Replacing deck support posts in concrete, low deck

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Old 02-28-14, 01:52 PM
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Replacing deck support posts in concrete, low deck

Hi,

I'd like to get a little advice. I have a 3 tier deck that I'm redoing the decking and railing in the next couple months as soon as it warms up a little. From what I've seen so far, the structural members are all in good shape. One thing that I see though that I do not like is that the builder (not me, we've only been here 4 years) built it with the beams in the ground and concrete poured around them. I know this is a very common practice. I would like to fix this eventual problem while it's accessible.

The lowest level beams are a foot or less above grade which would make pulling them out and redoing them or even digging next to them and pouring concrete with anchor bolts and installing post base connectors virtually impossible without removing all the joists and beams, which I'd like to avoid.

I've done a lot of searching and haven't seen much, but here's one idea I've found. Brace the beam and cut out the 4x4 post. Drill out as much wood as possible while also chipping out as much concrete as possible. Drill a couple holes and insert rebar. Using a portion of cardboard sonotubes, pour new concrete with an anchor bolt inserted. After it's dried, install the post base connector and 4x4 post.

My concern is the joint between the 2 sections of concrete. How good of a plan is this? Or should I leave it as is and address it when/if there's an issue down the road? This would be an easy fix if the deck were higher, but being low causes some issues.

I appreciate any help.
Paul
 
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Old 02-28-14, 02:10 PM
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I need to clarify a couple things... I meant that the POSTS are in the ground with concrete poured around them, not the beams. And I meant that it would be hard to pull them out and redo them due to the beams being so low. So I would remove as much from the top as I could and pour concrete on top (hopefully several inches thick) with an anchor or J-bolt installed while the concrete is wet. I hope that cleared up any confusion from my original post.

Thanks!
 
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Old 03-01-14, 07:34 PM
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I have had to repair some footings like that but only because the house was being sold & the inspector ordered it. What is your reason? Has anything shifted? Can you post some pics?
 
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Old 03-02-14, 04:27 AM
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Nothing has shifted that I've seen. So far all the posts are in good shape, but I haven't seen them all yet. This is just a thought to lengthen the life of the deck. I wish I could take some pics, but the deck is currently under a few inches of snow.
Did this repair work ok? I'm hoping it's an ok fix if the inspector ordered it???

Thanks.
 
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Old 03-02-14, 11:22 AM
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My repair worked fine. Anytime that I do that type of repair, I have to follow the architect's plans which are written, according to the local code.
 
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Old 03-04-14, 02:16 AM
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I would never (repeat, never) assume a repair is technically OK because "an inspector ordered it." Most of these guys have little (or no) technical background or qualifications to make them competent to recommend a specific repair.

Regarding the bonding of added footing concrete to existing concrete--it can be done successfully, as long as a few very basic precautions are followed. On the other hand, if short-cuts are taken, it can go completely wrong.
 
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Old 03-04-14, 09:03 AM
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Bridgeman, what are the precautions that you're referring to? I'm interested but would want to make sure that it's only done if it's done correctly.

Thank you.
 
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Old 03-04-14, 09:26 AM
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I wouldn't have been around very long if I second guessed the inspector. Not only that, how was the owner going to sell the house?
 
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Old 03-05-14, 12:50 PM
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Precautions for bonding new concrete to existing concrete:

1. Make sure all of the wood column stubs are completely removed. The easy way is to use a hi-lift (farmer's) jack, chaining tightly around each and pulling it out as a unit with just a few cranks of a jack handle.

2. Clean all the dirt and debris out of the square holes remaining, flushing with water and blowing out with compressed air.

3. To promote good bond, roughen the top existing concrete surfaces slightly, and make sure they, too, are clean. "Clean enough to eat off of," I used to tell my inspectors.

4. Slightly wet the surfaces with water, and then remove any standing water.

5. After the sonotube forms have been set, brush on a bonding layer of pure Portland cement and water (consistency of thick cream). Immediately place and consolidate fresh concrete on the still-moist bonding layer. Don't let the bonding agent dry, because it will act as a debonding agent if you do.

6. Tie the new concrete to existing by inserting a single rebar into the center of each placement, extending down into the square cavity where the column stub had been. Offset the top of each rebar slightly to enable a threaded anchor bolt to be centered in the fresh mud, head down, for attaching new column anchor brackets to.

7. Apply appropriate cure, and wait at least 4 days before installing anchor brackets.
 
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Old 03-05-14, 06:15 PM
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Thanks for helping me with this. It all makes sense and this helps out my confidence about getting it done and done right since I'd love to get the posts out of the ground and on top of the concrete with post caps. I do have a question or two:

As far as putting a piece of rebar down the middle like you mentioned, that piece is still only in the newly poured concrete, wouldn't it be better to drill a couple holes and inserting rebar in the existing concrete so the old and new are bonded that way too?

Also, as long as the post is not rotted, will it actually pull out of the concrete, leaving a square opening in the concrete? I've never seen it done, but if that works I'll be excited, that'll really help out.

Thanks you again, very much!
Paul
 
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Old 03-05-14, 07:11 PM
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I don't think drilling/anchoring rebar into the existing footings is needed, primarily because adequate bond between new and old concrete will be provided by both the cleaned and roughened top surfaces (with bonding agent applied as I suggested), and the additional bond provided along the sides and bottoms of the column recesses. Drilling more holes for rebar that's not needed just doesn't make sense to me. But if it makes you happy, then by all means do it.

I've pulled (or witnessed the pulling) a lot of timber posts and pilings out of concrete footings and slabs over the years. With very few exceptions, there's never been much of a bond between wood and concrete, primarily because the wood surfaces have always started to degrade and rot from moisture that gets trapped right there. Even very shallow surface rot will cause the wood to be almost slippery. In the unlikely event that the foregoing isn't the case in your situation, you always have the option of drilling and chipping, and drilling and chipping, and drilling and . . . . Well, you get the idea, right?

I almost forgot to mention--if you want to skip the minor hassles from installing rebar and anchor bolts in the centers of your new footings, there's always the option of skipping the rebar in favor of using a single all-thread rod in the center of each footing. They'll cost quite a bit more than rebar will, but if your placements are short enough, they might be worth it. Just remember to remove all of the thread-cutting oil they usually come with, as it would tend to inhibit bonding between steel and concrete.
 

Last edited by BridgeMan45; 03-05-14 at 08:36 PM.
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Old 03-05-14, 07:47 PM
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All execellent advice. I'm actually looking forward to this project, we'll see if that changes half way through, haha. As soon as the weather starts getting better I'm going to tackle this job, probably won't have an opportunity to start for a month.

Thanks a million!
Paul
 
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