How to fix an epoxy batch that isn't setting up?

[cornercanyon]

I need a little help. After mixing and working several gallons (a quart at a time) of epoxy one batch isn't setting up. 48 hours after I laid it down it is still tacky. I have been getting up at 4am and working until about 7am to beat the heat, so temp is not the issue. I assume this is caused by too little hardener or not throughly mixing? This particular batch is over the original hull interior and several other batches on either side set up fine. So, prep was the same for the entire area.

What do I do now to get this batch to set up and keep moving forward?

 

[chrishayes]

Re: How to fix an epoxy batch that isn't setting up?

I am using epoxy in my build as well. I am really happy that I have been through 3 gallons and havent had a bad one yet...except one. I knew that it would happen, I use mixing pumps on my bottles and I know to change them to a full bottle when the thing gets 1/8 empty or it will suck air and screw up the ratio. Well...I decided to "eyeball" it. Didnt work! you really have to be pretty close with the ratio. All I can say is that it took 3 days to cure but it did eventually cure. If it hadnt I wouldve tried to heat it up, if that didnt work I woulve tried to acetone it to see if I could get the slight stickeyness to go away(mine really was not that uncured, just tacky) or I would have as a last resort tried applying a nother coat over it. I doubt any of these would have worked to my satisfaction so I would likely have ground it out and started over!

How much did you use? Is it on glass?

 

[cornercanyon]

Re: How to fix an epoxy batch that isn't setting up?

Thanks for your thoughts chrishayes. I appreciate the help.

Sunday morning in preparation for setting my stringers I coated the entire bottom of the bare hull. So, I am adding a layer of epoxy over the original poly/fiberglass. This took quite a few quart batches. It appears one batch near the end of this session isn't setting up. It is still tacky (Tuesday) and I leave a print if touched.

I think I might be able to scrap it off with a plastic trowel, I don't think acetone would take it up.

 

[metriccrescentwrench]

Re: How to fix an epoxy batch that isn't setting up?

Be careful with epoxy. There is one and only one correct ratio of resin to hardener for proper curing. Anything else and, even if it seems to harden, it won't have the proper strength.

MEK usually works pretty well as a solvent for uncured epoxy.

 

[erikgreen]

Re: How to fix an epoxy batch that isn't setting up?

Yes, you can be about 10 percent on either side of the correct ratio and it'll still harden, but more accurate is better.

I don't even use the pumps, I measure by volume using marked plastic quart containers. I haven't had a batch fail to cure yet, and it's a lot faster than pumping.

Some people also mix by weight, but you have to be careful and calibrate first... measure out an accurate volume and weigh it, since you can't just use 3x or 4x the weight of the resin for the hardener... it's a different density.

Once you calibrate that way and use a digital kitchen scale you can easily mix exactly each time.

This time, you need to scrape the bad epoxy off and re-do it. Sorry :\


Erik

 

[cornercanyon]

Re: How to fix an epoxy batch that isn't setting up?

I use marks on my plastic containers. I must have just missed one of my marks. Anyway, I will clean it up with mineral spirits in the morning and go on. Thanks for your help.

 

[cornercanyon]

Re: How to fix an epoxy batch that isn't setting up?

Okay, well as most of you all know, mineral spirits didn't really get all the unset epoxy up. MEK sure did and as careful as I was in my "alien" suit I don't want to play with that stuff too often.

So this morning everything is cleaned up, a new (very carefully measured) batch is down and we are moving forward again. We will have stringers and floor in this weekend (unless I sell my FJ Cruiser to some folks in Tennessee and have to deliver).

Thanks for everyone's help.