Common myths about tiled roofs

The CSIRO has produced an information sheet dealing with some of the most common claims made by doubtful roof restoration firms. Here are the claims and how they stand up to informed scrutiny.

Myths and fallacy	Correct answer
"Tiled roofs need painting or coating".	This is not generally true, unless you are concerned about the appearance of the roof, or want to change its colour.
"The CSIRO recommends our paint treatment".	The CSIRO does not recommend products or roof-coating businesses.
"Prolonged weathering of the original surface makes concrete tiles porous".	This is not true. Some clay tiles manufactured more than 20 years ago have been known to absorb water or to fret or crumble under adverse conditions but coating won't fix this problem and such tiles generally need to be replaced.
"Concrete tiles absorb so much water that the roof can collapse and stumped houses can get pushed into the ground".	This is not true.
"Lichen eats into concrete tiles".	This is not correct. Lichen can sometimes block small drainage channels at the sidelaps of some tiles, but this is a minor maintenance issue.

Facts about tiled roofs

Leaks are usually confined to small areas and caused by one or more of the following problems:

Cracked or broken cement mortar bedding to the ridge and hip capping.
The capping should be rebedded or repointed.
Cracked or broken roof tiles (sometimes it's just one tile).
The individual roof tiles should be replaced.
Roof tiles displaced.
The displaced tiles should be put back into their proper position.
Blocked drainage channels under the 'sidelaps' of individual tiles.
Any build-up of dirt or debris should be removed.
Flashings blocked, damaged or displaced.
These problems should be corrected.
Blocked gutters (including valley gutters) and downpipes.
These should be cleaned out.

Download the entire CSIRO document