Moisture problem in new shop!

[Snipe Hunter]

I did the test as stated in another post.

Why do you think that the test was negative for water after six days?

I know you didn't ask this question of me but I think it's a poor test. It would not tell you the moisture content of the slab. To get moisture on the film, you would need to seal the edges to the concrete. You would also need to cover the entire floor to get a real clear picture. Using a moisture detector, I find huge differences in MC all over the place, I can see 30% (very high) and move the meter 2 feet and find 7% (quite low). The reason home inspectors use 19% as the critical MC is because mold won't grow well below 19% and the organisms causing wood decay will be much less active below 19%. 19% is still very high. As far as MC goes in a dwelling, anything above about 7% is a bit high but manageable with de-humidification. A radon fan and a proper vapor barrier will usually be closer to 0. But I'll still see 5-7% in the walls and 2-4% on the floor often enough. Especially in the humid summer months but that can also be attributed to condensation and moisture in the soil behind the walls. The idea is to stop the moisture intrusion, not remove it after it comes in. Removing it is always more difficult. In a home, a french rain is the last resort and a lot cheaper than digging up around the foundation, installing a drain tile system and a pump and re-sealing the walls.

The reason I recommend a radon fan is because I almost never find high MC in a basement floor with an operating radon fan with the exception of very old homes where the crushed stone under the slab is either non existent or water table is high enough to fill the voids between the stone or the voids have silted in or a sump pump has failed... any reason where the air gaps ave filled with soil or water.

[iublue]

I know you didn't ask this question of me but I think it's a poor test. It would not tell you the moisture content of the slab. To get moisture on the film, you would need to seal the edges to the concrete. You would also need to cover the entire floor to get a real clear picture. Using a moisture detector, I find huge differences in MC all over the place, I can see 30% (very high) and move the meter 2 feet and find 7% (quite low). The reason home inspectors use 19% as the critical MC is because mold won't grow well below 19% and the organisms causing wood decay will be much less active below 19%. 19% is still very high. As far as MC goes in a dwelling, anything above about 7% is a bit high but manageable with de-humidification. A radon fan and a proper vapor barrier will usually be closer to 0. But I'll still see 5-7% in the walls and 2-4% on the floor often enough. Especially in the humid summer months but that can also be attributed to condensation and moisture in the soil behind the walls. The idea is to stop the moisture intrusion, not remove it after it comes in. Removing it is always more difficult. In a home, a french rain is the last resort and a lot cheaper than digging up around the foundation, installing a drain tile system and a pump and re-sealing the walls.

The reason I recommend a radon fan is because I almost never find high MC in a basement floor with an operating radon fan with the exception of very old homes where the crushed stone under the slab is either non existent or water table is high enough to fill the voids between the stone or the voids have silted in or a sump pump has failed... any reason where the air gaps ave filled with soil or water.

Thanks. Quite amazing that the MC could change that radically that close together!

Very interesting.

[Snipe Hunter]

Thanks.  Quite amazing that the MC could change that radically that close together!

Very interesting.

The great thing about being a home inspector is that we don't have to diagnose or fix anything. We just report on the condition. But we also have to keep up with continuing education. Moisture intrusion is a big deal in homes and one thing I've made an effort to understand the best I can. I do a lot of 100+ year old homes and almost no care was taken back then to stop water intrusion. Nobody lived in basements 100 years ago. Nobody cared and building sciences really only addressed the strength of the structure and water intrusion from above, not water intrusion from below. It's probably the one thing missed the most by inspectors because they don't know where or how to look for it and it's not always visible to the naked eye.. The science behind it is basically simple and already done by those who walked before us. Give the water a path and the water will follow it. There are a lot of very expensive and very accurate moisture detectors but we don't need those for surface moisture. We just need a ball park idea of the MC and need to be able to spot anomalies. A cheap meter will do that. Think of a concrete lab like a big sponge. Painting the surface, assuming the paint actually sticks to wet concrete only stops the evaporation of the vapor. You still have wet concrete. Same with using DryLok on basement walls, you still have water in the block cavities or in the poured concrete walls. Wear rubber gloves and rubber soled shoes when doing electrical work.

