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Author Topic:   Gel Coat Hardening
rkong posted 10-10-2002 06:40 PM ET (US)   Profile for rkong   Send Email to rkong  
I'm trying out some spectrum gel coat for my boat. I did a practice run on some wood to make sure that its the right color. I'm concerned if it's actually curing hard enough though. It seems like it should be harder than what it feels like. If I drop a very small weight on it (say 1/4 ounce) or try to dig my thumb nail into it, it'll leave a mark in the gel coat. I don't think this happens in the gel coat on my boat. I follow the directions that come with the gel coat. However, the directions never call for sealing the gel coat from air. Any one have an idea on why the gel coat is a little soft? Thanks.
Tom W Clark posted 10-10-2002 07:58 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     
rkong ,

The usual culprit for soft gel coat is too much catalyst. It is easy to add too much.

You do not need to seal Spectrum's gel coat patch paste from the air but if you are using straight gel coat then it will need to either have wax added to it to seal it or else the gel coat will have to be covered with something to protect it from air.

Exactly what product are you using?

rkong posted 10-10-2002 08:05 PM ET (US)     Profile for rkong  Send Email to rkong     

I'm using the spectrum gel coat patch kit for my boat. I could be adding too much catalyst since I'm not measuring exact amounts. That's probably it.

What do you mean I need to add wax to it? I have to add it to the mixture before I put it on? Or otherwise I have to seal it?


Tom W Clark posted 10-10-2002 08:28 PM ET (US)     Profile for Tom W Clark  Send Email to Tom W Clark     

If you are using the patch paste kit then you do not need to add anything to it, the sealer is already in there.

If you were using straight liquid gel coat, then you would need to add a sealer additive which is also called wax. Chemistry is not my thing, but this is what it is sometimes called.

Gel coat will not get hard if it is exposed to air. When a boat hull is built, the mold seals the gel coat from the air. If you are doing a repair then something else must seal the gel coat from the air and this can take to form of something like an additive or a physical barrier like a sheet of plastic or something.

In your case, do not worry about all that. The gel patch paste kit you have is designed to work even though it will be exposed to the air.

jimh posted 10-11-2002 08:54 AM ET (US)     Profile for jimh  Send Email to jimh     
I have successfully cured gelcoat (that I did not prepare with the sealing wax additive) by spraying a coat of Poly-Vinyl Alcohol (PVA) over the gelcoat as it is curing.
DaveNJ posted 10-11-2002 09:08 AM ET (US)     Profile for DaveNJ  Send Email to DaveNJ     
Where can you get PVA ? I have looked around for it and can't find it.


John O posted 10-11-2002 12:20 PM ET (US)     Profile for John O    
Uses DURATEC HIGH GLOSS ADDITIVE. Spectrum color can give you all the info. Check there web site also
John O posted 10-11-2002 12:23 PM ET (US)     Profile for John O    
Sorry, just saw that you are using the patch kit. I used Spectrum Color Gel coat from a quart and had to use Duratec. Sounds like a mixing problem. I have used the kit for small nicks and it works well
kingfish posted 10-11-2002 02:22 PM ET (US)     Profile for kingfish  Send Email to kingfish     
PVA was in the West marine catalog last I knew-


DJS posted 10-11-2002 06:15 PM ET (US)     Profile for DJS  Send Email to DJS     

I am not exactly sure what the Patch Paste Kit's ingredients are but when I make up my own patch paste, using ingredients provided by Spectrum Color, I find that you use very small amounts of catalyst. Sometimes the catalyst is measured by a certain number of drops.

Here is a previous post where using the Patch Paste was discussed.
I corresponded with Newt (Nathan Rowe) and he basically told me that "I never figured out the correct proportions exactly". What Newt did was visually divide up the paste into equal proportions and then used the proportionate amount of hardner. Newt went on to say "I did not get it down to exact measurements".

When I bought Gel Coat from Spectrum they included a one ounce bottle of "Fiberlay Surface Seal" that faciltates the surface curing on the Gel Coat. This one ounce bottle is enough for one quart of Gel Coat. So you can imagine for a small amount of Gel Coat it sometimes takes only a few drops. The catalyst (hardener) is also mixed in these small amounts.

Hope this helps.

Taylor posted 10-11-2002 08:31 PM ET (US)     Profile for Taylor  Send Email to Taylor     
If you have the color matched $15.00 kit from Spectrum, that's the paste and it has the wax surface sealer already in it. All it needs is catalyst.

