laying hardwood over OSB over concrete

[ianhandel]

Hi,

I intend to lay a hardwood floor (20mm beech) over an existing concrete floor. I was planning to use 18mm OSB3 over a DPM then nail into the OSB. I've read that OSB shouldn't be used for floating floors. Will this be a problem?

Cheers
Ian

 

[Ukwoody]

For hardwood, I would just use a good quality faom underlay, then place the beech on that. This will create anice floting floor.

woody

 

[WoodYouLike]

And don't forget your DPM when installing directly (floating) on concrete.
What's the width of your Beech boards?
Leave a wider expansion gap with solid Beech flooring, it's a notorious 'nervous' woodtype and can expand/shrink 7mm per meter wide

 

[ianhandel]

Thanks for the help..

The Beech boards are solid wood 100mm x 20mm x random lengths

The floor area is two adjacent rooms with double doors between.

One room is 8m x 5m the other 6m x 4m. I planned to separate the two with a threshold strip otherwise there will be a 9m width.

The floor suppliers normally advise secret nailing to plywood but did cautiously mention glueing to concrete or floating. Is it a case that effective new methods just take time to get adopted?

cheers

Ian

 

[ianhandel]

Another question:

The Beech has been in the centrally heated room for a few weeks now. Can I assume that it is at minimum expansion? Or put another way - how much should I have under the skirting per metre width to allow for shrinkage?

cheers

Ian

 

[WoodYouLike]

The floor suppliers normally advise secret nailing to plywood but did cautiously mention glueing to concrete or floating. Is it a case that effective new methods just take time to get adopted?

New methods??
Sorry, just kidding, yes you're right. It's now more and more common to install wooden floors floating, depending of course on the type and quality of your underfloor.
Your Beech boards are small, that's good, you're planning to install the rooms as two separate rooms with a threshold, that's good.
No problem for installing floating (depending again on the quality of your concrete underfloor: any dips, steep sloops, bumps or even 'hills'?)
Use a DPM and sound-insulation underlayment (nowadays a 2-in-1 product for conveniences) and install floating. As mentioned before, use a wider expansion gap for solid Beech floors. What are you using to cover the expansion gap with? Skirtings?

 

[WoodYouLike]

Another question:
The Beech has been in the centrally heated room for a few weeks now. Can I assume that it is at minimum expansion? Or put another way - how much should I have under the skirting per metre width to allow for shrinkage?

The wood has acclimatised now (normally from a reputable supplier 3 -4 days would be sufficient). But don't be 'fooled' by minimum or maximum expansion. Your floor now is 'dry'. come spring (when central heating is off or lower) the humidity in your house will increase and you floor will expand a bit.
So it's the other way around for your question: how wide should your expansion gap be to tackle this 'Spring' expansion and how wide your skirting to allow for shrinkage.
With solid floors we recommend using skirtingboards 20 - 22mm thick and in your case (knowing it's Beech and the width of your rooms: 5 and 4) that's really the minimum. For Oak flooring you take 3mm gap per meter wide = 15 in widest room, with Beech I would use more, see 20 total. That leaves you with not much when the floor should shrink even more (remember Beech is nervous). If that should happen, the easiest way to tackle that is to install a flat beading to cover that extra expansion.
Hope this helps

 

[ianhandel]

Thanks again for that

Wide skirtings it is then and I may even chop out the bonding plaster a little at the base of the wall to allow expansion. Is that OK? I'd planned to turn the DPM up the wall behind the skirting.

The screed is a bit cracked at the edges where gripper bars have been nailed in. looks like the sub screed DPM was turned back and caused a weak layer in the screed. I'd planned to pull out the cracked bits and use levelling comp or sand/cement to level this.

cheers

Ian