Do you guys know if it is recommended (or not) to cut relief joints in a monolithic slab? Any opinions???

 

you should cut releif joints in any concrete slab. they help reduce the number of wild cracks in the slab. they will not eliminate them, but they will reduce them. just make sure you dont cut them very deep, 1/4-1/2 inch is plenty.



jim

 

What kind of pattern would you do in a 24 x 28 slab? I was thinking maybe one down the middle of the 24 and split the 28 with 2.

 

my 24x36 shop has one relief cut lengthwise, and two widthwise. No cracks in 6 years.

 

What you do to the foundation depends on what you are going to put ON it and what the soil is UNDER it. I have designed and poured over 2K of those things. Gimme some info and I will consort with you on it. The very last thing I would suggest is to saw cuts in the surface!
Big Jim

 

Hey it all depends on:
- if u have inslab heating piping in the slab
- are there any load bearing points
Its recommended to cut control joints @ min 1/4 max 1/3 slab thickness. (up here in canada)
cheers

 

Hey Jim,

The floor is 24' x 28'. It is a monolithic pour. The footing or haunch is minimum 18" wide by 18" deep. with a 5" floor on top of it. There is 6x6 10 gauge wire mesh through out the floor. The entire thing is on compacted sand/stone. I don't know how else to describe the earth the slab is on.

 

There is quite a difference in your frost line and ours here, we don't have one!
With that in mind maybe there are more qualified folks to give advice...
THAT SAID. I would make it float on the frost. I'd put enough steel in there instead of the wire, to make it lift on either end and still not go away!
We have really expansive clay down here, and it does a job on us too. That is a rather small foundation, and it could be reinforced to take whatever mother nature throws at it.
Big Jim

 

It also depends on if it is going to be an exposed (to weather) slab or covered in a climate controlled structure. An enclosed climate controlled building shouldn't need any cuts. Match your concrete strength to the maximum estimated load that it will support will help avoid fractures. If extreme loads are expected, consider fiber reinforcement. If this is an indoor shop, consider a taper to the center for a floor drain. Makes cleaning the floor a lot easier when it comes to getting the water out. Rebar, in addition to the reinforcing wire, spanning the floor N/S and E/W every few feet and tied to the wire mesh and turned down into the footing will help prevent stress cracks too. Soil compaction and moisture protection under the slab will "make or break" a good concrete pour in the long run. Pull the wire up as the mud goes down, so as to get it in the middle portion of the wet mud. Concrete bricks, broke in half and placed under the wire to hold it up, will help suspend the wire in the middle of the mud. If you decide to go with the stress cracks and have a floor drain in the slab, run the cuts from the corners to the drain to aid in water run off. Above all, don't put heavy loads on the slab till it has cured enough to handle it. And if it is a shop floor, seal it to keep the slab from absorbing chemicals and oils. You should be able to talk with your concrete supplier with your intentions for tips and advise.

 

I have had more complaints from sealed floors than I have had happy customers... If you are gonna get it oily DON"T seal it! The oil floats on top of the sealer and gets way more slippery. Folks find themselvs laying on their back when they have a sealed floor that is oily.
Big Jim

 

My shop is 24 x 32 on a mono slab with #10 wire and 1/2" re-bar around the footing ditches. I do not have any expansion joints and neither do I have cracks. However, do not let the finisher put caustic soda (think that is spelled right) in the concrete mix. That makes the cement set quicker and the finisher get through quicker, but my opinion is it want happen in my slabs. My shop is sealed with a 32" side door and an 8' garage door (which is to narrow). I poured the slab in Oct 99. And I live in the south. Hope this helps.

 

And do not let the slab cure quickly. Keep it moist and let it take several days to cure. The slower it cures the stronger it will be.

 

Concrete does not harden from evaporation!!! Concrete will get just as hard just as quick in the bottom of a lake as it will in the open.
Big Jim

 

As the concrete sets up immediately after the pour, the chemical reaction causes the mix to give off heat, which in the hotter season of the year can cause the slab to dry off faster than you can finish the surface if you don't have enough workers to keep ahead of it. Keeping it wet will allow you more time to work the surface and do a proper finishing job on the slab. Flooding of the concrete forms to keep a layer of water on top of a slab is a form of insullating the slab during freezing weather to keep the heat in the slab to prevent it from cooling too fast and, as a result, making the slab brittle. We do that after the surface is finished and everything is off the slab (and for several days). You don't have to worry about that this time of the year on a home project. Commercial jobs that have cylinder break requirements for strength tests rely on insullation techniques to achieve proper break pressures at required curing intervals. Way too much technical stuff to worry about in a shop floor. Just keep it wet enough so you can get it trowelled before it hardens!

 

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