What works well to reduce humidity in a large unheated shop??

[CodeMonkee]

I have a wood framed metal skinned insulated shop just shy of 2K SF.

Two large vehicle doors, one man door. Every week day I open one of the vehicle doors to get a vehicle out and drive to work, then park that vehicle again at night. If it was raining when I came home then the vehicle is wet and the floor around it will be wet.

I live on a mountain in a rainy region and while the lowlands get 40 to 50 inches of rain a year, up here on the mountain I get 80 to 100 inches per year (50 to 100 percent more). Also, it is always a bit cooler up here (nice in the summer).

So it came as no surprise, but I found to my dismay, that I have a mold problem on some of the items I store in the shop (I put a lot of stuff out there until I could "organize" - like that is ever going to happen).

One of the more upsetting items is a couple of Gorilla shelfs that have particle board shelves. They are covered in mold now.

So I need to try to mitigate this problem. I need to reduce the moisture as much as possible in the shop. I still want to park my vehicles inside as that is one of the main uses of the shop - so the wet vehicle parking will continue. I don't have a garage (I am planning on adding a carport on one side of it though - in part to store firewood).

I don't have a mold problem in my house - at least not yet. I have an electric furnace so it tends to keep things dry inside the house (I have a humidity sensor inside that tells me what the humidity is - I have noticed that as the weather has warmed up and I use the furnace less the humidity has risen).

But the shop is not heated and I don't plan to keep it heated 24/7 (I do plan to get an area heater and a radiant heater for when I am working out there in the winter, but that will not happen frequently).

I know there are things like Dry-z-air and stuff, but what works best (and affordably) for this kind of application where there is a large volume of space (the peak of the roof is 20+ feet up) and there are daily insertions of moisture?

Thanks

[Manuel Garcia O'Kely]

Mechanical dehumidifier, maybe two of them. Sears used to sell a decent one. Once you suck out the overload, one and a fan might keep up.

These are a refrigeration system with a fan, they add some heat by their nature.

[troidus]

The other thing you could do is blow down your car with a leaf blower before putting it in the building to cut down on the liquid water you bring inside. Won't do much good if it's still raining unless you install an awning over the door to keep the rain off while you dry your vehicle. Maybe also lay down metal grating at the entrance so there's a place for the water to drip without then tracking in mud.

[troidus]

Oh, and you don't have to heat 24/7, but maybe once a week get a good roasting wood fire going out there to drive off a bunch of moisture.

[RonS]

Insulation and a vapor barrier followed with heat. A metal shop will sweat pretty bad but if you really want to see it sweat, pour a fresh concrete floor inside.

[Pugsley/Hobbfather]

Solar Attic fan?
Heat and cool cycles will likely make things worse rather than better. Do NOT heat with propane or Kero, as these add water vapour...
Otherwise, seal out moisture from below. If no floor, then you're sunk, if concrete seal it. If rammed earth, seal it better!
As for the residual moisture from a car, this pales in comparison to the amount that will migrate from the ground.

If you had an open pool of water, you would get less evaporation than the surface area presented by moist dirt...even if the ground looks dry, it aint!

[CodeMonkee]

The floor is concrete. This summer I will clean it, etch it and reseal it. Possibly paint it somehow.

Heating choices are propane, electric, wood or kero/diesel.

Electric is prohibitive because the shop is not well insulated.

A wood stove could be put in (it would have to be certified and installed by a pro - Orygun law), but the time it would take to heat up the shop would be a day or two. I may put one in in the future but right now probably not as I will not be in the shop that much.

Thinking I will get a propane radiant heater despite the moisture propane gives off. Need it to keep from freezing in the winter when in there working.

I am thinking the dehumidifier would be the way I would go.

Beyond that there is not a lot to mold out there. Some of the cloth stuff molding didn't surprise me - I shouldn't have put it out there. The particle board did surprise me - other particle board didn't mold - not sure why the shelves did except that they were laying down flat horizontally and the other board is leaning against the wall.

[Dogscout]

Get some ventilation going if your building is sealed up to tight. Some air flow/exchange is crucial to removing trapped moisture. Waste oil heaters?
A buddy of mine did a waste oil heater years ago, but I am not sure if they are still legal in all areas.

