Water repellent
Water repellent turns up in 2 fields: waterproofing, textiles. Here is what it means to the people in each one.
Water repellent in waterproofing
A clear penetrating treatment that makes masonry and concrete shed rain while still letting vapor out.
Penetrating repellents, mainly silanes and siloxanes, soak a few millimeters into the pores and line them with water-repelling molecules without forming a film. Rain beads off, absorption drops sharply, and the wall can still dry. They do not bridge cracks or resist water under pressure, and they must go on after repairs, since they block mortar and sealant adhesion.
"Repair all the joints first, the water repellent goes on last or the sealant won't stick to the stone."
Water repellent in textiles
A chemical finish applied to fabrics to prevent water from penetrating the fibers.
This chemical treatment coats yarns with a hydrophobic layer, causing moisture to bead up and roll off the surface rather than soaking in. Unlike full waterproofing, these finishes allow air and water vapor to pass through, maintaining the fabric's breathability. They are typically applied during the final finishing stages of textile production and may require heat activation or reapplication after heavy washing.
"We need to reapply the water repellent on this batch of canvas because the sample failed the spray test."