RE: a call for chemists
- Thanx to all for responding to my call for bad mix counselling, especially
to John Bell for his professional insights. I've sort of broken the news to
my friend that he MIGHT (obviously) have to remove the failed epoxy and tape
and start over. At the time of my original post I did a bit of work in the
"lab". I butt jointed a couple of plywood scraps together with fibreglass
and a very weak epoxy mix to see what would happen. Similar to my friend's
kayaks, over several days the epoxy has cured to a point of non-tackyness.
But I'm able to bend the assembly at the joint, which I obviously should not
be able to do. I've offered to help my friend salvage his kayaks (I really
wish he hadn't tried to build them both at the same time!). However, the
weak epoxy seems strong enough to hold the shape of the hull so we can tape
and epoxy the outside chines and keel on each boat. My hope is that we can
remove an replace the inside epoxy and tape without his having to re-stitch
the panels together. Here are my questions for John and anyone else that
might have experience with an operation of this kind:
Is the weak epoxy still soluble with acetone even if it's no longer tacky?
If so, how should the acetone be applied?
Is my plan to tape and epoxy the outside a bad idea, re. acetone seeping
into and weakening joints?
- For what it's worth, I built a kayak from 4mm ocoume ply taped and epoxied only on the inside. The outside is finished with a nice varnish - no glass or epoxy.
The designer of this kayak, Lars Herfeldt of Berlin, has built 20-odd kayaks using this construction and they've all worked nicely, with none falling apart.
The reason for not glassing/epoxying the outside is for lightness - my kayak weighs in at 34 pounds, complete with all fittings. Of course care is needed when launching and landing not to get it scratched.
Anyway, what I'm getting around to saying is if the tackiness is gone from the inside seams, and the outside of the seams is to be glassed and (properly) epoxied, it could well have plenty of strength without re-doing the inside.
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- I am not a chemist, but I play one at work. Well, actually, I play a biologist, but I have fooled around a bit with epoxy.
I had some epoxy snafus this winter (possibly due to mixing MAS with Chinese measuring spoons). I found that the incompletely cured epoxy was somewhat removable with a scraper, and that vinegar would somewhat dissolve it.
Using vinegar for uncured epoxy cleanup (especially on skin!) is preferable to using toxic solvents.
I also found that Permatex Paint and Resin Removing (PARR) hand cleaner, aka Painter's Clean, will remove partially cured epoxy as well as 5200 from surfaces such as plastic and gelcoat, with a little scrubbing. If you use it on clear plastics, beware, it is abrasive and will leave scratches. The only trick is, it is virtually impossible to find at retail. Apparently you can order it from Grainger's, but Grainger's (at least locally) will not sell to you unless you have an account, and will not give you an account unless you are a business.
On my home computer I have an address to mail-order it, if anybody wants it contact me off-list.
- Schooner CASHIER Restoration wrote:
> Using vinegar for uncured epoxy cleanup (especially on skin!) is preferable to using toxic solvents.Yes, but please be aware that the non-toxic vinegar will quite happily
carry the nasties from the epoxy (mainly the hardener) into your skin.
It is much better to not get any on your skin in the first place.