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Old Aug 02, 2012, 07:05 PM
Brooklynite In Texas
Manor, TX. USA,
Joined Jul 2008
579 Posts
Discussion
polycrylic vs epoxy

my bird is at the point that I need to consider the surface covering. I am familiar with the epoxy and fiberglass method but what do you know about minwax polycrylic and fiberglass technique. I will not use poly for any structural areas only surface finish.

I applied fiberglass to balsa with the poly and it appears ok but it looks like it will take a lot to fill the weave.

If you have used it please give me some input. It is quarter scale and to have to remove........you know!

your help will be appreciated.
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Old Aug 03, 2012, 07:54 AM
ARFs Are Me
TomCrump's Avatar
Traverse City, Michigan
Joined Dec 2005
11,396 Posts
I have used polycrylic on a few models, using 1/2oz cloth.

I apply THIN coats. I have found that heavy coats take forever to dry, and gum up my sandpaper.

Three light coats are usually enough. High build automotive primer will easily fill any remaining weave.

The poly accepts most commonly used primers. As I stated, I use automotive products.

I must admit, however, that after trying epoxy finishing resin, I prefer that method.
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Old Aug 03, 2012, 01:23 PM
Brooklynite In Texas
Manor, TX. USA,
Joined Jul 2008
579 Posts
TOM Thanks for responding.

I use two coats and squeegee all excess, just to wet the glass and it looked good but it appeared to need bunches of filler which = weight. I don't know if is anymore than what the epoxy requires but I know it isn't as strong.

I don.t know what weight cloth I used, one was thin as silk the other was three times heavier. The thinner cloth looked better.

do you dope the balsa before glassing?

I have heard complaints of surface bubbling in this Texas heat.

your birds look great!
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Old Aug 03, 2012, 01:33 PM
ARFs Are Me
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Traverse City, Michigan
Joined Dec 2005
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Bubbling occurs if the Poly C is applied too thick, or, if it hasn't been allowed to thoroughly dry (at least a week) before paint/primer is applied over it.

Silk like cloth is probaly 1/2-3/4 oz. Anmything more coarse, is too coarse, in my opinion, and would require an excess amount of material to fill the weave.

I have sealed the balsa before glassing.

What are you working on ?
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Old Aug 03, 2012, 01:53 PM
Brooklynite In Texas
Manor, TX. USA,
Joined Jul 2008
579 Posts
Tom

That is the kind of response I was looking for. You answered a lot of questions.
I have a lot of glass cloth and am not sure of the various weights, I need something for comparison.

I do prefer the lighter cloth.

I am trying to complete a Nosen mustang I started many many many years ago.

Click on my avatar name and peek in on my blog you will see it all.

I except criticism graciously so please comment.

I read somewhere of a filler being added to the third coat of polly have you any info?
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Old Aug 03, 2012, 06:21 PM
ARFs Are Me
TomCrump's Avatar
Traverse City, Michigan
Joined Dec 2005
11,396 Posts
I've added microballoons to the 3rd coat of Poly C. Frankly, I thought that it wasn't worth the effort.

I also added light weight spackle, with similar results.

Your Mustang is coming along nicely, and I've admired your Bulldog for some time !
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Old Aug 03, 2012, 07:35 PM
Brooklynite In Texas
Manor, TX. USA,
Joined Jul 2008
579 Posts
Well you have just about summed it up on the polly I will probably use it with caution.

The mustang isn't any further along because of the bulldog and several other builds that caught my eye, I got involved in too many builds at one time and will try not letting that happen again.

thanks for your help!!!!!

Donny
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Old Aug 03, 2012, 08:29 PM
Registered User
United States, OH, Ashtabula
Joined Jan 2009
83 Posts
Hello,

Donny, I like Tom use automotive primers and paints on my planes. All these will go over polycrylic. As far as Polycrylic goes seal the wood first. I use Minwax spray lacquer, their sanding sealer, if you can fine it,or cheap hairspray. You want the poly to fill the weave and not the wood underneath. I usually apply two coats of sealer sanding between coats. This helps to stop the poly from penetrating to deep into the wood which will take more coats to fill the weave.

I also use sealer when I use expoxy resin or polyester resin. Also known as fiberglass resin for the same reason. Saves weight...

Also I have not had any success using fillers in polycrylic, it was to hard to sand.