[Stanley McMahan]

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???

I am sure you have checked that the meter is accurate? I may have missed it in the thread, but this is a possibility. Are your tools rusting? Lumber taking forever to dry? 

Wonder if the humidity in your house is high? 

An air conditioner tech came to my watchmaking shop to solve a humidity issue and swore the only way to get a really accurate reading of humidity was to use a sling psychrometer. His reading with the instrument was around 9 percent different than the electronic one I had in lab. 

Some things I learned from him is that humidity does not cause rust, condensation causes rust. The more humidity in the air, the smaller the temperature change that will result in condensation. 

Just my $.02 worth.

[JosephP]

Probably a good suggestion to recheck the RH with a more accurate instrument. I don't doubt there are digital instruments to do that, but a sling psychrometer is probably much more affordable than those. I wouldn't be surprised if the cheaper digital meters aren't spot on.

However, he's pulling out plenty of moisture with the dehumidifier, so it sounds like there is certainly higher than desirable humidity there.

[jteneyck]

Probably a good suggestion to recheck the RH with a more accurate instrument.  I don't doubt there are digital instruments to do that, but a sling psychrometer is probably much more affordable than those.  I wouldn't be surprised if the cheaper digital meters aren't spot on.

However, he's pulling out plenty of moisture with the dehumidifier, so it sounds like there is certainly higher than desirable humidity there.

You don't need to spend money to buy a sling psychrometer.  Any accurate glass thermometer becomes a wet bulb thermometer if you put a piece of wet cotton cloth on the end of it and blow air across it, or sling it in a circle.  

John

[iublue]

I am sure you have checked that the meter is accurate? I may have missed it in the thread, but this is a possibility. Are your tools rusting? Lumber taking forever to dry? 

Wonder if the humidity in your house is high? 

An air conditioner tech came to my watchmaking shop to solve a humidity issue and swore the only way to get a really accurate reading of humidity was to use a sling psychrometer. His reading with the instrument was around 9 percent different than the electronic one I had in lab. 

Some things I learned from him is that humidity does not cause rust, condensation causes rust. The more humidity in the air, the smaller the temperature change that will result in condensation. 

Just my $.02 worth.

The shop is separate from my house.

The tools are not rusting and I have very little lumber in the shop.

There is a RH meter in the dehumidifier and I bought a separate one that has temp and RH.   Both read a RH within about 2% of each other and they are in two different areas of the shop.  Separated by 2 ft or so.  The temp in the shop is 62 and the RH was just under 60% today.

Thanks for the reply.

[iublue]

Empirical evidence detector for $29.00

There are more accurate moisture meters than this one but this will be sufficient. You're just looking for MC/Moisture content at the slab surface.

The cost to operate a radon fan is a lot less than a dehumidifier

The detector you linked has pins.  So, I can just touch the concrete slab and it will read the moisture content?

Would one of the pinless models be better or is that just overkill?

I have a model I use on wood but I do not think it would work since I have to put in the species of wood before testing.

[Stwood_]

The pins would be handy for testing your woodworking lumber.

[Snipe Hunter]

The detector you linked has pins.  So, I can just touch the concrete slab and it will read the moisture content?

Would one of the pinless models be better or is that just overkill?

I have a model I use on wood but I do not think it would work since I have to put in the species of wood before testing.

You could use either one but you are really most concerned with surface moisture as that is what is evaporating into the air space. The pinless are great if you are looking deeper. Like into wall insulation.

I'll use a pin meter to verify moisture on the surface... say like on a basement floor or wall. But I want to know where it's coming from. Water on the base of a wall or on the floor near a wall doesn't necessarily mean it's coming into the wall there. It's just coming out of the wall or floor there. Like a roof leak. A water stain on a ceiling doesn't mean the roof leak is right above the stain. I'll check the wall above it. If it reads low MC, I'll break out the pinless. And start looking all over the wall for moisture inside the wall. Trying to find the path of the water.

The next step would be using an IR camera but they can be very deceiving unless you really know what you're doing. I'd take a class on it or do a ton of research before using one. New inspectors get in a lot of trouble misusing IR cameras. It's a good way to get sued.