First gel coat repair attempt = not good

Thanks Jim

I’ll check it out after work work and then report back.

I recently used flowable silicone
to seal the stitch holes in a new sil-nylon tarp. Hung it Friday evening and applied Permatex flowable sil. Saturday morning there was no evidence of curing. Seems that the RH was so low that there was not enough moisture available to start the curing process. Remembering that silicone caulk cures underwater, I used a sprayer to moisten the sealing, and by Sunday morn it was 100% cured.


Ok, I checked it and then doubled down

Got home and the stuff had set up. Certainly not completely hard yet. I could still mark it with my fingernail. Figuring that if the stuff is crap and I’ve got to remove it, it won’t be any more work to remove another coat. So, I added another leveling coat to the original one. The first coat fell short of the level needed for a nice repair.

We’ll see. This repair is in the stern of a WW boat that takes some occasional impacts and abrasiion. I just want something on there to protect the kevlar laminate. I’m not concerned about fancy.

looking at the MSDS Jsaults posted …

– Last Updated: Mar-08-11 3:09 AM EST –

...... I see Titanium Dioxide as an ingredient ... it may be being used as a photocataylst (it is widely used in this way) . The product (your Scratch Patch stuff) is actually a poly-urethane .

If the Titanium Dioxide is the primary catalyst , apply intense light or maybe UV light to help activate the ploymerization process and see if it cures ... scrape off the excess as outlined in the use proceedure first , just in case it does set up under the intense light .

Or just remove the stuff and use something other , like a polyester gelcoat (mekp catalyst) .

Titanium dioxide is also
a pigment used in white paint. Could be a dual use ingredient. Where are the chemistry majors?


one part??
if its one part…it isn’t gel coat. most won’t setup in an oxygen environment. For real gel coat you spray it with PVA to seal out oxygen while it sets.

Titanium Dioxide is a white pigment
Not a catalyst.

Gel coat is cured by mixing with peroxide.

This product looks like a moisture cure polyurethane & if so needs exposure to the atmosphere.

I personally wouldn’t use it on a boat.

I’m with sloop
My understanding is that gel-coat is the same polyester resin that holds the glass fibers in place, except instead of fibers, it holds pigment in place. The only real reason is to protect the glass from UV and abrasion.

Anything that doesn’t require a catalyst must be something else.

Here is the link to the product that Brian originally posted. Please read the product description before commenting or postulating.

This is NOT polyester gel coat.

This is NOT a waxed resin.

This is NOT an un-waxed resin.

This is NOT an epoxy.

This IS a urethane.

This IS a product designed for scratch repairs.

This IS a product sold by West Marine, a chain that deals in MARINE items.

This product DOES NOT require a catylist.

This product DOES cure in the presence of moisture.

In hindsight the bozos at WM should not have sold this product as a suitable repair for anything other than a scratch in a deep gel coat.

End of rant.


Thanks Jim
Looks like I’m going to have to remove this stuff tonight. The directions say that it is removable with mineral spirits up to as many as 5 days after application. I don’t want this stuff on there making any future repairs problematic.

Guess that’s what you get when you’re a rookie at this stuff. The owner at West Marine knew exactly what I was doing with this stuff and why I was doing a gel coat (supposedly) repair instead of epoxy … to make any future repairs work.

Just no substitute for experience I’m afraid.

cockney, didn’t I just tell you …

– Last Updated: Mar-08-11 12:22 PM EST –

...... that titanium dioxide "is" a photocatalyst ??

What , you think I'm stupid or something for saying that ... you must since you aspire to make the point (incorrectly BTW) that titanium dioxide "is not" .

Correctly stated was it's wide spread use as a pigment . It is aslo used as a UV inhibitor , which it excells at due to it's high absorbtion rate .

The reason I even mentioned it as a photocatalyst was because it was one of the ingredients in the "poly-urethane" product (Evercoat) . Obviously it is being used as a pigment in the "white" version ... but also I thought it possible that if that poly-urethane was a water (H2O) base , then the titanium dioxide may as well be catalyzing the H2O from liquid to seperate H atoms and O atoms (no longer water/H2O in any state) .

For basic edu. puposes this wiki. link has sufficient info. to help you understand more (or at least substaniate what I mentioned about titanium dioxide's photocatalystic properties) ...

Thoughts on another product
I bought some PC-8 from WM to use for gouge repairs in the white gell coat of my QCC. I have had good luch with PC-7 over the years, and figured I could save the painting step if I used the white PC-8.

But if I use this epoxy 2-part material it may complicate later repairs. Of course, I don’t plan on bashing it down the Slip!


Ive used this stuff in a narrow crack. i left it on for about 15 minutes and scraped the excess off but used a razer. It worked fine for that and cured fine. after using it, i dont think i would use it for a larger area than the crack i had. it was about 1/8" wide.

i meant evercoat…

I’ve used PC-11 on the stems

– Last Updated: Mar-08-11 2:59 PM EST –

of my Royalex canoe and enjoyed excellent results. It is truly tough stuff and sticks like a champ to both ABS and vinyl. It is definitely not as hard or brittle as gel coat, though. Not really white-white, either. More of a grey-blueish tint to it.

I don't know why it would cause problems with future repairs.

I think it has to do with

… vinyl ester resin being used int he initial build and then doing an epoxy repair over it. It kinda sucks when you’re a rookie at this stuff. Wish I had a shop close by that I could hang out in now and then. Maybe learn somethin.

Gel coat bonds to epoxy just fine.
Unless it’s not properly cured and prepped, it really shouldn’t cause a problem. I think I’d probably want to get rid of as much of any prior repairs as practical before patching anyway, though.

You’re right about the local talent, or the lack thereof, too. I’ve seen some real disasters even at the boatyard I frequent and they definitely don’t encourage witnesses hanging around asking questions. Sometimes I think they’d rather trowel 5200 on everything if they could get away with it.

I think the concern I’ve read about here
… I think Charlie Wilson mentioned it, is that future repairs to the laminate itself using vinyl ester resin may be compromised. This is a WW boat we’re talking about, and the area of concern is the stern. So, it’s not like future repairs are a long shot chance.

Coating Chemistry 101
TiO2 is a white pigment and (in a micronized = small particle) state is also used as a UV “absorber” in coatings and even in sunscreen applications.

It will NOT function as a catalyst in a unsaturated polyester gelcoat coating.

I am a polymer chemist who has worked in the coatings industry for over thirty years.

Great to hear of your expertise

– Last Updated: Mar-08-11 4:23 PM EST –

So, is this stuff going to complicate future repairs, or not?