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Timber to pier connection?

Started by shinnlinger, January 25, 2018, 07:20:43 AM

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shinnlinger

Hello,

This spring one of my classes is building a TF outdoor classroom.  It will probably be mounted on concrete piers and we came up with a simple little knife joint inverted T fastener but our local Votech hasn't committed to making them for us so I figured I would ask here.  Any recommendations on how to secure 6x8/8x8 posts to concrete piers?

Thanks.

Dave
Shinnlinger
Woodshop teacher, pasture raised chicken farmer
34 horse kubota L-2850, Turner Band Mill, '84 F-600,
living in self-built/milled timberframe home

Heartwood

Timberlinx is the way to go, IMO. The drilling jig is pricey but perhaps you know a timber framer that will loan you one, or just measure very carefully and make sure the threaded rod in the pier is plumb.

Ionel Catanescu

If the concrete piers are not cast, in the casting process, you could mount a stone on top of them and a threaded rod going thru the stone into the concrete.
You can have that bent into an L of J at the bottom to better grip the concrete.
If needed, a small mortise could be done 6" or so from the post base, enough to slip in a nut and washer but these are not absolutely necessary unless you have hurricanes.
The post can be scribed to the stone to be a perfect fit.
Search for stone scribing

If the piers are precast, you could try to get any pre made post bases.
Search for post base for options.
Some might not be a perfect fit but the posts can be "persuaded" to fit.

Whatever you choose, there's an important aspect.
If rain ever comes in contact to the posts, it will flow down due to gravity.
On reaching the base, it should be quickly disposed of.
If you have a closed post shoe, it will pool in the endgrain area where wood is most susceptible to water absorbtion and damage.
Even if it's suspended on a slim metal piece (like an adjustable post base), the water may still stick to the bottom of the post until it gathers enough to either fall or migrate to the middle of the post where the metal part is.
Either way, you don't want this.
This is why window sills have a drip edge / lip, so water can't go anywhere.
Without that lip, on a horizontal surface, water will stick to the underside and travel to the wall.

This is why a stone scribed post is better if you pick a non porous stone that is also sloped.
When water meets the very fine line between wood and stone, it will be "sucked" by the sloping stone and drain away.
This can be accomplished using metal parts but can get tricky.

Whatever you chose, sealing the endgrain is recommended, unless you're using a very rot resistant species.
Burning it a little and adding a bit of linseed oil (yakisugi) will work better than a lot of other things.

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