invertmast

My Feedback: (23)

I wish he made more colors! For authentic warbird colors in the WW2 era, i love the stuff!

sensei

I see you are going to build a Rare Bear, nice project indeed. Just try to keep the weight down...

Bob

stanj

What would be a european replacement for the Minwax?

vertical grimmace

My Feedback: (1)

Look for water based polyurethane. Minwax is just the brand name. Water based finishes seem to be prevalent these days for Eco reasons. I am sure there is a product across the pond.

T_om

Um, just saw this and wanted to add a bit of a second, and different, opinion..

There is a tremendous benefit to epoxy. It is shell hardness which is probably 50 times greater than MinWax polycrylic and strength. Also please note, Minwax is not a WBPU as it is often (and incorrectly) called in these forums.

Minwax has two supposed advantages over epoxy. One, it is easier to apply for novices. Two, it allows more working time than most epoxy formulations.

Advantage number one goes away after a bit of experience. Advantage two goes away when you realize using the correct resin formulations gives you WAY more than enough time to do any coating needed.

Using Minwax leaves you with a coating that is both weaker and softer than epoxy.

Just my 2 cents.

Tom

stevegauth30

After trying both, I would have to agree with that. I use west systems 105 and 206 and it gives WAY more than enough working time. I'm talking somewhere around an hour. The other thing I like about west is the mini pumps. No measuring and getting different batches. One pump of each and perfect amount. Just my opinion, but epoxy resin is the way to go.

MTK

You removed the most important items from your assessment and ignored certain key facts. The key thing is that if you are trying to make some coating very light, you must make it thin. If you make epoxy as thin as the coatings Bob and I mentioned, there will be no particular advantage to epoxy.

Thicker epoxy sections of good laminating resins will be more ding resistant. But that adds a lot of weight.

Strength in absolute terms (tensile for example) often favors polyurethane. However there are some epoxies (Poly Epoxy from Aircraft Spruce) that have very high tensile strength as high as 12,000 psi.But most are in the 5-9 ksi region. Polyurethanes usually come is at around 10-12 ksi. Obviously overlap quite a bit

Softeness/hardness, again it depends on the formula. Some polyUs have hardness as high as 90-95 shore A points, at least as high as just about any epoxy. I agree that Minwax has a hardness in the 50's and is a bit soft but unless one is about to bash their models in their hanger, it's hard enough. Just be more careful.

Density for either one is rather similar, so section is the key.

The biggest advantage of PolyU over epoxy is abrasion resistance. The material is plain tuff and can take much abuse. Think roller blade wheels here. You will likely not find epoxy in those wheels.

"That's the facts". I use what ever will work in my application. As a material scientist for decades, I know more than most about material behavior and use what's needed. One should not use absolute statements unless one is comparing identical preparations, with one prep showing an absolute clear advantage over the other. Apologies in advance to the OP for taking this thread on this particular tangent

vertical grimmace

My Feedback: (1)

I think there is adequate for your (our) application and best. It is not always necessary to go all out to get very satisfactory results. I have a Polycrylic glass job that is holding up just fine after 3 years, and it gets flown a lot. I use both methods, the polycrylic is just not as messy and expensive.

sensei

I don't believe in sugar coating the truth so here it is... This post is a case of the blind leading the blind and nothing more because in a lightweight topcoat preparation scenario of utilizing a singe ply of 1/2 to 3/4 oz. cloth as we have been talking about there is absolutely no tremendous benefit utilizing epoxy over Minwax, it will in fact dent just as easily as using Minwax, but for the novice there is a far greater chance of a heavier finish in the end. So in short, if you are dependent on strength within your airframe from a single ply of said cloth and epoxy resin then you should give some thought of going back to the building board because you are not done building yet.

Bob

T_om

No facts were ignored. The purpose of any coating over a layer of fiberglass cloth, no matter the weight of the cloth, is to fill the weave. Any additional amount of resin or acrylic coating over that adds unnecessary weight.

Given the proper fill of the weave with epoxy and the proper fill of the weave with acrylic, the epoxy will be both stronger and harder... and the weight will be so close as to be immaterial That is a fact.

