Thread: Salts on Carwlspace columns

Another crawlspace. This crawl was pretty dry and installers ran vapor barrier over piers. The columns still had the shingle underneath them but many of them had salt built up and what looked like moisture wicking. Not sure where the moisture came from as there were no signs of water in this crawlspace.

Any idea how / why this is happening?


//Rick

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Originally Posted by Rick Bunzel

Another crawlspace. This crawl was pretty dry and installers ran vapor barrier over piers. The columns still had the shingle underneath them but many of them had salt built up and what looked like moisture wicking. Not sure where the moisture came from as there were no signs of water in this crawlspace.

Any idea how / why this is happening?


//Rick

You said there was no signs of moisture (water) in the crawlspace, but the vapor barrier is an indication that moisture WAS a concern at one time.
Now that there is a VB moisture cannot escape except from around the columns.
Moisture is wicking up the column and causing the effervescence seen on the concrete.

Rick,

I am in the Pacific NorthWest. Vapor Barriers are part of our building code. The column is sitting on top of the vapor barrier and shingle. I doubt there was any transfer of moisture from under the vapor barrier as I didn't see any breaks in the barrier.

//Rick

I agree with Rick. Moisture most likely coming thru VB under post. The shingle would have torn the VB as it was driven tight. Vapor has no where to go but where there is a tear. We have some areas in California where you only have moisture in the winter months when the ground water is high.
Could remove posts, bituthene the VB at pier and reinstall with shingle at post beam connection retained by post top hardware.

I can't quite tell if the column has depressed the vapor barrier and soil (lower elevation) but in my part of the world when a crawlspace is ventilated to outside and a vapor barrier is installed, the humid air and fog condenses on the cold surfaces and puddles on the vapor barrier. It is a mess.

We prefer closed crawlspaces with conditioned environment.

Originally Posted by Ken Amelin

We prefer closed crawlspaces with conditioned environment.

We're going the same direction here.

A simple test to determine if moisture (vapour) is coming up through the concrete is to take a 12"x12" piece of 6 mil plastic and tape it to the concrete floor with duct tape and leave for 48 hours. If vapour is coming up the underside of the plastic will have condensation forming.

I have seen a very similar thing and I assumed that there was a break in the VB. Also could have something to do with the make up of the concrete for the pier.

There is a dark stain there as well, pic #1. If you had a sample of the white stuff, you could check it out in the daylight. Could be it is lime, put there to deter bug attacks.