Gravel base questions

[Smrtpunk]

Hello,

I'm going to be pouring a monolithic slab for my upcoming garage build and I want to obtain information on depths of excavation.

The building is being built in Ottawa, ON, Canada. How deep should I go to evade cracking in my concrete? Should I be going deeper around the footings of the slab.

I was thinking 4 ft deep around the footings and 2 ft deep everywhere else.

Ian

 

[kd3pc]

Your thoughts are good, but you may want to check with the AHJ to see what they say.

Concrete will crack, so you need to plan to cut control joints in it as soon as practical to do so.

If the AHJ, will allow, you can sometimes lessen the required depths by judicious use of insulation on that perimeter wall. Other times, they will want to see the perimeter part of the monolith several inches below the freeze line, usually 42-48".

There is no need for the slab portion to be 2' deep. Most of that depth would be fill, compacted to leave a 4" to 6" slab depending on area covered and the intended use of the slab.

 

[36truck]

Biggest thing to do is remove ALL topsoil. Then if it needs fill compact it very well with the proper moisture. Around here if you get an engineer stamped drawings you can do a thickened edge slab.

 

[Smrtpunk]

Thanks,

I had heard that before and at the same time I've heard to remove all fill that may have been placed in the ground during the construction. I thought that last part needing the fill removed was a little much as I imagine any fill placed in the ground during the construction would likely be compacted since the house was built 60 years ago.

Anyways, I think I'm going to remove the top soil and any other ground material down to 2' compact well, place one foot of gravel compact and place the other foot, compact and setup forms for concrete.

 

[machsnell]

yes place stone in lifts of 4 to 8 inches depending on what you are using to compact. unless you are using clean drainable stone. then you could go thicker. Dirt should be dry-ish. some moisture for compaction. after compaction is should be allowed to dry. dont lock in moisture before your pour.

If moisture gets locked inside walls, if it cant drain it will heave. no moisture much more limited heave.

rigid insulation helps a LOT. Under and on edges. Keeps concrete warmer.

Also use 6 mil plastic and tape seams or at least 2 foot overlap. this will keep the concrete from sweating and seeming damp.

Also, do it once and right. use rebar AND get microfiber in your concrete. TRUST me it will do amazing things for you.

My garage slab is a 5.5" slab and i used 4k concrete and had a 4 slump so limited moisture with 4 bar on 18" center both ways and had microfiber in concrete. i also had 3" rigid foam at 60 psi foam.

I have a 1700 sf slab and only cut two joints in it afterwards with saw. No cracks yet.

I will finish with epoxy and will cut one more joints but one of the joints that was cut within 3" of the wall hasnt even cracked on the cjoint yet.

goood subgrade and insulation means good concrete. good subgrade good subgrade!

You are on the right track. Good luck

 

[Pstychologist]

Are you planning on adding fibers? I've had very good luck with them, but the finish isn't as smooth.

 

[volleyball]

To determine excavation. Find your finished grade. Now add up slab, base and foam thickness and go down that far for the field. Your jurisdiction will tell you how far the footing have to go down.
Bad material, slope and such will also play with the numbers.