Gel Coat Air Inhibition

[kmclemore]

Gel will usually have a pretty runny consistency, but you can thicken it with a thixotropic agent. In a pinch, talcum powder will also do, but don't use tons as it will make the gel softer.

[baldbaby2000]

I've been told that it's best to minimized the excess gel coat you put on because sanding can be a lot of work. With fiberglass for example I sometimes start taking off the excess before it's completely hard. Any tips on how to avoid a bunch of gel coat sanding would be appreciated. Thanks in advance.

Daniel

[kmclemore]

If you really end up with a lump you've got to get down, you can use a Stanley Surform to cut it down quickly. The best time to use a Surform is just after it's kicked off, but before it's fully hardened - i.e. when it's no longer liquid but you can still press your fingernail into it. Shave it down to just proud of the surface, then let it kick off the rest of the way until it's crispy-hard... then sand it down using wet sandpapers and final finish with automotive rubbing compound.

Stanley Surform (they come in lots of different shapes/styles):

[baldbaby2000]

Thanks Kevin. Those tips will make the job much easier!

[baldbaby2000]

Has anyone used Seafit Gel Coat Quick Fix? I have some that's been sitting around and thought it would be easier to deal with than gel coat for my scratch.

[opie]

Bransher - To answer your question, gelcoat is the consistancy of thick milk-of-magnesia. When brushed on a horizontal surface, the small lumps and valleys of the brush hairs or mulitiple brush strokes (if using a foam brush) will show. That means gelcoat is not self-leveling and you can not do a perfect job on a surfaqce like you can with normal paint. You will HAVE to wet sand it That said, by being very careful and using a soft brush, you can get the gelcoat to be fairly smooth so that the wetsanding will be easier. The other question, about running and drips on a vertical surface is, yes, it runs if put on too thick. The instructions on the can says 20 mils per coat. I figure 20 mils is about 10 sheets of paper.

Now for some experimentation..... Since I have been having a fun time gelcoating every nick, scratch, crack and hole in my MacX all winter long (whenever the air temp rose above 60 degrees) I have some track record now. I fixed a place in the hull about 10" by 20" where the fiberglass was damaged and I put three gelcoats over 8 layers of new fiberglass. I fixed a 5 inch crack in the internal shell in the head. I touched up nicks all over the boat. I even fixed nicks in the non-skid surfaces and then used a hack saw to cut the gelcoat to match the non-skid raised ribbed surface. I fixed holes in the sink area and liiner where the factory didn't spray gelcoat thick enough and a finger push knocked a hole in the gelcoat and produced a deep black hole. And finally I fixed a 25 inch smashed rib rail with fiberglass and gelcoat (another thread).

All that said, I only tried to "air inhibit" and put a plastic cover over the gelcoat one time and that produced so many wrinkles I never tried it again. In all my gelcoat repair painting I always had a hard surface result that I could sand and I never had a tacking surface result.

So here was the experiment: Yesterday was 70 degrees. In a ceramic coffee mug, I mixed one ounce of gelcoat using, as always, the exact amount of catalyst drops that the can called for. The can was purchased from Boater's World. Evercoat Marine Premium GelCoat # 5613 (one pint size). ISO-NPG Formula for Repair and Construction of Marine Gel Coats. On the instructions it says - "A barrier film or spraying a PVA mist must be used for this product to dry tack-free."

In my test, at 9am, I thickly gelcoated 6 inches, all-round, of a large old wrench handle and I also gelcoated a 2 inch circle on a glass jar with the same gelcoat thickness. The wrench I left on a shelf and the 2 inch circle I covered tightly with a sandwich bag. At 4pm the wrench handle finish was hard and looked like it had a porcelin handle. Actually looked pretty good like that.... Now for the jar.... I removed the plastic and the surface was hard also. I used a nail and could barely scratch both surfaces, leading me to conclude the hardness was similar. I used 400 grit and could sand the wrench handle and the jar equally producing white sanding dust. Needless to say, the surfaces were not tacky at all. So, just like all my repairs on the boat this winter, the air-barrier was not required (in my case) to produce a tack-free surface. Interesting, I thought, since the instructions on the can and most websites all say this can not be. ??

The eureka - (I found it..) - moment was when I was cleaning up and looked at the coffee mug where I mixed the gelcoat (and forgot to clean it.) The gelcoat in the bottom, that was exposed to air just like the wrench handle was tacky and wet on top. When I pulled out the gelcoat stir-stick the whole plug came out in one piece and the opposite surface that was against the mug was hard and smooth.

Here is what I figure. The mug, being 3 inches deep, kept a layer of styrene fumes hanging over the gelcoat top surface inhibiting the hardening process. Whereas, with the wrench handle was completely open to air, and possible 50% relative humidity in the air. In a factory mold, where gelcoat is used to make the first layer of a boat hull or surface, the mold, being concave, will hold fumes and inhibit hardening. If a plastic layer or PVA spray was used over the fresh gelcoat, it would get hard. The manufacture of the gelcoat, not wanting to get in trouble with consumers, therefore says to "always" cover the gelcoat surface. They can not be sure otherwise the result will be satisfactory.

My conclusion: A plastic film or PVA spray mist will always produce a hard gelcoat surface. Exposing the gelcoat to completely free air in all my boat repairs produced (for me) a hard gelcoat surface. Leaving gelcoat in a cupped hole or cavity will produce a tacky surface. But, past results do not guarantee future results, so if your job is tacky, don't blame me. Experiment in a remote non-important area first.

[dancing_bear]

I had a couple of spots where the gelcoat was damaged due to a PO's grounding. I am getting ready to apply the first bottom paint ever to this 22 year old boat.

Last weekend I gel coated these spots. Of course I did not apply the wrap saran wrap; my product, WM Finish Gel Coat does not indicate this in the directions.

In addition I applied the gel coat during this lousy week. It has been extremely humid and about 40 degrees. It has taken four days for the thinner layers to dry out. It seems like it will all be fine, I doubt I will try and sand and paint this weekend. I think given the cool, wet weather, patience will make everything better.

[Catigale]

If you are covering the gelcoat with bottom paint, I dont think I would sweat the inhibition issues.

[Bransher]

Thank you Opie, Kevin, and everyone else that shared their wisdom gained from experience. It is great that those who come later can be one-step ahead just by reading the knowledge that is shared on this site.