Hello! Today we’re gonna talk about salts: how do they rise through masonry walls? How do they affect them? What can we observe? How do we treat them? Is the treatment effective?

Here come answers, with explanations, illustrations and a bunch of new questions!

Let’s first recap briefly were we left it last time. I just had added the salts solution to the walls. We were waiting on to see how fast it would rise through the structure and how long it would take to see the effects on the wall.  Well, after 24 hours, some of the solution has been absorbed by the walls; we can clearly see the level on the plastic tub is lower and the bottoms courses of the wall are wet. Every day, for 4 days, I keep seeing the level getting lower in the tub, and the moisture rising through the wall. Also, we can observe efflorescence on the bottom of the wall, with salt crystals on the lowest courses. After 4 days, no more changes. The salts solution is then removed so the masonry walls can dry. Right away, 24 hours after removing the water (salts solution), efflorescence on the bottom of the wall is everywhere; this is impressive.

Salt solution absorption trough time, on control test wall C2


Salts efflorescence after 4 days, on C2

After documenting the experiment with photographs, I ran a couple of analysis: moisture content (with a microwave moisture device from Trotec, T610), gloss (with a BIK Gardner micro-tri gloss) and color (with a Konica Minolta chromameter CR400). Those are taken to record values before any treatment is applied on the walls so we can later evaluate the effects of the treatment. Color and gloss are classic tests, and the results obtained are no surprise. Gloss value ring between 0 and 1.1 GU depending on the angle taken for the measurement (20, 60 and 85 degrees) and the different bricks analyzed. Those low values correspond to what we can expect for a mat material such as brick. Same for color analysis, on an l a b scale, no surprises there, with values fluctuating a lot depending on the bricks (some are very light and more reddish and some are more dark, like black painted). What’s interesting here is the moisture content analysis, which gives us relevant information about the distribution of water within the masonry wall. I take measurements every 2 courses, on the entire wall, and 6 analyses per course.

Taking measurments on the control test wall C1 with the moisture device Trotec T610

Let’s take the case of the control test wall C1. The measurements values are put into an excel file so we can see better the repartition of moisture within the wall and understand better what’s happening within the structure. I’m actually curious to see if we can accurately say wherever there is water or not in each course of the wall. Maybe we can picture it better that way. Turns out it is not that simple.  Average values on 6 measurements give us a good idea of moisture content per course, but there is no way we can picture the shape of water moving through the wall.

course measure 1 2 3 4 5 6 average average 1 to 3
1 57.1 75.3 75.6 51 41 68.3 61.4 51.2
2 32.8 38.8 33 33 37 31 34.3
3 33 35.5 35.8 38.2 26.1 25.2 32.3 average 4 to 6
4 38.5 37.3 30 33 33.1 33.1 34.2 32.8
5 33.7 33.1 32.5 31 30 26.7 31.2
6 26 28 37 41.3 33.1 32.2 32.9 average 7 to 9
7 41.3 38.8 44.5 34.2 34.6 28.8 37.0 34.6
8 45.2 32.8 37.6 33.1 37 37.3 37.2 average 9 to 11
9 31.6 32.8 28.8 30.7 26 28.5 29.7 31.2
10 38 39.2 45.2 30.7 31.3 31 35.9
11 31 27.6 27 29.4 25 27 27.8
Table of moisture measurements for C1 + graph
moisture content 96h after salts introduction

Moisture content 96h after salts introduction

The best we can do is to simulate, based on average values of moisture content on a group of 3 courses each time, the repartition of moisture content within the wall.

Clearly, and expectedly, the bottom courses are the ones containing the more water and salts, with an average moisture content of 43.2 units. The higher in the wall, the less moisture there is, even though level is quite the same everywhere apart from the lowest courses, with an average value of 35.5 u. Our salts solution – rising moisture experiment worked impressively good! And fast! Efflorescence is growing on the 2 bottoms courses of each wall. It is mostly small groups of salts crystals dispatched on the surface. Most of the crystals are similar, but several have structures very different.

Control test wall C2; moisture content 4 days after removing the salts solution


 Peculiar crystal salts on control test wall C1


Crystals salts on C2


 Crystal salts on W1


 Crystal salts on W2


 Crystal salts on W3


Crystal salts on W4


 Crystal salts on W5

It’s interesting to notice how different the crystals can be. It’s probably different type of salts. It would be interesting to study it. But this is for another time, another investigation. To be continued. For now, we’re happy we have salts. They grow big, they grow fast. Experiment successful! It’s now about time to test treatments. See you on my next blog to talk about anti efflorescence coatings!

National Center for Preservation Technology and Training
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