Working with Epoxy: Squeezeout, runout, cleanup?

[ian maybury]

I may be missing something, or over generalizing - and pardon me if i am as i'm not a chemist - but are you sure Tom? Either way i was just trying to paint a picture, and didn't set out to divert the discussion. None of the issues are blockers to using epoxies in most cases (one of my favourite adhesives), but the liking for heat, need for accurate mix ratios, need for choice of the right resin system, oxygen inhibition at the surface/wax/oozing of excess leading to the possibility of difficulty in bonding over a previous coating of epoxy are all pretty characteristic.

So far as i can recall most of the overbonding difficulty in standard resins arises from the inevitability of imperfections in the mix ratio, it's the UV/light curing variety that suffer most from oxygen inhibition. The wax issue relates primarily to laminating resins.

There are differences between formulations and resin types, but this link for example discusses the inhibition issue as it impacts UV curing resins (see from about eight posts down), an epoxy makers comes in at the end: http://forum.surfermag.com/forum/ubb...te_id=1#import Googling 'oxygen inhibition' brings up all kinds of tech papers on the topic - its an issue with many types of polymerising resin systems as well as epoxies.

Different strategies get used to tackle the re-bonding issue in different situations, and it's certainly got to be a minimal issue inside a sealed glue joint since it's unlikely to be re-coated - but it can be very significant if trying to recoat externally to smooth a fillet, or when adding a second coat to further seal a surface or something like that - especially if you end up cutting back through the top layer.

One essential difference between an epoxy and a polyester resin cure is that the epoxy is a stoichiometric system which to my only very basic understanding of the chemistry means that each molecule of cured polymer requires a given number of molecules of each of the resin components. Add a little too much of one or the other, and the surplus simply doesn't get used, and as well as producing side effects like the tacky surface mentioned the properties of the cured material rapidly disimprove. Polyester is different, in that it's a catalytic cure. The hardener by its presence triggers a cure in the already present resin. Adding extra speeds up the cure, but it makes little difference (within reasonable limits) to the final properties of the cured material.

[Mike Cutler]

Ian

You have it correct at least as far as I understand it.
A long time ago in a life far, far away, I worked in a boat yard. We repaired everything from 12 meter America's cup boats, to wooden pull boats. Now I use epoxies in high temperature electrical applications, think Nuclear Reactors.

Epoxy and Fiberglass resin both have a "cure time". Most "generally" available epoxies will have three time constraints. Open time, set time and cure. General use epoxies will set in about 24 hours and will reach about 80% of their bonding strength in that period. After about a week, it will be at full bonding strength.
Epoxies have a resin and a hardener. Fiberglass has a resin and a catalyst. Epoxy cures by heat and the resin/hardner ratio needs to be correct. Polyester resins have a catalyst and cure by chemical reaction.

Tom

I really like those golf rags. I have to get me some of those. Thank you for that tip.

[Shawn Crane Davies]

We use west systems at work. Xylene and denatured alcohol work extremely well for clean up. I prefer the denatured alcohol, slightly lower flash point, stays on your clean up rag longer. A slightly damp rag with either cleans easier than the water and white/yellow glue clean up gig. Leaves no damage/staining to the wood.

[Prashun Patel]

In general, the longer the set up time, the better the holding power in epoxies. I use system three.

the viscosity of a slow setting epoxy will be like thick or cold honey.

dont try to wipe up epoxy while it sets. Use tape to mask if you must or just chisel or plane it off when dry. Chiseling epoxy a little before fully cured is easy. It's soft enough still that it peels in ribbons. Or you can wait until it's fully cured and just plane it off or sand it off. I have never had issues doing it either way.

use the recommended solvent for the epoxy to clean up spills or tools. It's usually acetone. I would not apply the solvent to the wood to clean up squeeze out when wet. You risk the solvent thinning the epoxy by penetrating into the joint too deeply. Acetone penetrates through wood way more than water so don't think just because we can use water to clean wood glue from wood that we can use acetone to clean epoxy from wood.

[Tom M King]

The only "resin" I know of that contains wax is polyester get coat. Gel coat does not completely cure in contact with air. Some of it has wax in it that floats to the surface, so it can cure, and gel coat without the wax has to be coated with something like PVA. It will almost cure without the wax, but it will never get hard enough so that it can be buffed out to a gloss. I've never had any kind of experience with any kind of laminating resin that has wax in it. One of the things I do is boat repair.

I know the conversation got way more complicated than applies to the OP's question, but all of us enjoy learning something.

After thinking more about it, for a bench build, even with as much experience as I have working with epoxy, I would not use it for a Roubo bench build. Especially if there is little to no experience working with it, I'd suggest starting on smaller projects. It has its own skill set requirements that are best learned by hands on, but not on a big project that requires that skill set to start with.

One of the good things about Epoxy, with my favorite being West, is that I haven't found the end point of shelf life yet. I keep the five gallon kit in the tool trailer for working on old houses, and it lasts for years.

[John Sanford]

I have used that Loctite epoxy before and it does a decent job depending on what your project is.

The consistency is very much like honey. Also like honey the colder it is the thicker it is. Like everyone else stated it is easiest to shave off squeeze out before it is fully cured. The actual cure time depends on how warm the epoxy is, the warmer the faster it cures.

What are you using that epoxy for? What is your project?

The project is a Split Top Roubo. I am using it only for attaching the endcap and the condor tail joint. Everything else has been/is being done with TiteBond III. I'm using the epoxy for these two joints primarily because for the gap filling characteristics. To say that tail sockets are shabby would be too high of praise.

[Tom M King]

Yeah, epoxy sounds like the right choice. Just make sure to take the masking tape off right before it sets completely up, but not too soon for it to still be runny. Just like they do with the dripping down slobbers after the top lamination of a surfboard, slice it off with a razor blade just when it's easy to work with, but won't make a bigger mess. Wait a little too long, and it's 50 times more work. Too soon, and it makes a bigger mess.

[Christopher Morgan]

Acetic acid works well for cleaning uncured epoxy off tools, etc. And it is both cheap and safe enough to put on your salad.