Solid wood floor on concrete

[markb1967]

Hi,

I had a new concrete floor with a brand new membrane laid under, in my lounge more than 60 days ago. The dampmeter showed me that it was dry.

I laid some pine t&G floorboards over wood fibre underlay boards. Unfortunately I didnt realise I may have needed a plastic sheet under the fibre boards.

Given that the floor reading was dry do members think I will be ok to leave down?

Why should I need a plastic membrane given that the floor is dry?

There are no pipes or underfloor heating running under this floor.

Thanks for your comments

 

[tall_tone]

Hi Mark
What sort of damp meter? and what sort of reading did it give? The only reliable method is to use a hydrometer which is attached to the ground for 24 hours. These will detect evaporating moisture which instant sensors cannot. After 60 days a thin slab may be starting to dry but I would have thought it unlikely to be truly dry enough to fit wood.

A polyethylene membrane or even a liquid dpm is a cheap insurance policy on your floor to guarantee nothing goes wrong.

Tony

 

[WoodYouLike]

After 60 days a thin slab may be starting to dry but I would have thought it unlikely to be truly dry enough to fit wood.

A polyethylene membrane or even a liquid dpm is a cheap insurance policy on your floor to guarantee nothing goes wrong.

Rule of thumb: every inch (2.5 cm) of concrete takes 30 days to dry - how thick is a thin slab?

Even a liquid dpm doesn't help when the moist content of the concrete/screed is still higher than 4.5%

 

[mattybee]

hi its simple really

according to the concrete manufacturers association concret takes up to 60 years to fully cure
the curing process produces water as a by-product it has to go somewhere from your slab
now below you have a dpm to prevent external moisture coming in - this also prevents the cure-water going out so the only place it can evaporate from your slab is throught the top layer into your room

now if you lay a kiln dried piece of timber on top it will absorb the moisture

timber is kiln dried to season it - this involves a rapid removal of moisture from the wood cells - these cells exist in the tree to transport nutrients and moisture from the roots and leaves - so add water back through the conrete slab and the wood will behave like blotting paper and soak it up

over time your timber floor will start to cup, and move and will not return to its laid state

i would suggest you lift the floor and install an appropriate moisture barrier to the top of the concrete slab - this should preferablt be an epoxy barrier or similar (not pva - that just stops the dust ), if you insist on laying the wood as a floating floor then a really good quality polythene dpm will do the job. As the floor has already been laid how did you secure the t&g boards in the first place?