Leveling a basement slab

Posted: Wed Jul 12, 2006 1:51 pm

My basement concrete floor slopes toward a drain in that section of the basement.

My floor-ceiling height is 89" at a far wall, sloping down to 94" at the drain.

I believe I have to
a) build a wood skirting frame (not the entire basement) (5" tall, two sides of the 'room', as the other two sides have concrete foundation walls. Note sure if I need some sort of separator at the concrete foundation walls -- but there doesn't appear to be drainage there in my home, but I might skirt all 4 sides with wood to further isolate a bit, just in case. I have no plans to cut my basement slab floor for additional isolation at this time)
b) clean the floor
c) paint the concrete with a concrete to concrete preparation/primer (so the new concrete sticks to it)

THEN

At this point I think there are two options
1) NORMAL CEMENT
1.1) pour normal cement with stones
1.2) smooth the surface with a long handled smoother (skimmer?)
1.3) and let it sit for many days (< 28 days).

2 SELF LEVELING CEMENT
2.1) fill the and level the area with stones (3/4") till the lowest part is 2" deep, and pour in leveling cement mix (no stones)
2.2) 8 hours later fill another 2" with stones and pour in more leveling cement
2.3) 8 hours later level the remaining inch with just leveling cement.

But I'm not sure which way to go -- although I suspect that self leveling cement might be safer for a novice to actually get LEVEL.

(I used to think of building a wood floor and leveling it with a laser. And then there was my Kenetics RIM phase with leveling wood under the pucks. And then there was a while I considered building the room with an uneven floor to get a few extra square feet of volume. And then ...)

BTW, I called a couple of plumbers for estimates on how much it would cost to move the drain 3' (just outside of the 'room' area), and it was over $2000 CDN.

Anyway, any suggestions on how to level the floor?

Any additional details or watch out for this? (other than the famous Paul Woodlock recommendation of "Don't Sit In Concrete Young Lad")

Posted: Wed Jul 12, 2006 4:35 pm

Z,

This would be my recommendation -

http://www.ardex.com/prod-sdt-inst_gray.htm

You would want to properly clean the floor - and prep per the manufacturer's instructions - and you wwill probably need to set up some leveling poles to guide you through the process.

Your best bet would probably be to provide the materials and hire a pro to do the pour for you.

BTW - jack hammer up the floor yourself and move the drain - it isn't all that difficult.

Rod

Posted: Wed Jul 12, 2006 5:15 pm

Thank's Rod.

At 14' x 21' x 5" / 2 that works out to 735 ft^3 volume to fill.

That ARDEX SD-T looks similar in instructions the self leveling product brouchure I found at home depot (which I don't have handy), except for the pea gravel instead of 3/4".
But you answered another question of mine -- with this volume and at 5" thick to still use leveling cement.

Would the leveling poles be from the top suspended over and laser lines to line up, or from the bottom. I not sure if they'd have to be removed while wet. (Actually I figured with self leveling cement I wouldn't need leveling poles or lasers.)

Posted: Wed Jul 12, 2006 7:12 pm

ufortunately I know too much about construction. If you have a minimum depth to fill of 3-1/2" (and greater toward the drain) then regular concrete would work fine. When you consider that an 80 lb. bag of home depot concrete is equal to 2/3 of a cubic foot (or an area 4" deep, 1 foot wide and 3 feet long... you've got a lot of hard work ahead of you mixing and placing almost 85 bags... there isn't enough time in the day to get to the last bag before 1/2 of what you've poured is as hard as a rock). Your best bet is to have the concrete pumped into place as it comes out of a commercial cement mixer. There are advantages to not going the bag route; you can order high strength concrete with additives to either hasten or slow the setting process, add fibers to the mix to help bond against cracks, etc. The leveling poles Rod referred to can be as simple as concrete screws (tapcons) set at 3 foot intervals (or more) where the head is screwed down to align with what will be the finished elevation. Pump/pour the concrete and float it to these screw heads and you'll have a level floor; you don't have to remove them. Concrete sets up quick so you can walk on it within a few hours. It reaches 90% of it's strength in 7 days and almost 100% in 28 days. You can have a dance party the day following the pour.

I wouldn't put any gravel base down in this situation and then pour over it with anything because 1) the gravel base isn't stable and creates a ball-bearing effect above the existing floor... and 2) the leveling cement isn't strong enough to withstand the "give" as the gravel settles... unless you like cracks. Leveling cement still needs professional care in it's placement; there is no magic mud. Anyway, forget the "self" leveling cement... remember the bags and do what Rod suggested, call a company that does this stuff for a living. You'll live longer.

