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· I don't Exaggerate I just rememeber BIG!
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MT Stringer said:
Thanks for the feedback. Y'all brought some good things to think about/consider. I think I will give this project some additional thought and get a couple of bids from local contractors and see what they suggest.
Thanks again
Mike
Mike,
I have put in a few slabs in my time and with a little prep it is no problems.

First you can go over existing concrete and score/ruff it up as best you can. I would recommend going at least 4" above the existing slab. Rebar stands are standard height and you want to get that in the middle of the concrete as best as you can, so go 4" if you can.

Wherever the new slab will be overlapping the existing slab you will need to put a grade beam approx 6" wide by 10" deep . This will provide additional support around the existing slab in case you get a little setting.

You also need to put the same grade beam around the perimeter of the new slab and a stiffner in the middle of the new slab. A stiffner is the same as a grade beam 6" wide by 10" deep. I would make the new slab a minium of 5". This will not add much to the concrete cost because most companies will require a minium of 3 yrds. Use a factor of .4 sq. ft. per lineal foot to calculate the amount of concrete for the grade beams. Measure the perimeter and the length of the stiffner X .4 then /27 to get yards.

Probably the biggest mistake that most people make when pouring new concrete is that they do not properly prepare the subgrade (ground below the slab). This is usually the major cause of cracking in a slab. You will need to excavate a minimum a 4" below the bottom of your slab and fill it back in with sand and compacted down with a hand ram. This will provide a cushion so the speak between the concrete and the gumbo clay that we have here in Texas.

If you pour when it is real dry, water the night before so the the gound in moist not wet. This will allow the concrete to dry slow and not have the water suck out of the concrete by the surround ground.

A stated before use #3 rebar on the existing slab and overlap that at least 12" into the new slab area. I would use #4 in the new slab. Set at 12" O.C. Each way. Also use #4 in the grade beams and stiffner. One misconception the most people have is rebar gives the concrete strength, but it help keep it from cracking by reliefing and control the heat stored within in and controls the expansion/contraction of it. Also, when placing the rebar don't go any closer than 2" from the sides and bottom any exposed grades.

Get 3500/4000 PSI 5 sack concrete with 1 1/2" rock, do not mix your own. The size of rock give the concrete strength. You just can't get that in the sackcrete.

When calculating the amount of concrete add at least an additional 15-20 % for waste and usually most people can't get the depth just right, so this will give you extra.

If you decide to go with a contractor, make them follow the same specification stated above and be there when they do the pour!

Remember the As* Chewing for to much is better than not having enough!

If you have any other questions I will be happy to help

Good Luck!
 
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