Waterproofing Membranes

The most widely used waterproofing product in Iran is the prefabricated bituminous membrane known locally as isogam, produced in 3 and 4 mm thicknesses with either polyester or glass-fibre carriers. The polyester carrier is more elastic and tolerant of structural movement, making it preferable for roofs and floors subject to displacement; glass fibre is cheaper and suits stable, low-stress surfaces. Alongside these, crystalline cementitious coatings are common for pools and negative-side applications, and single-component polymer coatings for terraces and bathrooms.

Three critical locations account for most leaks: the floor-to-wall junction, the area around floor drains and pipe penetrations, and movement joints. At the floor-to-wall junction the membrane must run at least 200 mm up the wall and be properly bonded behind it. Pipe penetrations need local patches and reinforcing tape. Applying membrane to a dusty or damp substrate without bituminous primer produces no bond, and the sheet lifts in its first summer.

Other recurring errors include laps shorter than 100 mm, excessive torch heat that burns the bitumen and destroys the protective layer, and installing membrane over inadequate falls. Waterproofing is not a substitute for drainage falls; water that ponds on a roof will eventually find a way through. Leaving membrane exposed to direct sun without a protective layer cuts its life by more than half.

After installation, a 48-hour flood test on the roof or bathroom floor is the simplest and most conclusive check. Run it before laying screed and tiles, never after.