The floorboards we got for the lounge room are what’s called “utility grade”. Which is pretty much the lowest grade, full of knots and sap lines and holes here and there and quite a few with machine marks in them. We wanted the sap lines and knots for interest, but not the ones that were graded as such just because they were crappy or damaged in some way. Quite a few boards went into a reject pile, and we’ll use them for the shed floor which will be going in down by the orchard.
At any rate, we don’t want to spend the rest of our lives digging dust out of knot holes, so all those imperfections have to be filled so that the floor can present a smooth surface to our feet and broom.
We’ll be using a Livos oil to finish the floor, and the lady at the shop recommended just putting black putty in the holes, since she was certain my suggestion of using epoxy would result in black features anyway. This was all a bit confusing, so I got 1 black putty, one “hardwood” putty which looked to be around about a matching colour and a small amount of epoxy in one of those double-syringe setups. I got a couple of spare boards and filled some holes on each one using different methods, then finished them with a couple of coats of the oil.
The epoxy was far and away the best solution, so we went ahead and got a larger 1L container of the stuff. This involved a special trip to a sailor’s shop in the city. The holes did go quite dark, but there was still detail visible under the epoxy which was the effect we were after. The black putty just ended up looking pasted on, and the wood-coloured putty made it look like a mistake had been made.
It took a whole day in the end to epoxy up all the cracks. Some of them went all the way through the board and the epoxy just kept leaking through. Some holes needed 3 applications with drying time in between before the holes closed up. I’ll be taping the underside of any boards we do in the future before they’re laid.
The epoxy is by West Systems, and doesn’t smell or shrink upon drying. It went hard in 24 (cold) hours and sanded easily. 1.2L (1L of resin and 0.2L of hardener) was $54. We found that using a 10mL syringe was a quick and neat way of applying the epoxy to the holes, although it wouldn’t go into some of the smaller wormholes. We used a slow hardener that has a working time of around 45 minutes, and did 3 batches of about 200mL. I went wandering off while doing the first batch, rummaging in the shed for something, and I actually left it too long. It went hot in its container and then hardened up over the course of a few minutes. It must have been something to do with the amount that was in there, and the heat of the chemical reaction. The little bits on the floor stayed liquid for much longer. The next couple of batches went well, but the syringe and container can’t be re-used.
We came back the next day and sanded the epoxy back, then refilled any holes that weren’t flush with the top of the wood.
When the epoxy is being mixed it tends to get full of air bubbles. It’s best, when applying it to the wood, to pop the bubbles as you go. I was a bit lax and a couple of the holes end up with bubbles inside them, which catch the light and give a “cloudy” effect. Others that migrate to the surface leave a small indentation behind once the blob has been sanded back. It’s not a big deal, but it’s easy enough to circumvent.