by John H. Koester
One of the first commonly employed weep details was the sash cord or ‘rope’ weep. In some cases, this detail was expanded with sections of the sash cord laid in the cavity and then extended through the wall, usually at a head joint. In other cases, the sash cord was fastened vertically up the backside of the cavity. In yet other instances, it would be pulled out of the wall, leaving a hole through the head joint or bed joint of mortar.
How and when these sash cord sections were placed or embedded in the bed joint of mortar impacted whether they had any weeping capacity. If they were placed on the flashing and the bed joint of mortar was spread on top, the finished detail looked like Figure A. However, if the bed joint of mortar was spread and the sash cord section was laid or embedded into it, the finished detail looked like Figure B. The theory was the cotton sash cord (or a synthetic one) would ‘wick’ water out of the core or cavity and dry the units. However, if there is one takeaway from this article, let it be that one should not get into a wicking contest with mortar or masonry units—how can a 9.5-mm (3/8-in.) diameter sash cord compete against an entire masonry assembly?
Many have seen an example of a rope weep that has moisture stains around the outside end of the cord; it appears to have moisture ‘weeping’ from it. What is really happening is a small amount of moisture is actually exiting the cavity through small voids in the bed joint of mortar at the 5 o’clock and 7 o’clock positions on the bottom radius of the sash cord.
Various tube weeps—pieces of plastic pipe cut to length—have also been introduced to the masonry industry. Their installation procedure is virtually the same as the sash cord material and so are the shortcomings. Even when the tubes are correctly installed on the flashing’s surface, the weep’s wall thickness is still a water dam.
To read the full article, “Weep Now or Weep Later: Moisture management and risk zones for masonry,” click here.
