Subfloor flatness, would this need levelling? please help

[claire79]

Hello guys,

I've spent most of the day checking the flatness of my concrete subfloor today in preparation for fitting an engineered wood floor. To test for flatness i've been using a 6ft straight edge.

Please excuse my poor description but my method for doing this is outlined below:

I've moved the straight edge around in all directions (length of room and then across the width) and used a variety of plastic feeler gauges to test if I can slide them under the straight edge.

I've found the largest feeler gauge I can get under the straight edge in some areas is 5mm but this is not across the full length of the straight edge, just under some areas (max length 25cm), see drawing below:

Would you say the floor needs levelling before I can fit the engineered wood floor?

I will be using a 3mm thick underlay with DPM if that has any significance?

I would appreciate your views as I will need to get on to the supplier and cancel my order if the floor is not suitable and requires further work.

Thank you.

Claire.

 

[gregers]

i would say you need to put down some self levelling screed in the lo points?

 

[claire79]

That's what I thought however i've also read the following:

"Make sure your sub-floor is flat enough to receive your new flooring. A bumpy floor will still remain a bumpy floor, + or – 5mm over 2 metres is the accepted guide. To check this lay a 2M (6ft approx) straight edge on the floor in different places around the room. Check there are no bumps or dips causing the straight edge to rock or a gap under the straight edge greater than 5mm. "

Which suggests mine is within the tolerances?

 

[WoodYouLike]

How thick is the wood-engineered floor you plan to install?

 

[claire79]

The floor is 14mm thick.

 

[WoodYouLike]

Could flex too much over this gap.
Two options:

fill the gap with acrylic screed (stay away from latex screed, terrible stuff - builder's friend, but a pest for anyone else, specially floor installers) but make sure it's level and not higher than the surrounding area

use strips of hardboard, underlayment to gradually fill the gap - again make sure it does not come higher than the surrounding area.