Slab Moisture Testing Methods - Need Input

[mmhouse]

I'm in a high seasonal water table area. I'd like to put VCT on my garage slab but am concerned about it staying down over time due to water migration/wicking through the slab. I've read up on moisture testing and have found two methods:

1. Calcium chloride test kit or
2. Small digital meter placed in hole(s) drilled into slab.

- Does anyone here have experience with these...maybe someone involved in construction?
- Any suggestions on where to obtain them? Can the digital meters be rented?
- Any help would be appreciated.

 

[mmhouse]

Now,now...don't everybody rush to answer at once!

Here's some good information from the ASTM standards group for anyone who is interested.

http://www.astm.org/SNEWS/MAY_2005/capobianco_may05.html

 

[dxdexter]

We use the calcium chloride test kits frequently. The clacium chloride is exposed for 60 to 72 hours under a sealed plastic dome. The change in mass of the calcium chloride and teh exposure time is inserted into a formula and the result is lbs of water vapor per 1000 sq ft. in a 24 hour period. The recommended number of tests is 3 for the first 1000 sq.ft and then 1 per 1000 additional sq. ft.

You should know what the recommended value is from the flooring manufacturer. Generally it is between 3 and 5 lbs per 1000 sq.ft./24hrs. The kits are normally only available to commercial customers and cost $20 each here in Canada (probably cheaper in the USA). Most commercial flooring suppliers will have the kits.

Note that chances of achieving these low values within the first few months of concrete placement are rare unless you are in an extremely dry climate. I have done a few in the last month that have been placed since the early spring and they are still over 7 lbs/sq ft/24 hrs.

 

[mmhouse]

The age (or lack of) of the slab shouldn't be an issue....it's been in almost 7 years now. Water migration from below is what I'm concerned about at this point.

Thanks for the info.