Are there different catalyst's for gelcoat for different temperatures?

[sbklf]

It is in the 50's here in Houston. I heated my garage to about 65 and applied waxed gelcoat with a little extra catalyst to the hatches of my boat. After two days it is still tacky on top and I can take the gelcoat off with an acetone soaked rag. My resin supplier said the gelcoat did not cure properly probably due to the temp. He said that I should be able to run an acetone rag over the surface and remove wax only and no gelcoat after a day. I called a local shop who was careful not to reveal any trade secrets but implied that different techniqes and different products, one of which was different catalyst, could be used in the gelcoat to get it to cure in the cold temps as he does it all the time.

Is my supplier correct that the gelcoat probably did not cure and that it should not wipe off with acetone after a day?

Are there different catalysts for cold weather?

Can someone tell me any other tricks or clue me in on other additives I might consider using so I can finish now rather than wait till summer?

[the1much]

i've only used and heard of only 1 cat.,,,,thats mekp,,,and a little extra in cold weather is what we do,,,,,and is it the gel coat thats wet,,,or is it just the wax in the gel?.usually if its the wax thats tacky, you just wipe with acetone, and that takes the wax off, then you can sand the gel.and your temp really should be above 70 for the gel. its actually harder to get the gel to "act" right in cold temps then it is to mess with paint.

[sbklf]

Originally Posted by the1much

i've only used and heard of only 1 cat.,,,,thats mekp,,,and a little extra in cold weather is what we do,,,,,and is it the gel coat thats wet,,,or is it just the wax in the gel?.usually if its the wax thats tacky, you just wipe with acetone, and that takes the wax off, then you can sand the gel.and your temp really should be above 70 for the gel. its actually harder to get the gel to "act" right in cold temps then it is to mess with paint.

It seems the gel is still wet since when I wipe it with acetone white sticky stuff comes off. Now after about a week it is a little better but still slightly tacky. I originally purchased Pettit easypoxy for the deck but went back to gelcoat because it is more durable. I so need to push this project out that I am considering the paint again. What do manufacturers do in the winter, work in heated shops?

[the1much]

ya,, they work in WELL heated shops,,the paint will work ( but slow) in the 50's a little better,,it will still take it a few DAYS to dry,,and a week or 2 to "half cure"

[Fanie]

If I work in the sun (35 deg C) cures in < 3 - 5 mins. If I work in the shade greens about 15 / 20 mins, if I work at night about 30 + mins and in the winter below 20 deg C it could take days with the same amount of hardner. I vary my hardner to compensate for the temperature, but if you add too much it would go jelly too quickly. Best is to maybe add a little extra but get the job heated and if possible into sunlight. It seems the UV light has some effect. Make sure you mix well else you could get tacky spots and dry spots.

[AroMarine]

My frp supplier has switched our gelcoat catalyst to Akzo's "L" from a previous "M" I haven't yet spent the time with the techies to find out the difference however does not appear to have much handling differences. A couple ideas about your gel. For the wax to work properly the gel and your work surface need to both be warm. Gelcoat gun manufacturers for anything below constant 70 F reccomend heaters for barrels. For me depending on the size of the project I bring gelcoat in my house overnight (trying to keep it as far away from my wifes nose as possible) or heat it with a heat gun in its mixing pot. 70F seems to be the good temp for the wax to work properly. Also warm gelcoat facilitates the mekp mixing more thouroughly. Also I use L 50 at or close to 2%. There are different concentrations in catalysts. If you can heat up the gel you have already applied you might still get a little more curing.

[AroMarine]

One other thing I forgot. Just to say it, gel coat likes to be thicker, more mass more heat better cure. Applying to thin will be hard to cure

[sbklf]

Thanks for the replies. I just put some more on last night and one area I applied very thin. As you said, today neither are hard like I think they should be but the thicker applied is harder than the thin. I was kind of expiermenting with catalyst ratios. I have always mixed by volume but this time I mixed by weight. 8 oz with one tsp of MEKP. In the mixing cup it was well below the 8 ounce mark. So if you are supposed to mix by volume I still over catalyzed. I will try the heat trick with the resin and the surface.

[AroMarine]

Sorry about the ratio thing it is 2% by weight. Fiberglast.com has a good reference chart in their help section. Sorry I don't know how to make the Hyper link. For their web site. In general one pint of gel needs 10 cc or 2+ tsp of catalyst and a quart needs 20 cc or 1 tbl and 1tsp . Again this time of year I heat the gel while I am mixing it my heat gun has a base mount to point up so i can warm my fingers while mixing gel.

[CDK]

The reaction is exothermic, so a thin layer takes longer to cure at low temp. I use a 500W halogen lamp: it produces some radiation heat plus lots of light. Resin cures much faster with light, in fact it hardens out without catalyst after a few hours in bright sunlight!

[ondarvr]

It is much easier to get the large plastic tubs from the paint store with markings in CC's and liters plus oz's. If they don't have the small containers needed to measure the catalyst at the paint store, then go to a pharmacy, they have small measuring devices that will work very well.

It is very easy to get the correct % with the metric system, 100 cc's of gel coat needs 2% or 2 cc's of catalyst, you can scale up or down from there.

You can use volume or weight to measure the catalyst, there is a difference, but it's close enough.

[fiberglass jack]

go find yourself a electric blanket or heatpad, when your ready to spray the gel place the blanket over the repar area a hour or two and heat the area up, after you sprayed make a sort of tent with the blanket that hangs over the repar you may use some small blocks of wood and some batten with a hot gluegun or duct tape after a few hours you shouls be good we have being doing repairs like this in canada for years when its minus 35 out side its hard to warm up the igloo

[the1much]

nice hint Jack neva thought of that,,,i used to do boats in maine and never even heard of that,, sad how someone can do boats for 20 years and be as stupid ,,,i mean "kinda simple" hehehe

[fiberglass jack]

also a halagen light like the 500 watts are great to use as well they even come with a stand so you can place them where you want those suckers can throw a lot of heat so be carefull you dont burn the gel also a UV light helps big time

[sbklf]

I purchased 6 250W heat lamps and plan to do this job in 4 to 5 sections. I considered electric blankets but once the heat lamps are set you dont have to move or adjust them and they are easy to turn back on after the gelcoat is applied.

I also spoke to the manufacturer of the gelcoat and you are supposed to mix by weight and not volume. He seemed to have the attitude that close was good enough. With the specific gravity of this particular gelcoat being 1.36, 24 oz by volume is about 32 oz by weight. I have been undercatalyzing. I just applied some gelcoat on the first section mixed by weight and using heat lamps and it looks to be curing fine after only an hour. I do have another question.

How long should I leave the lamps on after the gelcoat is applied before moving on to the next section (my garage is about 70* F)? I want to make sure it cures as it is supposed to but need to finish this project.

Thanks for the replies, Kevin