F/G Resin, Bad Batch

-- Last Updated: Aug-23-10 7:37 PM EST --

Ok, I've been rebuilding the Malecite and cut out the new decks, same as the last but this time decided to put resin on it, no cloth. The batch mixed badly and is taking forever to cure. Doesn't help it has been wet and humid for the last few days. It's almost dry to the touch in most areas.

So in talking with a guru it was mentioned that he thought that a properly mixed batch of resin might be the fix instead of starting over. These decks follow the gunwales and are rounded on the bow and stern and then go back 28". I just like the bigger decks, don't ask. I'm using leuan (sp?) as it is light and seems to have held up well with the last set.

So, can a fresh layer be laid on even though some spots are a hair tacky or should I wait it out? My other thought was to lay on a few layers of spar varnish but am wondering about the chemical bond between the two materials? Done some reading on that. It seems sanding is a big issue but don't think I can get away with it with the "damp" spots.

Any opinions or advice would be gratefully listened to. I'd like to get this boat back on the water.

Many thanks.


Try working it over with a hair dryer/heat gun, be patient. I’ve been told that the slower epoxy cures the stronger it is.

Epoxy, Polyester, or Vinylester? NM

epoxy curing problems

– Last Updated: Aug-23-10 10:01 PM EST –

Hi Doug,

I had epoxy once that wouldn't cure in spite of time, sunlight exposure or heat gun application. It was brand name epoxy, so I called up the company to discuss my problem. They said the only way that could have occurred was from an incorrect ratio of resin to hardener. I had about ten years of amateur use of epoxy in boat construction and had never before incorrectly measured the ratio. I was sure the company was wrong and just to prove them wrong, I mixed up a new batch using the correct ratio. To my embarrassment, it cured properly.

Chastised, I then followed their suggestions of removing the week old and still tacky epoxy with acetone and redid the epoxy coating, measuring correctly. I haven't named the epoxy brand since it proved to be my improper measuring, not a flaw of their product.

The leun (sp) now sold is crap and the quality deteriorates more every year. While it was an inexpensive option a number of years ago, there are now extensive voids throughout almost every sheet. I suggest using 4 mm marine plywood. While much more expensive, it remains a very high quality product with almost no voids. If you don't want to pay the cost of 4mm marine ply, there is a floor underlayment sold that is vastly better in quality than leun(sp) and splits the difference in price.

Are you planning to go to Raystown this year? If so, are you bringing the Express? I'm enjoying the one I found; Thanks for the test paddle in yours. I'm now off the drugs that caused balance problems when we met.

Have fun, While the acetone fumes can be a cheap thrill-use a mask.


Mix, mix, & measure
I read that inadequate mixing can cause a batch to not harden properly. Are you sure you mixed well? Maybe you measured correctly but didn’t mix enough.

Regardless, I have had some batches that seem as though they are never going to harden. I mixed a lot, so I think I measured wrong. Eventually, everything has hardened.


F/G , maybe your catalyst (mekP) …

– Last Updated: Aug-24-10 7:19 AM EST –

...... is out of date , has short shelf life (6 mos.) . Maybe your mix ratio was incorrect or not well mixed . There are other possible reasons for the polyester to not cure out properly , but in any case it doesn't sound like it's going your way ... a few days is a bummer , way out of the parameters .

Another possible reason is it's just applied too thin , not enough mil thickness for proper thermal reaction .

General purpose polyester resin such as is used with cloth layups is not a very good choice for a top coat , it is not a clear gelcoat polyester .

If you need to , remove what will disolve with the acetone , what will not disolve is too far along in the curing process and should be able to be sanded away completely so you can start over . By using the acetone to disolve what will disolve , the remainder shouldn't clog up your sand paper nearly as much .

mixing up a new, good patch and applying it on the uncured patch will cure the uncured portions.

Call me if you want to get more technical. Easier to talk about then write.


802-496-5889 at the shop

If you’re using polyester resin…
…rather than epoxy…there are two possible issues:

1- You’re using a laminating resin which will not cure in the presence of air (this is the same issue people have with laminating gelcoat).

2- You used the correct resin, but mixed in too little MEKP catalyst or you have an old tube of MEKP that’s past its prime.

In the first case, the surface will not cure, so removing the soft material with acetone is the best way to go.

In the latter case, the resin will cure eventually and heating it will accelerate the process. Try placing a space heater or lamp near the area to warm it. If you’re doing a really large area, making a tent over the boat using cardboard or plastic tarps will allow you to heat the entire boat pretty evenly.

Bring it inside?
I’ve had resin not go off like it should and brought the parts inside because the AC made it dryer even though it was much cooler inside.

Just waiting and waiting will eventually make it go off in time unless you really messed up the mix.

It sounds like the typical humidity problem to me. If you have to leave it outside try peal ply or another plastic wrap.