View Full Version : OT fiberglassing a deck

07-30-2006, 09:52 PM
I helped a friend rebuild a deck which had rotted out. We surfaced it in fiberglass. Time restraints had us doing the glassing during some of the hottest days of the year so far. Because of this, we chose a time frame to do the initlal glass and resin work starting at 11 pm, and worked until about 3 am. Even starting the work that late, we had to reduce the amount of catalyst to give a pot life of about a half hour. When it came to the gel coat, we began that at about 9 am, and by about 11 we were done with that. I was getting a pot life of about 20 mins with the gel coat, but that was enough to apply the gel coat before it became unworkable.

I've left out all the details surrounding the rebuild, but suffice to say that a heck of a lot of prep work was done, and there was no moisture on the deck at glassing time.

With the sun beating down on the deck, it obviously became quite warm. I expected the curing to speed up because of this, but it didn't. I had gel coat 'rubberizing' in the pot at about the 20 minute mark, but the applied coat didn't begin to cure until about an hour had passed. No problem thought I, give this a full day and it will be cured. We were late to leave on our short holiday, but off we go.

Two days later (both dry and hot days with no precip) it was still tacky. A full week later, the deck is still tacky and is now holding every bit of dirt that has fallen onto it or been pressed into it from our shoes, etc. This dirt cannot be washed off.

Question- what went wrong? We have to assume the gel coat was waxed, since we were told it was. I personally mixed the catalyst into the resin so I know there wasn't any unmixed spots. My last mix had some left over in the pot after I was done, and that was cured completely long before the coat on the deck even started curing. I was mixing two litres at a time and keeping it out of the sun as well until I applied it. All the materials including the catalyst were purchased from a supplier who appears to be shipping this stuff every day. I'm satisfied that the materials were fresh.

Now the plan is to re-coat the deck with more gel coat to cover the dirty layer and give a clean look to it, which it would have had iin the first place f it had cured properly.

Anyone care to try shedding some light on this situation?

07-30-2006, 10:27 PM
Gel coat doesn't fully cure in the presence of oxygen. In a mold it is the first layer applied and is not exposed to oxygen. If you put a thin layer of resin over it it should cure.


The oxygen preferentially oxidizes the catalyst at the air interface so the catalyst can't polymerize the gel coat.

07-30-2006, 11:44 PM
Hm. That makes sense, Evan. Now I have to think that there was no wax in this gel coat, as the wax is supposed to form a surface barrier and that would have the effect of insulating the resin from the atmosphere and prevent the problem. Maybe the fact that the resin cured in the container is simply due to the vapor pressure of the catalyst in the container keeping oxygen away until cure has taken place. I have imagined that possibly the hot sun could have evaporated away any catalyst that was at the surface of our gel coat, and caused (or at least helped to cause) the problem. I don't know is this is a real effect or not. Pretty much all of my fiberglassing has been done in a shop or at least in the shade, but there was no shade to be had on this project.

Any layer of resin I apply over the gel coat would have the same problem to cure fully if it wasn't waxed resin, so that would then become a requirement if I go that route. I don't believe this problem should have occured, and now I'm thinking that the supplier gave us gel coat meant for applying into a mold, and not for deck surfacing. I think we're going to have to determine this somehow through the supplier and hopefully resolve it. He did in fact know what we were doing and supplied all the materials, including the actual 4x8 decking.

It's unfortunate that many people including a dog got to walk around on this deck before we returned from holidays. The dirt marks are not removable, and it's depressing to see that after having put all that work into the repair. Our top coat will have to be the color again.

07-31-2006, 12:49 AM
I would say that the gel coat must not have had an air dry additive added. That sucks. I would request the supplier at least pay for the materials to finish the job correctly.

07-31-2006, 07:14 AM
You say you reduced the amount of catalyst. I don't think you can do that and still have it set up properly. I think you need the specific proportions called for.

07-31-2006, 08:38 PM
The amount of catalyst can be adjusted to compensate for temperature- to what miinimum I don't know. I also don't know if gel coat needs a different minimum level of catalyst. I do know that we had enough mixed in because the remains in the pot cured fairly quickly and without the tackiness.

We'll be putting the vendor on the spot about this because I don't think he gave us the right gel coat resin for this application. He did know we were surfacing a deck so maybe it was a simple mistake on his part. I don't think we should be paying for the replacement resin, though we're still going to be out the time it takes to apply it again, plus the expendables. That's ok, we'll live with that.