Wood floor moisture readings

[engineer2]

So I got one of those inexpensive wood moisture meters just to check my latest project. Mfr wants floor/sub-floor to be within 2% of each other.
Interior application, no water issues, floor is above a heated basement. Indoor temp has been 77-78 and RH around 50%. AC running every day. Everything acclimated for two weeks.
5" x 3/4" pre-finished solid Oak is about 5-6% MC
25 year old 3/4" plywood sub-floor is about 10-11% MC.
The difference is outside the limits. Trying to figure out why the plywood sub-floor is higher and if it is anything to worry about. One online article indicated the plywood glue will give an artificially high reading. Any advice?

 

[Marctrees]

Until someone more knowledgeable comes along............

https://www.google.com/search?q=oak.....69i57j0l3.9647j0j1&sourceid=chrome&ie=UTF-8

 

[jake00]

I do hardwood for a living, Make it, sell it, install it. Those are fairly normal readings for our area, the oak seams a bit low especially for this time of year. It could be your meter. Can your Meter be set for specie and temp?

 

[kd3pc]

So I got one of those inexpensive wood moisture meters just to check my latest project. Mfr wants floor/sub-floor to be within 2% of each other.
Interior application, no water issues, floor is above a heated basement. Indoor temp has been 77-78 and RH around 50%. AC running every day. Everything acclimated for two weeks.
5" x 3/4" pre-finished solid Oak is about 5-6% MC
25 year old 3/4" plywood sub-floor is about 10-11% MC.
The difference is outside the limits. Trying to figure out why the plywood sub-floor is higher and if it is anything to worry about. One online article indicated the plywood glue will give an artificially high reading. Any advice?

moisture meters are pretty vague as regards accuracy. We use them a LOT in boat survey and repair matters, and there are a few out there that consistently give decent results. The rest are poor at best. I would not put a lot of stock in the readings.

The difference between sub floor and top wood is why an adequate underlayment, vapor barrier or felt is used by the craftsmen in the industry.

Glue, laminates, air, composites, moisture and anything in between the wood and the base material will do this. Changing the base material will result in widely differing readings.

Almost as much art as science when using a moisture meter. Better technology exists, but is priced beyond the casual user's budget.

bests.

 

[engineer2]

Can your Meter be set for specie and temp?

Yes it has 4 different wood settings that will change the readings about 3%. Admittedly it's a cheap pin-type meter, but it's for wood only, and claims ±0.5% accuaracy. Real world accuracy is probably like ±2%.
No idea if it has temperature compensation, I doubt it. I may drive a couple of nails into the wood and see what readings I get.

Those are fairly normal readings for our area, the oak seams a bit low

Do you go ahead with the install? I don't see how a 25 year old subfloor is going to drop MC.
I had to wait 3 weeks for the oak and Mullican date codes indicate it was manufactured in May. Seems to be decent quality from the few boxes I opened.

I've usually used tar paper as a barrier for strip flooring, but since the boards are 5" wide, everyone I've talked to says to glue it directly to the subfloor and staple it.

 

[engineer2]

Checked the underside of the plywood subfloor and it reads around 7-9%.
Floor joists read around 7% .
I think the glue in the plywood is messing with the meter since it is designed for solid wood and not laminates.

 

[ralphbrown]

I do hardwood for a living, Make it, sell it, install it. Those are fairly normal readings for our area, the oak seams a bit low especially for this time of year. It could be your meter. Can your Meter be set for specie and temp?

I do agree with him. Well what meter are you using?

 

[jake00]

You're good to go. Mullican makes a decent product.

 

[engineer2]

I do agree with him. Well what meter are you using?

Some $11 POS from Amazon. Seams reasonably accurate. Works OK on firewood. Putting the floor down and all should be good.