STIHAC

hallo,

question about poly-u.
i want to use poly for glassing my pica spitfire and i did some checking on rcu. i found people use water based or laquer based poly-u. anybody used oil based or is it the same as laquer?
please help.

stihac

dant-RCU

My Feedback: (3)

As far as I know, all poly-u's are either solvent or waterborne. Solvent borne (or "oil" as most refer) poly-u's may tend to yellow on white or very light surfaces (most cans even state something to this effect). Good waterborne's do not.

I use waterborne poly-u for glassing and fuel proofing BUT I ONLY use Flecto Varathane Diamond Wood Finish as it is a floor covering and is hard as nails. I don't waste my time on the cheaper stuff like Minwax, Deft, etc. They tend to be too soft, don't sand that well when you get two/three coats on the glass and don't hold up to nitro based fuel very well.

I am sure the solvent borne would work as well but it is less forgiving to use (you need a solvent to clean it up or correct some "ooops"), has a very strong odor (probably need to glass outdoors), is not safe to use around open flames (like the water heater in the garage), and it can make a mess if you get it (or spill it) where you don't want to.

My experience only here.....

Dan

A.T.

refer to the help listed under:

Fibreglass, Carbon, Resin Molding & Casting Cowls, Spats,Canopies etc. =

Composites Information
Covering Models With Fibreglass Cloth by Jim Ryan
Fibreglass Techniques & Information
FibreGlast.Com
How To = Ironsidz
How To Articles = The Composite Store
Model Car Tech - Resin Casting etc.
Molded fuselage pictures
The Cheap Little Sucker - make a vacuum pump
Vacuum Bagging Wings
at:
http://homepages.ihug.co.nz/~atong/
regards
Alan T.

Tmoth4

My Feedback: (1)

I glassed my last couple of planes with Minwax water-based poly and it worked out well. But you have to seal the wood somehow to keep the first coat of WB poly from raising the grain. Thinned epoxy or Deft clear finsh work but the solvent odors might be a problem. At least it's only one coat. Don't use an oil-based sealer to seal the wood, the WB poly won't stick as well.

I glassed a plane entirely with Minwax oil-based polyu once but it didn't apply as well as the water-based. The water-based seems stickier.

The Varathane clear mentioned above sounds like something worth experimenting with.

Jim

STIHAC

hi ,

thank you for your reply. this will help.
stihac

dainjarouz

I wanted to know what kind of wax i would need to fuel proof a big peice of plywood. I plan on using this plywood to keep my driveway from getting oily when i tune my plane at home. thanks.

rchazey2

dainjarouz


I would use Minwax quick dry Polyurathane. I comes in a silver and black can. Dries quick and is very fuel proof. I had 15% nitro sitting on a test board for 48 hours and poly did not even notice.

ProfLooney

I did a complete areticle on glassing with poly U and its properties. http://home.mchsi.com/~jahuntley/help.html its the link right under the word nav bar. One thing to watch about the oil based is the compatability to paints. we all know what happens when we try to paint over oil. be safe and use either the water or laquer based which dont leave a residue which will cause the paint to flake off over time.

joe

NE0

My Feedback: (9)

Can you use Deft Sanding Sealer to seal the balsa before applying the Minwax WB poly? Will the WB poly stick to the Lacquer sanding sealer?

Neo

ProfLooney

It should NEO as sanding sealer still leaves woodgrain fo it to get into and stick. the purpose of sanding sealer is just to close the little "straw" ends of the wood so they dont keep sucking in liquids but the deep grain of the balsa will not be filled. be sure to sand between each layer of sealer usually 2 to 3 coats will do it. what it will do after each coat is make all the loose hairs on the outside of the wood stand up giving it a rough feel. just knock this down with some 320 or a scotch brite pad and add another layer repeat then start glassing or add a 3rd layer. this will also harden the sheeting too making it stronger.

Joe

NE0

My Feedback: (9)

ProfLooney,

Thanks, I'm doing a test on 2 identical 7 x 7 pieces right now. I'm using the Deft Lacquer Poly to glass one, and the Minwax WB Poly to glass the other. This way I can compare the characteristics, ease of application, and weight between the two.

I'm weighing them every step of the way to see how the weight is affected. I plan to test primers, rivets, latex, etc. when done.

Oh yeah, I sent you an e-mail with a few other questions.

Neo

ProfLooney

yes i got it and replied neo. one thing i think i mentioned a couple threads ago is watch the minwax since it says OIL based and I would be worried abt getting paint to stick maybe some people here has had experience with it and can tell us how their paint help up on it.

Joe

NE0

My Feedback: (9)

No, the Minwax poly I got is the "waterbased" variety, like k_sonn uses.

Neo

Tmoth4

My Feedback: (1)

NEO,

I'm using WB Minwax clear to glass my Dauntless. It works nice. I sealed the wood with Deft clear laquer. I think the sanding sealer is almost the same stuff. I put one coat on to seal the wood and sanded with 320 paper the next day, then started glassing with the WB poly, 3 or 4 coats of the poly with light sanding between to fill the glass cloth, then a coat of laquer primer-surfacer the next day. Most of the primer-surfacer gets sanded off with 320 paper to get a nice, smooth surface.

