i did a white oak frame as a porch, my first solo timber frame, back in 2000?.

the posts sit on sills, i drilled 1" drain holes in the bottom of 1.5" mortises (should have made them through and been done!). sealed everything with anchorseal - end grain inside of mortises, tenon ends, shoulder end grain, etc. midwest in the summer, and saw a difference in checking from the timbers i prepared to the extras i ordered that were cut to rough length but not sealed.

in general, now, if i can get away with the design on an exterior stucture i do everything i can to avoid post on top of sill and into a mortise (unless it can be a through mortise). at one point when at NEW we were even designing brace mortises and housings to be angled down, to let water that may have run into a post from the top of the brace, to drain.

In the German tradition, mortises cut into the bottom sill are cut with a special angle at the bottom, with a hole bored down through or out at an angle to allow water to drain out should it get in there. I also know that sometimes the ends of joints, in the mortises or what have you, were sealed with wax or sometimes with paint, but I believe in normal practice they were not. It is worth noting here too that in this tradition the timbers are fully sealed with a mixture of linseed oil and blood paint, and never left bare.

Hello,

Through mortices and drainage holes 'n all address the water problems to a point but by sealing the ends with wax, for example, the natural ability of the wood, once is has gotten wet, to dry out is reduced. It's the trapped moisture rather than flowing water that causes the eventual damage as can be seen here.

First the water gets in there, the microbes and the vermin do the rest 'till the whole construction starts to sag, funneling even more water through the low spots where it stands and just wrecks the whole thing and you have to spend weeks repairing it all.

Greetings,

Don Wagstaff

I have to respectfully disagree with Timbeal. I buy Anchorseal in 55 gal drums. We've done side-by-side comparisons, and it makes big difference. It slows down the moisture leaving through the end grain and so reduces checking overall. CB.

Hi Clark, sometimes I post a perspective in attempts to spur debate. This is one. A bit of background, in part, I try to use a minimalist approach to my framing style, from simple tools to simple joinery and in regards to sealing timber I skip it, it saves a step in labor and material. I have used it in the past and find I enjoy working without it. I suppose it would depend on the style of work and or the job at hand.

For exterior work I would use cedar, tamarack or locust if available with the sapwood removed to avoid as much rot as possible, it all returns eventually.

That's a lot of mortices and tenons, or else really big ones.

I've been contemplating coating the tenons on some half-round white oak joists I have cut the last two weeks. Most of them are intact, a couple got slight checks when I end trimmed, and one has opened up 3/4" since I cut the tenon.

Don, do you mean 55 gallons worth of sealant?

I should also state I work mostly in soft woods.

If you have boxed heart timber and the pith is closer to one side than the others, I suspect you can't put enough sealer on to stop the check. Orientate the timber so the pith is closest to the boarded surface and or saw/force the check with a kerf. Will sealer stop timber from twisting, too?

Not in my experience. It would be nice if it did. The only thing that stops that is getting the frame up and the sheathing and flooring on in a quick fast hurry and that's not sure fire.

many have heard this illustration of how hard it is to stop the inevitable movement of wood, but I will share it here again in case some have not. In the past, for thousands of years going all the way back to the Egyptians, huge chunks of stone would be quarried by drilling holes in the rock face and stuffing those holes with sawdust and wood chips. Then water would be poured into the hole. The expansion of the wood as it takes on water is so unstoppable that it would expand and split of at times hundreds of tons of solid rock.

I realize that twisting is a different scenario than expansion and contraction, but there are nonetheless similar forces at work here. In my experience, it is best to assume that you can't stop wood from twisting, it will do it eventually no matter what you try and do to stop it. Perhaps the best we can do is slow it down, or hide it a bit. The best practice is to be selective with your wood. learn what trouble wood looks like. In general, the wood will tell you if is going to twist long before it ever does.

DLB