I understand the standard spec is 3/16 over 10' which is reasonable, but how flat do the pro's usually do?

For those guys who do this for a living, do you keep leveling until it's closer to 1/8 and exceed the limit? Do you make it mostly 3/16 and sometimes a little fatter and it still comes out fine?

I'm just wondering how neurotic most people are about the flatness. Is it worth the effort to make it better than that, or can I hit the 3/16 and it'll look perfectly flat?

Thanks!

- Bob

I know I'm human, but I try to get it as perfect as possible. I would hate to get a callback, and lose time and money, fixing a big hollow spot.

I can walk into any gluedown installation over concrete and find at least one hollow spot. The size of the spot is what matters. Small, and it is not a concern, but a big one, is a big concern.

If I have to do anything, I go ahead and get it flat. Might as well since I'm already doing it.

This is a reasonable question. I have been to a few professional schools and none have addressed the practicality of how to correct this problem. Other to say sand the high spots and fill the low spots. This is correct but how to practically get this done and exactly how to measure your results are not clear. I do not know of any contractor who carries around or even owns a 10' straight edge!

What I do is use a 6' tile screed and sand and level the floors to where when I lay that straight edge on the floor I will have gaps of no more than approximately 1/8".

This will suffice and also I believe if someone has that 10' straight edge it will meet the standards.

Interesting... may have to try that. Is the sand hard to clean up after you're done? EDIT - you mean "sand" the verb... right? At first I thought you meant you use play sand to gauge the gap.

I've been using some strips of 30# felt as feeler gauges to measure the gap underneath my 6' level. It's hard to imagine even fitting a 10' edge in the room!

Yes I meant to sand highs and fill lows. Though I have heard of using play sand instead of a tile thinset for a floating floor application. Though I would not recommend it.

If you have a stiff enough straight edge, you can mix tile thin set and pull it across the floor to fill depressions over larger areas. I use the flex thinset. If your straight edge flexes you should try and find a tile screed set to pull the thinset or some lengths of angle iron. You can then feather the edges of the areas you pulled the thinset across with a portland cement leveling compound. I like webcrete '98. It already hase latex in the mix and has a bit more "flex".

To level high spots, I strongly recommend getting an inexpensive #4 Stanley hand plane. I tried a good belt sander with a new 40 grit belt and barely made a dent. The hand plane really takes off the material! Stanley used to make a plane called a "scrub" plane with a radiiused leading edge which would be even better, but I don't think Stanley makes them any longer (Lie-Nielson makes one but it is expensive).

Barquios,

Is the tile thinset applied to the plywood subfloor, or is it applied to concrete only?

It can be used in both applications. For the wood be sure to get a "flex" thinset. It should help with the durability. Although, I have had no issues with either. I have used this leveling technique under carpet even. The key is using a tile screed or long angle iron that won't bend to pull the thinset.

Everyone has their own way of doing this, but, I don't use a thinset or a cement type patch if I am nailing a floor down. I do something else and that all depends on how bad it is and or what caused it.

For nail down applications or even for floating floors I will prefer to layer pieces of vinyl floor like a contour map to make up the voids.

That's exactly what I've been doing - I use 30 lb felt "feeler gauges" and mark where in the floor I need to add 1, 2, 3, ..., etc layers of the felt. Then I connect the numbers to make a contour map, then more or less follow that with the feathered layers of felt, going from smallest contour to the largest.

So far it's worked great, though some places needed 7 or 8 (or more) layers of the felt paper and I worry that it's too thick a layer. However I'm putting this under the 1/2 plywood and the floor will go on top of the plywood so I figure it's probably okay.

Your on the right track. Wont be any problem at all.