass clippings and anything else that came within range. I scraped the sticky stuff off with a razor blade. it was that soft. This is why I pass on the suggestion NOT TO USE MINWAX.
I relate my experience with this product in an attempt to prevent anyone having a similar problem. I'm sure there will be others who will have a different opinion

CafeenMan

Maybe I'm not understanding the question, but using Polyurethane to apply covering to an open bay is not going to work I don't think. Dope is the best choice. Why do you want to use Polyurethane?

dabigboy

Hmmm, I see you do live in OH, frugal. I'm in IN myself. Campy appears to be in CT, I wonder if it's less humid up there? I do know it's horrifically humid here much of the time, perhaps it is indeed related to humidity as you said. One thing, was the PC sticky right after the flight or was it later? I suppose there's a remote chance a bad batch got out and a few people ran across it, but that doesn't seem very likely.

I'm still planning to give the stuff a try as I don't know any better way to do what I'm trying to do.

-Matt Bailey

CadFlyer

My Feedback: (16)

I prefer the poly because it is less expensive and easier to clean up. I have seen poly used on open areas but they were very small areas. The Cub wing has quite large open areas.

Campy

My Feedback: (1)

PC can be applied either with a foam brush or spraying.

What I do is add 1 - 1 1/2 caps of FloTrol to 1 quart of UNDILUTED PC or latex, then I thin it down for spraying. The Flotrol retards the drying time so brush marks disappear and sags/runs are minimized since the paint has more time to "level itself". Latex/PC does not require over 30 psi for spraying. If you need to use over 30 psi, the latex/PC is too thick.

I suggest using water for thinning on clear and light colors. Windshield washer fluid works very well, HOWEVER, it does tint the paint. On dark colors this is not a problem.

I have use MinWax Polycrylic here in CT with no problems - humidity averages 70% during the summer flying season. Perhaps the the problems some of you were/are having was caused by a bad batch of PC.

What I found out using a test panel is:

After letting 2 sprayed coats of MinWax PC dry for 24 hours I poured some 10% nitro fuel on the panel and let it sit overnight. The next day I cleaned it off using Windex and a regular cloth. The PC was a "tad" soft. This could be felt as a dragging on the cloth. Since I do not let the residue sit on the planes, I do not consider this a problem. My oldest plane with MinWax PC on it is almost 2 years old and still looks good. The PC has not softened at all.

Remember, latex/water base PC takes 7 - 10 days to cure ON THE AVERAGE. It can take as long as 30 days depending on the temperature and humidity. A good test to see if it is cured is to press your finger firmly on a hard part of the plane (the cowl is a good place ). If a fingerprint remains, it is not cured. Don't worry about the fingerprint, it will disappear in a day or two.

Capt Jim

My Feedback: (168)

