Williamsburg School House Mortar Repair

In urban areas like New York City, one can see the ravages of Portland cement based mortars everywhere.

Portland cement
Failing bricks caused by the use of Portland cement mortar (click to enlarge)

We were called in to assess the condition of this wall in Williamsburg, Brooklyn in what had been a school, but is now a living loft building. The mortar that had been used was very hard and brittle, holding in a lot of moisture and crushing the brick.

Portland cement
Portland cement mortar can retain water and crush brick (click to enlarge)

In an effort to save the brick and keep the project on budget, we came up with a plan that was a compromise for the next decade, but one that would be effective at maintaining the health and breathability of the brick. We removed all the mortar in the wall about 1 ft from the ground, where the water was wicking up and brick damage was the worst.

Chiseling away the Portland cement
Carefully chiseling away the Portland cement to prevent damage to the bricks (click to enlarge)

We cleaned off the very hard and sloppy portland cement mortar from the walls, which required us to very carefully cut the joints and then chisel the mortar off without damaging the bricks.

Chiseling away the Portland cement
Using sand from upstate N.Y., we were able to match the original mortar (click to enlarge)

Chiseling away the Portland cement Chiseling away the Portland cement
Mixing the mortar on site with lime putty (click to enlarge)

We then cleaned all the joints and made our own match of the original lime mortar, using a blend of sands we brought from upstate. All the mortar was mixed on site with lime putty.

Chiseling away the Portland cement Chiseling away the Portland cement
Repointing with the new lime mortar (left). Using a churn brush to seal the cracks (right) (click to enlarge)

The walls were kept wet, and then beat with churn brushes to seal the cracks between the mortar and the bricks, pushing the mortar as deep into the joints as possible. We left the joints rough so they can breathe, in addition to giving the new mortar an aged look. The result is a very healthy wall that will breathe off the wicking water and have a mortar that is subservient to the brick rather than the other way around. The S&M Portland based mortar is still there on the upper reaches of the wall, to someday also be removed and repointed.


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