Help laying out gel coat

[mvoltin]

I’m trying to create a perfectly flat 8x4 ft panel using a melamine sheet as the mold surface. For the first panel, everything went smoothly: I applied two layers of Marine Coat One gel coat (about 1 gallon total), then laid epoxy and cloth. I used wax plus PVA as the release system, and the result came out great.

The problem is with the second panel. The gel coat is very thick and hard to spread evenly, leaving thin streaks. When I apply the second layer, it “crumbles up” (lifts) in multiple spots. At first, I thought I hadn’t let the first layer cure enough (I had waited 4 hours), but even after waiting 24 hours on the second attempt, the same thing happened. Each failed attempt costs me about $100 and a week of waiting for more gel coat.

My questions:

• Should I just lay down the entire gallon of gel coat as a single coat across the full 8x4 sheet?
  
  
• Is there a better way to apply it evenly (brush vs. roller, etc.) given how thick it is?
  

I’ve attached pictures: one shows the gel coat peeled off and flipped, and another (with partially peeled PVA) shows the first panel that came out perfect.

 

[kapnD]

Way too much gelcoat! Read the manufacturer’s recommendations for thickness.
Use a roller to apply, and apply second coat as soon as the first coat will hold up.
A make sure that the gelcoat is thoroughly mixed, before and after catalyzing.
I’ve never used PVA that thick, it only needs a thin film to function.
Alligatoring will occur if PVA is not completely dry.

 

[ondarvr]

One gallon should cover 80 square feet at the 20 mils (correct thickness). You could have done both panels with one gallon.

That texture is from the first layer not being cured enough when the next layer is applied. It can be under cured for many reasons, but thats the cause.

The bigger problem is using epoxy over normal gel coat, it won't bond well and will soon peel off.

Melamine does not need PVA, it barely needs any wax to release well, so skip that step.

 

[kapnD]

I don’t see any mention of the laminating products used, but sure, the gelcoat must be compatible with the resin.

 

[ondarvr]

I don’t see any mention of the laminating products used, but sure, the gelcoat must be compatible with the resin.

"I applied two layers of Marine Coat One gel coat (about 1 gallon total), then laid epoxy and cloth."

 

[kapnD]

Dang, missed that!

 

[mvoltin]

Way too much gelcoat! Read the manufacturer’s recommendations for thickness.
Use a roller to apply, and apply second coat as soon as the first coat will hold up.
A make sure that the gelcoat is thoroughly mixed, before and after catalyzing.
I’ve never used PVA that thick, it only needs a thin film to function.
Alligatoring will occur if PVA is not completely dry.

Yes, for the first panel, applied the second coat after ~6 hours and it worked just fine. For the second panel, applied after 4 hours first and then waited 24 hours for the second try but, in both instances "alligatoring" happen.

Used mixer and and used about 1oz per half gallon which is within the recommended range. Mixed for good 3 minutes with a drill-attached mixer.

Yes, put thick layer of PVA (3 layers) but that should could this cause alligatoring? I did the same for the first panel with no issues.

The last layer of PVA was dry - (24 hours post application).

There must be some reaction between the first and second layer - because alligatoring happens shortly after applying the second layer (within minutes) when the first layer seemed pretty hard and dry.

Potential solution: Perhaps, I will just apply one thicker layer with 3/4 gallons? This will result in about 1.mm or 30 mil thickness and then start epoxy and cloth after it dries? Considering that applying one layer was successful and stayed flat until I applied the second of gel coat on top? I can color epoxy and apply it after the first coat - this way epoxy doesn't react with the gelcoat but providers "color" consistency in case some of the gel coat areas are too thin?

 

[ondarvr]

I'm not sure what you're talking about, that gel coat is not compatible with epoxy!

The only reason for alligators is under cured gel coat, again, there are many reasons for it to possibly be under cured, but that's only cause. With that much catalyst it should be ready to apply another coat in less that two hours. How old is the gel coat and catalyst?

1/2 gallon is close to the correct amount on something that size. No need for excess gel coat, it only causes problems.

 

[bajansailor]

Excellent responses above, as always, from Ondarvr and KapnD.
I am just wondering what you are going to use these two 8' x 4' panels for - are you going to build a dinghy with them?
I built a dinghy using laminated fibreglass panels on a melamine / arborite mould surface - I did not worry to use gelcoat, as I was going to paint it anyway.

 

[starcmr]

I’m trying to create a perfectly flat 8x4 ft panel using a melamine sheet as the mold surface. For the first panel, everything went smoothly: I applied two layers of Marine Coat One gel coat (about 1 gallon total), then laid epoxy and cloth. I used wax plus PVA as the release system, and the result came out great.

The problem is with the second panel. The gel coat is very thick and hard to spread evenly, leaving thin streaks. When I apply the second layer, it “crumbles up” (lifts) in multiple spots. At first, I thought I hadn’t let the first layer cure enough (I had waited 4 hours), but even after waiting 24 hours on the second attempt, the same thing happened. Consulting an interior designer virtual might help with techniques for smooth finishes. Each failed attempt costs me about $100 and a week of waiting for more gel coat.

My questions:

• Should I just lay down the entire gallon of gel coat as a single coat across the full 8x4 sheet?
  
  
• Is there a better way to apply it evenly (brush vs. roller, etc.) given how thick it is?

I’ve attached pictures: one shows the gel coat peeled off and flipped, and another (with partially peeled PVA) shows the first panel that came out perfect.

The problem is that your gel coat is too thick and not spreading evenly, which causes it to lift when a second layer is applied. Do not apply the full gallon in one coat because gel coat should be applied in thin, even layers of about 15 to 20 mils. Use a short-nap foam roller for large flat areas and a brush only for edges. If it is too thick to spread, lightly thin it with a compatible gel coat thinner. Make sure the first layer is fully cured before applying the next. For best results, you can also consider spraying the gel coat to achieve an even coat and avoid lifting.