How do you check your subfloor for flatness. Do you use a straight edge or long level and drag over the floor looking for high and low spots.

Phil

I use a long screed that 3/4 by 4" x 5 or 6' long and check for dips and teeter tottering.

If you can find an aluminum level that is not anodized, or a magnesium straight-edge that tile guys use, sliding over a wood floor will leave a gray or black mark on the high spots. The high spots need to be dealt with before you start to add to the low areas.

The question to ask is, are we dealing with minor low and high spots or do we have a problem that is more dramatic? This is an old thread but this response may be helpful to some.

I had a contractor who began leveling our subfloor using long levels to establish the height of 2x6 sister boards that he and his crew would attach to existing floor joists. Early on I told him this was not going to work out and that he should use mylaser level along with vertical calibration marks on each wall. I had begun the work myself using the laser level and calibration marks with very good results. There is a chimney in the middle of the room which makes the job a little odd. The floor wraps around the brick chimney. With the contractor and his crew using long levels, there would have been about a 1/2" vertical transition that would have had to take place when they circled around the chimney back to the starting point. After I made this case to them based on measurements taken with a laser level and an offer to fire the contractor, they took up the laser level and ditched the long levels.

If you are considering using long levels to correct subfloor flatness, low or high spots should be localized. Otherwise you might consider a laser level with calibration marks on the walls. Error with a long level is additive from one location to the next. This is not the case with a laser level which is a needed benefit for leveling larger areas of a subfloor. Also, a long level will show 'level' even though it is out of level by something like 1/16" over 4 feet. This isn't much but remember that the conventional level will have you adding this error to the next setting of the level.

Feel free to send a private message if you would like further help with this.

I'd love to hear more input on this subject. Currently installing in a condo, 700+ units, and I have the unfortunate task of dragging the straightedge across each one to check for flatness pre-install. The concrete leveling company did a poor job and I'm left with several issues per suite to locate, document, and mark to have fixed. It takes me roughly 20-30 mins per 500-700sqft suite to thoroughly check for flatness over 10ft. Not to mention the physical stress on the body from all the up and down - I'd love a better solution.

I've tried the bosch rotating floor laser - the trouble is the way we calculate tolerance over 10ft or 6ft, and not to a uniform flatness. The bosch laser tells you how high or low any part is relative to the base height you set. I don't really need the floor to be at X height throughout the suite, or even level which it seldom is; only FLAT to 3/16ths over 10ft, 1/8th over 6. With a laser, you cannot determine the "over X feet" part, which most manufacturers require. At least, not any faster than the bar, which is very quick to visually locate problems.

Does anyone have any recommendations? I know fast and accurate aren't usually inclusive of each other, but I have 20 more floors to go, not to mention other buildings in the future.

You can use a bucket and a string.

I either use a four foot level for small jobs or a 10 foot scree for bigger ones. Use a self leveling skim coat to even the floor out if it looks too out of whack

Quin Cherry

I use a long screed