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Quonset Hut sweating

Peteracer

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Joined
Apr 13, 2016
Messages
6
Hi, I used to come here for answers to my questions about building my own garage but I ended up buying a property that had 4 buildings on it already.

One of them them is a Quonset hut, It has been built in the early 1970s. Its dimensions are 35' x 70', on a stepped slab that is 1 ft thick , I know, concrete was cheap back then, and fairly uneven seemingly lol.

The building is in great shape my issue is the fact that it sweats like crazy. I have moved equipment like lathe, milling , press etc... but I am reluctant moving my welders and other sensitive electrical tools due to that humidity that lingers in there.

The previous owners had the Quonset hut spray foamed on the outside ( open cell), the job was done a long time ago since chunk are missing here and there. Maybe birds are eating it too ...lol

There are 3 ceiling fans , and a small 12" exhaust fan on the back wall, that closes off when not in use. 1 service door and a 12ft garage door at the front. The heating system is two Schwanke LP gas radian tubes.

The fact that the building is sprayed outside makes its nice and inside , but the metal sweats , especially in winter if I turn the heat on the dripping from the ceiling starts almost immediately.

I dont heat the hut in the winter normally , just the in washroom to prevent the pipes from freezing, its more used as storage this year because of covid the business is slow.

The slab is obviously uninsulated, mayber the roof is leaking or its just condensation, but damn , I dont want to put 100k of equipment in there and get it all surface rusted ...it already started on the bridgeport.

I thought about respraying the exterior with closed cell this time just to water seal the building and add some insulation. but I doubt it will solve my sweat issue.

I dont spend that much time in it in the winter so I would like to avoid heading it 9 months a year, but if keeping it above dew point solves my issue...

The are already white spot (mold) on everything rubber in the shop, like my dirt bike seats , sled, etc.... Im reluctant bringing the rest of my tools in there until I fix the issue.

Sorry for the long post , what would you guys suggest?

Peter
 
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Peteracer

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Apr 13, 2016
Messages
6
Yes both...
the thing sweats like crazy even just used as an unheated storage space.
 

mcbane

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Joined
Jul 23, 2017
Messages
794
Location
California
No idea where you are located and what typical humidity is in your area but you obviously have a humidity issue so you should start by getting a good instrument to record humidity and temperature. Record temperature and humidity numbers inside vs outside (which you can get from a weather report). From those numbers an online dew point calculator can tell you if the air inside is wetter than outside.

Wetter air inside (higher dew point inside) suggests vapor coming through the slab - in which case you can try a penetrating sealer that works almost as well as a vapor barrier under the slab.

If air inside is similar dew point, you probably just want to fix any obvious air leaks and then get a desiccant wheel dehumidifier.



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nadogail

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Joined
Jan 23, 2009
Messages
31,946
Location
Coronado, CA
The moisture in Warm Moist Air will condense when it hits cold metal. My SWAG (Scientific Wild *** Guess) is that more foam on the outside will keep the metal from being so cold that the moisture in the air condenses on it.
 
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Peteracer

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Apr 13, 2016
Messages
6
I will invest in a Hygrometer to keep an eye on the humidity level inside the building and compare it with outside readings from the weather network.

We are located in the North East and we have big temperature swings but its not a humid climate like the Pacific North West. there is definitely some humidity coming from the slab, I don't think I ever seen this slab entirely dry since the day I bought the place. Before I moved in , I cleaned the floor, the slab had over an inch of oily crud all over it , it took me 36 hours of work to get it clean, but it still feels oily in places.

So if I was going to seal the slab ,I don't know what kind of prep it would need for the sealer to stick to it.

Now that summer is around the corner , I will get the garage door open for a few days and run fans , to try to get it all dried up, and then see where the humidity forming.
 
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billwood437

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Dec 4, 2015
Messages
92
Location
Massachusetts, USA
You need good ventilation and the problem with the insulation on the outside is it insulates the metal and concrete on the inside from warming up in the spring. It holds the overnight temperatures and condenses the warm moist air.
I am in Massachusetts and have the same problem every spring but only for a short time with the temperature swings. It is going to be hard to warm up that concrete mass with an insulated dome over it. Any propane heaters need to be vented outside as they produce water in their combustion gasses.

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Peteracer

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Apr 13, 2016
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the two radiant tube heaters are vented outside , they heat up the place very quickly but I would like to avoid running them all winter for obvious reasons.

because of the huge concrete mass and insulation on the outside of the building even on 90 degrees summer days , inside the hut feels like I had A/C on.

Outside foam has been sealed/painted white (very dirty mossy now) and I thought about re sealing it with an rubberized or asphalt based black sealer, to keep some heat and seal the exterior foam.
 

Showkey

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Aug 9, 2014
Messages
8,638
Location
Wausau WI
My well insulated,well sealed shop also does not need AC in the summer for the same reasons. But it does require a dehumidifier to maintain 50% levels or lower inthe summer. Winter, heat solves all the humidity issue and humidity runs 20-35%. Prolonged humidity levels above 70% will cause mold/mildew/smells/rust/condensation etc

There are at least 30-100 threads on the building sweating, floor sweating, dripping from the rafters, it’s “raining” in my metal shop, mold/mildew on the wood, my tools are sweating, my tools are rusting, my collector car is moldy inside, my shed smells like grandma basement, humidity problems, dehumidifiers..........

They are scattered in the general discussion and heat/air section.
Here’s a few using humidity as the search word:

https://www.garagejournal.com/forum/showthread.php?t=477103&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=477467&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=466765&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=459209&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=456763&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=445350&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=441809&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=260880&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=412631&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=410485&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=400737&highlight=Humidity

https://www.garagejournal.com/forum/showthread.php?t=336150&highlight=Humidity
 
Last edited:

Hank11

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Aug 19, 2019
Messages
1,151
Location
Tennessee
Its so easy to buy a humidifier and run it all the time. It will solve your problem. You will need to heat the building moderately (about 60*) during the winter for it to work.

I'd fix the exterior to be sure you don't get water inside the foam.
 
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Peteracer

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Apr 13, 2016
Messages
6
Thanks for the answers , I will buy a de-humidifier and get a quote from local closed cell foam sprayers to see if I can swing that this summer. Otherwise Id like to the least , reseal the exterior foam and stop roof leaks if they're any (its hard to tell sometimes when it drips from the bolts if its rain dripping or sweating)
 
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