Rick
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Old Aug 03, 2012, 08:46 PM
Brooklynite In Texas
Manor, TX. USA,
Joined Jul 2008
579 Posts
Rick

Thanks, I like hearing how others have achieve a process. and area I am weak.

filling the surface first was my intent, I do want a nice light finish on my birds.



I'll keep listening
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Old Aug 08, 2012, 09:22 AM
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United States, IA, Rockwell
Joined Jul 2011
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It is of my opinion the poly finish may be a bit lighter at the end of the day compared to epoxy. It is also my opinion the epoxy is a bit more durable. The Cap in my avatar came out a 7 1/2 pounds with an Enya 90 4C. It is all glass and epoxy over balsa with foam core wings. I thin my epoxy a bit (about 20%) to make it more workable (much controversy on thinning) but I have encountered no issues YET I also do not seal the wood first before the epoxy and cloth go on. I want the epoxy to soak in and bond with the wood.

I do need to say I have never used poly and glass cloth. My opinion has been formed from posts here and other RC forums. So, take my opinion on poly with a grain of salt.

Ken
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Old Aug 23, 2012, 11:23 AM
Registered User
Tucson
Joined Nov 2009
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Good discussion. I like the water based polycritic, because ease of use. But it's not going to be as strong as epoxy. And, I've never used it with glass cloth.

I have only used polycritic to seal lightweight aircraft dacron (aircraftspruce) over wood. The clear poycritic yields a finish on the dacron that looks something like the old doped silkspan, but much stronger.

Brushing the clear polycritic will get you drips on the inside of the fabric. You could probably water thin the polycritic and spray it on lightly for a perfect finish. You will see the cloth weave through the finish, if it is light.

If you are looking for strength, I wouldn't try to glass with anything but epoxy. But if you already have the strength in your frame, I like the water based polycritic.

I need to try the polycritic with water based dyes, and sprayed on.
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Old Aug 24, 2012, 02:10 PM
Brooklynite In Texas
Manor, TX. USA,
Joined Jul 2008
579 Posts
Thank you gentlemen!

I am beginning to form a technique at this point and it is as I originally thought.

Epoxy for structural...poly/c for covering. I am not too happy with the poly peel strength but it seems to fill the weave rather well. I will do more test samples before I finalize. I have a lot of nitrate dope and it works very well. we will see!
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Old Oct 16, 2013, 01:31 PM
Rangers Lead the Way
Joined Mar 2010
2,074 Posts
Old thread but worth a resurrection for the experienced replies.

One question: as regards glas over wood using polyurethanes, I am surprised that the seasoned builders are not using oil-based. Seems it would avoid all warping risk and save the weight of, and need for, a sealing coat. Am I missing something here, such as an issue with paint / fill primer adhesion or sanding?

I have not yet used it for covering, but in my woodwork with it, oil-based performs far better than water-based: it is lighter, won't ruin the work, and the surface is harder and tougher. Just my .02 of course. I know this stuff (especially the minwax) is getting harder to find. Varathane (spar varnish) also performs well in my woodwork.
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Old Oct 17, 2013, 07:49 AM
Brooklynite In Texas
Manor, TX. USA,
Joined Jul 2008
579 Posts
ttrotary

I started this thread trying to get more info on surface finishes.

I tried the polyurethane and am not impressed. so I used the old proven glass epoxy method. I am very pleased with the results. It did exactly what I needed it to do, with one coat of 25% thinned resin. the second coating will have a filler probably microballoons. I was surprised by the strength increase of the surface it is so much easier to handle now.

Oil based paints are not used because of weight and fuel proofing issues. I have used Rustoleum with good success but it has problems of it's own.

latex is a popular for finishes when clear coated. this is a subject that can go on forever because of the multitude of needs of different types of models but low weight and high strength are my primary concerns.

With wood working these are not commonly considered.

Notice the picture, only the wings are glassed. the FUSE. will get glassed as soon as I add a few details. The red plane is finished with brushed on Rustoleum.

DONNY
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Old Oct 17, 2013, 06:05 PM
Rangers Lead the Way
Joined Mar 2010
2,074 Posts
Re: Rustoleum: the results (red plane) certainly speak for themselves. That's some great work. No question the epoxy route is the only way to go if you want a hardened, strong surface.

My question was more aimed at those who choose the poly route and their choice of poly- urethanes / crylics, as the oil-based polys perform a lot better than the water-based stuff, yet I see them seldom mentioned.
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