eroc144

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Folks,

I recently started finishing my fully-sheeted planes with epoxy resin, and am having a hard time getting a relatively flat surface after applying the resin but before sanding. In most cases, I end up with small pits and pockets, kinda like the cheese on a pizza. I've tried spreading the resin real thin and glopping it on heavy but still end up with moon craters or ridges that need either a lot of sanding or second coats of epoxy. I sand the balsa surfaces prior to applying the epoxy, and am flying 1/2a planes so I don't need fiberglas for strength.

Any thoughts or comments are appreciated!

EG

Campy

My Feedback: (1)

What you may want to try is applying a fairly heavy coat of resin, then cover it with a plastic wrap (or the backing from Monokote). Then carefully squeegee out the excess resin. When the resin has cured remove the plastic wrap.

It is a little late for this plane, but you may want to look into the "polyurethane method" of glassing for future planes. About 60% of the strength of resin, but only 1/2 the weight.

Chip_Mull

My Feedback: (1)

You're using too much epoxy and it's not thinned. You only need one coat to attach the fiberglass cloth. Thin the epoxy resin 50/50 with 91% alcohol. It IS available but you may have to ask the druggest for it. It has the least amount of water and works the best with epoxies. After mixing the epoxy with the catalyst allow it to sit for a couple of minutes (you should also be using 30 or 60 minute epoxy). Then thin the epoxy 50/50 with the alcohol and apply only one layer.

Instead of filling the weave with another coat of epoxy, use a product called FC-900 from http://www.stits.com this stuff is solvent based and is a great filler. It also sands well. this will eliminate your clumps and will sand much better.

da Rock

Better bet is to drive past the drugstore to the hardware store. Buy DENATURED ALCOHOL if you must use alcohol. Denatured is 100% alcohol. No water at all. The 91% rubbing alcohol is 9% water, right? Water does not evaporate out as fast as epoxy cures and it winds up "rubberizing" the cured resin. Denatured alcohol is not expensive. I've got a can from 2-3 years ago.

Best bet is to pass by the denatured alcohol and get acetone. It says on the can that it's for thinning epoxy..... for what???? for thinning epoxy, yup. It's not very expensive either.

Hardware stores are everywhere, right?

Now........ all that said, let me suggest a trick the control line guys been doing since forever.
Spread the mixed epoxy around on the wing with a playing card. The technique presses the perfect amount of epoxy into the wood fibers and leaves a relatively dry surface behind. It's dead simple to tell where you've "carded" and if there's enough epoxy there or too much. If there is enough, the wood will look damp. If there is too much, it will look shiny. Throw the cards in the trash when they start to fray. If you have a shiny surface, pull out a new card and "scrape" the surface.
It's dead simple to do and amazingly "self controlling". The precision aerobatics guys did it for years, and nobody makes models that light, that strong, and that'll turn through those G's without blowing a wing.

jetpack

My Feedback: (1)

Cheap aerosol hairspray sprayed onto the wood before you glass helps seal the wood also, lessening the amount that gets soaked into the pores and lessens the amount of resin needed also.

eroc144

My Feedback: (1)

Thanks Guys! I'll buy some denatured alcohol and saran wrap and give all of these tips a try... on some scrap balsa!

EG

saramos

Here is the method I used on my TopFlite Spitfire. I am pleased with the results.

