Repairing basement slab - concrete advice & recommendations?

[czechm8]

We did some work repairing/upgrading our below-grade plumbing in our basement (and added a few rough-ins for basement fixtures), and are hoping to fill in the trenches in our slab shortly.

I figure we need about a cubic yard of concrete - maybe a little more as we will hopefully try to level the previously sloped floor at the same time as filling in the trenches. I've been on the fence about whether to mix ourselves (either pre-mix, or buy cement, have aggregate delivered & rent a mixer), or whether to have the ready-mix concrete delivered. Originally I was leaning away from delivery because it's in our basement (no walkout, only stairs), but somebody suggested that a simple chute out of plywood & 2x4s going through a window could help with that. I'm leaning a little bit back towards the delivery now and looking into that at the moment (some companies do smaller deliveries now, Astro & U-Cart).

Any suggestions from those that have done similar? Anything else we should be considering, or any concrete folks in Calgary that can weigh in?

[leo]

Redi mix is fine to infill your slab cuts, but not for leveling. There is self leveling grout available for that job.

[anchorman]

Hard to say without seeing it, but consider what your landscaping will look like after you back a redimix truck up to your window. Bags of cement work fine, and can be done over a day (or days),without the pressure of over ordering, small load charges, and finishing it all in a short time?

Concrete fever

[CaberTosser]

I used the U-cart option once and it was a good option for my needs on that project. I backed up the trailer and hand-bombed it in using 5 gallon pails. That would do for your patching, to level the rest I'd think a self-levelling product would do the trick. I forget if your floor has been painted, I would think that prepping any such areas for proper adhesion would be in order to keep it from flaking (depending of course on what flooring you have above that). I used a diamond cup grinder to do a final wet-surfacing around my basement floor drains and then gave the rest a quick pass as a surface prep where I was putting in the two-part epoxy Rustoleum floor finish.

[Sneeze]

Use redi-mix bags. The cost savings will pay for beer and pizza for your friends to come over and help.

Are you positive its a yard of concrete you require? That's equivalent to a 2 foot wide cut approximately 60 feet long.

Hardware stores sell 3/4 washed gravel in bags... use this to fill up the holes until the gravel is 3-4" below the existing slab.

You can't level with regular concrete unless you plan on going up 2" or so across the entire basement slab. You will have to do your best to make your new concrete flush with the cut edges of the existing slab and use a different product to level after the concrete is set.

[czechm8]

Thanks for the replies. I've been pretty busy looking into how best to do this. I'm still even going back and forth at times on whether to even bother levelling the area with concrete at all, or just cut sleepers to match the floor slope and build a subfloor. Either way the ceiling height will probably be the same, because if we levelled with concrete we were thinking to using the insulated dri-core subfloor that HD sells (pricey, but it's not a huge area).

Originally Posted by CaberTosser

I forget if your floor has been painted, I would think that prepping any such areas for proper adhesion would be in order to keep it from flaking.

The floor was painted - we got about 98% of the paint off with a grinder so we're good to go there, and would use a bonding agent to help the new bond to the old.

Originally Posted by Sneeze

Are you positive its a yard of concrete you require? You can't level with regular concrete unless you plan on going up 2" or so across the entire basement slab.

This has been the major source of complication for us. Concrete (quikrete or ready-mix) is the proper thing to use to fill in the slab, which we've now back-filled with gravel so it's only 4". We re-did the calculation and it looks like to fill in the trenches only we need about 20 cu.ft, or 3/4 yard.

However, the rest of the area is a sloping floor, which goes from 2.5-3" lower in the center to level at each wall. The trenches are roughly in the middle, so we were thinking that while we are filling those in we could put another 2-2.5" of concrete right on top of that, to fill in the deepest part of the sloping floor, and it would bond well to what we pour into the trenches (and also no reason to stop and level to the existing floor, as we would be pouring beyond that). After that I was thinking of transitioning to sand & topping mix (with binder) for everything between 1/2" and 2" deep, poured at the same time as the trenches to get a good bond.

I was wondering whether there is another product we could transition to for the last bit that we could screed to a feather edge? But that seems like it might be overly complicated (concrete in the middle at the deepest, sand & topping around that, and then a third product to give a feather edge).

I guess I was hoping we would be able to do those parts all at once over a long day and screed it as best we can, then come back and only have to use a minimal amount of the pricey self-levelling compounds to smooth out any areas that are less than 1/2" deep.

But, thinking about all of that sends my tail between my legs at times and makes me wonder whether a sub-floor on sleepers might be easier, and possibly better?

Background: The area is about 13' x 16', and three of the walls are already at the final height (the high spots) - the existing slab slopes to the middle of the fourth wall. So along that fourth wall, a 13' wall, the slope is at it's extreme, and is about 2.5-3" lower in the middle than on either spot.

[diamond k]

Call a couple of concrete pump outfits and tell them what you need. There is usually that much left in pump when pour is over. If one is close you can probably get concrete for free and would most likely just charge you 100 bucks and they don't have to worry about dumping overage.

[Sneeze]

There are a few how to clips on youtube - I think "This Old House" did a segment on leveling a floor. It was a different application but the principals will be the same.

If I was to tackle this project I would probably utilize PWF 2x4 sleepers scribed and cut level and PL'd to the floor in an array from the lowest point. I would then use a product like Deck Mud over a wet layer of thinset to bring my project close to level. Depending how the finishing was going I would stop slightly low and use a self leveling product or other product that allows for feather edges.

I think some guys would even suggest wire mesh in the bed. Probably would want to rent a mixer as you would have to go pretty quick to prevent any cold joints.

Just throwing 2" of redi-mix over top could get ugly after it shrinks. You might have a floating slab on top of a floating slab.

Good luck with your project.