Replies

1. 
   Chris_Koehn | May 23, 2001 07:01pm | #1

   *
   John-

   Pretty common physics problem. Warm humid air meets cold surface. Same thing happens on my beer glass in July. a few thoughts:

   1. Try a fan. Moving more air over the floor might encourage evaporation.

   2. Dehumidifier. If you keep the garage closed up most of the time you can probably lower the humidty level in there enough to at least reduce the amount of condensation.

   3. Last option (most difficult) is to look at ways to warm the slab: I insulated under mine. It's also got radiant tubing in it. Trouble is the ground below yours is likely cold, and you are trying to warm the earth below as well as the slab.

   Good luck!

1. 
   David_Thomas | May 24, 2001 12:27am | #2

   *What's the opposite of preaching to the choir? Are Chris and I high priests of comfy garages advising the pagans? I have 2" of blue foam under and around my radiant garage slab as well. The slab is the warmest surface in the garage and can't ever have condensation. Meltwater from the just-parked frozen cars evaporates very quickly from the slab.There are natural gas "radiant" heaters (not tubing in the floor, but putting out infrared heat) that could be pointed at the garage floor (at least when the cars aren't parked there). That would add more heat to the slab than most heating systems which result in hot air going high and slab remaining cold in the low, cold air.A dehumifier would work, but might have to a very large unit (they are rated in pints/hour) to keep up. As you observed, the more air exchange, the more condensation. If you can seal up the structure, especially the garage doors, then a smaller humidifier could keep up.A radiant floor can be retrofitted by pouring on top of the existing slab. Anything that heats hot water (water heater, boiler, solar panel) would then allow you the heat the slab. Even a air-to-water heat exchanger (such as an automotive radiator) would allow you to get free heat on a hot summer day. Since the problem is worst on hot, humid days it would be a pity to buy fuel to heat with when there are plenty of BTUs floating around already. -David

1. 
   calvin_ | May 24, 2001 01:58am | #3

   *John, This happens to ours here in Ohio the first cpl warm days of the spring when there is a big swing in the temp. After that, no matter how humid or large the temp swing, no more condensation. Where are you located and is this problem evident year round?

1. 
   David_Thomas | May 24, 2001 04:07am | #4

   *If Clavin's thoughts about this being a springtime problem apply, there is a totally different approach. You could think of the condensation as a very effective way to warm up the slab each spring. Water vapor has a huge amount of heat in it and if you open the doors to INCREASE the condensation (while you run around with a shop vac), you might get through the rest of the spring with a dry slab.I tried to hand dig a fence post last week and got stopped by frozen ground 4 inches down. Ground temperatures and slabs always lag behind air temperatures in the spring and early summer. -David

2. 
   John_Davidson | May 24, 2001 04:07am | #5

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   When the air is hot and humid, water condenses by the gallon on the slab floor of my attached garage. When I open the overhead vehicle door and the pedestrian door to the backyard for cross ventilation, the problem seems to get worse. I can minimize but not eliminate the condensation by keeping all the doors closed. The garage ceiling is finished and insulated. The walls not shared with the living quarters are unfinished, with the studs still revealed. I would be grateful for suggestions.