Prep. I sanded and filled any imperfections I could find with a final sanding with 320 grit. I then gave everything a coat of Deft Lacquer sanding sealer.
After the sealer was dry, I covered the area with .5 oz glass cloth and used a drafting brush to smooth it out and give it some cling.
I used West Systems epoxy diluted with 1 part denatured alcohol to 4 parts epoxy. This just slightly thinned the epoxy and eliminated any bubbles in the epoxy that formed during mixing.
I mixed one ounce at a time using the West Systems metered pumps.
I applied the epoxy using an acid brush. I would start in the middle of the cloth and work outwards to avoid wrinkles. Once covered with epoxy, I used a small body putty spreader to squeegie off as much of the epoxy as possible, once again starting in the middle and working outwards, wiping the excess epoxy off the spreader with paper towels.
Next, I took a roll of toilet paper and rolled it over the surface. As the paper loaded up with epoxy, I would discard some of the paper, exposing new paper. I did this until the surface lost all its gloss.
Once the glass cured, I applied a high build sandable primer and wet sanded most all the primer off, being careful not to sand through the glass. I repeated this process until the surface was smooth and the weave of the glass was filled. Then I filled any remaining low spots and sanded until the surface was smooth and level.
Panel lines were added using chart tape and primer and is now ready for paint.

Scott

bfd04

Here is a site I use regularly, it is not an RC site but has some good ideas, that you may be able to use in this hobby also. Has good tips on painting and finishing also.

http://www.info-central.org/index.cgi?construction


John

the-plumber

Last year we hired a new tech, and it turns out his wife is a chemical engineer. She came to the office one day for some reason I never knew, and had to wait for her spouse to get back from a service call, so we all yakked a while. I asked her which was better for thinning epoxy, denatured alcohol or acetone, but she said she had never worked with epoxies.

Couple of weeks later to my surprise she called and told me she'd researched the question I posed (I'd forgotten about asking) and said that acetone is the thinner du jour for epoxy, not denatured alcohol. I _think_ I recall her saying that acetone is not hygroscopic, and therefore doesn't absorb water or water vapor, which can be an issue with alcohols.

FWIW.

As for 'glassing with thinned epoxy, I use 7" foam paint roller covers from West Marine. I cut the foam roller covers in half on the band saw and load 'em on a 3" roller - makes it a good bit less 'clunky' than a full size roller. I give the roller frame a wash in denatured when I'm finished, so it's ready to go next time. Very good _even_ coverage of the thinned epoxy with no pin holes at all.

marwen1

My Feedback: (6)

Hi there Fred:

U R 100% right ON!

For the longest time, I scrambledall over my city looking for DENATURED ALCOHOL. Shucks! Noone even knew what it was let alone having it.

I know from years gone by, ( while I lived in the US) I could go into any pharmacy and ask for a quart of just that. Five minutes later, I had what I went in for.

With a non-souce of availability up here in Canada, (practicaly), I did my share of reseach on it. The feelers went out and a local professor from the University here in Winnipeg, was an avid Rcer. He jumped into the whole conversation with my thread.

ACETONE, over the counter (if you will) about $6/litre at Home Depot.

I find that I make the finising epoxy mixed the way it sould be, 1:1 -- and I use a hypo to pull out 50% of my acetone (for accuracy) --- mix it up and VOILA! the rest is total history. SMOOTHE as silk

marwen

Square Nozzle

My Feedback: (1)

One thing that may have been missed here is the previous coat of epoxy has to be sanded before the next coat goes on. The cured epoxy has a "wax" film on it when it cures. If you don't get that film off, the next coat can't bond and will usually "fish eye". I experience this many times when I'm sealing the interior of one of my racing boats.

bipeaddict

Here is my technique

- Sand all surfaces with 150 grit. Fill all holes and imperfections. Sand with 220. Finish off with 320 grit.
- Mix up West System 3 - 207 hardner and resin This is a special hardner that is slow and thin.
- Lay down .56 oz fiberglass cloth.
- Apply your resin being careful to saturate the cloth and underlying surface.
- Take a roll of toilet paper and roll across the surface soaking up all the extra resin. The fiberglass will appear to be dry but their is plenty of resin left
-Let dry.
-Knock off all sharp edges with 320 grit. Don't sand through the fiberglass.
-Mix up West System 3 - 2007 hardner and resin (105).
In a ratio of 2.5 parts micro-balloons (West Microlight) to Hardner (207) and Resin (105) mix up your weave filling paste. This paste will be nearly the consistency of almost peanut butter.
-Apply the paste to the fiberglass. Although thick it is a slow cure so it will flow and form a smooth surface.
-Let cure.
-Get out your sandpaper starting with 150 grit and sand it off. The low spots will now be filled. The weave will be filled.
You will have a surprisingly smooth surface.
- Apply your primer (Klasskote Epoxy Primer). Sand it off. Only the low spots will be left.
- Get out your squadron green putty and fill and pinholes and imperfections.
- Sand whole structure with 400 grit.
- Spray on primer (Klasskote Primer). Sand with 600 grit
Paint.