Hey guys....I have no idea where you went wrong with using Minwax Polycrylic, but it seems like such a fine product should not be bad-mouthed due to an individuals misfortune is his own application, or perhaps mis-application. It is only logical that if a product was as flawed as some few individuals describe it to be...it would not be on the market for long...and certainly not under the high quality name brand of Minwax. As for humidity, there are fewer places on earth more humid than where I am in S. Florida right on the ocean. I have been using Minwax Polycrylic and let me tell you...I will never go back to any kind of epoxy or polyester resin. This stuff is the easiest, simplest to use, and cleanup is with water! What could be better. I simply lay my 3/4 ounce glass cloth onto the nicely sanded balsa...brush it lightly into position with a clean dry soft paint brush to help smooth out wrinkles, and this brushing actually creates some static electricity to help hold the very light cloth in place. Once satisfied with the lay of the cloth, simply apply the Minwax Polycrylic onto the cloth with the same good quality soft brush. The Polycrylic will immediately soak through the cloth and get into the wood. You will see the cloth seem to disappear as it wets out with the polycrylic. Be sure to work gently, keeping the cloth smooth as you go. No need to rush, this stuff doesn't "kick-off" like two part resins do. It will form to compound curves almost as easy as spraying paint. Before you have gone too far, go over the wet cloth with a credit card, or a playing card, used as a squeegee. Gently drag the card over the surface...it will drag much of the excess poly' as you go....simply keep wiping the card clean on a rag, or on a newspaper so that you dont just carry the excess poly' with the squeegee. Make as few passes as you can in doing this so as not to disturb the cloth....one light pass should do it...you'll see the difference immediately. The squeegee process further presses the cloth onto the wood as well as removes the excess poly'. Let it dry, which is usually a couple of hours for me. If it is taking longer for you, then you are most likely laying on way too much poly', and that is to be avoided. As with paints, nice thin coats are just what you want to achieve. That first coat is just to bond the cloth to the structure. When it is absolutely dry, brush on a second thin coat. Use a good quality brush so you dont leave brush hairs in your work. Use a good brush technique as if you were applying a finish varnish to a fine piece of furniture. When the second coat is dry, you may lightly sand if needed. Go lightly or youll go right through the cloth and back to the wood. You can then go to your first coat of primer, or some folks do a third coat of poly'. You do not want to add more weight so keep all coats thin. The primer will show you all your defects. After repairing those it's on to the finish paint. If you have reservations about using the polycrylic, as I did at first...try some on scrap pieces of wood. You too will begin to love it. As for applying a sealer to the balsa before starting...I have tried it both with sealer and without. Without sealer, I see no tendency toward warping. The only difference I may have seen is a very slight raising of the tiny hairy fibers of the balsa, but in all honesty, I have elected to skip the sealer, in the interest of keeping things light. My finished surface has not been degraded as a result. I think that this process will become the modelers standard as it becomes more widespread in use. Right now, there seem to be only a few folks using it...many modelers have not yet been educated to this new process, while some are sticking to the old fashioned, expensive, smelly and hard to deal with processes. As the old commercial used to say....Try it...you'll like it".
Jim

CadFlyer

My Feedback: (16)

Capt Jim,
I am with you totally. I have been using this methid now for a while and the more I use it the more I like it. Once completed it looks and feels just like glassing. I am about to use this methid to cover my Patriot. I am very anxious to see the results. I am very much in favor of this.

Capt Jim

My Feedback: (168)

Hi CadFlyer. What have been your experiences with primers over the Polycrylic? I am going to do a latex paint, so I thought a latex primer would be the way to go...and it may be...however my first tests on scrap pieces showed me that the latex primer doesn't sand into a nice fine dust as would be hoped for, (like with balsa-rite or spackling compound) but rather the sanding tended to produce tiny curls of balled up crud. I'm going to get some of the more standard primer to try, possibly a "High-Build" type from the auto paint store. IN fairness to the latex primer, I rushed the job, placing it under a warm lamp to speed up the dry time. It was dry, but surely not cured. That could play a role in the results I experienced.
Jim

CadFlyer

My Feedback: (16)

Well, I have never had a problem using plain ol spray primer over PC. I lay a couple of good coats of primer over the PC waiting 1-2 days between coats. Once the 2nd coat of primer has cured for 3-4 days I lightly sand the primer and go straight to paint and it always works for me. However, this is all done in low humidity and temps around 80-90 degrees. It appears that most people do not allow the PC, primer, paint, etc, etc. to CURE long enough. If some of these guys would wait 3-4 days between the PC and applying the primer they would not have near as much trouble. Give the primer a day or two to cure good and then go to paint and it should be fine. I find that the curing time is the key to having success in any application such as this. As far as the fuel proof, I have never had a problem there either because the automotive acrylic enamel i use of fuel proof when it cures. I did a Ziroli Corsair a few years ago and I did it exactly as I have describe and it turned out gorgeous and it is still looking good.

Campy

My Feedback: (1)

I normally use automotive "high build" primer over the PC. I have not had any problems with it adhering or with sanding.

On a personal note, I prefer the high build primer since it will normally fill in any sanding scratches I may have missed in the sanding process.