The Woodshop Shed

Moisture problem in new shop!

Furnished content.
(from WoodNet.net)


I have a moisture issue that I can not figure out.

Some background first -

The slab was poured in July of 2022.
The all metal building in September of 2022.
The foam was sprayed in October of 2022.

Once the overhead door was up, I used propane heaters to heat the space.
I stripped the building out with 2x4's and hung drywall in December of 2022 and January of 2023.

In February of 2023 once the electrical was installed, I switch to a 220 electric space heat with the propane as supplemental heat.
I started running a dehumidifier and was emptying it twice a day. I know the propane put a lot of moisture into the air but with emptying the bucket twice a day, I was taking out about 1 3/4 gallons a day! I bought a hygrometer when I started to use the dehumidifier and the relative humidity was almost 85%!
It never did rain! Whew.

Using the dehumidifier brought that number down to around 70%. I wasn't really worried because I assumed that going through the summer and using the air conditioner would bring that number down further and it did to a little under 60%. Not bad.

I quit using the dehumidifier and now into this heating cycle and the number went back to 70%!
So I started it back up and empty it about 1 1/2 times a day. The number is back down to 60% but no lower.
One day I was gone and the RH went back up 2%!

WHERE IS THE MOISTURE COMING FROM???

The concrete has been poured almost 16 months so I would think that it is fully cured and no moisture coming from it.
The building is on a slope lot so the slab has approximately 2 1/2' of pea gravel under one end and 1' under the other end.
The gravel and the fact that the concrete is not wet tells me that no water is coming through the concrete.
For the framing lumber, I used kiln dried pine and once again, I would think any moisture in that component is gone.
I assume that the foam might have a water component but after well over a year and using the AC and dehumidifier, wouldn't that moisture have off gassed?
I do not store any quantity of lumber in the shop - green or otherwise.
I do use water based finish but I haven't sprayed anything in quite a while and even then I exhaust the over spray outside.

I found an absolute humidity calculator online and it had 9 pounds of water in the shop volume with and RH of 60% and a temp of 62F. That surely can't be right since I am removing close to that much every day. I must have made a mistake.

I have racked my brain and tried to think of every contingency and I have got nothing.
I have asked friends family and once again nothing.

What does the Woodnet brain trust say???

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