I have used both epoxy and Poly-c.
Epoxy is normally a two coat process
Poly is, for me at least 4 or more coats to fill the weave.
Both have garnered very good results.
but remember! poly-c is water based, and what happens when balsa is wet? It becomes soft and absorbs the water. This is why you have to seal the wood with some sort of sanding sealer. It will seal the grain of the balsa and the poly with not be absorbed. Use at least two coats of sealer and sand with 400 after its dry.
And best of all......you can finish the entire airframe in a day.
Good Luck

I have been following this discussion since it started, and posted a reply regarding my use of epoxy, since I have not tried the poly. I am still not convienced that poly is worth trying for several reasons. One is the fact that the balsa has to be sealed prior to putting down the glass to avoid soaking up a lot of water, My second concern is the bond between the sealer and the glass cloth. Those advacating the use of the WBpoly don't mention the application of the first coat to ensure the glass is firmly down on the surface, and not floating in the wet poly. I know this can be a factor using epoxy. If the epoxy resin is applied too heavy, and not squeeged out as much as possible, the fabric may float up. Then when sanded, you go through it. Finally, after three or four coats of poly is applied, I assume one still has to sand it down to the surface to remove any imperfections. then you start with the prirmer?

And as was mentioned before, it cures (dries out completely) for a week or more, and continues to shrink for even longer. Not for me. The epoxies mentioned in several different posts all cure chemically, and after about 24 hours, sand very easily, some maybe better than others. There will never be a problem with bonding, as with epoxy that is not an issue. Idon't think anyone here will argue that one. Epoxy will have a harder finish.

As for the difference in weight between a .5 oz glass and a .75 oz glass, I doubt it will really make a noticable difference. The final finsih might be .001" thicker, and that won't be much. What WILL make a differance will be how much you sand either type of finish in preparation for your final color application.

Dash

It may have been mentioned and dismissed, but if so, I missed the discussion. So. my question is why not use polyester resin instead of epoxy for this process? Since we are primarily talkng about surface preparation for painting, and not necesssarilly about adding strength,wouldn't polyester be a good candidate? It cures faster than epoxy and does not warp the wood like water based polyurethane. Boats use it, why don't we?

Thanks.

regards,

Richard

Well, PolyC cures also "chemically" The correct word is exothermically for curing resins.
Second, PolyC is water based not made out of water.
If you are concerned about "water" then use the lacquer based form...
The curing is not an issue, because there is prep work to do before the final paint. You can apply primer within a day or two.


Further - shrinking? My P-38 is still the same size before and after I applied PolyC[8D] And there are no cracks...come on. The Eifel tower shrinks by 3 feet in the winter - and PolyC may shinks a 10.000th of an inch.


Dash, try it. Take one piece of balsa sheeting and try it - you will be surprised!






As I stated in my first post, the hard core Epoxy Guys will come and praise the ultimate method.

Mainly about the weight

I used the polyC method last year on my pusher CF-188. I had to seal the balsa surfaces first against the water based polyC. It took several coats to fill at least 6. It is best use talcum. I used 75 oz. cloth. I generally found the surface wasn't very hard and is easily dented. I haven't tried an epoxy method yet, but one of the other club members swears by the West System.

I did find that the polyC had enough of an odour to not want to apply this in the house in the winter months.

Jim

While I haven't tried the WB Poly method I have used both Epoxy and Polyester resins. If applied correctly there is very little weight gain to the over all finish. The best method I have found for applying the resin is using a small roller. The its simplay like painting your wall. There is no need to scrape off the excess because there isn't any. Two coats and your good to go.

Tom Pierce's use of WB poly works but to me it doesn't sound like much less work if you have to seal the balsa and then sand and then apply 4 or more coats to get a proper surface.

But there are many ways to accomplish the same result in a finish. As to what's best is oft a matter of opinion

Oh wow - we agree Cool...

And you what they say about opinions, and what they are like? Everyone has one!

Regards,

Richard

Ok i think this is the rub for me. I dont know how to apply epoxy and after building a wing etc i just dont want to risk it. I need somthing thats idiot proof. Now with that said i use west for makeing parts so if i did try epoxy thats what i would use.

tfarmer, If you use a small roller as I suggested in my last post you don't hafta worry. If you can paint a wall with a roller then you can apply the Epoxy to the wing. The LE and TE are put down using a small acid brush or similar object.

I have a spitfire that will soon be ready for glassing i guess i should try it out. Atleast that way i can know for sure if its not for me.....

I am going to try it first on a sample basis with a simulated built up fuelage and wing section. I have used silk/dope, silkspan/dope, Monokote, Sig Koveral/dope, Solartex/WBPU, and dress lining material with dope and with WBPU, but am always interested in new (to me) covering/finishing methods.

