I have a heck of a time trying to get gel coat to harden. I mix gel coat with a few drops of hardener, cover a small area (such as a ding repair), and cover the gel coat with mold release. Several days later the gel coat is still a little tacky. What am I doing wrong??? Jim Schaff s/v Savannah
soft Gel Coat
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Mold Release
Jim, Mold release is a bit like a plasticizer and is possibly acting as an inhibitor to your gel coat curing process. Dry (not hot) warm air is what is need for the gel coat to cure. Mold release is used in the boat making process but is treated into the molds and heat controlled so that it does'nt affect the cure. John
Jim, Mold release is a bit like a plasticizer and is possibly acting as an inhibitor to your gel coat curing process. Dry (not hot) warm air is what is need for the gel coat to cure. Mold release is used in the boat making process but is treated into the molds and heat controlled so that it does'nt affect the cure. John
try premixed gel coat
Jim: Maybe you want to try some pre-mixed gel coat. If you only need a single coat or it is your final coat, this may help with your problem.
Jim: Maybe you want to try some pre-mixed gel coat. If you only need a single coat or it is your final coat, this may help with your problem.
Solution is dead simple
The solution is simple, get a new bottle of hardener. This is a common problem, hardener is usually in plastic bottles and the outgas some essential properties over time. That is why many places do not carry gelcoat, but instead order on demand.
The solution is simple, get a new bottle of hardener. This is a common problem, hardener is usually in plastic bottles and the outgas some essential properties over time. That is why many places do not carry gelcoat, but instead order on demand.
Surfacing Wax
Jim, It is the nature of all polyester resins to stay tacky when allowed to cure exposed to air. This is how the multiple layers of glass bond to one another. In order to inhibit the exposure to air during the repair process you have to add a surfacing wax to the resin or gel coat before you add the hardener. The soluable wax floats to the surface of the repair and blocks the air and then your patch will harden all the way through. You can get this at the local fiberglass store. PM
Jim, It is the nature of all polyester resins to stay tacky when allowed to cure exposed to air. This is how the multiple layers of glass bond to one another. In order to inhibit the exposure to air during the repair process you have to add a surfacing wax to the resin or gel coat before you add the hardener. The soluable wax floats to the surface of the repair and blocks the air and then your patch will harden all the way through. You can get this at the local fiberglass store. PM
Paul M is correct
air (oxygen) is an inhibiter which prevents surface polymerization of polyester resin for a long time - sometimes not ever. I doubt that the hardener has gone bad. That is a popular myth unless it is very very old. You do not want to use excess amounts of it either - another "bigger hammer" approach which will not work. Mold release is permeable to oxygen and so it will not help this problem. It is definitely not a plasticizer and I doubt that it is an inhibiter in and of itself. You need to seal out the oxygen long enough for the surface resin to set up. Polyester resin comes in two main versions - laminating and surface coating. The surfacing mix has about 2% wax added. If you have an area which still needs to cure, I would wipe a very small amount of peroxide or bleach over the surface and soon afterwards follow that with some wax. You can use just about any solid wax. Crayons or candles come to mind. Wipe it on and heat it with a heat gun to spread it around over the entire area. The heat is probably needed to help the resin to set up too. Without heat, it may still take a few days to harden even after you seal the area. Once the surface is hard, you can scrub off the excess wax so use plenty of it. Some paints will work for this purpose too and some will not. I think polyurethane or oil based paints will work but I am not sure which is best. Water based paints probably won't do as well.
air (oxygen) is an inhibiter which prevents surface polymerization of polyester resin for a long time - sometimes not ever. I doubt that the hardener has gone bad. That is a popular myth unless it is very very old. You do not want to use excess amounts of it either - another "bigger hammer" approach which will not work. Mold release is permeable to oxygen and so it will not help this problem. It is definitely not a plasticizer and I doubt that it is an inhibiter in and of itself. You need to seal out the oxygen long enough for the surface resin to set up. Polyester resin comes in two main versions - laminating and surface coating. The surfacing mix has about 2% wax added. If you have an area which still needs to cure, I would wipe a very small amount of peroxide or bleach over the surface and soon afterwards follow that with some wax. You can use just about any solid wax. Crayons or candles come to mind. Wipe it on and heat it with a heat gun to spread it around over the entire area. The heat is probably needed to help the resin to set up too. Without heat, it may still take a few days to harden even after you seal the area. Once the surface is hard, you can scrub off the excess wax so use plenty of it. Some paints will work for this purpose too and some will not. I think polyurethane or oil based paints will work but I am not sure which is best. Water based paints probably won't do as well.
Right off the can
I just read the directions on a can of SeaFit white gelcoat. It states that you must use a barrier coat (plastic wrap?) or a PVA mold release over the Gelcoat to prevent tacky cure. I have to admit though that I've been getting good results without coating it on small dings. I've used the PVA in the past with good results also. Go figure.
I just read the directions on a can of SeaFit white gelcoat. It states that you must use a barrier coat (plastic wrap?) or a PVA mold release over the Gelcoat to prevent tacky cure. I have to admit though that I've been getting good results without coating it on small dings. I've used the PVA in the past with good results also. Go figure.
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