Cut a hole...

[Spam16v]

Doing some measuring, I'm going to need to put a lift post on an expansion joint/seam in my garage floor, so I cut a 4'x4' hole in my floor with a wet saw, quartered it and pried out the pieces. Initially tried to smash and remove parts, that was stupid and futile, so I borrowed some demo bars from my family.

Alright, it's 4'x4' and going to dig deeper than the 4" that's there, and go under the other floor already there a few inches and put some wire mesh in it. Any other words of advice? I'm torn on mixing bags, or borrowing a mixer, or going to a readymix place that rents a trailer with the 'crete in it ready to go. The latter sounds excessive since there's so little that I need. How many bags do you think 4'x4'x6-7" would add up to?

Thanks
-Zac

 

[csp]

4' x 4' x 6" = .29 cu yards.

4' x 4' x 7" = .35 cu yards.

If you use bags of Kwikcrete they are printed with how many bags are needed for a yard, so do the math from there.

 

[lametec]

14 80lbs bags of Quikrete for 6". 17 for 7".

 

[Spam16v]

14 80lbs bags of Quikrete for 6". 17 for 7".

definitely not shovel mixing that much. Going to investigate renting a mixer for a day, thanks. I didn't trust my google-fu concrete volume calculations.

 

[Jack Olsen]

Rent (or buy a cheap) hammer drill so you can tie the new piece into the adjoining concrete with rebar. It's easy to do. (I'm the proof of that. )

 

[lametec]

definitely not shovel mixing that much. Going to investigate renting a mixer for a day, thanks. I didn't trust my google-fu concrete volume calculations.

http://www.quikrete.com/Calculator/Main.asp

 

[Edger]

Do not mix in too much water! I found out that the hardness of the concrete is in direct proportion to the water/cement ratio. Forget about how much cement is used, it is the ratio of cement and water that determines hardness of the cure.

It is much easier to mix with lots of water and easy to pour, but the concrete will end up soft. If you mix well with just enough water to give you a heavy pour it will be hard.

 

[Spam16v]

Rent (or buy a cheap) hammer drill so you can tie the new piece into the adjoining concrete with rebar. It's easy to do. (I'm the proof of that. )

Should the rebar be bonded into the drilled holes, or just crammed into them? I've got access to anything I want from a local rental place, so a drill is no big deal. They owe me a few favors, free rental on a shindaiwa concrete saw, and a 5" core drill to vent my pellet stove out my brick wall thus far.

 

[Steves32]

Use a 2 part epoxy.

Like this.

 

[ratdoggy]

Rent (or buy a cheap) hammer drill so you can tie the new piece into the adjoining concrete with rebar. It's easy to do. (I'm the proof of that. )

VERY important what Jack said.

 

[darkk]

I think you should have the local concrete company pour your slabs with the correct concrete. The concrete for the lift is going to require a minimum of 4" thick of at least 3000psi concrete to be safe. I don't think you are going to have a structurally or chemically correct mixture using quikrete/sakrete.....

 

[ConCretin]

Should the rebar be bonded into the drilled holes, or just crammed into them?

Bars are in shear, not tension so there is really no need to spend $ on epoxy.

 

[Spam16v]

I think you should have the local concrete company pour your slabs with the correct concrete. The concrete for the lift is going to require a minimum of 4" thick of at least 3000psi concrete to be safe. I don't think you are going to have a structurally or chemically correct mixture using quikrete/sakrete.....

5000psi quikcrete is available, so even if I screw it up a little bit and it's a tad on the wet side, and end up with ~3500psi @ 7-8" depth, I'm still over the standard. I have 5" everywhere else as far as I can tell. I did a few test drills far away from where I planned to mount the right side lift pier, and it was over 5" in the 4x4" squre I just removed over that expansion joint.

Drilling and using rebar shouldn't be a big deal, plenty of room to swing a drill and bore to a good depth. It's already wire reinforced so I should be in good shape. Gonna get some bags and bring a friend or two over to run the shovel, or bring a mixer home in a few days. Will report back when progress made.

 

[ncfireman1918]

May be a little late, but I saw a tool on some PBS home improvement show the other week that might help you out. I don't remember the name, but it was basically a thick tarp with some handles around the perimeter. You dump the concrete powder in the middle, add water, then you and a friend (or two, don't remember) just jostle the thing around to mix it. Beats the hell out of a shovel, and was designed for areas where it would be difficult to get a wheelbarrow or mixer in (basements, garages, etc.). Looked like a good design, now if only I could remember the name...

 

[lametec]

Creter.

 

[Frank The Plumber]

View media item 10346
To remove a section or so of concrete flooring you would use one of these expansion anchors. You drill your hole, place in your anchor, expand it, place in a short section of all thread rod tighten it down and you lift it straight out. Usually only the first section requires this and you may stake off a bit of timber as a 2x4 or something and sink a second anchor on a large one. Saves a lot of time and keeps your edge nice and unmolested from trying to drive out this chunk.
Pour some concrete under the existing slab as part of the footer to keep the floor from cracking or sinking.

 

[Spam16v]

Ended up borrowing a mixer, 20 bags (had to fix my mailbox too) later, 5 spans of #4 rebar, we were in business.

 

[Falcon67]

http://www.quikrete.com/Calculator/Main.asp

Dang I could have saved $1300 on my slab with a mixer and 797 bags of Quikrete.

 

[buzz4041]

That quickrete is hard work. I used 28 bags of Maximizer recently with a mixer to install 6 post for my new build on a pavilion. I was plumb wore out at the end of day.

You would probably have spent more in the hospital Chris.