Floor leveling

October 11, 2022

While evaluating flooring options, I took some measurements to see how flat the floor was.

In the worst area, there was a 3/4 in. difference in 12 ft, but the flooring I want to use requires no more than 3/16 in. in 8ft.

I had a feeling it wasn’t perfect, but was disappointed to find it was too uneven to put most flooring down on without leveling it first.

I used a small cordless metal cut-off tool with a 3 in. carbide blade to trim the drywall back, and then cleared out the debris with hand tools.

I first had to cut the drywall back away from the concrete, which was an issue the drywall hangers caused by improperly placing the material directly against the concrete, where it can wick up moisture and ultimately rot.

The foam used here is a low-expansion type usually used for doors and windows.

I then sealed up any gaps under the base-plates or between the drywall and the framing with spray-foam, which I later trimmed flush.

The grinding process took about 5 hours and was very boring.

I rented a special concrete prep tool and a floor buffer and completely stripped the concrete of all the dirt, paint and plaster that had accumulated on it over the last six years, and especially the last month.

Small dams at the door frames reinforced the foam, ensuring no concrete escaped.

Then I stapled and caulked sill-sealer around the perimeter to ensure the self-leveling concrete has an expansion gap and was properly contained.

I calculated that just over 20 bags would be required at minimum, so I purchased 40 to over-fill and account for errors.

My wife and I bought and transported the self-leveling concrete and stacked it inside.

At 52.1ºF we could have poured, but it’s right on the line.

The self-leveling concrete, as well as the primer used to ensure a good bond to the existing substrate, require the ambient air temperature and surface temperature to be 50ºF or higher.

The building is so well insulated, these two small space heaters easily brought the ambient air temperature on the first floor to a 70ºF in just a few hours – over 20ºF warmer than outside.

I was nervous that the overnight low of 44ºF would bring it down, so I ran some heaters inside to be safe.

The initial pour was supposed over-fill and cover the center, but the tried to feather it out instead, using only 23.5 bags.

The next morning, 3 guys made pretty quick work of it, however I measured again after the concrete set-up and discovered some low areas.

I assisted the second time, and as he poured I would check the level with the same laser-and-stick technique I used to do the initial survey.

A few days later one of them returned to pour some more, dealing with a low area in the lobby and a few smaller low spots as well.

The floor is now within 1/8 in. overall throughout the lobby and live room.

After letting it dry for a day, I put some fans on it to speed things along.