Attaching wooden posts to a poured concrete slab
I have an old concrete slab in my backyard from an outbuilding that I tore down. I’d like to put a pergola on this slab. What would be the best way to attach the posts to the slab?
I think I remember seeing a product that you pour into concrete after drilling a hole in it, when it dries you can drive regular hardware into it. I was thinking of using that and attaching L brackets to the slab and then to the posts….
Thanks for any thughts, M
Replies
big
Check out the post connection hardware from Simpson.
Some are made to place during the pour, others to bolt down. If necessary, there is an epoxy that can be used to hold anchors in a predrilled hole.
What size posts are you working with. Simpson has post anchors from 4x4, 4x6, 6x6 and I think 8x8.
Here's once section to look at: http://www.strongtie.com/products/categories/post_bases.html
You can also contact them and hopefully be able to talk to a human being.
post anchor
also remember to keep the post off the concrete to prevent rotting
How do I keep the post off the concrete to prevent rotting? Just shim them like 1/16" above the slab, attach them and then remove the shims?
Thanks, M
You keep the post off the concrete by using the metal connector that keeps them off the concrete. Have you looked at the Simpson link yet?
So it seems like the post is kept off the slab becuse it is on top of the plate of that Simposn connector...
The classical post-on-concrete metal anchor (of which Simpson likely has several models) has a little "chair" that the end of the post sits on to keep it maybe 1/2" off the concrete.
You can make your own "rod-and-ring" system: the rod is a length (about 12-16") of 1/2" galvanized pipe; you hammerdirill a 7/8" hole down thru the concrete, and a matching hole, centered, up into the bottom of the post, about 4-6" deep. The rod slips into these holes. The ring is just a short--maybe 1/2" long--section of 2" PVC pipe that you place over the rod and which makes a separation between the post and the concrete. The rod provides lateral stability and the ring carries the weight.
If the pergola has a solid roof that could catch wind that might uplift it, you need to also anchor the posts down with galvanized L brackets or other means.
red alert
You have a slab designed for one type of building and you are now placing more or less random point loads where none were intended
Yeah, but a pergola just barely qualifies as a "building". So long as the slab is reasonably solid there should be no problem.