Waterproofing and protection

Waterproofing is the final stage of a roof restoration, and doing it out of order is why most home attempts disappoint. A repellent applied over embedded dirt seals the dirt in. The fabric has to be clean and dry first; everything in this section assumes that has happened.

What the treatment actually does is restore surface tension. Convertible fabric, whether woven acrylic, canvas or mohair, is a textile, and it behaves like outdoor clothing. New, the fibres shed water because their surface chemistry makes droplets bead and run off. Over years of rain, UV and washing, that chemistry degrades and the weave starts absorbing instead. A waterproofing treatment re-coats the fibres so water beads again, and as a side effect it slows the rate at which contamination gets into the weave.

It is worth being precise about what that does not mean. Waterproofing is not sealing. A roof that leaks into the cabin is almost never leaking through the fabric; it is leaking past a perished seal, a blocked drain channel or a rear window bond that has let go. No amount of repellent fixes any of those, and applying more of it is a common way to spend money on the wrong problem.

How long it lasts depends more on where the car lives than on the product. A garaged car that comes out at weekends holds its proofing for years. A car parked under a tree, or one that gets jet-washed regularly, loses it far faster; pressure washing strips proofing in a single session. The practical answer for most owners is a reproof whenever water stops beading, which is a better signal than any interval on a bottle.

A new roof is the one case worth treating on a schedule rather than a symptom. Fabric arrives with factory proofing that is good but finite, and putting a treatment on while the roof is still clean and undamaged is the cheapest protection available.

Authored by Danny Argent. Reviewed by Gary Wray. (id=695)