Gelcoat as non-skid on Deck

That is the nightmare we all dread; removing uncured resin. I feel for you man.

 

I didn't feel so bad because it was just a 1 sq ft test area. Just imagining what it would have been like if I had done the whole deck is enough to make me accept this setback as nothing.

 

Great attitude.

The first day at my first yard.

The yard had just changed epoxy brands.

I used brand 1part a and brand 2part b.

Three weeks to fix remove all the non-curing mess.

 

What about polyester resin over pine wood knots? Does that also not harden?

 

Wood knots can contain extra tree sap.
Tree sap is often acidic.

Could be the same acidic reaction preventing gelcoat cure.

Shellac is also acidic.

 

The styrene will dissolve pine resin. I think that it mixes with the polyester resin and creates a problem.

 

My curiosity got the best of me and I repeated the test on an easier area to clean off the gelcoat in case I have another fail. The gelcoat, MEKP, wax quantities was identical to the failed test. I cleaned the deck test area with water then baking soda and water, then sanded it with new 8o grit dry, then again cleaned with water then baking soda and water. Finally, I cleaned it with 90% Iso Alcohol. I used clean cotton t-shirt rags wipe on, wipe off, and dry, never using them twice.

I mixed the gelcoat at 3:30pm and by 5:30pm the gelcoat on the tape to mark off the area, and on the brush and in the mixing cup were all hard, but the gelcoat on the epoxy was wet. This morning at 9am the gelcoat over the epoxy areas is wet as if I just applied it.

Bottom Line: From your very kind and informative responses here and my tests, I conclude that if one wants to use gelcoat over epoxy, only go with West System epoxy, and as far as the gelcoat, do not use Fiberglass Supply Depot gelcoat over epoxy. And test it on a small area first.

 

Three days ago I brushed some polyester resin (no wax) onto the epoxy deck and it hardened fine. The next day I brushed on top of the poly resin the same gelcoat I have been using in these tests and it hardened perfectly. So, I am back to the original plan to gelcoat the deck, which I can now do, by first laying on polyester resin. It "appears" the gelcoat I am using is sensitive to epoxy.

I will perform one more test with a different brand of gelcoat directly over the epoxy deck. I will get a small sample from someone that has done gelcoat over epoxy many times with no problems.

 

1-31-2022 – Test #15 FGCI brand gelcoat directly over epoxy deck – Taped off a 1 sq ft area, sanded it with 80 grit dry, vacuumed, and cleaned with water, cleaned and dried with a t-shirt, and cleaned with alcohol and dried with paper towel. Then applied FGCI gelcoat to exact ratios as tests before: 2.5 oz gelcoat, 60 drops MEKP, 2.5 cc wax. Mixed at 1pm. Also applied leftover gelcoat to a plywood box which had been epoxied 2 years ago.

Checked it at 2 hrs and it was hard on the masking tape and the brush and mixing cup, not sticky, but not fully hard. The gelcoated areas over the epoxy floor were still wet. I went to take off the masking tape and it peeled off the gelcoat on the deck like a sheet, leaving nothing behind, so I put the tape and sheet back on. The plywood box was all wet.

At 4 hours the plywood box had spots not wet but not hard. The epoxy deck was the same. I peeled off the tape and it took with it the gelcoat like a sheet and dropped it on one half of the 1 sq foot test area, like a folding sheet of gelcoat. I left it like that.

This is another brand of gelcoat that did not harden over the epoxy. So I think the problem is with the RAKA epoxy, since the person that gave me the FGCI gelcoat sample to test says they use it all the time over epoxy with no problems.

 

Here is what it looked like the next morning, still wet and folded areas rubbery, I can easily remove it all with a spatula.

 

This is good information. I have never used RAKA epoxy. Never had any problem with gelcoat over WEST or System Three.

 

This type of reaction takes place every now and then, and it is difficult to determine the exact cause without some lab time.

 

Can the title of the thread be changed to "Gelcoat Over Epoxy Failure" by a moderator?

 

Are you 100% positive that is Raka epoxy on the floor of your boat? I have the same materials as you do (i buy from FGSD a lot). I have raka epoxy and a few different gelcoat brands including the supply depot and FGCI gelcoats. May try my own tests

 

It is all RAKA 127/606, it is the only epoxy I bought.