Laying 10mm T&G engineered oak over warped pine boards?

30 Nov 2011
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United Kingdom

Downstairs I have laid 20mm unfinished solid oak T&G over 20mm lightly warped floorboards in the lounge using a secret nailer, and the same in the dining room but had to float and edge glue 75% in here due to the extension's concrete floor.
Did these rooms 5 years ago with Osmo finish and still perfect.

Earlier this year I floated and edge glued a 10mm T&G engineered unfinished oak floor over a newish concrete floor to the study. Worked out great again, with Osmo finish. First time using engineered flooring and the bevel edge finish is really precise and tight compared to the solid wood of the other rooms. But the latter looks more 'real'!

Now upstairs everywhere is carpeted but my wife would like Oak again in the master bedroom. This is carpeted and has three doorways: 1) to carpeted landing. 2) to carpeted en-suite (poss. to be tiled soon). 3) to carpeted dressing room.

The original pine boards from the 1960's are now a little curved so that their edges are slightly higher than their middles. This wasn't a problem with the 20mm oak boards used downstairs as they are thick enough not to flex and I wasn't butting up to lower carpeting. If I overlay in the bedroom I only have 10mm thickness of carpet/underlay to butt up to and I'm worried a floating T&G edge-glued 10mm oak floor (laid at 90 degrees) will flex on the edges of the original boards. Is this the case? Or will the 125mm centres of the original boards mean that 10mm thick oak boards will easily span these and not flex?

I could take up the original boards and relay 18-20mm oak (400mm centres to joists) as another alternative. Might even be easier secret nailing these than all that edge gluing and wiping of excess glue!

Any suggestions gratefully welcomed.

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Hi Oaklover,

The problem with a warped sub-floor is it can greatly increase the pressure on your engineered floor. Engineered floors expand and contract naturally, but if there's no flat, found and level sub-floor to put it on your greatly increase the risk that your flooring could lift.

There are products on the market that helps with uneven sub-floor's so there's no need to put down a new floor covering beneath. Something that does this would be a Fibreboard underlay. It takes out any deviations in the sub-floor. It's sold in most DiY stores as it's one of the 3 standard underlays that are used.

I would opt for replacing your existing floorboard with new ones and save yourself a lot of headache.
10mm boards rather flex and fibre board underlayment will not help here - could make the bounce even more noticeable

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