View Full Version : How to level a basement floor

02-15-2009, 02:50 PM
I find this forum helpful so I hope I can get some help with this problem... I am finishing a basement in a 60 year old house. I have a very uneven floor and it slopes what seems like about 2 inches or so from highest point to lowest across the basement. I am putting up partition walls and the finished area will be sandwiched in between an area of about 8 feet on both outer walls to accommodate storage, utilities, sump. etc...To explain it better.. if you were looking at the house from the front you would see from left to right, foundation, 8 foot area then a wall, then 17 foot area then another wall and another 8 foot area and then foundation. I hope that makes sense.

My idea was to put down the floor plates and pour self leveler and have it contained by the floor plates but the concrete is so wavy that the plates don't sit flat.

My Dad's advice is to move. I rope him into all these projects that seem easy at first and they never are.

Any advice is much appreciated...

02-15-2009, 03:38 PM
My idea was to put down the floor plates and pour self leveler and have it contained by the floor plates ...

I would first use a transit or a laser to establish and mark a new level-and-flat floor line along the walls, and then I would drill a grid pattern of holes in the floor (maybe 6' x 6' or so) for some short pieces of rebar to be driven in and to stand as posts for holding leveled screed guides. When you pour the concrete, the guides can be removed and the posts can be driven down as you go along, and that should leave you with a nicely-finished level and flat floor for your remodel.

Note: Do not drill into or through any plumbing!

02-15-2009, 04:12 PM
The idea is to "level" the finished room, right? How much deflection do you have in that new "room" ? Self leveler works great - but is very, very spendy... If you have a 2 inch drop - you'll spend a ton of $$ getting it flat.... I've done a few basements with this problem.. and for the really bad ones - have resorted to a layer of thinset - followed by 1/4 - 1/2 CBU - followed by self leveler (the cheap stuff takes up the most of the deflection)... My tile work on these floors has lasted 2+ years so far - with no cracks/drips/errors.....

02-15-2009, 04:27 PM
How much can you afford to lose in headroom? A concrete pour could work, but it needs some minimum thickness. What may be eaiser, but expensive, would be self-leveling cement (slc). The least expensive thing to do would be deck mud (mostly sand with some cement in it). Mixing, carrying, and screeding the stuff is heavy work - think of working with wet beach sand. Deck mud would be a fine base for tile and possibly other finished surfaces (it can't be left uncovered - it's not good for abrasion, but is fine for compressive strength - it's the same stuff they use to set tile floors and shower pans). SLC isn't a finished surface, either. A concrete slab pour can be, but finishing it so it is flat and level takes more skill than the average homeowner has. Concrete pours usually don't work all that well if they taper to zero at the high point, so extra thickness is better so it has strength. To bond the concrete pour, you'd want to using a bonding agent. SLC needs a special primer. Deck mud you can prime the slab with a slurry of cement...cover before it sets.

SLC pours can be made a little more ecconomical if you use some pea gravel in the thicker areas to use up some of the required volume. SLC will essentially level itself IF you can mix and pour it fast enough so what you have is still liquid (think pancake batter). Some versions start setting within 10-minutes of when it gets wet, so you have to mix and pour quickly. There are versions that set slower - up to about 30-minutes. If you don't pour quick enough, it's sort of like moving a partially cooked pancake...really messy, and not smooth! The stuff is expensive, but if done right, is quick and produces a great result, or can be a very expensive mess.

02-16-2009, 12:17 PM
I like all of the ideas, thanks... seems like more work than I thought. Can I put down bottom plates for the wall in different pieces to compensate for the difference in the floor and then just cut each stud to fit. I don't plan on putting flooring down that needs to be level although I would like it to be... I'll live without a level floor if this is possible... Thanks

02-16-2009, 02:29 PM
Your stud idea seems like a lot of work. I would build the stud wall to the minimum size and just shim it out with ripped 2x4's. Then I'd screw the bottom plates through the shims into the slab. Basement walls are non weight bearing. You just need to make sure they will stay up. Now the drywall job after that will also be a easy because you just hide the unevenness with the wall trim.


02-17-2009, 07:33 AM
Do it right. Level your floor, you'll be happier in the end. You don't have to cover the whole floor with self leveling cement. Just the low spots to make them even with the higher ones.

Build your walls with one bottom plate(put a piece of plastic between the wood and cement) and then just cut the studs to fit.

Put your sheetrock(paperless preferred for basements). Finish your walls and ceiling completely with paint. Then level your floor. Then put your finish floor material. Then your mouldings last. Everything will look straight, the way you want it. No slants.

The extra money and work to MAKE your floor level is necessary in my opinion.

02-17-2009, 12:00 PM

His basement is domed in the middle. I've seen this many times. The only way to fix this with any reasonableness is to do a pour. But due to minimum thickness he's going to have to pour a lot of cement in there.

From my perspective it depends on what he wants to do with it. Though in general I agree, level it first.