Thread: Cleaning up rough sawn posts

Rusty

Welcome to the Forums.

The job you are contemplating is both simple and troublesome all at the same time. I am assuming that the posts are green and this being the case there is a lot of drying ahead of them in that dimension. This means they will be relatively easy to plane, but they will want to crack as they dry particularly in such a substantial size. A hand planer may be awkward as most of them have only a 3 1/4" cutting width (82mm?) You could arguably plane in three passes and tilt the plane very slightly down towards the outer edge on each of the first two passes. This is better than having a groove or step down the middle and then a final light pass down the middle. A thicknesser would be the way to go, but I don't recall off the top of my head whether the bench top models will cope with 200mm deep: Maybe only 150mm. You may have a mate with such a beast or try the local men's shed for the price of a donation.

You certainly need to seal the posts on all sides immediately they are dressed. Once you have removed the sawn edges you may be surprised how much they have opened already. At least for a pergola this is probably acceptable. The sealer will depend on your final finish.

Regards
Paul

Sand them and seal with any good quality varnish or decking oil subject to your preferred look. If you plane them they will surface check worse then just sanding alone.

Thing to remember with surface checks is that while they might open up and be horrible for a bit most will close up again in a year or so once the core of the wood dries below FSP so dont be too worried when that happens - thas just how large section wood dries.

John has much more experience in this area than I. I didn't suggest sanding as I felt the green timber may clog the belts (assuming belt sander) too readily, but you will soon find out how that goes and providing you already have a sander, a coarse belt or two will not set you back too much.

Regards
Paul

Course sanding is a much better option than planing. An even better option would be running them through a fine blade bandsaw if you feel the current saw finish is too course. A sawn finish will withstand weathering better than a smooth surface. An oil coating would be the way to go.

Thanks to everyone who has offered their advise, to clarify the beams have been dried so I have taken to them with a belt sander starting at 80 grit with the intension to finish off at 120 grit before filling cracks with epoxy resin and priming with International Everdure. Next decision is what clear coat to use.

I have been told to use a high UV 2 pac but not sure what is on the market

ahhh... you're scaring me.

Heres the thing right, 200 x 200 hardwood posts have a couple stages of drying.

Stage 1 is off the saw to 20 %, during which the wood losses the water between the cells in the wood. Timber has to be at 20% MC or below to be graded. Appearance wise not much happens during this phase if they're good clean boards like 200 x 200's are supposed to be. This stage is pretty quick and probably takes 6-8 weeks in that sectional size, and the water transpires along the length of the board and out the end grain.

In stage 2 they start losing bound water, which is the water inside the cells themselves. And they dry from the outside in, obviously. So what happens is the outside rows of cells shrink as they dry, because thats what woods cells do during drying. But they're trying to shrink over the inside cells which havent lost any moisture yet, so cracks open up in the wood. This is normal, the cracks allow water from deeper in to get out, but its also the mechanical response to shrinking the shell over the core and it dun wanna fit. This takes... yeah give it a year to 18 months.

In stage three the inner cells have lost water as well. You've got a moisture gradient that isnt anywhere near as steep as before so with shrinkage of the internal cells the external ones become less distorted. And at some point usually after the second wet season you find those ugly drying cracks start to disappear, because the outside of the post being wet makes those cells swell somewhat so the whole thing is brought back into something approaching equilibrium.

Thing being is you need to know where you're at in that drying cycle, before you start filling cracks with epoxy. otherwise you got wet wood trying to shrink over epoxy that doesn't want to give and that can make them crack elsewhere to relieve that stress. (This is all appearance stuff BTW - its not affecting the structural soundness of the post just how it looks, you can have cracks an inch wide to the middle of the post and it barely changes the strength of the column.)

My advice to anyone doing this kinda thing is if you must fill cracks for appearance reasons before the posts have stood a few years.... using a bit of Sika or some other flexible type bog that will still allow the timber to expand and contract around the cracks.

my $0.02.