SOG & moisture.

[kaisersoze]

In a recent meeting some folks were having a debate about how to approach a SOG where the floor is going to be covered with Mundo. Obviously they are concerned about the slab drying out before they covering can be placed. Some things I picked up in the meeting which I did not know before:

1) Slab needs to achieve 80% moisture evaporation in order for the flooring warranty to kick in (true/false?)
2) If the finish on floor is tile, then we need not worry about the moisture getting trapped as tile is breathable.

How would you guys approach this, because I also heard that in one instance they put fans for the floor to dry for months but no good came out of it. What type of concrete mix would you suggest and when can the start with the flooring?

Kaiser

 

[kaisersoze]

Any opinions???

Kaiser

 

[hokie66]

Maybe if you tell us what "Mundo" is, someone may have an opinion. I googled it, and came up with a tapas restaurant in Sydney.

 

[kaisersoze]

Sorry, I was on the phone while typing this question.

Its basically a turf, so non-breathable, won't allow moisture to escape.

Kaiser

 

[Ron]

kaisersoze....

80% moisture evaporation in a slab is not a practical measure, nor is it reliable.

Most manufacturers of barrier floor coverings will limit the relative humidity in the slab to a maximum of 75%. Some will allow up to 85% on an isolated basis.

For your second statement, that is not why moisture in the slab is somewhat irrelevant for tile. First of all that only applies to ceramic tile or any rigid tile placed with a cementitious "adhesive", commonly called "thin set". It does not apply to resilient tile placed with a conventional latex or urethane adhesive.

The reason the moisture is somewhat irrelevant in the application of rigid is tile is not that the tile is breathable (glazed ceramic tile doesn't breathe), it is that the moisture doesn't adversely affect the adhesive and much of the moisture can dissipate through the grout joints.

This can be a very complicated subject. It is not so simple as just measuring moisture vapor migration (using calcium chloride tests) nor measuring the in-situ relative humidity of the slab.

Moisture vapor transport and condensation within a slab can be complex. Most moisture that creates problems with floor coverings is inherent in the concrete...it doesn't have to come from the ground, from plumbing leaks or other sources. There is enough free water in the concrete to create problems if it shows up at the right location (condensation at the top surface of the slab).

 

[a2mfk]

Like Ron, I have been involved with building forensics, and have dealt with moisture and vapor intrusion issues before. But for me these were on existing residential structures, usually when they altered the flooring to something that prohibited the vapor transmission into the building. Example would be a vinyl floor installed over an existing wood floor, the vinyl prevents the vapor from being released into the air and causes wood rot, swelling, fungus, etc. etc. in the wood. Also these issues were usually directly related to a high water table (Florida).

To cut to the chase I agree with Ron in that this is a complicated subject, and is likely becoming more and more litigious, especially the more that projects are fast-tracked and a slab has less cure time.

Vapor barriers of 10mil or greater are a general suggestion for SOG to prevent long-term moisture migration into the slab, but you are more concerned with latent moisture in the slab from the curing process. If the moisture level is critical I'd want some type of air conditioning and de-humidification program along with monitoring/testing of the moisture content of the slab to ensure it meets the flooring mfr specs.

I would steer clear of direct involvement as an SE and just say that if they are really concerned they need to hire an expert in this area.