Tom

stevegauth30

I'm only glassing my sea fury so as I can paint it how I want, and not have to iron the colors on. Before I ever started fiberglassing I thought it would help to ding proof it, but quickly found out otherwise. Also, I weighed the control surfaces before and after laying the glass and filling the weave, and there was really not much of a difference, although I was pretty determined to remove as much excess epoxy as possible. But that's just me, and I'm still new to this. I say if it works for you and you like the finish, that's all that matters.

T_om

Well, well, well, Bob. I am sure everyone here is appreciative of your genius in discovering the blind among us. And you declare that you are so blessed with insight as to be able to proclaim the "truth" when everyone else is wandering about in the darkness... why, that is truly exceptional. Were you born with that talent or did it just come to you on stone tablets? However, I would suggest some remedial reading is required in your case, perhaps in braille, before pontificating on just who is blind and who is not.

Nowhere did I mention anything about "...if you are dependent on strength within your airframe from a single ply..." or anything concerning airframe strength at all. The discussion was the merits of epoxy vs. Minwax acrylic in a specific application. Finishing preparation. Shell strength and hardness between the two coatings cannot be dismissed so cavalierly. If anyone, you included, believe that polycrylics like Minwax are just as strong as epoxy, or just as hard as epoxy... well, you are welcome to your opinion, however, you are not welcome to your very on "facts".

Tom

invertmast

My Feedback: (23)

OH the good ole Epoxy Vs. PolyU wars.

kwblake

[QUOTE=T_om;11686604]Well, well, well, Bob. I am sure everyone here is appreciative of your genius in discovering the blind among us. And you declare that you are so blessed with insight as to be able to proclaim the "truth" when everyone else is wandering about in the darkness... why, that is truly exceptional. Were you born with that talent or did it just come to you on stone tablets? However, I would suggest some remedial reading is required in your case, perhaps in braille, before pontificating on just who is blind and who is not.

Ya just gotta love that pontification stuff.........

I'm about 10 posts late, but, lets get ready to rummmmmmmbbbbbbbblllllllllleeeeeee.

redbiscuits

My Feedback: (6)

+2 more cents. I have used both methods, and I will NEVER go back to Minwax now that I have done a few planes in epoxy.

The three biggest problems I have with Minwax/Polycrylic
1) It doesn't bond the glass to the wood as well as epoxy.
2) The water-based Poly stuff will swell the wood and could cause it to buckle after it soaks it up.
3) Not near as ding resistant as epoxy, that is a FACT, not fiction!

I could list a lot more, but the truth is, nothing looks as good and is as durable as an epoxy/glass job.

sensei

Got your blood boiling I see, feels great to be alive, doesn't it? Anyway it doesn't matter what matrix you use when applying 1/2 or 3/4 oz. cloth, they hangar rash the same, and they break up in to lots of pieces when they hit the ground the same, it's only a means to hold the swell back down of the wood grain for top coating purposes and nothing more. In this case there is no mythical super added strength benefit from using one matrix over the other. So you see Tommy Boy there is nothing genius about it, I have just applied a little common sense to this scenario because I may not possess your vast composite experience so common sense is all I have to go on, but then again, you never know. With that said the fact still remains that ignorance of a novice is truly bliss..... LOL.

Bob

stevegauth30

Wow, feel the love. If nothing else, there's a lot to be learned here, at least for me.

oliveDrab

Yes - it swells the wood and can cause it to buckle and warp. I tried WBPU on a horizontal stab and have spent an inordinate amount of time trying to fix the buckles, warps, and lumps. Should've used Minwax OIL-based polyurethane as I have done many times before.

