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Old 01-20-2008, 12:50 AM   #1
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Well, I had a slab poured underneath my deck. This spring I need to do the posts correctly, as they were buried in the slab (not up to code). I was going to use these pre-manufactured concrete posts. They are basically made to support a 4x4 post. They sell them at Lowes or Home Depot.

I figure I can support the deck and then simply cut the current post where it goes into the slab. Then place the concrete block in place, on top of the slab, then simply cut the post where needed and place it into the concrete 4x4 block.

Any suggestions or advice?
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Old 01-22-2008, 02:17 AM   #2
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Old 01-31-2008, 03:42 PM   #3
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If these posts are supporting an elevated deck, those pier blocks will not work. You need to anchor the post bottoms in such a manner as to prevent uplift AND to prevent the post bottoms from getting knocked out of place.

Use your basic thought -
Support deck beam w/ temp supports
If you have a break in the beam over a post, you will have to support the beam on both sides of the post
Cut off posts at concrete w sawzall
Remove posts from beam
Buy sonotube footing forms (12" diameter x 12" high should be fine, check with your inspector to make sure)
Drill 2" deep holes and epoxy 4 sticks of 1/2"x13" rebar into your existing concrete (where the sonotubes will go)
If the concrete patio that was poured is deeper than 3 1/2", you can drill down deeper - you just don't want to punch through the bottom of the concrete
Call for rebar inspection (city will need to verify rebar placement)
Pour new concrete in sonotube footings (Concrete - 2500-3000 psi, 1/2" mix)
Tap sides of sonotubes to "settle" concrete and fill voids
Add Simpson post bases to wet concrete (in line with beam above)
After 2 days, measure height from top of post base to bottom of beam
Cut posts to fit, install
LEAVE TEMP SUPPORTS IN PLACE FOR TWO WEEKS (to allow concrete to cure fully)

If this is daunting, I would highly suggest hiring a professional. You don't want to mess around with elevated decks. People die when they fail.

DO NOT USE THOSE PIER BLOCKS. FOR THE SAFETY OF YOUR FAMILY.

Mac

Last edited by BuiltByMAC; 01-31-2008 at 11:57 PM. Reason: spelling!
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Old 01-31-2008, 04:26 PM   #4
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Originally Posted by BuiltByMAC View Post
DO NOT USE THOSE PIER BOCKS. FOR THE SAFETY OF YOUR FAMILY.

Mac
Thanks for the info!

So, even with Simpson Strong Ties anchored into the pier block & the post, it would still be a bad idea?

What would the labor to do it the way you recommended cost???
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Old 01-31-2008, 10:47 PM   #5
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Not sure what you're asking - Simpson StrongTie is a company and brand, not a specific fastener.

The pier BLOCKS (didn't even realize I misspelled it above!) have no solid connection to either the post that sits in them or the concrete that's below them. There are some concrete blocks that have a metal strap sticking out of them - those you can bolt to the post bottoms. However, that doesn't solve the problem that the block itself can be knocked out of position since it would just be sitting on the concrete patio. That's where the epoxied rebar and poured concrete come into play.

Regarding labor costs, I don't share $$ info online. You'd be better off contacting a couple of reputable builders in your area to get a bid from them.

Mac
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Old 02-04-2008, 04:01 AM   #6
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BuiltByMAC -

Thank you for the information. I will go with what you stated. I went to Lowes and figured out how to do it. It shouldn't be that hard. The sonotubes seem pretty easy to do. The drilling is simple, as is the epoxy & bolt/rebar install. I will go with 5,000 psi for the concrete.

What would you recommend for the temporary deck supports while this is going on?
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Old 02-04-2008, 10:01 AM   #7
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For Temp support,
1' chunk of 4x12 (lying flat) as a base under 4x4 posts up to beam
Screw everything together solidly (don't want your deck wandering while the new concrete sets up).
You can find beam ends (4x12, 6x15, etc) at new construction sites (just make sure to ask before removing any material, you do speak Spanish, si?)

Another option would be to use those preformed concrete pier blocks you mentioned in your first post under 4x4s.

Temp supports should be positioned within 8' of each other and within 2' from the end of the beam.

Remember to check if beam breaks (has a joint) over a current post, you'll need temp supports on both sides of current post to support both sides of the joint.

Edit to add: You might want to add knee bracing for additional stability. Knee bracing is diagonal bracing that goes from post to beam. 2x4s run in both directions should do it. 4 screws per end. See illustration below.

Be sure to take pics of the progress and post them in this thread when you're done!

