Uncured epoxy problem

To mark a recent significant birthday (ain't they all?) I received from a frend in Canada beams to incorporate into a cast iron framed bench installed in a wood that I planted some years ago. The maple beams have been milled out in places and sections of small trees have been inserted within a black matrix, which I think is formed by a two part epoxy. The problem is that under bright sunlight the matrix melts, bubbles and becomes soft and very sticky. I don't want to go back to the donor so I need to work out a way of dealing with the problem which is quite local to one part of one beam. Any ideas welcome

Are you sure it's the epoxy and not resin from the wood?

David

Is it the resin and not sap? I think you will need to start by identifying the type, eg polyester or epoxy maybe by smell?

I had a similar issue with cross laminated Cedar planks - Eventually discovered that the resin in the raw wood was not fully dried when embedded in epoxy, and the heat frmm the epoxy exotherm during curing ( about 40 to 45deg C) caused the wood resin to exude and this inhibited the epoxy cure in a number of places. In direct sun the epoxy would soften more and dribble out in the wood grain.

There was no cure (sic)..

Subsequent laminations were preceded by long periods of drying in a wood curing oven - 3 weeks @ 40dec going down to 30degC in the last week.

I suspect in your case the 'small tree' sections were uncured and high in wood resins, maybe even wood sap.

I think the only way out is going to be to cut out the offending area completely, and redo it with cured wood..

I would agree with Joseph, dig it all out and remake it

Brian

Before you lose hope and commit to digging ugly big holes in your beams, it might be worth living a bit dangerously. try cooking the exudate with an hot air gun. Heat the mess up to just below the temperature at which the wood chars (that's the living a bit dangerously part). With luck, whether it's uncured epoxy or resin, it will harden to the point where it can be chipped or scraped off (when cold). Alternatively, you could try rubbing the stuff with rags soaked in acetone. Happy birthday!

Edited By Kiwi Bloke on 11/04/2023 03:28:50

Oops, double post. Is there any way of deleting an entire post?

Edited By Kiwi Bloke on 11/04/2023 03:28:12

I fancy it is resin, be it natural or chemical ! Acetone will remove uncured resin but only on the surface so it looks like a real problem, time might solve it ? Noel.

I have cast polyester resin and the only reason it will not set correctly until much later than usual is if not enough hardener is used. Even then it will eventually set none of those have ever gone soft after it has hardened when it has got hot.

Not had any experience of some of the other types of resin but could imagine that they will eventually set if too little hardener is used.

When was this made it looks like a good depth of resin some do not like thick pours (over 2" depending on the resin) these are normally poured in small thicknesses then the next is poured this does need to be done at the right timing as if one layer is allowed to harden fully you will not get a good bond to the previous one.

Looking at the picture it appears to only have bubbled around the wood and not in the centre of the resin

Could be trapped air pockets within the resin pour expanding with the sunlight, just a thought I had.

MichaelR

Many resin casters use a pressure pot to reduce the size of any air bubbles and once set they will not expand or cause the resin to go soft.

none of the pens that I have made using resin have either gone soft or exploded due to air bubbles expanding(some have exploded due to me doing something wrong)

Thanks to you all for some very useful insights. I now agree that the exudate (I only knew this as a medical term for pus!) is almost certainly wood resin probably mixed with a small amount of uncured expoxy paste which gives it the black colouration. In which case it is a long term problem, rather like the tar coming out of some railway sleepers I used as a raised bed edge on hot days.

I am a bit reluctant the get the bench back from the wood into my workshop as it is a long carry but I will try the acetone cleaning and physical removal in the hope that eventually the leakage will cease.

The wood was planted on a bit of rough land we own using a grant from the Woodland trust that commemorated all who were involved in the 1st world war and the bench has a plaque that mentions the death of a great uncle of my friend who sent me the pieces - unfortunately he sent two right-hand end castings as can been seen in the photo - however it does not detract from the peace to be gained from sitting and looking at the 650 young harwood trees I planted in 2018. Being stuck to the seat with resin is however not conducive to calm thoughts.

.

I’m not sure if this will help, or hinder, Tony … but I would just mention that the best solvent for Canada Balsam is Xylene.

If you can scrape out some of the offending exudate, it would probably be worth doing some sample tests before proceeding much further.

MichaelG.