Instructor

My Feedback: (16)

There is a lot to be gained from this thread. Either way you do it, 1/2 or 3/4 oz glass cloth will not add any strength to the surface you are covering. The glass is there to give you a smooth and durable surface to paint. It's there to keep the amount of paint you add to a minum. I must say I have never used the Minwax method. I have been using Zap Z-Poxy finnishing resin for about 15 yers and I wont use anything else. It works well and sets up in three hours, ready to sand. One light coat spread through the glass with an old credit card, worhing out from the center to the outside edges. I overlap my seams 1", and I start from the bottom first. Use a single layer of toilet paper, blotted down with a large bundle of paper towels. Remove the toilet paper by pulling it back over itself, and dropping it into a paper bag. After this is sanded, I thin out the Z-Poxy with rubbing alcohol, about 60/40, and brush this on. Sand this with wet 220 and it ready to prime. Sand down the primer until most of it is gone and them add a second coat. Wet sand this with 400 wet and paint. Remember this, the final results is as smooth as the prep. Don't use fillers to fill voids. If the surface was smooth before you started and then you have voids after you glassed the surface, you must remove the extra epoxy you just applied.

This is how I find low spots in a primmed and glassed surface. After sanding the first coat of epoxy, shine a light on the surface and look for shinny spots. These are the low spots. Keep sanding until all the shinny spots are gone. Now you have a smooth surface to prime without using fillers. The fillers are what add the weight.....

Larry

T_om

Hello Larry.

The only problem with your statement above is that it contradicts itself. You say it will not add strength then go on to say it needs to be durable. Strength = durability. See the problem? This confuses a lot of people, like Bob for example, when comparing finishing techniques.

Your finishing regime is fine, but you are indeed adding strength with your resin finish compared to polycrylic. Your application technique is very good and people here with limited resin experience can benefit from your explanation.

The problem with novices like Bob is that they have zero actual composites training combined with very limited experience. If he had, he would not be making the silly statements he is coming up with up out of thin air.

Tom

impulse09

My Feedback: (3)

Can't we all just get along?

rcsws

My Feedback: (3)

With regards to strength, nobody has addressed what type of strength. Are we talking compression or tension? My opinion, glass coating adds a great deal of strength in tension and very little in compression. Try glassing two equal size sticks. When dry, attach both stick to your work bench, one glass up, one glass down. Keep adding weight equally to both peices. I am sure the one with the glass in compression will fail first. The balsa will actually fail first in both cases, not the cloth. The difference being is that the compression will fail earlier.

So the question is, what forces are you trying to prevent. Compression of tension. I would think in a crash, stronger compression. In flight, tension. Realistically, a crash of a magnitude to test the strength of the glass will likely cause a great deal of other damage.

Adding layer of glass cloth on a wing will indeed let the wing take more loading as long as it well adheared and the adhesion does not fail. Heck, using shipping tape on a foamy wing is common practice for tension strengthing. Why would fibreglass not do the same thing. Now if you tried and just did the top of the wing I do not think you will add much in wing loading strength as that would be compression.

As to what to use to attach the glass- go with what you feel comfortable with. My guess is that for what we are doing they all will work.

Okay, enough structure lessons, go fly or build something if the weather will not permit flying.

Oh and as to my background- I am in the demolition business for 35 years. I know how to break things and what makes them break. That, thirty years flying/building R/C, and a few dollars will get me a cup of coffee, but I do not like coffee.

Happy Holidays!

sensei

We are getting along, just having a little fun...

Bob

impulse09

My Feedback: (3)

Some of yall have having fun, I agree.

MTK

Steve, it's a shame that so many of these seemingly easy questions become subjects of pissing contests. However, there is a lot of good information in our posts. Unfortunately you have to wade through the chaff and make somewhat blind decisions on folks' credibility.

One thing certain, no matter how you slice it, if you're gonna use a plastic, any plastic except teflon and polyimide, (epoxy, polyU, polyester, acrylic, dope, epoxy paint, what have you) to bed the covering, they all have densities that are fairly close to each other. So it becomes a issue of thickness. Surface toughness pretty much equals applied thickness. If you want a tough coating it will need to be thicker. It also will be heavier. If you are trying for lightweight, then make the coating as thin as possible that will cover the wood underneath. Thin and tough do not go hand in glove. Would have been nice to have, but is not possible with today's plastics

BTW- in case you wondered, Teflon (PTFE) is the densest plastic available at a density well over 2 grams per cc. All the others range from 1 to about 1.3 grams per cc

Good luck....stick a fork in me, I'm dunn! If you want any more details, contact me (or Bob, "Sensei"?) direct.