Not enough fiberglass hardner

Submitted byUHBlackhawk onSun, 04/26/2020 - 09:02

Well, day 1 of my wood kayak build and I made a dumb blunder. Read the manual twice. Reread the instructions. Then dutifully pumped twice on the resin once on the hardner. The application looked really good. I'm thinking I got this.

Day 1, still tacky. I'm thinking it's maybe a little cool in the basement (it's between 65-70) so I get a space heater.

Day 2, still tacky. I reread the directions again. I followed them. Then it dawns on me. I put a restrictor on the hardner container so 2-1 is one pump of each. Instead of 2-1 I mixed 4-1. What an idiot.

Ideas? This is on an inside seam. It's a fiberglass strip with mylar over it.


Given enough time and ventilation the acetone should evaporate completely without raising the grain. The fumes are nasty so work with as much ventilation as you can get. Portable fans are very helpful.

Uncured epoxy can also be removed with vinegar, available at the grocery store. Use it full strength as it comes from the bottle, which is usually around a 5% solution of Acetic acid. It also will evaporate completely but being mostly water it will take a little while to dry. It will soak into the wood, which might raise the grain or swell the wood if it has not been previously sealed. After drying, the wood should return to close to original size but might require a quick touch up with sandpaper to tame any swollen grain. You might use gentle heat, say from a hairdryer, to encourage the wood to dry.

Vinegar is cheaper and a bit safer, but give it longer to dry and get rid of all the moisture before applying your epoxy.  Trapped moisture has a nasty way of turning into water vapor under the fiberglass and causing ugly bubbles and delamination when the boat is left in the sun on a hot summer day.

Removing partially cured epoxy is a messy business. Sorry to hear you have to deal with it.





Sun, 04/26/2020 - 16:35

It's a rare epoxy user who can't say "Been there; done that" about mixing mistakes.

Absent-mindedness or interruptions can cause similar problems.

Once I had pumped out 'x' portions of epoxy and got interrupted. When I came back it was a case of "Was that 8 or 10 shots of epoxy??". Since then, I always pump 'one resin, one hardener,one resin one hardener....'

Many many gallons of epoxy later....

...I used three times as much resin as I needed while I was attempting to give my hull a graphite/epoxy layer. I was very successful in scraping off the gooey mess and using acetone to clean off the residues with no traces remaining of my forgetfullness. Use acetone with good ventilation. Note that nitrile gloves will start to break down after two acetone soaked rags worth of work...toss the gloves after a few minutes, do not try to keep using them. Acetone soaks into the skin, faster through thin skin, slower through the thicker skin on your hands. It will not kill you if it gets through your skin but it is a bit hard on the liver, like alcohol. I used those blue shop towels to do the job, they are cheap, do not break apart so easily, and allow the soaked in acetone to evaporate fairly well, so the risk of leaving flammable garbage laying around is further reduced. Let them dry off outside in a bin.

I recoated the hull...all is well now.

Robert (Do)N('t be me) Pruden

I made that mistake when I first started building 20 years ago. Hmm, has it been so long now? Feels like it has. Back then I was not a rich man so I was epoxy cheap, making a mixing ration error could get me frustrated with myself. I started doing the 1 and 1 thing. Forgot everything after the long winter...ah well, I got it right the second time...again. 

Robert N Pruden


Fri, 05/01/2020 - 09:23

Now I'm befuddled and frustrated. I did the correct ratio. Glassed two panels. Came out perfectly.

So I moved on to doing four panels. I know I used the correct ratio. Thirty-six hours later... still tacky. So I talked to the manufacturer and per their directions cleaned it off and tried again. This time I wasted a little resin and hardener "priming" the pumps in a separate cup to ensure the ratio was correct. They said since I was using so little a small "gap" in the pumping could make a difference. Twenty-four hours later... and still not curing.

I'm doing this in my basement. Temperature is about 65-70 degrees. I purchased a thermometer. The lowest I've seen was 63 this morning. When applying it's been 67-71. I put the resin and hardener in a warm water bath before using it.

So... I've tried to fiberglass 11 panels and have been successful with two. I'm getting ready to put this in the yard and torch it.

I am not sure what system you are using but weighing epoxy on a digital scale is always the safest approach. Just make sure you follow the vendor’s guidelines.  For example, the MAS ratio by volume is 2:1 but, by weight,  it is 100 grams epoxy to 45 grams of hardener.

I am following the vendor's instructions. There is a "restrictor" on the hardener, so 1 pump of resin and 1 pump of hardener gives a 2-1 ratio. I was afraid after the first batch didn't cure that maybe resin or hardener wasn't coming out right away so I "primed" the pumps.



Fri, 05/01/2020 - 11:54

It sounds like you are using System Three 2:1 Epoxy with a plywood kayak kit (Mylar for joining panels). Is this correct?

David has given you excellent advice.

It's a lot more tricky to measure and mix small batches.


Aside from checking the pump calibration, you can check your mixing technique.

The pumps are on the correct bottles? 

I've used a lot of epoxy -WEST and SystemThree and can't recall having many cure problems. Once in a while I notice I've had 'a close call' when the leftover in the mixing container doesn't cure really hard, because I didn't scrape the sides of the container properly. A square-ended mixing stick is 'a must' to get all the epoxy mixed. If you are using tongue depressors for mixing, saw or sand the end square.

Once I get a set of pumps working properly, I keep the same ones in use for years. 


Fri, 05/01/2020 - 11:56

Try warming the 'still sticky' joints to eliminate time and temperature as possible problem areas.


Fri, 05/01/2020 - 12:52

I talked to the vendor and we calibrated. I found the issue. The hardener restrictor was not seated correctly so not pumping the correct amount. Reseated, calibrated, and it's fine now... I hope.

Cleaned the wood surfaces with lacquer thinner. How long should I wait for reapplication to let it dry?


Fri, 05/01/2020 - 17:32

Excellent,  but please think about weighing in the future.   I have had pretty good luck with the West pumps but even with these the first pumps after an extended period without being used the initial pumps are a little suspect.   Here is the scale I use -  $14.  ( I actually sneak ours out of the kitchen when my wife is not looking and put it in a ziplock bag to avoid the inevitable drips).   It is easy to weigh to a gram and the accuracy seems pretty good


Sat, 05/02/2020 - 18:32

I'd probably assume the lacquer thinner was evaporated when I couldn't smell it any more, sniffing the boat.

You might consider doing a test piece that's been given the same lacquer thinner treatment, just to make sure there are no adhesion issues.

About digital scales - I've used a few different ones. Be sure to test the scale - a lot of them 'go to sleep' after a very short working time and you can lose your measurement. That happened to me when I was halfway through adding the hardener to the resin. Result was wasting quite a few dollars worth of epoxy.


Sun, 05/03/2020 - 08:32

No matter how much you scraped and cleaned, sand the area before you re-glass. You will see clogged sandpaper fast. Just do that as a last prep step. Been there, done that. I don't trust pumps. I just always used small containers - 2 of this and one of that etc. Yogurt containers, coffee creamers, etc. Once you make the epoxy ratio mistake, you will never have it happen again.