epoxy question

[snuggles]

Hi , building rocket w TTW fins.
Left aft MMT bulkhead off so I could pour epoxy.
Mixed epoxy with a bit extra hardener.
Rolled rocket around to get epoxy where it needs to go.
Checked after a couple hours.
Some small leakage past FWD MMT bulkhead.
Quite sticky in spots.
How do I get rid of the stickiness????
Thanks
Mark T

 

[cjestice]

Let me get this straight? you're using epoxy and are complaining that things stick? :wink:

The right thing to do is to lay down tape ahead of time over the area where you don't want epoxy. Once the epoxy starts to firm up, peel off the tape and the remaining epoxy will be firm enough not to run.

Cal

 

[Rich Holmes]

From https://www.westsystem.com/ss/problem-solving/

Off ratio: Too much or too little hardener will affect the cure time and thoroughness of the cure.

1. Remove epoxy. Do not apply additional material over non-curing epoxy. See epoxy removal note in User Manual.
2. Check correct number of pump strokes: Use equal strokes of resin and hardener. DO NOT add extra hardener for faster cure!
3. Check for correct pump (5:1 or 3:1 ratio) and pump group size (Group B resin and Group B hardener).
4. Check pump ratio (see pump instructions). See Dispensing in the User Manual.

As I understand it, and I am no expert, extra hardener does not make the epoxy harden harder or faster; it just finds it has nothing to do, because there isn't enough resin for the hardener to interact with, so it just stays there being gooey. It's possible it may lose its stickiness slowly. Maybe give it a day and see what happens.

 

[AlexK]

Epoxy is pretty vastly different from polyester resins in that the hardener is part of the reaction. Polyester resins use the hardener as a reaction catalyst, so adding more hardener (within reason) will speed up the cure. That doesn't work with epoxies, as the extra hardener will effectively be 'left over' after the reaction is finished and the resin is consumed. That extra hardener will basically never cure - it'll be an oily, sticky residue effectively forever. I'd give it a while longer, just to make sure you let it get good and fully cured, before declaring it a problem. If it's just inside the body tube, it may not be a big deal - there's nothing in there to stick to.

 

[G_T]

How much extra hardener?

You might want to make a tool from some rod to scrape it off and start again, if it is more than a tiny bit extra.

Gerald

 

[TheTellurian]

Remove as much as possible then powder it with talc or baby powder.


Richard

 

[hornet driver]

Epoxy is pretty vastly different from polyester resins in that the hardener is part of the reaction. Polyester resins use the hardener as a reaction catalyst, so adding more hardener (within reason) will speed up the cure. That doesn't work with epoxies, as the extra hardener will effectively be 'left over' after the reaction is finished and the resin is consumed. That extra hardener will basically never cure - it'll be an oily, sticky residue effectively forever. I'd give it a while longer, just to make sure you let it get good and fully cured, before declaring it a problem. If it's just inside the body tube, it may not be a big deal - there's nothing in there to stick to.

Yep +1. I just got done putting 3 epoxy coats on my 20 mill nose cone the second batch was just a smidge off---seemed to stay a little sticky for days, finally cured but it had me worried, and I was only a tiny bit off.

 

[snuggles]

Yep +1. I just got done putting 3 epoxy coats on my 20 mill nose cone the second batch was just a smidge off---seemed to stay a little sticky for days, finally cured but it had me worried, and I was only a tiny bit off.

Thanks for the tips. Everything worked out OK this time.
I used finishing epoxy on another build.Mixed up a batch, (using the patented calibrated elbow approach) Poured the mix (not a LOT) down the BT to the upper CR to lock it down.
!@#$%$#%$thing never dried completely!!! Ended up putting baby powder inside to fix problem.
Hoping to avoid a repeat.
Mark