The drain is there for a reason... if is this an old house (early to mid 20th century) it's there to collect the water that comes in through the foundation walls. If the house is of the more recent variety, chances are it's there because a laundry was set up at one time in the basement. If your foundation walls and the footing they sit on are below grade you have to be certain no water ever penetrates those walls... they must be water-proofed from the exterior with a drain pipe running along the footer to daylight that allows any settling water to run away from the basement... but now I'm guessing about what's going on at your house and going off the cement topic. Just make sure that drain isn't there for a specific purpose.

Call the concrete contractor and be done with it; there are some projects that homeowners should not even think about.

Posted: Wed Jul 12, 2006 8:35 pm

The house was built in Dec 1993.
The drain is equidistant between the washer/dryer and the hot water tank, and has two rubber hoses into it under the concrete slab -- one from the furnace air conditioner, and the other a 'priming' hose from the laundry bason. I'd be moving the drain from the middle of the floor, closer to all these things.

I figure:
a) the leveling would occur after I've figured out what to do with the i-beam (still planning on removing a lolly column)
b) after moving the floor drain
c) possibly after putting in a new floor drain for an alternate washer/dryer location (done at the same time as 'b')
d) and after I've moved everything in the basement to a storage facility.

The cement that Rod found said it sets in about 10 minutes. Whereas the self leveling cement that I found I thought said it set in about 30 minutes.

By my math, at 735 ft^3, and at 12.5 sq. ft. per bag at 1/2" thickness, that's .52 ft^3 per bag, or 1411 50 lb. bags of ARDEX SD-T, or 70,560 pounds of concrete mix. That seems like a lot for two guys to mix in a wheelbarrow.
EDIT: Actually it seems a lot for a single cement truck. I'm pretty sure a cement truck won't fit in my basement. Ah -- I made a boo boo. 735 ft^3 is like a 9' cube. I multipied by 5' instead of 5". So it's only 61 ft^3. That's 118 bags, or 5889 pounds of concrete mix.

Posted: Wed Jul 12, 2006 9:19 pm

Just about to go get a life and your response popped up on the email.
You've got about 5 cubic yards of concrete to fill the space 5". A concrete truck carries 10 yards. The truck sits out in the street and a line pump is used to convey it as far as you like up to about 350 feet (but you were kidding about the truck in the basement part?). The column bearing the I-Beam is engineered to sit exactly where it is. Below it, below the existing floor is probably a 3 foot square x 16 inch deep concrete and steel re-inforced pad. If you move it you will probably need two to replace it... set at whatever distance each way from where it currently sits to compensate for the move (an engineer should be consulted... a structural engineer, that is). The drain is an active drain, so you will have to move it or run all the drain lines currently feeding into it to a pump so you can pump the water out. It might be cheaper to build an addition onto the home. Remember, forget about the leveling cement... at any thickness. You'll kill yourself. 5 cubic yards = 125 cubic feet = blood, sweat and tears. Good luck.

Posted: Wed Jul 12, 2006 9:48 pm

Z,

Last year I bought 10 bags (500 pounds) of the self-leveling cement from Home Depot, and we had a crew of 4 people working quickly on a day about 75 degrees Fahrenheit. I wouldn't do this on a hotter day. The goal was to level an area of only about 220 square feet that was off between 1/8" and 3/4".

I was told by the company that makes the stuff to hustle up a crew of four people:

We had a fourth person who just spread the pours. Mixing was timed to two minutes only, then it was time to pour and spread. The mix started to congeal in about 10 minutes in each poured area. The whole process ended up taking about an hour and a half including clean up. (I wore only the most basic dust mask, and regretted it. I started coughing up grey stuff for the next 3 days. Fortunately it didn't kill me, but there are carcinogens in concrete mix—crystalline silica—so wear only the BEST respirator.

It went smoothly enough, but even with only 10 bags, faced with the same choice knowing what I know now, I'd pay anybody else whatever to do it instead.

Lee

Posted: Wed Jul 12, 2006 10:24 pm

motz:

Don't worry about the i-beam in this thread. I think I understand how to do that (yes structural engineer, etc, I've got three sets of good examples with pictures). I don't know anything about leveling a floor other than reading one pamphlet from home depot -- so I'm asking.

I didn't mean that the concrete truck would park in my basement. Smile

It was simply a question of volume. I've seen a cement truck and how big that is. I've seen my basement and how big that is. If I want to put a little bit of cement on the floor, and it takes more than a cement truck's volume then I've made a boo boo in the math.

