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Questions from a first time glasser...

Lemmingman

Well Known Member
Hi folks, tonight I did my first glassing on the project. I added some fiberglass to the inside of the wing tips to provide the 1/8" build-up around the edge that mates with the wing. While working on it a few questions came up that I wanted to run past you.

What do you mark you fiberglass cloth with? Sharpies run into the fabric. A ball point just snagged the weave and pulled it. I ended up with a carpenters pencil. It was pretty clumsy, but it made a mark I could see without damaging the cloth.

I am using West Systems 105 and 206 slow hardener. My garage temperature is 83* tonight. I started by pumping 1 pump each into a cup that I threw away. I just wanted to make sure there were no air pockets. I then pumped 4 ea of the resin and hardener. I hand mixed with a popcycle stick for about 3 minutes. I wetted my work and got the layup in place in just a few minutes. I know that mixing the compenents creates an exothermal reaction and it can get warm. But when I checked my cup about 5-minutes ago it was 313* and solid. The mixure had completely hardened. I touched my layup and it is still quite wet, so I assume the heat had the affect of hardening my cup. Is this normal? I thought my pot time was going to be far longer than 10-minutes and I was certainly not expecting a 300* reaction.
 
Sharpies are fine. The ink becomes encapsulated in the resin/cloth and isn't a problem down the road, in my experience. Pencil is fine too.

Regarding your exotherm, you mixed a lot of epoxy in a warm environment. It is hard to control the environment, but you should mix smaller quantities and get the resin applied quickly in warm conditions to avoid a repeat performance.

I've never seen an exotherm burn, but have ended up with a couple that got hot enough to smoke. When that starts, I carry the cup outside and put it somewhere it can't cause a real fire or make a big mess.

And, yes, high temperatures (like your exotherm) greatly decrease the cure time.
 
I've seen epoxy mixing cups that are large diameter and shallow. That would help to keep the epoxy from heating up as much. The thinner it's spread the slower it will cure.
 
2 pumps

2 pumps in the wide (approx3") cups is my limit.
In large layups one can go through a lot of cups. That is ok, the cost of doing business as they say. You can set the used cups aside and once cured you can use the cup again.
Buy lots of cups, sticks, brushes!
You should get and read Burt Rutan's book on fiberglass from the 70's...still great info on basic glasswork. It will explain all this.
 
Once your layup is done, a heat lamp or two for gentle heating is a great way to speed the set up. Don't set them too close. :cool:
I use lamps I bought at Tractor Supply for warming baby chickens and they work great.
 
Be careful with leftover resin. More than one composite shop has burnt to the ground due to careless treatment of exotherming resin. We usually keep a bucket about half full of water in the shop so that small amounts of leftover resin can be poured into it. Larger amounts are left outside away from anything flammable, often with the container filled simply with cold water. Sometimes come back the next day to see the water has boiled away!

BTW, Continuously holding the container of resin in your warm hand while doing the lay-up can also contribute to the heat build up and shorten the pot life.

Clive Whittfield
 
....

BTW, Continuously holding the container of resin in your warm hand while doing the lay-up can also contribute to the heat build up and shorten the pot life.

Clive Whittfield

Yes, but it gives the best indicator yet of when to dump the container in a fire safe location...:D
 
2 pumps is my limit as well, that or pour it on to the layup, distributing it over as large an area as possible right away, then brush it out. But it is better as a beginner to just apply 2 squirts at a time.

My Dad and I decided to reglass his cedar strip canoe. HE bought a quart of resin/hardener (epoxy), we draped the cloth over the canoe and we mixed 'er up - all of it! I was holding the tomato juice can and it started to get warm. Real warm. Oh @#$%. We poured it all out and started frantically rolling and brushing. It was thickening up, dripping all over the floor - it was a total mess and complete mayhem. It did not turn out very well. If we had mixed it 2 oz at a time it would have been a very relaxed enjoyable process with a good outcome. But at least I learned something :eek:

The rule of thumb is that every 10 deg F cuts the cure time in half. The nominal temp for which they quote pot life is something like 70F. So at 83 you were cooking right along. Go slow, use plastic cups from the dollar store, lots of them and have a friend mix while you apply and it will go fast but you won't have to panic and rush - you want to avoid that if you want a good job.
 