[slackmeyer]

This is actually a pretty complicated question. We're all talking about relative humidity here, which is good, because it's what will cause mold to grow, etc. OP lives in an area where RH is high almost all year round. When temps are low and he's heating in his house, raising the house temp causes indoor RH to go down without actually getting rid of any moisture- it's just that the capacity of the air to hold water goes up quite a lot. That's good, because between old leaky houses with several air changes per hour and lots of stuff indoors making humidity (breathing, house plants, drying dishes, showers), it takes quite a bit of work/energy to get rid of moisture. Your shop is harder to dry out because you don't want to keep it warm enough to keep the RH low, and it's too leaky/wet (I mean leaky from an air movement sense) to dehumidify it electrically (essentially air conditioning and then warming it back up). Also, dehumidifiers work well when the air is warm, and not very well when it's cool, because in order to have the coils below the dewpoint of the air, they are below freezing. With cool air the dehumidifier ices up, and then has to thaw before it can run efficiently again.

Hopefully summers are less humid up there, they are around here (bay area). My recommendation for your shop would be to build a small-ish enclosed space, either with standard walls (like a closet) or just connected cabinets that seal, and condition that space for the stuff you need to protect. A small electric dehumidifier should handle that.

[neanderthal]

Rock salt is hygroscopic.

Either leave it in bowls or hang it in cloth bags. Then you can dry the salt out and re use once the salt has absorbed as much water as it can.

[slackmeyer]

Originally Posted by neanderthal

Rock salt is hygroscopic.

Either leave it in bowls or hang it in cloth bags. Then you can dry the salt out and re use once the salt has absorbed as much water as it can.

How do you dry the salt out without putting that moisture right back into the air in his house or shop? During the winter, I'll get a couple quarts of water every day out of the air in my small (900 square feet) house, running the dehumidifier about 4 hours a day. I try to keep the RH below 60%.

[squish]

Im no expert, I just live across from the ocean and it's cool and damp in my shop and house.

This is what works for me.
Ventilation, you have to have air flow around stuff, wire racks are better then wood, I tried to seal as much of my wood as I could. I panted my drywall instead of leaving it with the face paper and tape lines.

I'd like to seal the exposed concrete.

I heat locally when I'm in it working. On dry sunny days I open the doors and run a big fan to move some air around.
Tools and thing I worry about are stored with a desiccate pack that I dry out.

Dehumidifies only work above a certain temp. You have to warm the shop up that much to have the dehumidifier work.

Also make sure that your roof is not leaking.

[neanderthal]

Originally Posted by slackmeyer

How do you dry the salt out without putting that moisture right back into the air in his house or shop? During the winter, I'll get a couple quarts of water every day out of the air in my small (900 square feet) house, running the dehumidifier about 4 hours a day. I try to keep the RH below 60%.

You can put it in the oven.... Yes, oven.

[DriveShaft]

Originally Posted by slackmeyer

My recommendation for your shop would be to build a small-ish enclosed space, either with standard walls (like a closet) or just connected cabinets that seal, and condition that space for the stuff you need to protect. A small electric dehumidifier should handle that.

This sounds smart.

[Mr_Gone]

I work for a mold remediation company, and the best advice is twofold: dehumidify, and air movement. If you can, set a couple fans on your vehicles if you park them wet.

Dehumidification works in the summer, when temps are above 70° F and the air can hold a lot of excess moisture, and the dehumidifiers are in their optimal temp range. A large dehumidifier will work then.

In the winter, when temps are cold, even if the relative humidity is high, there's not actually a lot of moisture in the air. This is where air movement is key. By exchanging air during the winter, you will reduce the excess humidity inside the shop. This is called "burping."

Also, mold cannot grow on any surface that has air moving across it. Air movement, again, is key. Fans or a ceiling fan will greatly help in moving air around and preventing mold growth.

Also, don't try to "kill" mold with bleach. Use warm water and Dawn dishwashing soap. Trust me, Dawn the best stuff unless you want to start buying industrial-strength antimicrobial biocides. Once you've removed the surface mold, spraying a product like Kilz (available at Home Depot/Lowe's) should prevent further mold growth.

Hope this helps.