Curing Fiberglass resin

[Per Walthinsen]

Since this job doesn't have much to do with electricity I'm more in need of help than usual.

I'm reinforcing the shower pan around the edges and preparing to paint it with some Interlux polyurethane. It was looking unappetizing and had developed a few hairline stress cracks around two of the edges.

Using a heavy-duty fiberglass mat with some Evercoat 499 resin under and over I made a test strip on one of the edges. Mindful of the Scamp debacle I was careful to ventilate and not use electrical devices with switches or motors.

That meant that the temperature was too low, but I tried to play it safe and eventually unplugged the trailer from shorepower overnight. The temperature had finally turned mild, but it still bottomed out at 36 degrees F.

This morning the resin was about as liquid as when it was laid down. I have since dug out one of those oil-filled electric radiator-style heaters which I will switch to 600w and crank the thermostat up completely, which should eliminate any kind of spark-ignition possibility.

Question: since the curing has been delayed from the mixing with the catalyst by more than 12 hours will it cure normally if I apply this heat now, or is there something which demands that the temperature be high enough from the get-go? I will remove the test strip if it coes not cure properly. Anyone with experience or knowledge about this?

I used the FantasticFan in conjunction with a small bathroom fan I recently installed, yet I am still leery of creating an explosion hazard, which is why I didn't use fan-forced heaters continously through the night. Am I being too cautious?

[Dan Quinn]

if it was mixed right it should have set up within about 10 min it sounds like there was either a bad batch or mixed wrong ....

[Per Walthinsen]

Dan:

I've used that resin before, and it has been OK, but the catalyst strength was keyed to 70 degrees, and the temp was MUCH lower, which is probably why it hasn't worked yet. I have now put the radiator in the shower and am waiting for the area to heat up to see what happens.

[Con]

Usually when the resin won't set like that it means your catalyst is old. You need fresh catalyst and you probalbly will have to rip out what you have done and redo it. I have had resin kick of in a matter of minutes even in low tempertatures. I all ways get new catalyst when I am going to do some glass work and I aways add a little more catalyst then they tell you to use. There have been a few ocassions over the years where I tried using outdated catalyst and I regreted it. The darn stuff never did get hard and I ended up tearing it out and redoing it.
And Yes! You are being over cautious about using heaters. The most dangerous thing is the fumes in your lungs. Wear a respirator!

[Loren G. Hedahl]

I would do something similar to what I do when coating a pre-stressed piano soundboard with epoxy in my semi-heated workshop in the winter. Once the epoxy is sprayed on (I spray to get a beautiful piano finish) I tarp it with an air inlet and outlet at opposite sides. Then I heat it with a standard barn heater with a fan piped through a short section of ducting.

I let it blow without heat for a few minutes to establish an air-flow and blow out any build-up of vapors, then turn up the heat. I want a complete cure, so it stays on for a couple of weeks. I comes out real pretty with the slow cure and I've had excellent results re-establishing the soundboard "crown" that older pianos have lost over many years, but is so necessary for good tone and sustain. I know this is not fiberglass RV related, but the method is the same.

The trick is to be sure any ignition source (switch spark or hot element) is not immersed in flammable vapors. Only warm air can be permitted near the curing epoxy. If you are sure the above is true, it is safe. But if your are unsure, don't do it.

[Bigfoot Mike]

High humidity can interfer with fiberglass resin curing as well.

[Per Walthinsen]

I knew I could count on helpful replies!

The stuff remains wonderfully messy even with heater going, so I will take it out.

Mike: The weather happened not to be overly humid, so I'm hoping that will not be an ongoing concern as I finish this. (Caution: check my location, but please do not laugh).

Con: I believe you have solved the mystery. The can was old, and the little catalyst left was equally old (it looked like most of it had somehow evaporated). I got new stuff a short time ago and will start from the other side as a test. Good thing it was just a small test area. I used a respirator with the appropriate filters for this, and I could not smell the odor through it. Fans going at the same time, natch.

Loren: In effect I try to have somewhat of a tunnel effect in that large but enclosed bathroom space. My computer fan (brush-less) methane extractor in the ceiling is remarkably effective, and I learned from my friendly local hardware man this morning that the fumes are lighter than air, meaning that pooling at the floor level is unlikely, so my "radiator" on the floor should not pose a problem.

(Aside to Loren): I have a much simpler task finishing harpsichord soundboards: a couple of wipe-on coats of quite thin wax-free freshly dissolved shellac is all it takes to protect the spruce. Much easier to paint all those flowers, bugs, and bees on that kind of surface too. For the ultimate in true 18th C. effect it needs a gentle layer of dust, of course.

[Andrew Gibbens]

Per,

One further trick you might want to try before ripping all that goo out is to get what you've done as warm as possible and then overcoat it with a really 'hot' resin mix - say, three or four times the normal amount of hardener. This will go off so fast that it will often trigger the reaction in the layer underneath - I've seen this used to kick off gel coat resin that had no catalyst in it at all.

Andrew

On edit: Did you close the door after you had laminated the first lot of glass/resin? To cure properly, polyester needs to be well-ventilated. If not, styrene (which is heavier than air) given off from the curing resin - the powerful smell - can pool on the job and this will prevent the cure from happening. So if, for example, you wanted to laminate a bowl shape, you should either tip the job on its side so the styrene drains out or set up a table fan (quite a small one will do) to blow into the job.

And before I lead anyone astray - does anyone know if all polyester resin in the US is now low-styrene, or just some? 'Styrene attack' can still happen with low-styrene resins, but it is rarer.

[Per Walthinsen]

Two more of the edge sections have now been attempted, with new resin and new catalyst. 3 hours later: hard as a rock. Thanks much for your help!

Andrew: I left the gooey mess for the time being as a control, and it is still a gooey mess. Tomorrow I will make the decision to either remove it or "spur" it on as you suggested. At the moment I would guess that the original catalyst was DOA and may not be fit to be rescued. We'll see. The original section was very well ventilated, so styrene pooling was probably not an issue but dead catalyst was. Fortunately I found out that the local hardware store sells the catalyst separately (which may be another indication of limited shelf life). Thanks to all of you I'm back on track with this project!

[Con]

I have tried the hot mix resin overlay with very little success. Even if the the lower layer is still gooey the catalyst will not penatrate to the lower level well enough to give you a proper bond to the area you are trying to repair. It will likely peel later.