I’m underpinning a concrete porch in Toronto Canada. The existing foundation is cinderblock and only goes down 3ft. I’m trying to order concrete but don’t know the required strength. I was told MPA 30 but that doesn’t tell them everything they want. What kind of aggregate? Strength? Fibre re-enforced?. My form is down 4ft X 4ft by 2ft.
Could someone please help. What should I order?
Erik
Replies
3000
Aggregate 5/8"? 3/4"?
I lost the orginal threa but mpa 30 is a 4000 psi, size of rock doesnt matter, just order a 4000 and you be fine
Was gone for awhile. Thanks for the info.!
Call Lafarge and tell them to send you the Mike Holmes special mix!
Have a good day
Cliffy
Was gone for awhile. Thanks for the info.Erik
Speaking of underpinning, do you have any pictures and advice for how to underpin?
I have a corner of my garage that moves seasonally and racks an entry door so it will only stay closed two seasons a year. I am thinking about underpinning it. My thought was to auger a 12" post hole as close as possible and maybe at an angle? Don't want to excavate too much as there is a propane line running 4' out from that corner.
Then I would do some hand digging to roughly shape into a decent enough void so as to make a square plywood form or use a cardboard tube form? Square ply form seems easiest to build a concrete funnel onto.
I also thought it would be prudent to drill into the slab from the underside and somehow affix some rebar dowels? I assume when the concrete sets up there will be a small gap at the top to fill with mortar or something?
Does this sound right? am I missing anything or making it more difficult?
This seems like one of those jobsite type of issues that not many REALLY know about; it's up to the carpenter to make it up as he goes. So why is it that this sort of article never seems to make it in an issue of FHB? Seems like 5 issues a year tackle how to flash a window or install a door! jeesh.
DC
I'm just learning as I go. You gotta go down at least 4ft or the frost will heave the concrete.Erik
Before moving forward with under pinning you should consider if there are any large trees near your home. If so your footers may already be deep enough to prevent frost heaving. You may have an issue with the tree roots drawing water out from under the house causing the problem. I built a house a number of years ago where we put the footers well below the frost line in rock and it had heaving problems. Turns out two big oaks were sucking so much water out of the ground that it caused the movement. The home owner had two choices. First to water the trees in the summer or second cut them down which he did. No more problem. Built another house and 10 years after completion had movement problems. Looked at a number of possible caused like smashed drain tile or leaking down spout lines. Finally had soil borings made. Turns out about 50' below the house was a pocket of expansive dirt. Had to drill 80' down and pin the footers.
No trees in the vicinity. Soil is all clay in this area, not much I can do about that now. I have reason to believe that this corner always moved due to the state of the floor and wall when I bought the house; but not knowing how much it moved, I poured a new floor over the old using a 5" sand buffer to isolate the new slab. The door location is new as well, and I already adjusted the strike twice before I realized there were two cracks in the original slab about 6' each way from the corner. The seasonal movement is somewhere almost an inch up and down as witnessed by laying a straight edge across the trusses in the winter. I sorta figured this would be a "figure it out as you go" situation. I guess what I am most confused by still is how to pour concrete up to the bottom of the slab, which will likely be rough on the bottom, and still make a tight connection, especially being in such a confined space.
You need to find O'shans, they are a slab jacking company.
My friend bought a house with the corner broke off the slab. They had poured a slab on top of slab, done something to fix the framing so everything looked right. He called O'shans, they came out with people,dug perimeter where it dropped, and started putting the piers or whatever and jacking them down until it hit solid and it pushed the slab back into place.
This had dropped so much the brick had to be taken off of that corner of the house.
It cost about 17K IIRC. about a 2500 sq ft.
Thanks but no thanks.My slab is not sunken, I simply don't have adequate foundation depth so the wall moves with the soils. AND if I just do it myself, I would go in saving about $16,942.00
Check out concrete vendors for "Slab Jacking".
There a is a load of information at http://www.cement.org/
You can take good concrete and make it bad by improper curing.
The same batch of concrete can vary greatly in strength by curing alone.
Take a look at http://www.precast.org/publications/mc/2006_julyaug/wc_ratio.htm
and http://www.tkproduct.com/Curing%20Concrete.PDF
Typically 3000 psi concrete is adequate in most construction situations of your case
I live in western Canda and 30 MPA is more than adequate. There is no need to worry about aggarate size or anything like that. You can also call the building inspector office and find what they call for. Here the city requires 30 MPA type 50 (sulphate resistent). All batch plants know what is required so there is no need to stress over everything. Only thing is to consider is what the engineer might want, that is if you have one
30 MPA type 50 (sulphate resistent).you cannot buy type 50 here, nobody makes it, no body have indgreiates to make it
you cannot buy type 50 here, nobody makes it, no body have indgreiates to make it
Well, the two of you are about 3000km apart, so, raw stock at the mix plants are likely different. Their sand, out in western Canada (and likely OP's Toronto, too) probably under cover. Mixmaster probably does not calculate the entrained water in the sand for the mix either, unlike over by you there in MS/AL.
Mind you, our Canadian neightbors have probably never had concrete delivered with block ice instead of water, for that matter. Makes the placing crew ever so happy; pump truckers similarly so.Occupational hazard of my occupation not being around (sorry Bubba)
I got a pour tomorrow at 4am in gulfport
got a pour tomorrow at 4am
Bet there's not a mix plant with anti-freezing admixtures nearby <g>
Around here, a 0400 start meas you get two hors of the temp dropping to the overnight low, just before the sun comes up to start the process all over again.
0400 start does keep the finishers all on the same calendar day, for payroll purposes, it's also light to see by for finishing.Occupational hazard of my occupation not being around (sorry Bubba)
Are you sure it was not Type V?