The cotton can absorb the moisture inside the wall and wick it to the outside, but the converse is also true - it is possible for the cotton rope to wick a small amount of moisture from the outside to inside the wall. The process of evaporation is slower than with weep holes. Also, the cotton could catch fire. Tubes Another type of weeps is a tube that can be made formed by using hollow plastic or metal. The spacing between the tubes is about apart. The installation of the tubes are done at angle to allow water to drip out. If the angle is too steep, the opening hole inside the wall cavity will be too high for water to come out. If the angle is too flat, the mortar used in laying the bricks may drop into cavity and block the tubes. Sometimes a shallow layer of gravel is laid to prevent mortar dropping from blocking the tubes. The thickness of the plastic tube, however small, will create a small dam that allows water to pool inside the wall cavity. Another technique to form tubes instead of using permanent tubing material is to use oiled rods or ropes. The oiled rod or ropes will be placed and mortared into the joints. The oil prevents mortar bond and the rods or ropes can be removed after the mortar is set, creating a hole similar to the use of a tube. The advantage of the tube type is that it is less conspicuous. However, the small holes may not allow air to circulate and vent out the moisture very well. Corrugated channels A newer weep technology uses corrugated plastic to create weep channels/tunnels that form the bottom side of the bed joint of mortar. These tunnels rapidly conduct the water out of the wall through multiple weep hole openings and ensure that the water can exit at the lowest point in the wall. Corrugated plastic weeps generally blend into mortar and are less conspicuous than rope weeps. References Architectural elements Geotechnical structures