Efflorescence at the bottom of a Common wall !?

[Christian Tag]

Hi Everyone,

I need your help on this one, I've noticed efflorescence (white powder) at the base of a Duplex concrete ''common wall'' in the garage.

Efflorescence is a fuzzy white crystalline deposit on the surface of concrete. Water seeping through the concrete wall dissolves salts within the material; when the water evaporates it leaves salts or efflorescence on the surface.

I've seen efflorescence many occasion on foundation walls because of negative ground slope but how could it be possible on a ''common wall''??

I don't know if I'm using the right term here, excuse my english I'm a frenchie from Montreal.
By ''common wall'' I'm talking about the wall that separates a Duplex.

[John Arnold]

Could be wicking up from below, non?
Or maybe the guy on the other side is obsessive about washing his garage?


Hi Everyone,

I need your help on this one, I've noticed efflorescence (white powder) at the base of a Duplex concrete ''common wall'' in the garage.

[Raymond Wand]

One thing I do see and maybe you addressed it, but thats a copper feed line from the oil tank.
The line is susceptible to damage and corrosion from the concrete. It is now a requirement that the oil line be protected in a plastic sleeve from corrosion and it should be protected with a plank or elevated off the floor.

As to the efflorescence whicking of moisture from the sub soil.

[Don Putnam]

Hello Christian,

The whitish powder in your photo looks much deeper and in greater volume than one would normally see with efflorescence, especially since there is not a lot of surface area of efflorescence sloughing off from higher on the wall and collecting at the base.

In my experience, most foundations in duplex construction are continuous between units, and vertical concrete common walls are a separate pour on top of an uninterrupted slab. The vertical pour may or may not be 'keyed' to the slab. This can be easily verified by inspecting the exterior of the slab. If the slab has a joint aligned with the common wall, there is a greater likelihood that water is coming up through the joint. If there is no joint, water may be entering at the base of the slab, usually at the rear of the structure if the grade is too high or the slab was cut into a hillside, and the water is drawn into the building along the joint at the base of the vertical wall.

___________________________
Don Putnam
Austin, Texas
www.roofconsulting.com

[Ken Rowe]

When I see that here in Minnesota it's typically from the road salt dripping off the cars in the winter. Garage slab slopes to that wall. Could even be the adjoining unit's slab sloped toward the common wall.

[David Edenburn]

I see this sort of thing all the time here. It is usually a corroded copper water pipe embedded in the concrete that is leaking. I have also seen it from concealed A/C pipe condensate. As Raymond said, concrete can corrode copper water lines. They should put them in a plastic sleeve or pipe, but they figure once it is buried in cement no one will see it. And since it is a jack-hammer job to fix, it usually never gets taken care of. Does the neighbor have the same problem on his side of the party wall?