Mac
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Last edited by BuiltByMAC; 02-04-2008 at 10:10 AM.
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Old 02-04-2008, 12:16 PM   #8
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Maybe i missed something here, was the deck already there befor concrete was poured? if so You wouldn't have to do anything. a four inch band around that 4x4 won't harm anything. as long as post is not submerged in concrete the post will be just fine . post rot when water cannot exit away from. if this post is merly going threw concrete then water can shed from bottom of slab into earth below . Are the deck post themselves IN or ON concrete below grade?
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Old 02-04-2008, 02:52 PM   #9
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Where are you located? - Telling people that always helps to get a meaningful answer quickly.

If you have frost, immediately set out to correct the problem and put in decent concrete footings for the existing posts. That should help you. - Assuming your deck is built properly and supported correctly off the house with flashing.

Your slab is probably not structural, so it was not intended to carry concentrated deck post loads. Raise the exterior end of the deck slightly and support it with a false temporary wall spread out on the slab length. You can saw and knock out squares of the slab and dig/auger post holes, insert Sonotubes, backfill with gravel, fille the tubes with concrete and then insert post connectors into the wet concrete. The set the posts into the connectors after the cncrete has cured a couple of days.

This is a simplified method and you will have to accurately set the post connectors at the right height to maintain an acceapable grade for the deck surface, in addition to coming up with a temporary support system for your particular deck configuration.
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Old 02-05-2008, 01:58 AM   #10
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Quote:
Originally Posted by JackOfAllTrades View Post
Well, I had a slab poured underneath my deck. This spring I need to do the posts correctly, as they were buried in the slab (not up to code...
Quote:
Originally Posted by big daddy-o View Post
Maybe i missed something here, was the deck already there befor concrete was poured?
...if this post is merly going threw concrete then water can shed from bottom of slab into earth below .
Am I to understand you think the original posts holding up the deck were sitting on dirt?

Your post also doesn't address the situation that the current setup is not up to code. Regardless of whether you feel the post is fine buried in concrete or not, building to code is a pretty good idea. Overbuilding is usually better.

Mac
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Old 02-05-2008, 02:02 AM   #11
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Originally Posted by concretemasonry View Post
Your slab is probably not structural, so it was not intended to carry concentrated deck post loads.
Honest question, what is your definition of a structural slab?
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Old 02-05-2008, 02:19 AM   #12
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Am I to understand you think the original posts holding up the deck were sitting on dirt?


Mac
The original posts were set in concrete footings. The footings were the sonotubes, that went down about 12" below grade. Later. I had a slab poured (3 1/2" @ 4,000 psi). When the slab was poured, it buried the posts in concrete. I would estimate about 2"-3" at max.

I know posts should NOT be buried in concrete but there was no other way to do the slab, as the deck was already there.

Why would the slab not be able to hold the weight of the porch? The slab had 6 footings set-in, with rebar, about 16" deep. I don't believe the slab will go anywhere.
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Old 02-05-2008, 02:30 AM   #13
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Where are you located?

If you have frost, immediately set out to correct the problem and put in decent concrete footings for the existing posts.

Your slab is probably not structural, so it was not intended to carry concentrated deck post loads. R
I am located in Brighton, Colorado.

The current posts are set in concrete footings. It is just that I had a slab poured over them, at a later time, thereby burying the posts in concrete.

How would I know if my slab is "structural"? It is 3 1/2" @ 4,000 psi and it had 6 footings put in (16" deep) with rebar to keep the slab from pulling away from the home.
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Old 02-05-2008, 11:04 AM   #14
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you state that when deck was built, post were set IN concrete correct? there is two types of treated post. those are treated right? standard 4x4
is .30 retention, must set ON concrete footing then back fill with gravel or earth. then 6x6 (pole barns ect) .60 can be set IN concrete. Picture this, you dig a hole , throw concrete in the bottom, put post in hole ,then concrete around it. what you have created is a cup effect around that post. any water from grade (down spouts , rain ect ) collects around post but has no way out. result is post sitting in water and eventually rotting. I would say at this point, if in doubt digem out!
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Old 02-05-2008, 11:18 AM   #15
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As I understand it -

Your posts were not supported properly, as you stated in your original post. You then poured concrete over the entire thing and embedded part of the posts in the slab.

Your slab provides no structural support for the posts since it is only 4" thick, the slab is above the concrete post supports and the posts are probably near the edge. All the concrete does is make water run off and make any repairs more difficult. The rebars into the foundation mean little to the deck support.

Live with what you have created and watch it. You might get lucky! - If you end up with heaving or settlent, be prepared to tear up everything up put in in proper concrete post supports with simpson brackets to keep the wood high and dry. Then you can address the details of how to support your deck during the reconstruction.

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