undulating floor question

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New Member
Feb 22, 2021
I'm trying to determine if I need to specifically avoid flexible or rigid LVP for my large undulating floor.
I plan on laying it in this one giant great room with kitchen and dining area. I've done about as much leveling as I can (Johnson rubber wedges in between the 2 sub-floors) and it's pretty good - I still feel the slopes but guests likely would not.
And the undulations go both ways.
Anyway, a Floor and Decor sample had a cork backing and was a very flexible plank while a Lumber Liquidators sample was much more rigid.

Which would be better to go with?

I also want it to have a soft feel and be quiet.

Most grateful for an experts advice


Mar 6, 2011
The flatness specs for most locking type planks are a big deal. Typically the maximum difference allowed in 10 ft is 3/16 of an inch. If you laid an 8 or 10 ft straight edge on the floor, at no point should you be able to slide a Ritz cracker underneath the straight edge. How's that for a visual 😁
If the floor is not flat, then once locked together, every time you step on the floor it will flex a little bit. Depending on how much it flexes will determine how long it will take for the interlocking joints to start to break. The joints are not intended to flex up and down.
Most people don't have a 10 ft straight edge laying around, but a 6 ft level would be much easier to obtain. A 6 ft level for this type of use is not used as a level. You just want to use it as a straight edge. A level is much straighter than any piece of wood that you might have around the house. Using a 6 ft level you're going to have to change your tolerances, to less than 1/8 of an inch in 6 ft. I'm guessing that a nickel would work for a thickness gauge instead of a cracker.
You could also tape a string to the floor, pull it tight across a 10 ft span and use that as a straight edge.
I just went to look at a job Friday. the vinyl laminate plank has been installed for about a year annd a half. There's a place towards the middle of the large room that has a plank with a broken tongue the entire length of the plank. Just walking on the floor I could tell it wasn't flat. It actually felt spongy right there. 😱
The manufacturers of these planks for some reason don't drill into your head how important flatness is. I'm thinking if they made it too complicated to install these products, people wouldn't buy them, so even though they gloss over the flatness tolerances in the instructions.... I think the flatness tolerances ought to be in bold print, with a visual diagram to make this easier to comprehend.
Nobody could visually see 3/16 of an inch deviation in a 10 ft span, but when you say undulating, that tells me it's noticeable or visible. I'm not able to know exactly what you mean when you use that word but I would take a wild guess it needs a lot more prep work.
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