masonry today: end dams

by Patrick Conway, CSI, AIA


some designers assume masons install end dams as a matter of general practice - this is not the case

Dam it!

Please keep these two words in mind when specifying and detailing through-wall flashing systems. Lack of properly installed end dams - or worse, no end dams at all - can be a major source of water entry into masonry walls and interior spaces.

Here is a very short course on water movement characteristics. Water moves down. However, if water meets an obstruction to its downward path then it moves laterally in its quest for another freeway to the water table. End dams will stop horizontal water movement and help divert moisture to the exterior of the building.

Ends dams should be installed at longitudinal ends of flashing over lintels, at column abutments, adjacent to building expansion joints, or other flashing interruptions. It has recently come to my attention that some designers assume masons install end dams as a matter of general practice - this is not the case. Trained masons are very careful to build your walls exactly as planned. Consequently, if you do not specify end dams you may not get them.

This past summer I visited a recently completed church project that had water problems around a window in a lower level classroom. The window was installed at the top of a semi-exposed foundation wall. In other words, the window interrupted the through-wall base flashing and no end dams were provided. I heard there were many fingers being pointed in all directions. In my church one Sunday morning, we were told, "Remember, when you point your finger, you have three fingers pointing back at you." Extend your arm and test this for yourself.

I have three hot buttons when it comes to end dams.

  1. Do not call for exposed end dams. As specifiers, we must be careful with the words "expose all flashing." You may end up with what I jokingly refer to as "University of Texas details" above all windows (no offense to the Longhorns).
  2. End dams should be a minimum of one and one half inches high.
  3. Specify sealant at end dam seams in all flashing systems, including self-adhered rubberized asphalt membranes.

[Want to know more about masonry? Visit Ed.]

This article series is authored by International Masonry Institute's Wisconsin Area Director, Patrick Conway, CSI, AIA. IMI is a nonprofit trade organization representing all trowel trades: brick, block, stone, tile, marble, terrazzo, plaster, cement finishing and restoration. IMI is funded by the International Union of Bricklayers and Allied Craftworkers and the Contractors who employ them. Pat can be reached at In Minnesota, contact Olene Bigelow, CSI, at 612-332-2214, or,
This article appeared in the December 1999 issue of "mad-spec", newsletter of the Madison Chapter, CSI. Reprinted with permission.

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Patrick Conway, CSI, AIA

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