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Old 08-27-2007, 09:05 AM   #1
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new concrete floor next to old concrete floor


My basement has a concrete floor. There is a small half-oval shaped area of about 3'x5' that is bare earth, from where an old coal furnace used to be. The concrete floor is perhaps 3" higher than the bare earth and there is a raised "curb" of concrete separating the earth and concrete floor (in the half-oval shape) that is 2" higher than the concrete floor (and thus about 5" above the bare earth section). It's a huge tripping hazard and currently the 3'x5' area is a useless part of my basement.

I'd like to fill in the section with concrete. What steps should I take to ensure I end up with something flush to the old surface? How deep should the new concrete be? In particular, I'm going to need to saw down/off the curb and want to make sure the new concrete doesn't crack where it meets the remainder of the sawed curb. Do I need to lay down gravel or some wire mess in the area where the new concrete will be poured? Should I be concerned about an expansion joint type of thing over an area this small?

Thanks for any advice and/or references!

Matt

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Old 08-27-2007, 10:23 AM   #2
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new concrete floor next to old concrete floor


It sounds like the curb is wood? Remove the wood completely. The slab depth should be about 4". If you need to dig out some dirt. Don't disturb the soil deeper then 4" or you will need to tamp it down. I would drill in 1/2" rebar along the perimeter and hammer in 12" pieces, about 4". Then mix the concrete and fill the hole. Use a 2x4 to screed the top even with the existing slab. The tricky part in then floating the top so it's smooth. After it sets so it's firm, cover it over with plastic so it dries slowly. You can dampen it down the next day to slow the curing process and recover.
There's a good chance the new part will get shrinkage cracks where it contacts the old concrete. I don't know if this can be avoided.
Ron

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Old 08-27-2007, 10:44 AM   #3
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new concrete floor next to old concrete floor


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It sounds like the curb is wood? Remove the wood completely. The slab depth should be about 4". If you need to dig out some dirt. Don't disturb the soil deeper then 4" or you will need to tamp it down. I would drill in 1/2" rebar along the perimeter and hammer in 12" pieces, about 4". Then mix the concrete and fill the hole. Use a 2x4 to screed the top even with the existing slab. The tricky part in then floating the top so it's smooth. After it sets so it's firm, cover it over with plastic so it dries slowly. You can dampen it down the next day to slow the curing process and recover.
There's a good chance the new part will get shrinkage cracks where it contacts the old concrete. I don't know if this can be avoided.
Ron
Good plan but I think I would go a step further by attaching a length of rebar from the pieces you mentioned from one side to the other so you would have a continued piece, something like the pic I attached. But then I maybe wrong.
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Old 08-27-2007, 10:50 AM   #4
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or you could add black dirt and a grow light over the top

people pay big bucks for indoor planters like this.
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Old 08-27-2007, 10:52 AM   #5
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or you could add black dirt and a grow light over the top

people pay big bucks for indoor planters like this.
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Old 08-27-2007, 05:52 PM   #6
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Thanks for the advice. The curb is actually concrete as well. I've never used a concrete saw so I'm wondering (1) is this something I could do myself if I rent one from Home Depot? And (2) if I saw straight down will I likely run into rebar or something that the saw will have trouble with? Thanks!

In case there was any question, here's my artistic rendition of the concrete-curb-earth profile...


___
__________| |
|__________
concrete earth

^
|
|--- Considering sawing here.
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Old 08-27-2007, 05:53 PM   #7
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Okay, so despite using the Courier font, the website screwed up by beautiful drawing. Sorry.
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Old 08-28-2007, 08:31 AM   #8
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new concrete floor next to old concrete floor


Leave rebar if you can... it will only help with your tie-in to new concrete. You might find 6x6 wire mess but saw will cut this
blade will cut rebar too but will eat your masonry blade ($).

Rebar should not be near the edges, but the oval won't work well with a saw.

Have you tried a sledge hammer on the curb yet?

What will be your finished new floor?


If you are going to leave finish floor the concrete, Know that it is tricky, even for the pros, to give it an aged look and not have it look like a patch job.

another way:
Hammer drill holes 5/8" or 3/4" 6" apart or closer. Drill straight down. Caution if you drill bit hits just to the side of a rebar it will twist very hard in your hands.

Tap soft then harder between the holes with old framing hammer (will bruise the head) this will create a fine fracture and aid in concrete removal. Under mine area before you hit with a sledge. ( give the concrete someplace to go.)
I still like the planter idea.

Last edited by Big Bob; 08-28-2007 at 08:35 AM.
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Old 08-28-2007, 09:39 AM   #9
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new concrete floor next to old concrete floor


Do they even put rebar in residential slabs? Try the simplest first. Hit the side of the curb with a sledge hammer. Any high spots left, knock it off with a chisel. The curb was probably put on top of the slab, after the slab was poured. Then it should pop off with little residue.
Ron
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Old 08-28-2007, 11:49 AM   #10
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new concrete floor next to old concrete floor


I'll get a sledgehammer and give it a whack. That'd be great if I "pops" off. I plan to have concrete as the finished floor. I'm sure it won't match the existing stuff (although any hits on getting it as close as possible would be appreciated) but it's a dark, dingy, unfinished basement so I'm more interested in functionality that aesthetics.

Thanks,
Matt
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Old 08-28-2007, 01:32 PM   #11
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new concrete floor next to old concrete floor


Matt, once you get your curb off and slab edges clean (Use water and an old stiff brush) you could paint the edge with a concrete bonding agent to help with adhesion. Follow Ron's post #2. This will shrink ( part of the trick is to leave it a little high)

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