Thread: Filling defects in redgum slab

David,

Epoxy is your best bet.

It can be tinted, used clear and it can be sanded, waxed, coated with other finishes... the list goes on.

I would go along with epoxy being your best bet, but I wouldn't be betting the farm on it. Anything you use is likely to separate or breakdown when exposed to the elements for a long time. The timber in the slab will expand and contract with the seasons but the filler will not and it's inevitable that it will separate over time. I have experienced this first hand with epoxy filler in a crack in a black butt handrail. It looks great for the first few months but as the seasons change, the crack opens up again and then you have crumbling epoxy resin to deal with as well.

You might be OK with borer holes, which are likely to be more stable that an actual split in the timber. But gum veins are associated with fissures which will change in size with moisture and temperature changes.

If it was me, I would consider leaving it as is.

Black Sikaflex will allow for movement, not sure how well it will take finishes though.

Yeah I wondered about that. Never tried it. Some if not all of the Sikaflex fillers are paintable. Could be worth a shot but I'd be using an oil finish rather than something that will dry hard - so like a decking oil or similar.

I'd guess that any that are paintable will take an oil finish

Epoxy will be fine so long as you seal the whole surface afterwards, including the underside. If the surface is totally sealed it can't pick up moisture so remains dimensionally stable.
Other then that use a good quality flooring/parquet sealer. They're designed to be neutral coloured, hardwearing, and you can oil/varnish straight over them

don't add saw dust and dont try colour match the filler to the wood.

I have seen so many people try and do coloured fill on redgum slabs and it always looks terrible.

keep the filler (epoxy) clear or black. maybe a marine type finish. Anything outside though subject to the elements will need maintenance and not stay nice for ever.

Seconding the 'dont add saw dust' comment. It always looks horribly fake and plastic. A translucent red-black sap-like colour is so much better, or even a bright, completely contrasting colour (think opal in rock).

Thanks for all the info. Epoxy sounds good and with the red/black colouring added, should be quite striking. Good advice not to fill cracks. Whats the difference between casting resin and epoxy? Is Black Sikaflex filler an epoxy? As this table top will be outside in the weather, the Sikaflex with an oil finish could be the answer. Any comments.

The Sikaflex I've looked at was polyurethane.

FWIW for redgum (and other) bowls I favour a mix of 50:50 epoxy and unused coffee grounds. The result is dark brown and looks like a sap line or pocket. Can't comment on its weather resistance though.

Sikaflex is stuff in a tube, a bit like gap filler or mastic to use. Difficult to get a nice finish on because it is tacky and I don't believe it can be sanded.

Regarding movement, there's no finish I know of that will completely seal out moisture. Maybe something from the boat-building world would do it. I would personally not go for any kind of hard finish. Most outdoor furniture is oiled for a good reason. I have seen the results of people using hard finishes outdoors and they rarely last more than 12 months before they start breaking down. Oil breaks down too but it is very easy to replenish.

I reckon if you plan for your slab to move (because I am almost certain that it will) then you will avoid disappointment.

Casting resin is essentially the same stuff as builder's bog (a styrene resin) but without the talc filler. Generally poorer adhesion to timber than epoxy. Epoxy (such as Botecote) is essentially Araldite without the expensive price tag and with better performance. They build large ocean-going yachts with epoxy as the only thing holding them together and keeping them dry.

If your slab has been stored in a dry environment for several years, you may have a chance of stabilising it if you coat it all over in 3-4-5 layers of epoxy; this'll slow water movement down to an absolute crawl (6% weight gain in 8 weeks at a constant 40 degrees C and 100% humidity).

The only weakness of epoxy is that it doesn't like UV, and you really need to add a varnish on top to act as a sacrificial layer to be replaced went it starts to look scruffy.

Whats the difference between casting resin and epoxy?

Price. Casting resin is less expensive, and I think it's a polyester resin. Both casting resin and West system epoxy work well, and I've never had any problem with adhesion. Both seem to stick like merde to a blanket.