Thining Gelcoat question..

[boatdude]

Do you calculate the catalyst amount based on the original gelcoat amount or the final amount total after it is thinned?




Also, what are the limits on catalyst % at 70 degrees?

Is the same for gelcoat thinned 10% with acetone?

Just doing small throw away tests I've found the thinning with acetone really retards the cure time at 2% catalyst. I need a faster cure when using gelcoat thinned with acetone.


I know some guys are going to yell at me for thinning with acetone.





Thanks.

[the1much]

how come your not using styrene to thin?

[tinhorn]

Acetone. Tsk, tsk. They say that if you need to thin it at all, you don't have a gelcoat problem, you have an equipment problem. Yup, my equipment problem was that I was too cheap to spend thousands of dollars on a dedicated system that would take up half my shop space.

I was one of those guys who didn't keep a gallon of styrene around just in case I needed to thin some gelcoat. I read some guy's theory once that acetone evaporates between the gun and the mold, so it was actually preferred to styrene. Perhaps he was just trying to justify being a cheapskate.

I wouldn't go much hotter than 2%, measured against the thinned gelcoat. To quicken the kick times, I used a 5000-watt electric furnace in a small shop to control the temperature. Spray, clean the gun, turn the thermostat to the max, go drink coffee...

[boatdude]

Thanks guys.

Does thinning with styrene retard the cure time?

[jim lee]

Acetone has styrene in it. But it can contain other stuff as well and you can't be sure what the other stuff is. From what people tell me, its the other things in there that can cause unpredictable chemical reactions to your resin. Mostly it works, but some times your reaction times are way off or behave oddly. Hence using straight styrene is a the better choice.

Anyway you initialte the resin at your 1% or 2% by weight of the resin alone. (At least thats what I was taught and what we do in our shop.)

As for spraying unthinned gelcoat, like into a mold, have you tried a dump gun? They're only $130 and dead easy to clean up after.

Hope this helps.

-jim lee

[ondarvr]

Small amounts of acetone or styrene can be used and may have few negative results that are noticable, but it can affect how well the gel coat holds up over time.

While not recommended, if you stick with less than about 5% of either product you normally won't see any issues, the problem is, in the field that 5% turns into 25 to 40% and then there are major issues to deal with.

Styrene is a very important component of gel coat, but it is not as water or weather resistant as the base resin used to make gel coat, plus it has little strength and can be brittle. These are not features you want in a gel coat, so that's why we recommend against using it.

There are products designed for reducing the viscosty of gel coat so it can be sprayed easier, they will work better than acetone or styrene and will hold up better over time. You can get patchaid type products that will reduce the viscosity and speed up the gel time, or just one or the other.

Gel coat can be sprayed through many different types of equipment and when done correctly they can all produce good results. For small jobs a dump gun or pressure pot will work, as the part gets larger and the volume of gel coat being sprayed goes up, then the specialized equipment becomes more important.

It's best to stay around 2% on catalyst, but going up to three may be needed at times, more than that and you may start having problems with the quality of the cured gel coat.

[Roly]

I haven't heard of patch aid here. What is in it?

so that's why we recommend against using it.(Styrene)

I guess you sell it, so that is a million dollar question.
sorry.

[ondarvr]

I normally refer to them as a patchaid type products. There are many different formulas for these products and several companies make them. Some have styrene and some don't, but they may also have other ingredients to lower viscosity and speed up the cure. Even these products which are designed for this purpose can have a down side, especially when too much is added.

[jim lee]

Originally Posted by boatdude

Thanks guys.

Does thinning with styrene retard the cure time?

Well I just went and asked the guru and the answer was Yes it does retard the cure time. And it does it in an odd way; The resin stays liquid longer, but when it does go off it does it much faster. I've seen this in person where a bucket of resin was runny then one second or two later was solid. It was older resin we'd thinned with either styrene or acetone.

-jim lee

[fiberglass jack]

resin and gelcoat contain promoters like dma and colbalt, this is what makes the resin go hard when the mekp catalist is added. you can buy unpromoted resins and gelcoat that you can mix with a lower ratio of promoters ie a summer or winter resin, by adding styrine or acetone you are reducing the ratio of promoters so it will take longer but the quality and propertys are lost some what, what i would do is thin your gel with styrine and add some colbalt say 1% this way the cure time wont long be careful and do some tests first for the pot life and what ever you do DO NOT MIX THE COLBALT AND HARDNER TO THE GEL AT THE SAME TIME the 2 will combust . its this reaction that makes the resin get hot and cure

[dereksireci]

While not a self proclaimed "guru", this is my take.

Acetone is a solvent which dilutes the material to be sprayed but does not participate in the chemical reaction. It can have adverse effects including changing the color of the gelcoat.

Patchaid is a resin product sold by Cook Composites and Polymers. It comes in formulas to speed cure or to extend cure depending on the size of the repair. It also appears to contain wax so the resin will cure in the presence of air as well as light stabilizers to help the patch not dis-color.

I've never seen gelcoat thinned with anything other than Patchaid or a similar product at a boat building plant. Out in the the trenches of the boat yard it may be a different story. I showed a "how to" video to my composites class a few weeks ago and the guy on the video thinned his gelcoat with acetone. There you go. Maybe he was a guru!

In the world of manufacturing we don't take chances.

djs