Applying gelcoat

[Jared1989]

I have applied new gelcoat to a couple of surfaces on the top half of my boat. I applied 4 coats with the last coat having wax added to it for curing. I have done something wrong in that parts of the surfaces have cured and parts of it haven't. I am guessing I did not distribute the final layer completely over the previous layers. I waited for about 1.5hours in between applications. And it was roughly 70 degrees here in Oklahoma. Can I spray on a layer of PVA and get the tacky spots to cure?

 

[ondarvr]

PVA only works while it's curing, not after the fact. If the surface is just tacky you can wipe it down with acetone to remove the uncured surface.

 

[Jared1989]

It also didn't adhere to the fiberglass in spots. I used TPS and cleaned with acetone before i applied gelcoat.

 

[ondarvr]

If it didn't bond well then either the surface wasn't sanded, or it was contaminated.

A pic, or more details will help to supply a better answer.

 

[Woodonglass]

Details??? How did you mix the gel Coat? What Ratio of Hardener? What did you use to thin it? What ratio of Wax? When you did the prep work, did you sand with 40 or 60 grit and then was down with TSP and then do a final wash down with acetone right before you shot the Gel Coat?

 

[Jared1989]

I brushed the gelcoat on with a regular paint brush.

The gelcoat definitely set up in the mixing containers I bought. Hard as a rock and hot! It usually set up in the mixing containers at about 30-40mins

I used the factory recommended amount of hardener and styrene. For hardener: 16oz. of gelcoat to 1/8oz. of hardener. For Styrene: about 8% by volume. Then I did some conversions to get into units I'm accustomed to. I admit my measuring techniques are probably lacking. I went and boat a food scale at Target so I can do mass to volume conversions easier.

I sanded with 40/60/80 grit. I scrubbed the surface down with TSP probably 4 times and then went over it with Acetone. I applied the TSP with a brush, so maybe not enough TSP came in contact with the surface. I'm not sure.

I waited about 1.5 hours in between coats. And Attempted to apply a final coat with wax added to the mix. I'm guessing I didn't complete coverage all over. But I bought some PVA that I am going to spray on in addition to the wax.

I bought some new gelcoat from Spectrum that matches the color of white I have on my boat. I'm brushing it on, so the guy told me that I wouldn't need to wait longer than about 20mins before applying another coat. This is without styrene. Is that normal?

Is isopropyl alcohol a good contaminate removing agent? I'm wandering if a film of acetone is sticking to the surface and preventing adhesion? Is styrene okay to use for cleaning?

 

[ondarvr]

You need to add about 1.5% catalyst, which is more than what you used. Depending on the temperature the container should be hard in about 20 minutes.

If you just sanded the surface, skip the TSP cleaning, just wipe it off and and apply the gel coat. If you need to clean the surface many things will work, acetone, alcohol, styrene, etc.

No need to sand with 40, 60, 80, just sand with 80, or actually any of them, no need for multiple grits prior to applying gel coat.

More details will be needed to determine why it didn't stick. Are you saying that after it became rock hard it just peeled off?

 

[Jared1989]

I sanded the old gelcoat down to bare fiberglass. And there appeared to be some sort of red compound right before you reach the bare fiberglass, but it was under the gelcoat. I'm assuming that this was some sort of primer. I didn't attempt to reapply an of the red stuff. I just went over the bare fiberglass with new gelcoat. A small amount of the new gelcoat could have peeled off, but I just used Acetone and a rag to remove it. Here is the kicker, The parts of the new gelcoat that had a hardened surface worked just fine. I was able to sand these areas down and it stuck perfectly. But, the areas that were still tacky to touch I was mostly able to wipe down with Acetone down to bare fiberglass again. But, in spots, the underlying layers of new gelcoat hardened and stuck to the fiberglass even if the outer surface was tacky.

Is 20min between coats long enough?

The stuff that was rock hard stuck very well. It was the tacky stuff that was easy to remove with acetone.

 

[sphelps]

Maybe it was not mixed up well enough before application ... Just an uneducated guess .. :noidea:

 

[ondarvr]

We're getting a little closer to the cause. You didn't have a bonding issue, you had a curing issue, most likely not enough catalyst, and not enough mixing, combined to creat an uneven cure. The cured part stuck well, there is no way for the uncured portion to stick.

You need to increase your catalyst level to at least 1.5% and mix for at least one minute

 

[Jared1989]

I mixed it for close to 2 minutes each time,

I just finished putting Gelcoat on the boat. I will see what happens.

 

[Jared1989]

It worked. Thank you for all of your help.

 

[Jared1989]

I turns out that I need to add one or two more coats of gel. Can I use the Evercoat brand to go over the non-Evercoat brand gel coats without it causing any weird problems besides maybe the colors not matching?

 

[ondarvr]

The colors most likely won't match, but could be close. If you added wax to any of the prior coats you will need thoroughly sand the surface or the next layer will get a poor bond.

They two products will work together just fine.

 

[Jared1989]

Is there a good spray gun system for gelcoat that doesn't require a stand alone air compressor? I would really love to use an electric hand-held spray gun that you can buy to paint your house. I don't have the ability to have a big air compressor at my rent house.

 

[kcassells]

put some pics in for us to look at. BTW I haven't gotten to the paint stage yet but all of it sure looks like a pia no matter which way we go. Anyway pics will help out a lot.

 

[ondarvr]

You can use the type for painting a house....but.

It can be tricky because if something goes wrong and it begins to set up in the pump you just destroyed the whole thing. The pumps on these units get warm, so it speeds up the cure process even more. I've used one to spray gel coat many times, I did have it gel gun once, and it wasn't pretty.

You need one that is powerful enough to spray gel coat, it can be harder to spray so the cheaper units may not work.