There's a convenient 28" x 10" window that with any luck they can push a pipe or something through. Unfortunately that window is about 20' from the close corner of the 'room' and about 40' from the far corner of the 'room' to be leveled. There's a 4.5' wide hallway between the window and the 'room'.

The last time I did anything serious with cement was almost two decades ago making four 1' thick x 8' tall x 9' wide foundation walls for a very solid green house with a contractor. Or more accurately I was watching and asked "Do you think that wood is going to hold?" And he said "Kid I've done this a thousand times". It collapsed mid pour, he gave up and was about to abandon, at which point I took over the crew. We used hydrolic jacks and forced the walls back into place, bursting two hydrolic jacks in the process. It was a lot of weight to move back upwards, but in the spirit of "Give me a lever strong and long enough, and a fulcrum upon which to rest it, and I can move the world" we got that soupy concrete wall back into place, bashed in some more wood until I thought it would hold, and finished the pour. Worked great. But I didn't do anything with the concrete itself (didn't order it, didn't mix it, didn't do much of the pouring except the last couple of cubic yards).

Leveling cement supposidly works down to wafer thin without problems (the high spot -- I don't want to loose ANY room height). I'm a little more woried about regular cement there.

Nobody's mentioned rebar so I'm glad I don't need that.
I know that one tells the cement truck company what the job is, and they mix the appropriate concrete for me. Might even through in a few of those bags of fiber reinforcing stuff (there seem to be a few different types: glass, nylon, polyester, polypropoline, plastic), although I probably don't need that either.

I assume I don't need to worry about the 5" tall cliff breaking after I remove the wood pour framing and start putting tapcons into the edge and putting a semi-load-bearing wall up on it.

Posted: Wed Jul 12, 2006 10:27 pm

jazzman_in_pa:

Good story.

Last christmas I remember complaining about sturring some thick caramel sauce making my arms tired (it took an hour). That weighed about ten pounds. [sarcasm] So sturring 6000 pounds of liquid rock should be easy.

Posted: Wed Jul 12, 2006 10:36 pm

BTW, pictures of the basement at
http://www.bobgolds.com/Basement/home.htm
and
http://www.bobgolds.com/HomeTheatreDesign/OLD/Basement_layout.jpg

Posted: Thu Jul 13, 2006 5:57 am

Ah, pictures and a thousand words.... The floor drain probably runs back toward the utility sink to the large vertical pipe along that wall, so you'd be making the run shorter. The $2,000 bid sounds very excessive and you should get some more bids. You could jack-hammer the floor yourself (16" wide x max. 36" long area toward that stand-pipe) and help to lessen the plumbers cost. Based on your studio drawing, you can set up forms that define the perimeter of the room and pour within that specific area (you already intended to do that?) Then, yes, use the leveling cement to the full 5" depth (no gravel... except now I suspect the gravel was to be used in the depths greater that 2-3 inches and mixed in as a part of the cement mixture and not a separate bed below the pour). Yes I understand about the feathering and not wanting to lose height. The forms at the perimeter only need to be ripped to fit the contour of the pitched floor below what you need as the finished elevation. The width of the room isn't so much that any leveling points would be needed... but I would suggest you contract with someone who plays with cement as a living.

Considering you're going from 0 inches to 5 inches in a 14 foot x 21 foot area (+/-), that's about fourty 80 lb. bags cement... still a lot of work.

Good luck... it doesn't look all that difficult now that I see what you're doing and where you're doing it. Nice basement.

I know you said not to discuss the column / I-Beam... but. The strength of the I-Beam is concentrated in the height/size of the vertical member, though the top and bottom flanges certainly contribute to this, their design is to stabilize the main vertical run to keep it from twisting under the weight it’s carrying. You might be able to eliminate the column by welding sections of plate steel (called flitch plates… though the term is usually used when discussing wood beams)) to either or both sides of the vertical member for a distance of “x” each way from center to compensate for the reason that column is placed where it is. OK, that’s enough out of me.

Posted: Thu Jul 13, 2006 6:39 am

Quote:

The floor drain probably runs back toward the utility sink to the large vertical pipe along that wall, so you'd be making the run shorter.

Actuallly it runs 90 degrees to that, towards the narrow part of the room where the stairs are. I can only tell about a foot though, due to the trap, however there are several clean outs in the floor in that direction. I'm not sure if it connects to the city storm drain or to the city waste water drain.

Quote:

The $2,000 bid sounds very excessive and you should get some more bids.

Two bids. About the same. Included putting up plastic sheeting to keep the dust down, and complete clean up etc. One bid was two guys taking notes, and the bid showed up a couple of days later. Another bid was one older guy who looked up in a large binder the sub-parts-of-the-job, added them up, and that became the quote.

