White stains / Efflorescence

 ["The following is a follow-up on a question regarding white/yellow stains on concrete columns in Canada"]

As you suggest, I obtained samples for analysis and tested for salts and sulfates.

The following results were given.

Ca 22.6%; Si 0.46%; Sr 0.12%; P 0.19%; S 0.02%

The material appears to be primarily CaCO3 in composition. This was confirmed by performing a acid test on a sample of material.

Sincerely Yours S.J.M 
These results are classic efflorescence, where soft rain water leach out the calcium hydroxide Ca(OH)2 from the concrete. Then it gets to the surface and is exposed to the CO2 in the air. The result is precipitation of white crusts of calcium carbonate on the surface when it dries (not freezes).
As I mentioned, in the long run, and in severe cases, the concrete will lose strength and become porous.
In your case, with non-structural concrete, it may be enough to clean the surface from the deposits, and provide some protection from rain water. You may even consider painting it with cement-colored or transparent paint AFTER THE CONCRETE IS TOTALLY DRY!!! But careful, a bad paint job may peel, and/or look worse than the original.
Hello, Doctor Mor I am a C-54 tile contractor with a re-occurring efflorescence problem in my garage. My house sets below another lot where water migrates towards my foundation .  Is there anything next to r/r [Remove & Replace] slab and using moisture barrier that will send minerals back down.
It is starting to deteriorate surface.

 

 1. You cannot send the minerals down, but the limited loss so far cannot be significant.

2. Preventing the problem can be done in three main ways:

- Prevent the water from getting under the slab in the first place by installing cut-off walls and French drains around the house. This can be quite expensive. Its success depends also on the natural water table and your ability to dry out the area under the house.

- Apply sealant to the top of the slab. This is a tricky operation and usually requires a dry slab before application. Many of the advertised sealants do not really work so well. The good ones may cost a lot (epoxy based membrane)

- R&R [Remove & Replace] the slab. This way you know exactly what is under that slab and you can make sure it is done right. Just make sure you take the Visqueen [brand name of plastic moisture barrier used under slabs] up and seal it to the foundation walls since this may be the weak point of the system.

By the way, did you try to talk to your neighbor about reducing his water bill? This could really help. Maybe use low flow sprinklers instead of flooding the whole yard.