Why do red clay tiles crack, and which cracks matter?
Clay tile cracks when a load lands on it at the wrong point or when movement in the frame pushes a tile out of line. A hairline crack in a tile that is still fixed and still overlaps its neighbor is often left alone. A crack that lets water through, or a tile that has dropped out of the course, is repaired.
Clay is strong in compression and weak across a point. A tile that was set on a batten with a gap, or that was walked on by a previous worker in the wrong place, can split along a line that does not show until the next rain. Older tile roofs have usually been patched at least once, which is why the technician looks at the earlier repair as well as the tile.
The test is simple: does the tile still lie flat, still overlap the one beneath, and still shed water into the channel below? If the answer is yes, the tile can usually stay. If the crack runs through the nib that holds it, or if the tile has moved, it is replaced.
How is the underlayment checked under a tile roof?
The underlayment is the water-shedding layer under the tile, and on an old roof it is often the part that has failed. The check is made where tiles are lifted, at valleys, around vents and along the eaves, because those are the places where water gets past the tile first.
An old felt or paper underlayment dries, cracks and tears at nail holes. Once it has lost its flexibility, a tile repair that does not address it will leak again within a season. The technician records the condition of the layer where it can be seen and says plainly when a larger section needs to come up.
Where the layer is sound, the repair is kept to the tile. Where it is not, the affected area is replaced in the same course, so the new tile is laid on a sound surface and the old leak line does not reappear under it.
Can a clay tile be matched when the original stock is gone?
Often, though not always. The first step is to salvage tiles from the least visible part of the roof, such as a rear slope or an outbuilding, and to match the profile by eye and by measurement before ordering anything new.
Clay tile is made in profiles that have changed over the decades, and an original roof may use pieces no current catalogue lists. The technician measures the lap, the width and the curve, then checks whether the salvaged stock covers the damaged area. Where it does not, a close match is chosen and set in a discreet part of the slope first.
A visible mismatch is not a leak, and it is not always a reason to re-roof. The owner is told plainly what matches and what does not, so the choice between a tidy repair and a full re-tile is made on the facts.
How is a loose ridge or hip piece fixed?
A loose ridge or hip piece is re-set on its bed of mortar or on the mechanical fixing the roof was built with, and the joint is sealed so water cannot run back in under it.
Ridge pieces move when the mortar cracks, when the batten under them loses its fixing, or when a previous repair used the wrong material. The work is done from the ridge, with each piece lifted, cleaned, re-bedded and checked for level before it is secured.
The technician does not seal the whole ridge with a coating as a shortcut. A coating can hide a loose piece for a season and then trap the water that gets under it, so the fixing is corrected first and the joint is finished after.
What should a homeowner check between visits?
Look at the roof from the street and from the patio once a season, after a windy day or a heavy rain. Note any tile that has moved, any ridge that looks uneven and any stain on a ceiling under a valley or a vent.
The most useful observation is a change: a course that was level last year and now steps down, a ridge that has a new gap, or a stain that grows after rain. Photographs from the same spot at the same time of day make these changes easy to see, and they give the technician a record to start from.
Keep the gutters and the roof valleys clear of leaves and tree litter, and ask for a check after any branch has fallen on the roof. A clay tile is not damaged by a light branch, but a heavy one can crack several tiles in one blow.
