Dark grey spots (like humidity spots) on parging.It does not seem to be water. How do I remove them?

[MiniMe4Eng]

They look like below.
I was told that it is humidity that ascends through the wall due to capilarity
I have watched the area for around an year. We had a very dry summer in Toronto.
These spots have not changed at all. I tried to dry them up with a hair dryer but I had no luck
I seems to be some sort of salt.
The area has roof above and gutters. The problem was originally caused by an incorrectly sloped patio that was sending the water toward the wall.
That was fixed. What could these spots be and how do I remove them?

 

[Ron]

The light residue is efflorescence. It is caused by water going into the wall, taking calcium into solution (calcium hydroxide), moving to the surface where carbon dioxide in the air reacts with the calcium hydroxide creating calcium carbonate and other minor reaction residues.

You can also see that the dark spots appear to follow mortar joints in the underlying masonry wall. It is likely that the masonry has a lot of moisture in the unfilled cells that bleeds through the more porous mortar joints and causes the staining. I see no weeps for the underlying masonry wall, so likely the moisture continues to collect.

 

[MiniMe4Eng]

This is what I thought too. I was thinking about removing the drywall and the insulation and drilling holes in the cinder blocks in order to dry them up
Then I did that test with the hair drying and nothing happened
I also removed the power plugs from the wall and I tried to sniff the air from beyond the wall.
If there is moisture trapped there it should also radiate toward inside and ..no there was absolutely no smell

As indicated the problem used to be because the patio used to be sloped toward the house! That is fixed, I see no water there anymore.
Below is what it looked when the wall was receiving the water from the patio.
I would say that now I am seeing just salts which refuse to go...

 

[MiniMe4Eng]

BTW there is another epic thread in the Ground/earth works section about the whole context around this

http://www.eng-tips.com/viewthread.cfm?qid=391109

 

[Ron]

If you are in a cold climate, you likely have a vapor barrier on the inside of the wall, so trying to dry the masonry from the inside won't work.

 

[MiniMe4Eng]

I am in a cold climate
I would have removed the drywall, the vapor barrier and the insulation if I wanted to put that in practice

 

[LehighLarry]

This looks to be only an aesthetic issue. I agree that moisture was the original cause for both the efflorescence and the dark shadowing at the mortar joints. If you can't live with the look try a bond coat then a skim coat of cement paste or finely sanded grout. This will leave a slightly textured monolithic appearance. Try it in an out of the way area first to make sure the look is what you want. Keep in mind the bond coat will essentially seal in whatever moisture enters the wall. Be sure there is adequate moisture/water drainage for the whole assembly or this could add to the issue.

Larry from Lehigh White Cement Company

 

[MiniMe4Eng]

I bought a moisture meter from Canadian Tire here in Toronto and I measured the humidity of those spots
and the humidity of the wall in general. Absolutely no difference between spots and the surrounding area.
It was under 0.8% (I believe it was around 0.6%) so yes it is confirmed this is salt. I am now fixing other issues around the house while the weather still allows this and I will try to wash these spots with an light acid solution to see if it works. I am tempted to redo the parging for the entire house not sure if this is a DIY job I have to read about it but besides the less aesthetically results I do not know what else can go wrong...
I will report back when I have the results

 

[Ron]

Moisture meters, particularly the inexpensive ones, are not designed to measure moisture in concrete, so don't be mislead by the results. Also, they don't measure humidity. Actually they measure conductivity, correlated to moisture depending on the material....mostly wood or drywall

 

[MiniMe4Eng]

Well this is not concrete, it is the parging ...
The scale says it is for construction materials, not drywall only
Yes the conductivity is what they measure that way but there is a correlation isn't it?

 

[Ron]

Parging is a cementitious material, much like the cement paste in concrete. For moisture purposes, the same limitations apply.