Moisture in my subfoor - before laying oak.

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Useroftheforce

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I bought a moisture meter to test the timber joist and board subfloor.

It seems to mostly be at 12%. However each board that is near an exterior wall has the first 6" with higher moisture. This first 6" is around 20% moisture.

//
I had planned to lay 6mm ply over the existing 22mm floorboards which are structurally sound, but a little cupped, 2 mm at most I would say. Is that acceptable?
//

I presume the first paragraph means no oak floor for me then?
 
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Correction - the whole floor seems to be at about 20% moisture. When I got underneath it and poked the joists and boards that was the reading throughout.

Strange - becuase you can feel the draught from the air bricks...
 
Hmm more panic.. and confusion...

If I just rest the meter on the surface of the timber it's 12% everywhere, even at the edges.

If I push the probes into the wood 1 - 2 mm then the moisture content increases alot - to between 16 and 20%. This seems nuts. The underlay I removed has a plastic backing on it so would have effectively stopped the floor from breathing into the house. But the floor is supended above the earth foundation between four and eight feet. (house is on a hill).

Now I am thinking that the underlay was trapping moisture and the removal of it is allowing the timber to dry out.

Really need someone who is experienced to work out what is going on and where we are with this.
Any of you know an experienced individual in the Berkshire area?
 
Useroftheforce said:
Now I am thinking that the underlay was trapping moisture and the removal of it is allowing the timber to dry out.
Click to expand...
That's a feasible conclusion. Let it dry out a while longer and make sure you ventilate sufficiently so the excess moist can escape.
Then measure the wood again to see if that has indeed been the cause of the high readings.
 
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Even on newly purchased oak flooring you will find a difference in moisture readings between each plank and by resting the meter on top of the wood then inserting the pins deeper. albeit, not from 12 to 20%.

It's important to re-test in a few days time using the same methods, i.e same depth pins and in the same places as previous.

How are you going to fit the floor ?
 
If there is any doubt whatsoever - I won't be fitting one.

Perhaps you could elaborate more throughly on what I should be expecting to see in ideal conditions from both the newly purchased oak and an acceptable sub floor upon which to install it?

The method i plan to use would be 6mm birch ply overlay with 5mm gaps between the sheets. Then Glue the edge peices and secret nail the rest of the floor. There will be no bevel on any of the timber and it will be finish sanded by the supplier (using their extreemely expensive sander) after installation before applying three coats of osmo oil.

Since the rooms are quite small and it's a period house, the chosen timber is 85mm X 20mm character grade english oak. Personally I don't think a larger section would look right.
 
And elaborate i shall !!

Most would not consider fitting a new oak floor with a moisture content of 8 - 11% over a timber sub-floor moisture content of 16/20%. You can however, use novia building paper www.novia.co.uk a 3ply bitumen based moisture repellant..

WYL would argue that this paper will stop the sub-floor from breathing as it is a moisture barrier.

In fact, when you have punctured it with 1000 nails it is no longer a moisture barrier but a repellant. it is the ideal membrane for your problem and i would have no problem in guaranteeing your newly laid floor if i was to install it, having done so for the past 12 years with no problems reported.

You staple it to your sub-floor prior to 6mm ply then secret nail your new floor. With the very steady escape of excess moisture form your sub-floor, your new floor will acclimatise slowly but surely, hence the requirement of expansion gaps.
 
Oh I see...

Thanks very much for the answer.

I have read that the subfloor really should be within a couple of percent of the new delivered Oak. So ideally 10 - 12% moisture.

Since the final quote for the floor hasn't been compiled yet; and thereafter it's 10 days to run it through the feed moulder and deliver it - I imagine there will be plenty of time to monitor the drying process of the floor as is.

Since there really is no obvious entry point for such a uniformly high moisture content, I am expecting it to dry out.

But in case it doesn't if I understand what your saying - the current moisture content of the floor will gradually bleed into the new floor. (With the use of novia paper)
 
20% MC in timber will cause degradation and, eventually, rot. Are you sure the floor is sufficiently ventilated? If on a hill you might have an issue with cross ventilation.

Also, I would test the meter on something you can be 100% certain is MC stable. Something like the top of a door architrave where the pin marks won't be seen. I would expect to see an MC of about 12 - 13%
 
At long last... after four days of leaving all the windows and doors open the floor is finally starting to show cracks between the boards.

The moisture content is comming down to between 10% and 18% - mostly 12 - 15%. Still a way to go yet though I should think.

It must have been all the water in the plaster soaking the floor out.
I also cleared out all the air bricks which were clogged with cobwebs.
 
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