Very grateful for advice on the best resin to use for filling in cracks etc in the body of wood blanks and bowls that I'm turning (or about to). Also interested in using resin dyes to give different effects. Have had mixed results so far using cheap makes - some have bad shrinkage after hardening; others never harden, whatever mix I use.
Resin
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NikNak
Established Member
Bad shrinkage during/after hardening would point to the probable(?) use of a polyester resin. Depends on the size/depth of the 'crack' but yes polyesters do shrink on hardening.... the bigger the crack you're trying to fill the bigger the shrinkage. Is it just resin you're using or have you mixed it with a thickening agent, sawdust, filler powder/fibres etc. as thickening will reduce shrinkange.
If its not going hard then the mix ratios and temperatures are wrong. You can reduce/increase the amount/ratio of MEKP catalyst in polyester resin to increase/decrease the curing time but this WILL affect the final hardness of the cured resin. You're better off mixing to the correct ratio but in a smaller amount (and at the recommended temperaturs e.g. 18-20c NOT 3-6c for example) let that go hard and 'cool' then add some more until you reach the volume you require etc.
If it never hardens it could be to do with the wood you're applying the resin to. Its a long time now since i used to be involved in such things, but i seem to recall that bare wood generally will 'suck' the hardner out of the mixed polyester resin, leaving you with what effectivly is goopy uncured resin that never really cures. Again i seem to recall we used to 'paint' the wood first with either a mixed resin and let that stand before carrying on. Or apply an accelerator to the wood prior to working on the item.
Epoxy's generally don't shrink, they just go hard. But mix ratios are to be ahered to (see what i did there...)
Hope this helps....
Nick
30yrs experience of polyesters, vinylesters, furans, epoxy resins and glues.
20yrs retired
If its not going hard then the mix ratios and temperatures are wrong. You can reduce/increase the amount/ratio of MEKP catalyst in polyester resin to increase/decrease the curing time but this WILL affect the final hardness of the cured resin. You're better off mixing to the correct ratio but in a smaller amount (and at the recommended temperaturs e.g. 18-20c NOT 3-6c for example) let that go hard and 'cool' then add some more until you reach the volume you require etc.
If it never hardens it could be to do with the wood you're applying the resin to. Its a long time now since i used to be involved in such things, but i seem to recall that bare wood generally will 'suck' the hardner out of the mixed polyester resin, leaving you with what effectivly is goopy uncured resin that never really cures. Again i seem to recall we used to 'paint' the wood first with either a mixed resin and let that stand before carrying on. Or apply an accelerator to the wood prior to working on the item.
Epoxy's generally don't shrink, they just go hard. But mix ratios are to be ahered to (see what i did there...)
Hope this helps....
Nick
30yrs experience of polyesters, vinylesters, furans, epoxy resins and glues.
20yrs retired
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Nick, your reply couldn't have been more helpful; a one paragraph 'zero to hero' course in the use of resin. What you describe as 'goopy uncured resin' is exactly what I have. I'll clean it out somehow and will then start again with epoxy resin from a reputable manufacturer. A good tip, too, about using sawdust as a thickener. Thanks again,
Paul
Paul
NikNak
Established Member
You're welcome 
I've assumed you're using a resin that has been pre-accelerated, so all you needed to do was add the MEKP.?
I'd advise cleaning the old 'goopy' stuff out as best you can, and then use acetone on cotton buds to further clean the crack/hole before trying again. It NEEDS to be clean/clear of all traces of the previous mix or the new mix won't stick to the wood. If you have a Dremel with a fine sanding bit, again advise is to give it a sand even after the acetone wash.
If its just tiny cracks/splits in the wood and you just want to fill them as its a 'nice piece of wood' and you're not really worried about the overal finish (unless the resin has been coloured it'll just appear as a blackish line anyway) you could try the old trick of stuffing/ramming the crack/hole with sawdust of the same type of wood (doesn't have to be...) and using thin superglue dribble it into/onto the sawdust. Let it go hard and continue.
Nick
I've assumed you're using a resin that has been pre-accelerated, so all you needed to do was add the MEKP.?
I'd advise cleaning the old 'goopy' stuff out as best you can, and then use acetone on cotton buds to further clean the crack/hole before trying again. It NEEDS to be clean/clear of all traces of the previous mix or the new mix won't stick to the wood. If you have a Dremel with a fine sanding bit, again advise is to give it a sand even after the acetone wash.
If its just tiny cracks/splits in the wood and you just want to fill them as its a 'nice piece of wood' and you're not really worried about the overal finish (unless the resin has been coloured it'll just appear as a blackish line anyway) you could try the old trick of stuffing/ramming the crack/hole with sawdust of the same type of wood (doesn't have to be...) and using thin superglue dribble it into/onto the sawdust. Let it go hard and continue.
Nick
Ollie78
Established Member
I don`t do much turning, I have yet to get good at it. But for filling smaller holes in other work I use black superglue.
I also have a Boegh consult knot filler which I find pretty useful, its basically a glue gun with different coloured filler sticks, you can get loads of colours. Just fill the gap or knot with it, use a block of aluminium to cool it, cut off excess with a sharp chisel.
The only downside is if it gets too hot it will melt again.
Ollie
I also have a Boegh consult knot filler which I find pretty useful, its basically a glue gun with different coloured filler sticks, you can get loads of colours. Just fill the gap or knot with it, use a block of aluminium to cool it, cut off excess with a sharp chisel.
The only downside is if it gets too hot it will melt again.
Ollie
Nick,You're welcome
I've assumed you're using a resin that has been pre-accelerated, so all you needed to do was add the MEKP.?
I'd advise cleaning the old 'goopy' stuff out as best you can, and then use acetone on cotton buds to further clean the crack/hole before trying again. It NEEDS to be clean/clear of all traces of the previous mix or the new mix won't stick to the wood. If you have a Dremel with a fine sanding bit, again advise is to give it a sand even after the acetone wash.
If its just tiny cracks/splits in the wood and you just want to fill them as its a 'nice piece of wood' and you're not really worried about the overal finish (unless the resin has been coloured it'll just appear as a blackish line anyway) you could try the old trick of stuffing/ramming the crack/hole with sawdust of the same type of wood (doesn't have to be...) and using thin superglue dribble it into/onto the sawdust. Let it go hard and continue.
Nick
Thanks very much for these tips. I'll winkle out the old stuff as you suggest. While we're at it, is there any particular brand of epoxy resin you'd recommend?
Thanks again,
Paul
Ollie,
Thanks for these ideas - neither of which had occurred to me. I get through quite a lot of CA and wasn't aware it came in colours!
Regards,
Paul
When I do wooden clock cases I sand them down on a big sheet of paper and collect the dust, very useful for filling later.