How much? When you work with fiberglass/resin products you start out measuring carefully and pretty soon you are really doing it by eye. Something like a dollup of paste and x drops of catalyst. I think its the fumes that brings on this behavior, but it usually works out.

If there is any catlyst mixed in, eventually resin will 'go off', more calayst makes it go off faster, and (as Tom mentions) too much may interfere with the process.

Spectrum's directions for paste say: "approximately 12-15 drops per ounce of patch paste, 2% by volume) If 6 teaspoons = 1 ounce then you need just two drops per level teaspoon of paste.

That strikes me as a little on the low side, but that's what they say.

Remember to mix well, with such a small amount of catalyst I'd want to be sure it was evenly distributed.

One more thing... try a little fine grit sanding on your sample and see if this takes off a tacky outter surface and leaves you with something harder.

kingfish posted 10-13-2002 09:11 AM ET (US)     Profile for kingfish  Send Email to kingfish     
Well and clearly said, Taylor-

I've used Spectrum patch paste kits extensively (as well as Spectrum gelcoat by the quart); I've always got a patch paste kit around.

2 to 3 drops per teaspooon of patch paste does the trick, and it cures up hard without PVA or any other barrier. The most difficult thing for me, just because I can't see that it is really happening I guess, is mixing the paste and catalyst at the outset.

When using amounts of clear catalyst like 2 or 3 drops, the catalyst disappears right off the bat, and the consistency doesn't change; I just keep folding and mixing the concoction with a wooden mixing stick or popsicle stick until "it be's right". There is no way to tell by looking at it, so I try to err on the side of mixing more than it needs, but not so long that it starts to set up.

Worst thing that can happen until you get the feel for it is to waste a teaspoon or two of the patch paste, or maybe have to re-do a patch. Nothing earth-shattering.

NEVER SCARED posted 10-14-2002 03:41 PM ET (US)     Profile for NEVER SCARED    
I was under the impression that gel coat cured by either time or warm air. I went through 5 $18.00 jars and couldnt figure out why it was always tacky. I thought I mixed it wrong or it was too cold. You have to cover the gelcoat with wax paper to harden it. Since using wp, each repair was super hard in about 1hr in any temp. and ANY mix ratio! The directions dont mention covering it. What a shame!

Never scared

flaglerdave posted 10-14-2002 04:41 PM ET (US)     Profile for flaglerdave  Send Email to flaglerdave     
I do not use pre-made paste kits I usually make them myself.( gel coat, cab-o-sil, patch-aid,and MEKP )BUT when brushing, spraying, or making a paste to fill holes etc. There is an additive called Speedpatch or PatchAid that helps take the tack out and helps harden gel coat perfectly. You can get it from or mix the stuff around 30% to amount followed by the MEKP about 2%.
Hope this helps !
kingfish posted 10-14-2002 05:11 PM ET (US)     Profile for kingfish  Send Email to kingfish     
In an earlier thread of similar content, someone mentioned a (the) wax that when mixed in with the gelcoat before the catalyst was added, removed the necessity for a barrier like wax paper or PVA. Styrene wax, maybe?? Anyway, I presume that "wax" must be the basic ingredient in Speedpatch or PatchAid?? Whatever it is, that must be what Spectrum uses in their patch paste kits, because those kits do not require a barrier in order to cure.

Flaglerdave - what is cab-o-sil?

flaglerdave posted 10-15-2002 10:36 AM ET (US)     Profile for flaglerdave  Send Email to flaglerdave     
Cab-o-sil is a product that is fiberglass foam milled to dust. It is a thickener to make any resin or gel coat to a paste consistancy you desire. To buy a quart of gel is pricey ( average $50 to $70 a quart )and has a shelf life that is normally a few months to a year.( Depending on mainly storage, climate,etc.) Speed -patch or Patch aid solution is about the same and has a couple of years shelf life. But this is the way all good boat manufactures ( BW, Sea Ray , etc.) use daily. ( Believe me )
using the pre-made paste kits do work and cost less then the items I mentioned BUT if your Whalers are like mine there are a couple of spots that could use a little repair.
p0rshman posted 10-26-2008 04:11 PM ET (US)     Profile for p0rshman  Send Email to p0rshman     
you need to add speed patchaid to your gelcoat along with the MEKP ,you can get this from spectrum colors
jimh posted 10-27-2008 08:14 AM ET (US)     Profile for jimh  Send Email to jimh     
I wonder if the original gel coat resin application has finally cured after six years.

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