Be sure to use sanding blocks when sanding. This will keep the low and high spots from appearing.

jetpack

My Feedback: (1)

As a new boat builder and one that has never fiberglassed before, I would like someone that has, to tell me if something like this is possible or should even be attempted.

The hull in the picture is a 36" hydroplane. I wouldn't know where to start with cutting the cloth on something like this, but it actually could use fiberglass. Wood boats, due to them being quite solid, tend to develop cracks from engine vibration and eventually open up.

Every corner needs to be kept as sharp as possible for it to be a "clean" running hull. Any suggestions? Would not putting any glass down be the answer? What steps are required just to use epoxy and get a glass smooth finish with all the tight corners? How do I keep from ending up with a blob?

jaka

Hi!
The pictures looks to be a finished boat...not a boat needing any glasfiber..?!

Regards!
Jan K

jetpack

My Feedback: (1)

I asked if something similar could be considered.

jaka

Hi!
Of course...Boats like the one in your picture are always made of glassfiber ...never...or at least very seldom made of wood. Glassfiber is much more durable than wood and very exotic shapes could be reproduced. 24 hour epoxy should be used or polyester resin, but 24 hour epoxy resin is stronger. Use a professional 24 hour epoxy, not the stuff you found in hobby shops as those epoxies are not that good. West systems epoxy are fairly good but there are much better 24 hour epoxies available if you just search the market

Regards!
Jan K
Sweden

yakman

methyl-ethyl-ketone(MEK) is the general thinner for epoxy. Dimethyl-ketone(acetone) is fine.

jetpack

My Feedback: (1)

The idea was not to make it out of fiberglass, just to skin it with fiberglass so nothing splits.

gsmith6879

My Feedback: (37)

Quote:

ORIGINAL: Chip_Mull

You're using too much epoxy and it's not thinned. You only need one coat to attach the fiberglass cloth. Thin the epoxy resin 50/50 with 91% alcohol. It IS available but you may have to ask the druggest for it. It has the least amount of water and works the best with epoxies. After mixing the epoxy with the catalyst allow it to sit for a couple of minutes (you should also be using 30 or 60 minute epoxy). Then thin the epoxy 50/50 with the alcohol and apply only one layer.

Instead of filling the weave with another coat of epoxy, use a product called FC-900 from http://www.stits.com this stuff is solvent based and is a great filler. It also sands well. this will eliminate your clumps and will sand much better.

I just tried Chip's method of priming the glassed cloth using Stits FC-900 and it works better than anything I have tried to date. I applied my .58 ounce cloth with unthinned West Systems epoxy. I use the toilet tissue roll method of removing every drop of excess resin. I just keep rolling the surface and discarding the saturated paper until the surface looks dry. This method also presses the cloth firmly down on the wood surface. Let it cure overnight and very lightly sand with 320 grit paper and then spray on 2-3 coats of the Feather Coat FC-900 and sand that with the 320 grit paper down until you just start to see the cloth weave and stop. It dries very fast so you can do all this in one session. You can also mix up some of the FC-900 with micro balloons to get a paste filler that applies and chemically bonds to the FC-900 and after it dries sands as easy as the original primer. The downside of the FC-900 is that it is pure white and makes seeing those minor imperfections in the surface hard to see. I have added a little of some black Stits Polytone paint to make it a nice light grey for my use. You might be able to talk F & M into tinting it for a small fee?

Much less work, very light, and very nice final finish.