Thread: Old epoxy weird behaviour (??)

Corflute is made from polyethelyne (sp?) aka HDPE or LDPE - in solid blocks it makes reasonable bearings, but very few things will stick to it (unless you don't want them to ). Most Velcro type products are also made from slippery plastics like nylon, HDPE etc. so its no wonder you had to get extreme with the preparation and application - I'm a bit surprised you didn't just get peeling off every time instead of have some stick and the glue fail.

As for glue failure - many things have been marketed as 'epoxy' glue over the years and only some of it is the real thing. If it is actually a polyester based resin with a filler and MEK catalyst as the 'B'part, the MEK could have partly evaporated which means it won't set to full strength. Some Polyurethane curing agents also have a definite shelf life due to internal chemical reactions or evaporations. And some real epoxies are just plain very sensitive to the correct amount of curing agent, often in the range of 1/100th of a gram or less for some specialist formulations.

Basically, if the glue fails use it to repair broken plant pots or something non-critical and get a new lot of Epoxy from a reliable company like Selley's, BoteCote or West, which are formulated for people like you & me.

Try using contact cement instead. AKA Shoe Glue

If you are not sure of the epoxy, try it on some timber.

Originally Posted by bsrlee

Corflute is made from polyethelyne (sp?) aka HDPE or LDPE - in solid blocks it makes reasonable bearings, but very few things will stick to it (unless you don't want them to ). Most Velcro type products are also made from slippery plastics like nylon, HDPE etc. so its no wonder you had to get extreme with the preparation and application - I'm a bit surprised you didn't just get peeling off every time instead of have some stick and the glue fail.

As for glue failure - many things have been marketed as 'epoxy' glue over the years and only some of it is the real thing. If it is actually a polyester based resin with a filler and MEK catalyst as the 'B'part, the MEK could have partly evaporated which means it won't set to full strength. Some Polyurethane curing agents also have a definite shelf life due to internal chemical reactions or evaporations. And some real epoxies are just plain very sensitive to the correct amount of curing agent, often in the range of 1/100th of a gram or less for some specialist formulations.

Basically, if the glue fails use it to repair broken plant pots or something non-critical and get a new lot of Epoxy from a reliable company like Selley's, BoteCote or West, which are formulated for people like you & me.

I was not surprised by the initial un-keyed failure. I could see that the plastic was going to be a tough cookie. But when the glue basically disintegrated, that was a surprise. Interesting about the velcro. I could agaon see it was a slippery plastic, but it looks as if it has a weave or grain so I was expecting it to take.

I did not know about the dodgy "epoxies". I doubt this is polyester, as it has worked well in the past and polyester AFAIK is never a good adhesive.

Originally Posted by Cliff Rogers

Try using contact cement instead. AKA Shoe Glue

If you are not sure of the epoxy, try it on some timber.

I have never had much luck with contact and small areas.


HAH! I was just walking around this morning thinking about doing just that with the wood!

Originally Posted by Cliff Rogers

Try using contact cement instead. AKA Shoe Glue

If you are not sure of the epoxy, try it on some timber.

You guys gave time and advice, so here is the wash-up.

Cliff, I owe you an apology. I thought about my dismissal of your shoe glue idea, and felt I owed it to you to give a go....and it worked a treat! So. Thanks

And I took some 20mm ply and glued it edge on to a piece of scrap pine with the Epoxy (which is Polymer Daystar BTW) and left it lightly clamped. It took a fair whack to break the join with a hammer. The glue gave, not the wood. However there were two things, it was only overnight and most of the morning, and I was separating the pieces by applying force along the grain of the wood, where I reckon tear-out would be less likely. I am going to have another go, leave it for a good 24-48 hours and try again, maybe across grain this time.

Again. thanks for everybody's help.

Horses for courses, some things just work where others don't.

Yeah. The epoxy I have is quite a "soft" dry. (Compare Selleys with ...whatever there was a glue that was genuine thixotropic gel and not just thickened, but I am not sure of the name, that set very brittle.)...anyway...so it should have been tough even in a slippery situation. But I think shoe glue has solvents that aid adhesion....just hope they don't bugger up the velcro backing.

Why not just use stick on velcro peel off the back and slap it on.

Originally Posted by REALOldNick

.... I think shoe glue has solvents that aid adhesion....just hope they don't bugger up the velcro backing.

I've used it to hold velco on rotary sanding pads, works well until you overheat it.

Originally Posted by Rod Gilbert

Why not just use stick on velcro peel off the back and slap it on.

Now with _that_ I have had just too many failures. The number of times the velcro has been stronger than the adhesive amazes me, especially if the velco sits for a while of gets some pressure. IT can cling very strongly, if helped.

Originally Posted by Cliff Rogers

I've used it to hold velco on rotary sanding pads, works well until you overheat it.

hmm...I have a large disc sander, and I use velcro-backed paper. The glue that holds the backing to the disc failed just from being in a hot shed in Summer.

Originally Posted by REALOldNick

And I took some 20mm ply and glued it edge on to a piece of scrap pine with the Epoxy (which is Polymer Daystar BTW) and left it lightly clamped. It took a fair whack to break the join with a hammer. The glue gave, not the wood. However there were two things, it was only overnight and most of the morning, and I was separating the pieces by applying force along the grain of the wood, where I reckon tear-out would be less likely. I am going to have another go, leave it for a good 24-48 hours and try again, maybe across grain this time.

Again. thanks for everybody's help.

A follow up. I have not tested the epoxy, but I did try some PVA glue on the same pieces of wood/ply. I left it for 24 hours. I tried to break the joint with a hammer and the ply snapped in half. It took several hard blows, so I don;t think the epoxy effort "loosened it" for the PVA