Fiberglass resin not setting up on cowl

[Webb]

Here are the results of getting this @^@%$@%@#%$ off.

Scrub down with Dawn - Didn't phase it. Although it is supposed to be water soluable, got news - it doesn't wash off.

Wipe with acetone after a scrub down, 50% reduction in sticky.

Water sand - 90% reduction in sticky. Much better but can't tell how smooth due to water ripples.

Dry sand after wet sand. Perfect with no sticky.

Bottom line. If you have an amine blush, get out the hose and wet sand. Allow to dry and then finish up with some dry sanding to catch any irregularities in the epoxy.

Glad I only tested this on the top cowl outside. Due to the time constraints, I've ordered Loehle's aerocoating which fills in the pin holes. Sand it, rub in on, wipe if off after dried, and shoot paint. Will use on the top instead of a second round and once on the bottom.

We all learn from others issues. Take note builders - bypass the thinned epoxy and spend 50 bucks on the Leohle product and be ready to paint in 1 hour. My time is worth more than the cost of a quart of space age filler.

Webb
RV7A - N32WW

[rocketbob]

All of the race shops here in Indy that I've been to that do composite work exclusively use Shell 862 epoxy resin. Its not uncommon to see a 55 gallon drum of this stuff in the corner. Its half the cost of West Systems, longer pot life, and wets out better. A friend of mine gave me a gallon of this stuff out of his drum and some hardener and I won't go back to West Systems. Not as convenient to mix up as the West Systems but I do like it better.

www.avtcomposites.com is the local supplier...

[DanH]

Webb,
Based on your description of the removal process, you had uncured epoxy, not amine blush. Two possibilities:

Did you ask anyone at PTM&W about thinning Aeropoxy?

Which hardener did you use? There are three choices, and two of them do not fully cure without additional heat in the case of low mass applications:

http://www.ptm-w.com/dynamicdata/dat...20bulletin.pdf

It is an designed property, probably to lower the chance of exotherm in thick structural layups. All epoxy is not the same, just like all aluminum is not the same. It is important to read the technical material.

[RVadmirer]

Have been around a fair number of composite builders and never heard of anyone "thinning" epoxy with acetone. Never had a need to. What do the manufacturer's say about this?

[Webb]

Originally Posted by DanH

Webb,
Based on your description of the removal process, you had uncured epoxy, not amine blush. Two possibilities:

Did you ask anyone at PTM&W about thinning Aeropoxy?

Which hardener did you use? There are three choices, and two of them do not fully cure without additional heat in the case of low mass applications:

http://www.ptm-w.com/dynamicdata/dat...20bulletin.pdf

It is an designed property, probably to lower the chance of exotherm in thick structural layups. All epoxy is not the same, just like all aluminum is not the same. It is important to read the technical material.

Dan.
I did have a hardened epoxy layer below the layer but I agree with you. It didn't fully cure. I will do a complete watersand scrub tonight and pretend it was a bad dream and start over. I'll just chalk it up to a bad day. Luckily, this is recoverable and will take a only a bit of time to fix - Not hours.

I'll check out the hardener when I go back out to the shop.

[Jekyll]

I tried the acetone mix with West; it took 48 hours in a heated garage to have a semblance of curing. That was my only attempt at using the acetone. It never really seemed to fully cure even after 3 full days.

I switched to using full strength coats with heat applied to assist the flow. My 1st coat was stippled in with a short bristle brush and then squeegied in to ensure I filled the pin holes. The second coat was applied with a brush (painted on, not stippled) while green.

After 24 hours, the epoxy was good-n-hard. Took the cowling to the tub and scrubbed it with dawn and a green scrub pad (it takes a lot of elbow grease) and it was ready to sand.

No pin holes.

As for amine blush being water soluble...maybe it is but in my experience, that's akin to saying an ice berg will melt in 32.1 degree water. While accurate, I wouldn't get my hopes up on it being quick and easy.

Jekyll

[DanH]

<<I'll check out the hardener when I go back out to the shop>>

If you order a quart kit from Spruce, they send 3660 hardener. You would need about 100F to cure it in a thin surfacing layer. Adding acetone would lower surface temperature initially because of the rapid evaporation rate, which would also condense water vapor on the surface if humidity was moderate to high. That would worsen an amine problem. I have no idea what acetone does to the chemistry, but figure if acetone was good they would have put in there to start with <g>.

I'd suggest System Three ClearCoat if you want a brush-on water-viscosity epoxy for pinholes and surfacing. Good method for small parts like scratch- built gear leg fairings and tail tips.

West with fast hardener works very well using a 3-coat squeegee method at about 1 hour intervals. Slop it on and spread it around. Squeegee off all you can get while holding the squeegee kinda flat. Good method for large panels.

I'll be shooting a primer check-coat on a bunch of parts in the near future and will report on some method and material combinations.

[AlexPeterson]

Originally Posted by Webb

snip

Time 48 hours - shop temp ~ 65 - 70F. And I know the proportions were correct because I mix by scaled weight to the gram.

snip

What's up????

Maybe someone mentioned it, but I didn't see it. Most epoxies are mixed by volume, not weight. Perhaps your system says to mix by weight?

Amine blush will wash off with soap and water quite easily, so I agree with a couple others who have said you have some under curing going on.

[Ron Lee]

Alex, the epoxy I have has mixtures for weight and volume.

[Webb]

Got to tell you guys that I think that everyone is a bit right here.

I have a bit of amine blush. It does come off easily with wet sanding. It doesn't wash off worth a darn.

I have some uncured expoxy but did put a space heater blowing directly on the cowl. After wet sanding, I can see some irregular areas of hardened epoxy.

I used the hardener that was the 3660 not the 3630 and slow to harden. Verified what was printed on the can. You can bet the farm that I will order the other hardener for some of the other jobs. I would like to paint the inside of the cowl with a coat since oil does get there and it would make for easier cleaning.

I can tell you what I'm going to do. I am going to wet sand and get that junk off. I will then dry sand to make sure that it is smooth. I will then use the Wonderfil product by Loehle which I tested out on a piece of lower cowl. Rubs on like paste wax. Allow to dry, buff off, and then shoot with primer.

I will also cuss like a sailor during the whole process, have a huge belly laugh, scream just a bit, drink at least a beer or two, and then smile from ear to ear because when I'm done, I'll be almost finished and thinking about how close I am to not renting those tin cans that you always wonder if they'll make it for one more flight.

What a PITA but what the hey. Ending the day on a good note, the airport manager called today and they have a T hanger for me on May 1st. I've been on a waiting list for over a year and the timing is perfect.

One last thing - I have to tell you folks that I really appreciate the help and the fact that it was handed out without kicking a guy when down. One very good thing that this will have helped someone not go down that road.