JEM Watercraft

I've hit my first minor snag & wouldn't mind some advice from those with more experience.

On Sunday night I mixed up a batch of epoxy/woodflour to join 2 upper side panels.
Yesterday afternoon I went to sand & found the joint extremely flexible & the consistency of old chewing gum. You could dig your nail into the glue & you could get a 25-30 degree bend on the joint.
I remember thinking back that when mixing that it might need a bit more wood flour but decided it would be fine.

I'm now not sure if it's like this due to not enough wood flour or if my resin/ hardener mix ratio was a bit off (it was a small batch & this seems the most likely cause).
Tonight it seemed a bit harder but still a lot more flexible than all of the other joints.

Anyone else had this issue & if so, is it worth loosing another day or so to wait & see if it goes hard or should I just cut it off & re-glue?
Thanks.

Al

Al;
I would guess a bad mix ratio or inadequate mixing. Mix the resin & hardener throughly together first, then add the flour. The addition of wood flour should have no effect on the time it would take for epoxy to fully cure.

I like to keep the mix cup I used at the time around to check to see how it cured, if the slag in the cup cured, so did the stuff on the boat.

Give it another day and see, especially if your weather is on the cooler side, you might hang small light over the area to give some gentile heat to bump the temps up a bit and see if that helps.

DM

Sounds like a bad mixture.

Al
From my own limited experience, and it may just be me (someone is bound to get a chuckle). The smaller the batch in a big cup it’s hard to get everything mixed consistently. Also trying to get consistent measurements for small batches is hard for me. I use a cup that looks like Matts in this thread for three ounce batches http://jemwatercraft.com/forum/viewtopic.php?f=7&t=721 . I also measure my mix this way. For six ounce batches I use a 16 oz cup. I even have some condiment cups (I’ll have to check the size for real small batches, ¾ oz comes in handy for gluing stuff. I have just found a short cup with a narrow bottom is easier to get stuff mixed up. Like DM said if it's a bit cool and you are using slow hardener it could take a couple of days. HTH.

Joe W.

The wood flour would not have anything to do with the epoxy setting up, that is a chemical reaction between the two and not the wood flour.

The wood flour is like the flour used in baking , a filler. I would say it was a bad batch when mixed ( something really easy to do ). I like to use the measuring pumps , they provide the correct amount all the time , if you are careful. Yep , my mistake on it a couple of times and one took for ever to set and one set up before I could use it. Most of the time they provide the correct amount especially when I pay attention to them.

I also like to use the resin and then add the wood flour , when everything is mixed then I add the harder , since when it is added there is a time limit on when you can work with it before it sets up. If it is not just right it is really easy to add a pinch more wood flour when mixing the hardener in the batch.

All of us have different ways of mixing everything and what ever works for you is the way to go.

Chuck.

I've contacted a couple epoxy vendors and they say for best results to mix the resin and hardener before adding any filler. So that the "official" recommendation from them.

jem wrote:I've contacted a couple epoxy vendors and they say for best results to mix the resin and hardener before adding any filler. So that the "official" recommendation from them.

As Matt said.......
Best to follow there recommendations , especially since I march to a different drummer. Instructions , WHAT instructions ????????? ( It's a southern thing , we never think inside the box but we are good swimmers . )

Chuck.

Thanks for the quick replies guys.
As suspected it looks like a slightly off measure on the epoxy.
It's gone hard now (3 days on) so I'd say I was a fraction short on the hardener.


For the joints I'm mixing in cough medicine cups purchased in a pack of 50 from the chemist . They measure in 2.5 & 5ml increments & initially I was mixing 30ml at a time (don't ask me what that is in ounces or whatever you lot on the wrong side of the world measure in because I have no idea).
I've been trying to minimize wastage so have been mixing smaller & smaller batches. This batch was 15ml so I guess I know where the limit is now.

I always mix the epoxy for at least 5 minutes & there's no doubt in my mind that the hardener that was in there was well mixed. As suggested I mix first & add woodflour afterwards.

I could probably get away with the joint now but I'm a bit worried that the flexing will have damaged it so I'll cut & rejoin tomorrow. No big deal.
As far as mistakes go, this was a good one to have at this point in the build.
Thanks again.

Al

Sounds like you have a good plan to recover. Well done.

Not wasting epoxy is an art form. I won't even tell you how much I used on the first row boat I built yeas ago.

Here's a tip that Matt gave me. Take two, plastic cups - a kind you can see through. Put "magic" scotch tape on the outside of one so you can mark on it.

Put the two cups together. Add 1/2 oz of water to the inside cup; mark and label the level on the outside cup. Pour it out and add 1 oz. Again, mark and label the OUTSIDE cup. Same procedure for 1 1/2 oz, 2 oz, etc. on up.

NEVER PUT EPOXY INTO THE OUTSIDE CUP. Keep it clean. Use a new cup inside for every batch of epoxy.

Thanks, Matt