Quote:

Based on your studio drawing, you can set up forms that define the perimeter of the room and pour within that specific area (you already intended to do that?)

Yes.

Quote:

Then, yes, use the leveling cement to the full 5" depth (no gravel... except now I suspect the gravel was to be used in the depths greater that 2-3 inches

Yes. (as in: not the top bit)

Quote:

and mixed in as a part of the cement mixture

No.

Quote:

and not a separate bed below the pour).

My read of the pamplet was that the stone would be placed first to a depth of 2", and the leveling cement poured over it, and the leveling cement would flow into and fill the spaces between the rocks. The rocks would not be "under the cement" but would become part of it.

Quote:

The forms at the perimeter only need to be ripped to fit the contour of the pitched floor below what you need as the finished elevation.

Why bother ripping them? So what if they're high.

Quote:

The width of the room isn't so much that any leveling points would be needed...

OK

Quote:

but I would suggest you contract with someone who plays with cement as a living.

Three recommendations for that. Smile

Posted: Thu Jul 13, 2006 9:18 am

z60611 wrote:

That's 118 bags, or 5889 pounds of concrete mix.

Z,

Isn't that an error also?

Isn't the floor basically level at the edges and 5" deep at the drain?

That would calculate at an average of 2 1/2" thick for the entire floor - and a percentage of that for one section.

For example - if you were to break the pour at the drain itself - it would be nothing at the existing 2 wall edges - 0" to 5" at the 2 inner wall edges - which would be 2 1/2" averaged over the pour.

You need to redo the math based on the pitch.

Also, one of the reasons to use pea-stones is to be able to pour to a thinner edge.

Yuo would want to set your pour with the pea-stones to only run to a point where the pour was about 1/2" thick - and then complete the pour with no aggregate for the remaining 1/2" to nothing at the edges.

Sincerely,

Rod

Posted: Thu Jul 13, 2006 12:26 pm

5" / 2 = 2.5"

14' x 21' x 5" / 2 = 61.25 ft^3.
61.25 ft ^3 / 0.52 ft^3/bag = 118 bags.
118 bags * 50 pounds / bag = 5900 pounds.

I'd have to do an entire 2D survey every few feet to be sure, but my quick survey:
at drain: 94"
4' away: 93"
8' away: 92"
12' away: 91"

Quote:

Isn't the floor basically level at the edges and 5" deep at the drain?

The floor at the 'top' wall on the diagram is also sloped, with the floor higher on the right (further from the drain).

Quote:

Yuo would want to set your pour with the pea-stones to only run to a point where the pour was about 1/2" thick - and then complete the pour with no aggregate for the remaining 1/2" to nothing at the edges.

Yes. The pamphlet said the last layer should have no stones and would be less than 1" thick.

Posted: Thu Jul 13, 2006 8:24 pm

z60611 wrote:

Quote:

The floor drain probably runs back toward the utility sink to the large vertical pipe along that wall, so you'd be making the run shorter.

Actuallly it runs 90 degrees to that, towards the narrow part of the room where the stairs are. I can only tell about a foot though, due to the trap, however there are several clean outs in the floor in that direction. I'm not sure if it connects to the city storm drain or to the city waste water drain.

Quote:

The $2,000 bid sounds very excessive and you should get some more bids.

Two bids. About the same. Included putting up plastic sheeting to keep the dust down, and complete clean up etc. One bid was two guys taking notes, and the bid showed up a couple of days later. Another bid was one older guy who looked up in a large binder the sub-parts-of-the-job, added them up, and that became the quote.

Quote:

Based on your studio drawing, you can set up forms that define the perimeter of the room and pour within that specific area (you already intended to do that?)

Yes.

Quote:

Then, yes, use the leveling cement to the full 5" depth (no gravel... except now I suspect the gravel was to be used in the depths greater that 2-3 inches

Yes. (as in: not the top bit)

Quote:

and mixed in as a part of the cement mixture

No.

Quote:

and not a separate bed below the pour).

My read of the pamplet was that the stone would be placed first to a depth of 2", and the leveling cement poured over it, and the leveling cement would flow into and fill the spaces between the rocks. The rocks would not be "under the cement" but would become part of it.

Quote:

The forms at the perimeter only need to be ripped to fit the contour of the pitched floor below what you need as the finished elevation.

Why bother ripping them? So what if they're high.

Quote:

The width of the room isn't so much that any leveling points would be needed...

OK

Quote:

but I would suggest you contract with someone who plays with cement as a living.

Three recommendations for that. Smile

you obviously already know what you want to do and what's involved... like the commercial says, "do it" Wink

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