Last month I did the windshield faring and the "targa" canopy strip for my M2 with the same West Sys stuff. I mixed my first batch like you did and it cooked too quick. I found 3min mixing is too long, so I went with what I typically do with 2 part epoxies - given that the two parts have different consistencies, when you can no longer see the difference, youre done. Might be a min, might be 90 secs. If you hit it really quick with a heat gun, any bubbles you mixed it come out pronto. But after a while I skipped that step esp when doing wet out - its already got lots of air in the layers to squeeze out so it academic.

I also found that 2 pumps (4 total) is about right for straight batches and augmented batches (ie when adding micro balloons or fairing powder) and I'd get about 15 min working time, outdoor temps in August mid '80s here in the mid-atlantic.

FWIW, my windshield strip is fiberglass but my targa strip is carbon fiber. I didnt do anything different wrt the application and it worked super.
 
A cup of epoxy needs to be well mixed, including scraping the sides, and getting into the corners in the bottom. Don't rush mixing.

Throw the pumps away and learn to use a gram scale. You can prepare any batch size, with any epoxy, at any ratio.

If you must use pumps, mixing in large batches makes small ratio errors less critical.

Do get it out of the cup ASAP. Whenever possible, stack the plies on 4-mil plastic, dump the cup on the plies, add a cover sheet and use a roller to do the wet-out. It gets the resin into the fabric weave while it's least viscous, and it will not exotherm, period. Once saturated, it won't matter if it sits there a while. Even if the epoxy starts to gel, the saturated plies are plenty flexible and floppy enough to drape over a form.

Only time you need to hurry is when the form has many compound curves. The plies must be able to slide around on each other, and shift fibers in the weave. To do that, the the layup has to be shaped to the form before the epoxy gels. Can you say "temperature control"? It ain't gonna happen in a hot shop.

Here I'm going to wrap this entire duct form with four plies of 8.9oz 8-harness, in one piece, at one shot, right after some wax and PVA:

IMG_1174%20800W.jpg


A single ply of fabric being cut to shape as a pattern. This is 8-harness, so forming it around the extreme curvature is no big problem:

Fabric%20Wrap.jpg


IMG_1185%20800w.jpg


With rough shape established, stack it on the other plies and cut them to rough shape also:

Fabric%20Pattern.jpg


A big batch of epoxy is dumped on, and then it gets a cover sheet and a roller session:

Fabric%20Wet.jpg


Peel one side, and transfer the whole layup to the form....

Fabric%20Draped.jpg


....then peel off the plastic top sheet and start wrapping. Best tools are gloved hands, and a cut down chip bush for stippling. 8-harness will wrap very well. A few plies of plain weave tape finishes out the attach flange. A peel ply "bandage" wrapped around the snout ensures the wet fabric doesn't sag away from the form :

IMG_1192%20800w.jpg


Remove the foam, do a little trimming, a little sanding, and ain't that pretty?

IMG_1205%20800W.jpg


You could do the same thing by wetting out four plies with a brush, one at a time, in place on the form, but I guarantee it would not be as easy, or turn out as well. For sure the layup would be far too resin-rich. And yeah, you'll exotherm a few cups while you're dabbing with that brush.
 
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That is some pretty slick looking work! So you stack them up before wetting? I have to be honest, that had never even occurred to me. I thought you pretty much had to do one layer at a time. Would that work for (as an example) the graduated size strips used to fair in a windshield? I don't have experience to know if pieces would slide around and turn into a twisted mess while trying to roll the epoxy in.

I'm about to build a new canopy for my -12, so this is really interesting.
 
That is some pretty slick looking work! So you stack them up before wetting? I have to be honest, that had never even occurred to me. I thought you pretty much had to do one layer at a time. Would that work for (as an example) the graduated size strips used to fair in a windshield? I don't have experience to know if pieces would slide around and turn into a twisted mess while trying to roll the epoxy in.

I'm about to build a new canopy for my -12, so this is really interesting.

Sorry, missed your question.

For a windshield I'd do a wet layup, in place, mostly because I'd want to align the edges of the plies along the tape line on the plexi. It's also an example of a layup which should probably be a little wet (high percentage of epoxy to glass fiber), as we're looking for maximum adhesion to aluminum and plexiglass substrates.

Break.

Regarding exotherm, the classic problem of epoxy curing in a runaway thermal reaction while still in the cup....

Microbubbles are hollow spheres, phenolic (red) or glass (white). Being hollow, they are good insulators. Heat can't escape the cup very well and exotherm can be a real problem. The answer is to get it out of the cup immediately after mixing; just dump the whole batch on a sheet of 4 mil plastic or a paper plate, and spread it out thin. Since it can't trap heat, it will remain usable for the entire normal pot life.
 
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