Deteriorating bricks
DPiNLWPHNo
| Posted in General Questions on
Hi,
[The exterior walls of my house, above grade, are faced with bricks and mortar.] I had bad mortar and it appeared the water was very slowly pouring out . I started re-pointing the bricks in this location. As a result there seams to be a line where the face of the bricks fell off (some were covered with salt. Also below this line the bricks darkened. I also parged the foundation and it looks like I have wet spots. I did this work about three months ago. Any ideas on what is happening?
Thanks,
Carl
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Replies
Did you parge over the weep holes?
Rising Damp. The water rising into the brick by capillary action was, from your description, exiting through porous mortar joints. If the mortar wasn't exfoliating, you probably should have left it as it was.
Now that you've sealed the mortar joints with non-porous cementitious material, the water is leaving the face of the bricks and leaving behind mineral salts as it evaporates - efflorescence.
Those salt concentrations in the surface of the brick now draws water by osmosis, which is ten times as powerful as capillarity - 3,000 to 5,000 psi, or greater than what most cementitious or fired clay can withstand. Hence, spalling of the surface.
You need to get rid of the ground moisture problem at its source, which is most likely roof runoff (gutters, downspouts, leaders?), and divert what does hit the ground with proper grading (minimum of ½" per foot for 10 feet). Use swales or French drains to intercept surface or ground water.
And then, if the problem persists, remove the cementitious parging and replace with a sacrificial layer of lime mortar (such as is common on 500 year old brick buildings in Europe).