Installing an Arbor over a concrete slab--how to anchor the posts?

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Old 09-13-08, 01:00 PM
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Question Installing an Arbor over a concrete slab--how to anchor the posts?

Hi, Boardies. I'm new to this forum so please excuse any faux pas in advance.

Our house has a concrete patio, probably about 50 years old. The previous owners built a deck over it, complete with an arbor. they used untreated 2 x 4's for all construction, even the "planter boxes" they built on top of the decking.

Needless to say, it all rotted out. I cut out a huge swath of deck last week that was a giant fungus fest, but I'm hoping to preserve the arbor. The top slats are OK, but the posts holding it up are all rotten at the bottom. They were only attached to the joists of the deck anyway.

Obviously I want to replace the 2 x 4 "posts". I'm thinking of some 4 x 4 treated cedar posts. Attaching them to the crossbeams of the arbor is not a problem. Attaching them at the bottom, to the concrete slab, is worrying me.

My initial thought was to make some concrete "feet" for the posts:

Put the post in place and secure it at the top
Put a little hardware cloth around it for a "form"
Use cut out plywood pieces to make a mold for the foot, which would enclose the metal form,
Spread a layer of cement slurry at the base of the mold/form/post assembly
Pour concrete into the mold and let it set
Remove the mold and do a little art carving on the foot.

I've done art concrete before--stepping stones and tables--so I'm OK with the mechanical aspects of molding and carving concrete. But I'm no engineer and I'm not sure if this method will give me a structurally sound basis for my arbor.

I've been reading about using brackets that you drill into the cement to secure the posts, but this slab is so old and tough, I'm not sure I can drill it! It's full of ~ 1 inch diameter smooth rocks as the aggregate, which is very decorative but worries me as far as drilling goes. I've never drilled masonry before and it sounds difficult.

Any comments or suggestions out there? Will my little feet, slurried onto the existing slab, be strong enough not to shear off iin a good wind? Do I need to embed a piece of rebar wedged against each side of the post to keep it from tipping?

The arbor has 12 posts holding it up, and is about 30 feet wide. It has a wisteria wrapped completely up one side and across the top, which seems almost strong enough to hold the whole thing up by itself.

I'd appreciate any advice. Thanks.
 
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Old 09-13-08, 02:48 PM
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either rent a hammer drill or purchase a hammer drill and mount steel post anchors to your concrete. that would be the best, buy a top quality drill bit for your hammer drill it will be faster and longer lived than a cheap drill bit.

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