Richard

For my perspective, what ever you like to use is the best whether it be Poly-C or Resin. What ever works best for you is going to be the best product for your covering job.
Personally I have never covered a balsa plane with glass before so I don't speak from experiance.
I do speak from fiberglass experience in general though. I was in fiberglass fabrication for ten years.
I do have a project coming up, TF Giant Corsair, that will be glassed.
I will be covering it with epoxy and light cloth. Epoxy and glass will make the plane stronger, there is no two ways about it. It is physically impossible for the glass/balsa combination not to be stronger. When you apply the resin to the glass the resin soaks into the wood making the glass, resin and balsa a single composite. No wonder boat builders have used balsa as a core material for decades and still do. Epoxy itself is superior because it has physical strength properties that the others don't. Here again boat builders use epoxy to add strength in areas under decking and such.
I understand that the motive here is to cover the plane to get a good paintable surface but epoxy and glass do add some strength to the balsa.
Applying just enough resin to make the glass stick and conform so you don't have any air or resin bubbles. Second coat fills the weave, then you can use primer finish.

A good number of guys approach the problem of applying the right amount of resin from a slightly different angle.

They apply the resin to the glass on the model using any method that seems right. Then to insure there isn't too much resin they roll the surface with a roll of toilet paper. Put down a layer of paper. Soon as it's down, peel it off and it takes some excess resin with it. Trash that and roll it again. When it looks uniform and looks like no resin is puddled anywhere, you're done. You got a lot of resined toilet paper in a pile, but no excess on the plane.

Like almost everything in our hobby, you gotta get the feel for the job. But it works once you got the hang of it.

poly resin is inferior to epoxy, but it's cheaper. It's still strong enough for our toy airplanes, though.[sm=tongue_smile.gif] If you're applying the glass to wood, you can use poly, but not on foam, it will melt it.

The one thing I don't like about WBP is having to seal the balsa with sanding sealer, which stinks and could make the glass not bond well.. I hate mixing different products like that.

What I do like is how easy WBP is to use and apply, less mess, and easier to get light in my book

So what if you bought WBP in the rattle can, and apply a very light coat, let it dry and apply a couple more very light.... just enough to seal the wood and not warp it... give a light sanding then put down your cloth and use WBP from the can like normal?

The next thing I glass I would like to try a test piece and see if it works...

2 words. West System. Great stuff.

west system is a rip. I order my epoxy from http://www.uscomposites.com/epoxy.html They sell a thick epoxy (like the epoxy we use for gluing firewalls) and thin layup epoxy. Cheaper than terrible hobbies epoxy, too.

No one uses lightweight fethering additive (west system) to fill in weave?

Interesting thing about cowls and wheel pants from ARF manuafactures, doesn't seem like they use ANY
epoxy, and the structure gets it's strength from some sort of heavy polyester primer or spray, (Alway white
This is then painted with color.

This can be seen anytime someone chips up there cowl or cracks up there plane..

Take a look next time you see one....You would be amazed at how these are put together...

Most of them use polyester resin. Polyester has a distinct smell and you really notice it when you drill or cut the part. The only strength to the whole structure is provided by the resin and fiberglass fabrication. One is useless without the other. The parts are built from a "plug" with one or two layers of glass/resin layup.
The primer is only there to cover imperfections and provide a smooth surface for the paint. It has no structural properties at all. Too much primer and the paint job will crack link crazy.

Regarding the filler:

When you guys mention talcum, do you really mean talc?

A lot of guys reach for common baby powder which is really just cornstarch that's why it feels so light.

I did a search and found this on talc vs cornstarch:

http://webcache.googleusercontent.co...&ct=clnk&gl=us

This describes many properties of each compared including strength and weight. The materials involved are slightly different than what we're using here but I think the principles still apply.

I hadn't realized talc was being debated for long term exposure health issues but it might be worth considering.

Studies using talc on infants indicate that there were respiratory problems induced by the talc. It was recommended to stop using it. I can't speak to the risks amoung the general population.

I use either baby powder or foot powder to thicken up dope. I don't use it in resins or epoxies.

For me, 2 coats of Envirotex and then 2 coats of Poly-C, wet sanding between each of the 4 coats. Been doing it for around 15 years now. I suggest you try Envirotex from Menards. A lot cheaper than Z-poxy with better results and ease of wet sanding....it is not gummy like Z-poxy always seems to be.

Jeff

I use diatomacious (sp) earth (DE) as a filter medium in my swimming pool filter. I have often wondered if this material which I think is the fossils of marine crustaceons (sp) would be any good as a filler for resins. It seems to have a lattice or crystalline structure. As with talc, cautions against breathing it are on the package.

It dates me, but we used talcum powder (baby powder) on our bamboo slide rules to keep them sliding fast. You could tell an engineer geek by the baby powder smell on his slide rule.

Comments please. Thanks.

Regards,

Richard