Damp concrete shop floor

[vizmark]

I had my shop built a year ago and have had a problem with dampness. I live on the northern coast of California. Humidity runs from 60% ish during the day to 100% at night with temps in the low 50's to 60's.

The concrete slab is 4" thick with a black plastic vapor barrier. It has 2x6 construction and is fully insulated including the rollup doors. All down spouts are directed away from foundation. A French drain is on the up hill side of shop. This summer I had a 50" ceiling fan and a wood stove on the large side of shop.

Now to the problem....
Today I made a fire in the stove and had the ceiling fan on high. The floor was dry, but became damp as shop warmed up (cool sunny day). I knew I had a problem with outside humidity making the floor damp, but wasn't expecting it to happen with everything closed up. Should this be happening with a slab that has a moisture barrier? What else can be done? I have additional interior pictures of the shop in my album.

 

[uppster]

This is just a guess, do you think it is too air tight?

 

[The Cobbler]

the colder slab is condensing the moisture in the warmer air.
just like if you put a glass of ice water in the room, it condenses on the outside of the glass

 

[lakeroadster]

Nice shop

Humidity issues.. in a humid climate.. It's the nature of the beast. The faster the heat source heats the space, the more noticeable the problem will be.

A large dehumidifier would help if it is a tight space, but as soon as you open the overhead doors, it's a do over.

I had the same issue when I lived in Ohio and used a salamander heater to warm up my shop quickly.

 

[Will S.]

Get a couple of these https://www.amazon.com/ThermoPro-Hygrometer-Thermometer-Humidity-Temperature/dp/B01H1R0K68/ref=sr_1_5?ie=UTF8&qid=1479129394&sr=8-5&keywords=humidity+monitor and put around the shop. I think you will find the humidity/dew point in there, much too high.

So you will need a dehu; even one like you find in the box stores will probably do the job, but better would be 2, or a single larger one designed for basement/crawlspaces.

Just set it to 60% and let it run. Keeping the ceiling fan on low will help.

 

[samarcus77]

I think it happened because it was in an enclosed space.

 

[Garage Flooring]

For starters add some ventilation, even temporary and see if it helps

 

[vizmark]

Thanks for all the replies. The strange thing is my garage that's attached to the house stays dry all the time and isn't insulated.

 

[Shea]

Thanks for all the replies. The strange thing is my garage that's attached to the house stays dry all the time and isn't insulated.

That makes sense. The air in your house garage is closer to the slab temperature since it isn't insulated or heated. Cooler air holds less moisture and will not condense on the slab since it's a similar temperature.

The slab in your shop is surrounded by cold ground and keeps a much cooler temperature (relatively) than the air in your insulated shop. The warmer air holds more moisture than you think. When it comes in contact with the cooler slab it condenses. If your slab was heated you wouldn't have the issue. Air moving across the slab can make a difference sometimes in reducing the problem since it doesn't have a chance to settle on the slab.

 

[LegacyIndustrial]

Dew point issue. Will sweat no matter what is on the floor. As the previous posters mentioned ventilate and/or dehumidify. Moving air should help the problem.

 

[Armorpoxy]

Agree with above, better ventilation will help, but this is standard condensation as to be expected.

 

[vizmark]

Bummer. It's frustrating.