Epoxy problem - advice please!

[Poignard]

2 days ago I repaired a wooden grab handle by gluing a new piece of wood to it using WEST epoxy thickened with colloidal silica. I did the job in a hurry and, as I didn't need much epoxy, I mixed the resin and hardener without using the calibrated pumps so as to avoid waste. [Yes I know, mean b-----d!]

Although the bond is very strong, the epoxy has not hardened properly and has dried to a very thick rubbery state. Obviously I got the mixture wrong.

Question is: Is it ever likely to harden properly? Is there any way to speed up the hardening?

 

[oldsaltoz]

G'day Twisterowner,

Assuming you have not got the mix right {and it sounds like it) it will not fully cure so you have a weak joint.

Also note: adding colloidal silica is not a good idea if you are looking for a strong bond, as only acts to reduce slumping.

You should consider starting over again, as you only need a small amount of resin it's not going to be expensive.

Using a small bottle cap measure your resin to hardener mixture and mix well, then add some Micro-Fibres to get a mixture about toothpaste thickness, let it stand for about 10 minutes then spread a layer on both surfaces to be joined and press together till the excess material squeezes out; do not clamp it as you do not want the layer to be too thin or it will not be very strong, clean up all material that is squeezed out because Micro-Fibres and epoxy are very hard to sand.

Let it cure for at least 24 hours, more if the can, then wash with fresh water and rub with a plastic kitchen scourer till the water no longer forms beads. This will remove the residue left from the curing process, now you can sand it without spreading any contamination.

Also note: epoxy is not UV stable so will need to coated to protect it.

Hope this helps.

Avagoodweekend......

 

[Poignard]

[ QUOTE ]
Hope this helps.


[/ QUOTE ]

It does [mind you, it wasn't what I wanted to hear! I was hoping for a magic fix to save me having to do the job over again!].

Thanks for your help.

 

[sandeel]

I've done this as well!!
I found that it is the cold weather that causes the slow cure as well as getting the proportions wrong. it might go off eventually especially if the weather warms up.You might be able to paint the surface with just hardner but I have no experience of this. might be worth a try before having to redo the lot.

 

[alistairh]

do not paint hardner on top as it will do nothing and will not mix with rest of mix. only thing to do is redo it I'm afraid, I'm doing up a wooden boat and you have to get the proportions exactly right. i know because iv found out the hard way, more than once.

 

[Woodlouse]

The nice thing about west systems epoxy is that you can do the 5-1 ratio by weight aswell as by volume. So if you want to do small mixes then just sit a plastic container on a set of kitchen scales and pour away.

As has been said, use micro fibres to get a strong bond, but, if the grab handly isn't on a horizontal surface then a bit of colloidal silica won't hurt.

It's also worth remembering that epoxy doesn't like either the cold, or hot when it's curing. I think between 5-20 degrees is optimum (when the temperature gets to above 25 degrees it's recommended that you use a different hardener for hot climates. It's not in very high demand in this country though). It also melts when exposed to very high temperatures so to remove the rail before resticking it I suggest a hot air gun. With care it ought to soften the resin up enough for the rail to be pulled off without damaging the wood its self.


Another thing worth noting, for large mixes, is that as stated before, epoxy doesn't like heat. However, the reaction with the resin and the hardener is exothermic. So, if you mix too much in a narrow pot, or in a warm area then it will start to smoke, and the whole mix will solidify into a kind of honeycomb. The best thing to do is mix it in a wide, flat, plastic container that will give the most surface area to disperse the heat. And don't mix a batch of any more than 200 grams. Otherwise it'll start to go solid before you've finished using it.
/forums/images/graemlins/smirk.gif

 

[tobble]

[ QUOTE ]
if you want to do small mixes then just sit a plastic container on a set of kitchen scales and pour away.


[/ QUOTE ]

if you're feeling especially mean or have a small job like that, postal scales are more accurate, unless you have very posh kitchen scales - in which case don't let SWMBO see you doing it...

 

[Boathook]

You can also / always put the posh scales in a clear polyethelyne bag to protect or even buy a pair of scales (electronic) for the job. I did this last year and it worked a treat as you can just about use any container for mixing with the zero setting button.

 

[oldsaltoz]

G'day Woodlouse,


Quote:
As has been said, use micro fibres to get a strong bond, but, if the grab rail isn't on a horizontal surface then a bit of colloidal silica won't hurt.

Why would you want to add colloidal silica when mixing Micro-Fibres to a toothpaste consistency? hardley likely to slump and stronger without it.

Avagoodweekend......

 

[Woodlouse]

[ QUOTE ]

G'day Woodlouse,


Quote:
As has been said, use micro fibres to get a strong bond, but, if the grab rail isn't on a horizontal surface then a bit of colloidal silica won't hurt.

Why would you want to add colloidal silica when mixing Micro-Fibres to a toothpaste consistency? hardley likely to slump and stronger without it.

Avagoodweekend......

[/ QUOTE ]
Thats just the thing, you can add microfibres untill the cows come home but at the end of it the mixture will still slump. Just try mixing it up and then holding it up on a stick. If you want to put a blob on epoxy on a vertical surface without it slumping then you want to add colloidal silica (preferably with the fillet mixing compound). Yes there may be a slight difference in the strength, but it's still going to be stronger than the wood so whats the problem?


Also, a point I forgot to mention earlier, you mention washing the cured epoxy with water untill it stops beading to remove the residue prior to painting. A much more efficient way is to give it a wipe down with a degreaser. Only takes 10 seconds and it's then ready to start painting immediately.

 

[William_H]

As I understand epoxy the hardener and base resin resin together form the bonds. Such that if you have too much resin or too much hardener then tha material remains in the resin unbonded. Also when you added silica it is more material that will be in the glue but not part of the bond.
I would suggest you wait for some more time until you can be sure all of the hardening that is going to happen has happened. Then scrub as Oldsaltoz suggested. You can then decide if the bond is strong enough for the required job as is. If you need it strong and have doubts then you will have to pull it apart using heat to soften the epoxy. You will probably find out then that it is stuck very well.
good luck olewill

 

[Pasarell]

I believe the minimum curing temperature for West epoxy is 10C.
Epoxies are susceptible to amine sweat during curing, especially if the temperature drops during the cure, and this is the greasy film that forms on the surface and causes water to bead up. It should be removed with fresh water and, if necessary, a nylon scourer before second coats or UV pretection coat.
I certainly wouldn't recommend any form of solvent to remove the amines as it could cause an adverse reaction in the epoxy and weaken the end joint. Anyway, water is cheaper!

 

[oldsaltoz]

[ QUOTE ]
I certainly wouldn't recommend any form of solvent to remove the amines as it could cause an adverse reaction in the epoxy and weaken the end joint. Anyway, water is cheaper!

[/ QUOTE ]

Also less damaging to people and the environment.

Avagoodweekend......

 

[Lakesailor]

Stick wood flour (dust) in. then it won't slump. Also easier to sand and matches colour if you've used the same wood dust as the wood you're repairing.
I mix by volume using either spatulas marked up or small bottle caps like Oldsaltoz suggests.
The stuff I use doesn't go off properly below 15 C.