NE0

My Feedback: (9)

Tmoth,

Thanks for the info, that's what I'm testing now (see post above) and I think I'll go the route you're going. Those lacquer fumes are unbelievable... sealing the balsa is enough... don't want to glass with it too!

Neo

Tmoth4

My Feedback: (1)

I know. I almost passed out just putting that one coat on. You could seal the wood with dope too but that's just as bad, just a different smell.

NE0

My Feedback: (9)

Tmoth,

How many coats of WB polycrilic are you finding that you need? Also, are you sanding between coats?

Neo

Tmoth4

My Feedback: (1)

NEO,
I put on 4 coats sanding lightly in between. After the first coat I sand just enough to knock of dust specks and fuzz. After the second coat I sand a little more aggresively. The overlaps of the glass almost dissappear. I'm using 3M 320 grit wet or dry sandpaper and dry sanding. 4 coats of this stuff fills the glass about equivalent to 2 coats of epoxy but it feels much lighter after it dries. I also found that it's better to wait a day for the final sanding because the poly "sets up" harder and sands better.
Jim

NE0

My Feedback: (9)

TM,

At what point are you going around and sanding off the excess fiberglass cloth around the edges? I found that after 1 coat, it still didn't look like it would hold onto the wood if a sanded the excess glass around the edges. Waited until after the 2nd coat and it seemed fine. I guess that would mean you'd have to 2-coat one side of the wing before flipping over and doing the opposite side.

I can't stand the fumes off the lacquer test, but I'll admit that the excess glass sanded of much easier/cleaner. It seemed to make the glass more brittle and easier to cut through with the sanding block. Not a huge difference, but noticeable.

I definitely think they both are much easier to apply than epoxy resins, but they don't seem to hold the glass down as well when you're laying down the first coat. When I used finishing resin on other attempts, the glass seemed to lay down and stay down over corners, curves, etc. Both urethanes (Lacquer & Waterbased) each have difficulty keeping the glass down flat over corners and tend to produce more bubbles/wrinkles. Again not a huge difference, but noticeable.

Three coats down on each urethane test now... we'll see how it goes.

Neo

ProfLooney

Neo that is why I mist 3m adhesive as it tacks it down and i never have a problem with it laying down. also remember poly U is a lot lighter weight of a finish than epoxy thus the reason you notice it not laying down as well.

Joe

NE0

My Feedback: (9)

I did the 3M glue mist trick on both, maybe I didn't put enough down, or just didn't get it over the corners/edges down onto the "sides" of the piece. The pieces I'm doing are about 7 x 7 square, but only 1/4" thick. It's going over the edges and sharp corners onto the 1/4" sides/edges that presented a problem. Up on the main/top flat surface there were no problems.

Neo

ProfLooney

Thats your problems the sharp square corners. First on a plane you dont have the sharp corners. Second when glassing a square piece of balsa block like that you have to do some cutting on the glass in the corners. you cant just lay a piece of glass over a block the wet it out and it will lay down. you will have to cut excess glass from the corners before you try to wet it and lay it in place. Kinda like if you was to take a carboard box apart and lay it flat.

Joe

PS you also have to slightly radius the sharp cornersso the glass goes nicely over it

NE0

My Feedback: (9)

Yeah, I kinda figured that to be the case... same as if when you're using Monokote (cutting the corners).

Neo

Tmoth4

My Feedback: (1)

On some of the compound curves I have to cut some slits in the glass cloth to get it to lay down, and corners need to be cut too. I agree the WB poly doesn't seem to stick the glass down tight at first but after a few coats and hardening up for a day or so it's a pretty tough surface. I like it because it's so easy to apply, sands easier than epoxy and you can sand out overlaps better.

Jim

NE0

My Feedback: (9)

Well, I've got all my glassing done, primered, and sanded down ready for panel lines. So far the 7 x 7.5 pieces each gained the same amount in weight... 5 grams (.2oz).

I calculate this area to be .365 square feet. I guess that means that the glassing phase gains .2 oz for every square foot of surface area (not including final primer, rivets and color coats). My best guess is that my SBD has about 20 square feet of surface area which means about 4oz to glass! Now I need to weigh the painting phase.

Both tests seem to have a hard surface, but I've noticed that after 24 hours, I can "dent" them both with my fingernail. I've not noticed this on my previous attempts with epoxy finishing resins. I can only assume that more curing time will make them both even harder. In all fairness, my epoxy coated job was laid down much thicker and has cured for weeks.

My question now is "when is the right time to apply raised rivets?" BEFORE spraying the next coats of primer over panel line tape, or AFTER? I'm ready to lay down my panel line tape, but don't know if I should put rivets down next or after shooting the primer coats?

Neo