Laying 6mm MDF ready for carpeting... expansion gaps needed?

[LONESOMESOUND]

I realise that similar questions have been raised before, but I couldn't find a definitive answer to my question which is why I'm starting a new thread...

Basically, I'm laying six millimetre MDF boards (8' by 4') onto existing floorboards, to give me a nice flat surface to carpet onto. I'm screwing the boards down onto the floorboards (countersunk, natch...) but am unsure as to whether I need to leave expansion gaps around each board, or whether I can butt each board directly onto the others (which to me would seem to give the best surface for carpeting). I've heard that it's best to wet the boards before putting them down so that they contract and tighten into place as they dry out... yes? If so, how much water, and how long to leave them for?

I'm going to be fixing the skirting afterwards, by the way, but assume that, since the boards are fixed rather than floating, a large expansion gap around the perimeter of the rooms won't be necessary (unlike laying laminate, say).

Any advice gratefully received!

 

[jbonding]

i dont think mdf likes water, once water gets in it it expands and buckles, but ive never used it below a floor.

 

[LONESOMESOUND]

Hmmm, now you mention it, that might have been advice for hardboard rather than mdf!

 

[kevplumb]

it was

 

[masona]

I've heard that it's best to wet the boards before putting them down so that they contract and tighten into place as they dry out... yes? If so, how much water, and how long to leave them for?

If you mean hardboard then 1 pint of water per 8'x4' sheet

 

[Thermo]

and make sure you do, cos if you dont its really funny hoovering over a bumpy floor!

 

[LONESOMESOUND]

Thanks for the replies guys, but I still need an answer as to whether I should leave gaps or not!!! Sorry for the impatience but I am under pressure here :-/ As before, grateful for any help. Cheers, Martin

 

[masona]

Thanks for the replies guys, but I still need an answer as to whether I should leave gaps or not!!! Sorry for the impatience but I am under pressure here :-/ As before, grateful for any help. Cheers, Martin

No need to have gaps.

 

[Thermo]

and fix the skirting before you lay the carpet as well!

 

[LONESOMESOUND]

Cheers people!