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Discussion Starter #1
Follow up from the car cover question.
Concrete has alot of lime in it.
In the spring, the floor has a tendency to "sweat".
The tarp on the floor is for which factor?
I am going to put the "moisture absorbant" in the interior, but the car will be stored on a 4 post BendPak lift. Being a few feet off the floor and a de-humidifier to the side, is the tarp needed? I occassionally put a car under it during the winter. The garage has drains so the snow melt will not collect.
Any opinions? ::
Walt
 

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concrete doesn't sweat due to the lime, it sweats because it is a big cold mass. Airborne moisture will also condensate if the air is warmer and the slab is colder.
I put 4 X 8 sheets of styrofoam insulation on the floor under the car for a thermal block. It seems to help. But, I also don't have a lift.
I don't know what else you asked earlier, but, is the garage insulated and relatively draft free? South facing windows unblocked?
 

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I plan on placing a moisture absorbant underneath the cars. I will also have a heavy duty tarp under the cars. I will see how this works out.
 

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Discussion Starter #4
Please let me clearify the lime theory. Have you ever left a piece of galvanized metal on a garage floor for an extended amount of time? It gets "crusty". :p I always thought there was a chemical reaction going on. Untreated wood "wicks" and rots much faster on concrete. Is the concrete being porous the issue or the lime in the concrete? ::

I have heard the "legend" of not storing batteries on a concrete floor. Any idea why not?

4 x 8 sheets of insulation is a great idea! I think this would work well with my situation! ::

The garage a three car and well maintained but detached. The floor drains work well. I would prefer not to heat the garage all winter, for the Chicago winters can be brutal.
 

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Roddster is correct (as usual) regarding why PC concrete slabs sweat in the spring time. A concrete slab has significant mass (typical density of 145 - 150 lbs/cu ft) so after being cold all winter; it takes quite a while for it warm up. Add to that there may frost or frozen ground underneath it (if unheated all winter) and your slab will sweat (air borne water vapor condenses on it) for quite a while. Placing a tarp on the concrete will make no difference but may make things worse in that it can trap moisture between itself and the slab.

In regards to the corrosive or moisture affinity issues of concrete. While it's true that typical concrete does contain components of lime (it's in the cement and around here we typically use crushed limestone as the coarse aggregate), what you have probably experienced is the result of adding calcium chloride as an accelerant to concrete during it's plastic state. This was, unfortunately, and sometimes still is a common practice to help wet concrete set faster. It's a bad idea because it accelerates corrosion to any reinforcing steel in the concrete and it not only increases the concrete's porosity but it tends to make have an affinity for moisture. Because of this increased moisture migration, you end up seeing more evidence of efflorescence, i.e., the white powdery lime substance. There are plenty of non-chloride accelerants on the market nowadays, so the use of calcium chloride is declining. A typical visual cue to the use of calcium chloride is a blotchy, un-even colored surface. Sorry, I've rambled too long, :eek: I hope this answers some of your questions.
 

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Discussion Starter #6
I am glad to see topics taken seriously on this forum!

Thank you for the responses! :)
 
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