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I'd like to start by admitting that everyone makes mistakes, and our team is no different.
So, here comes the confession: when we installed our recent demo floor at Penn State's Innovation Park, we figured that the subfloor was a professional pour, and it would probably be fairly flat. In retrospect, we obviously should have checked! In reality, the subfloor was DEFINITELY not flat. Instead, the subfloor was crowned in the middle, and had dips as big as a 1/2". We learned that our very flat flooring boards can bridge some subfloor imperfections, but over a 1/4" and you'll get some bouncing and light creaking noises. Lesson learned: follow your own subfloor specs, Steller!
One piece of good news was that since we hadn't glued or nailed down the floor, fixing it wasn't going to be expensive or time-consuming. Since the space is used as a conference room during the week, we had to quickly fix the problem over the span of a weekend, and we wanted to cause as little disruption as possible. So, on a Friday evening, two of us took 45 minutes to remove the whole floor from the room (275 sqft) and we arranged the boards in the hall according to their original location in the room.
We had an idea of where the problem areas were based on how the floor behaved, but we wanted to know exactly how bad the subfloor was. Completely flooding the floor with a liquid leveler is sometimes an option, but in this case, we didn't want our concrete to accidentally end up on the carpet or in the hallway. So, to measure the dips in the subfloor we rolled a straight, 5' long 1/2" metal pipe on the floor to find the peak (which was in the middle of the room). Then, we laid the pipe out with a level, and measured how many 1/16" washers we could fit under the pipe. Areas that needed more than 1 washer needed to get leveled.
How to level a subfloor—its easy
That evening, we did a quick crash course in liquid floor leveling (because we are not contractors, we are wood products nerds). Evan had worked with concrete during his time in AmericCorps, but we wanted the floor to turn out well and not need to be ground flat (which would create a ton of dust).
So, we studied up here:
On Saturday morning, we gathered our materials and followed the directions on the bag to maximize the amount of water in the mix. For us, the first pour was probably not mixed well enough (maybe 30 seconds more mixing with the drill would have made it better), so that first pour created a slight, 1/16" crown where there used to be a dip. The mix should seem very much the consistency of pancake batter, and you will need to push it around to get it level. We dragged our 5' long pipe across it, but it would have been nicer to have an 8' long pipe on hand. Luckily, the second two pours went much better than the first. The leveler did cure pretty quickly, and within 15 minutes was at the point where you wouldn't want to mess with it because at that point you could create more problems than you can solve.
We rolled in a dehumidifier to make sure any water from the mix that ended up in the air was removed, and we let the concrete set up overnight. On Sunday, we came back to find a nice level subfloor that deviated no more than 1/16" over a 5' span (approx 1/8" over 10'), and we reinstalled the moisture barrier (6 mil poly) the 275 sqft floor in about two hours.
After the subfloor was repaired, the Steller Hardwood Floor doesn't move underfoot, and as the floor settles into its new position we expect a light snap-crackle pop for a week or two, but with use and weight on the floor, it will settle in. As we continue monitoring the floor, we will keep an eye on the humidity in the room to make sure it isn't too wet or too dry. Plus, at some point soon, we also expect to get some neat removable baseboards (made by the James Wood Company) installed to complement the floor!
