Gelcoat hardening problems....

[bchesley]

I had to do some fiberglass repairs this winter on my floor and stringer in my 83 2001. I finished the repairs and tried to redo my bilge coat and am having problems getting it to harden. THe first batch of gelcoat never set but stayed tacky. The second coat, and third coat the also stayed tacky in places. The first coat was wiped out with acetone before recoating as with the second. I am using the right amount of wax and hardener. I have sections of each batch that will harden and then some will not. I dont know what I am doing wrong?? Has anyone else had a problem like this.

Brad

[ag4ever]

RE: Gelcoat hardening problems....

Gell coat must be sealed from the air to fully cure. Some spray wax on it, some mix a wax like substance in the wet mix, and some lay saran wax on it to seal it off. Either way gell coat can not be exposed to air and fully cure.

[bchesley]

I mixed the wax sealer (gel coat surfacing agent) that you are supposed to put in it. What gets me is sections of it hardened and then other areas did not. I mixed it with the exact amount of hardener and wax that the specs call for? I dont know what to do next. This is really cutting into my season.

[MHayes]

My only guess is that you are not mixing it as well as should be?

[ag4ever]

Has it been really humid or rainy up there?

If the humidity is toohigh it will afect the cure time.

Also if some cures and some does not it sounds like either too old of a product, not enough hardner or not mixed well enough.

The hardner ratio is kinda an art. If it is cooler, you need more, if it is hotter you need less.

Don't work on it if it has rained within the last day or two.

[bchesley]

It has been extremely humid lately. Good news though a cool front came through and dried up the air. I am going to try again today and pray that it works.

Thanks.

[DavidF]

You should never work with gelcoat in temperatures less than 65 degrees as the cold air AND surfaces will prevent it from curing. Remember the curing of gelcoat is a chemical process that produces heat. The heat is necessary for a proper cure. Cold surfaces and temperatures prevent adequate heat for a proper cure.

I suggest you warm the surface you are attempting to gelcoat with a heat gun. Then, after you apply the gelcoat, use the heat gun to keep it warm until it kicks.

You may want to try using a bit more wax and a bit more MEKP. If I remember correctly, I used between 15-20 drops per ounce of gelcoat in the color weather. 10-15 in the hotter weather. If some parts stay tacky by the next day, it may be just the surface that can be wiped off with acetone (i.e. the wax did not do its job). The wax/styrene solution seperates in the bottle and MUST be properly mixed before use (or it will not properly work). Warming the bottle with a heat gun helps termendously.

Let me/us know if you continue to have problems.

[ag4ever]

If you have seen the work that David has done, listen to him. He is amazing with fiberglass and gell coat work.

[DanielC]

Polyester resins and gelcoats harden by two processes going on. First, the solvent evaporates, and then the resin cures, and sets by forming long interwoven molecule chains. Humidity inhibites the surface cure, so more can be applied later without sanding. Anything that seals off the surface will allow the resin, or gelcoat to cure. Covering the gelcoat with a plastic film is one way. Adding wax to the mixture is another. However, if the layer of gelcoat, or resin is too thin, the wax cannot migrate to the surface of the fresh gelcoat, and no surface cure. If you are not spraying the gelcoat, sometimes it might help to let it sit for a while, and let it thicken up. There is an art to working with gelcoats, but it takes some time to figure out. Take very careful notes of everything, tempeture, humidity, amount of gelcoat, amount of hardner, amount of surface cureing agent (wax), time of day, any heat applied, and anything else you can think of, and after a while, you can start duplicating setups, and have more sucesses. I have gotten good results with cold semi humid days in Oregon. I like taking a little more time in the winter for monor gelcoat repairs, and play with the boat in the Summer.

[bchesley]

Thanks for all the info. I think that we have it figured out. It has been really humid and unseasonable hot the days that we were working on it. We put less hardner in it this last time as well as a cooler day, and it hardened like it should. I also was really thorough when wiping down the areas that it was applied to, because I think some of the residue from the uncured gelcoat from my first try was also messing it up. My theory is that the mix was too hot and it was setting up before the wax could rise to the top therefore not sealing and allowing it to cure. Hopefully monday I can put the interior back in it and hit the lake next weekend.

Brad

[DavidF]

You will know when you add too much MEKP as the gelcoat will boil (i.e. have tiny bubbles in it). The only time I ever have gelcoat curing problems is when applying over fairing compounds.