posted 11-24-2002 01:02 AM ET (US)            

The spray can of gelcoat must be mixed with hardener, turning the whole can into a curing mix that must be used immediately.

posted 12-02-2002 04:11 PM ET (US)            

I've used the Preval for paint and it works superbly to shoot oil based enamel thinned 50% to a watery consistency. If you can do the same with gelcoat, it would be terrific.

posted 12-02-2002 05:05 PM ET (US)            

"Gel coat may be thinned for use in a siphon put gur aor preval Sprayer with Acetone of Sstyrene Monomer. Do not use more the 20% by volume of thinner, and always add thinner first then add the Catalyst or Hardener and mix thoroughly."

posted 12-02-2002 06:42 PM ET (US)            

My experience is that you *cannot* thin gelcoat enough to effectively spray it with a Preval sprayer. The Preval set up worked OK for spraying the barrier coat on afterwards, but not being aware of Spectrum's 20 % maximum thinning statement, I just kept thinning until the gelcoat would pass the spray orifice. By that time it was so thin that most of it drifted away in the air before it got to the surface; the rest went on so thin that it would have been a full time job replacing the propellant cans, etc.

I found some throw away splatter paint kits that had bigget propellant cans under higher pressure and bigger orifices that really did an OK job. If/when I do it again, I will have a small spraygun or air brush or some kind of real spraying equipment. I've spent all the time I'm ever going to trying gelcoat with Preval sprayers.

posted 12-03-2002 06:37 PM ET (US)            

Taylor and I had really good success with the Preval sprayer while working on Taylor's boat. I will not hesitate to use one to spray gelcoat again.

I have quite a bit of experience with the Preval units spraying both latex and alkyd house paints. The Preval unit has not always worked well, I suspect because of the thickness of the paint I have at times used, so I admit I was a bit skeptical when Taylor and I decided to use one for the gelcoat. But as it turned out, I was pleasantly surprised by the results. Read about it here: http://continuouswave.com/whaler/reference/whalerRepair.html#01-10

posted 12-04-2002 09:21 AM ET (US)            

I had previously read the article and as usual was impressed with the quality of your craftmanship; I had not paid attention to the remarks about the Preval sprayer though.

I have a lot of respect for your work and your opinions, and for your veracity; I don't doubt for a minute that the Preval experience went just like you and Taylor said it did. I can't square your experience with the one I had though. I can tell you that my experience was just as bad as yours was good, and I've worked with tools all my life so I'm not too concerned that I did something "wrong". The only variables I can think of are the possibilites that the areas I was working were simply too large for Preval usage (one area was about 1 sq. foot, the other was between 3 and 4 sq. ft.), or that there was something inherently different about the raw gelcoat we used.

I'm confident enough in my own mechanical skills that I can't in good faith take back everything I said about problems with Preval sprayers and gelcoat, but I may now give it another try, at least on a small area.

I'm certainly with you about brushing gelcoat - no way, no how!

posted 12-04-2002 04:36 PM ET (US)            

Our technique with spraying was the same as with spray paint in cans. Nothing special here. I start a sweeping motion outside of the intended area, triggering down on the spray head to start the flow just before I enter the target zone, and then continue sweep as I let off the nozzle. Tom masked off the rest of the boat, ground, plants, neighbors' cars etc, I think he anticipated who was going to be spraying (me!) but it helped to not have to worry about overspray, although overspray adjacent to the repair wet sands off just fine.

To Jim's question about the Spectrum gelcoat, it is a little thicker than regular polyester resin, maybe the consistency of blackstrap molasses. We thinned with acetone a full 20%, plus the wax additive which thins a little more, plus it appears when the catalyst goes in the mixture initially gets even thinner. So what we put in the Preval bottle is about the consistency of oil house paint, maybe a little thinner. That still seemed to thick, but it worked.

The spayed gelcoat does *not* self level, we ended up with a pebbled texture from the little droplets that has to be wet sanded smooth. We also kept going back over the work in progress, just as with spray paint, adding more material. I'm not sure what the wax additive thinks about that, but it seemed to be ok.

Tom is correct, we used a single sprayer (only one can of propellent) over three days, with three or more different batches of gelcoat. I still have the second one sitting unopened in my workshop.

posted 12-12-2002 01:03 PM ET (US)            

Tom and Taylor: Can you please and would you be willing to provide careful specifics on your process, including materials used, in what order, catalog #s if possible.

I have a 6 inch gaff gouge in the side of my Nauset that had been previously filled with auto filler by the previous owner. It now looks like a grey patch the side of a little leauge football. I want to repair and had bought a spectrum patch kit, but like the idea of building it up by spray.

Thanks, guys, for the differing experiences and the great information.

posted 12-12-2002 02:19 PM ET (US)            

You should start be reading Taylor’s reference article which will answer most of your questions: http://continuouswave.com/whaler/reference/whalerRepair.html

posted 12-13-2002 02:30 PM ET (US)            

Thank you.

Now a question please. I have this gouge that I previously mentioned. It is above the chine about 2/3 back on the side wall. It appears more cosmetic and it is pretty ugly. I had not considered glassing it over as it is small (1/4" wide by 4 inches long). Plus the bondo that is in it now has filled it pretty good.

Was thinking of an exterior only West epoxy patch and spraying some gelcoat. Am concerned about the color match. And also concerned as to how to feather the new gelcoat into the existing. Don't know if the question makes much sense...

Thanks again for an interesting post and any thoughts you might have.

posted 12-14-2002 02:28 AM ET (US)            

This thread is about the Mini-Craft and Preval spray unit and gelcoat. I would be happy to answer your question about hull repair but I think it would be best if you reposted it in the other thread where it is more on-topic.

In regards to the divergence of John's experience vs. Taylor's and mine, it could have been the gelcoat itself or it might have been temperature and humidity? or it might have been the Preval unit itself.