Repair on loose roof tilesA Photo Library of Slate Roof Defects

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Slate roof defect photo library: this slate roofing photo series shows all kinds of roofing slate defects. Here we give photographs of slate roof conditions including normal wear on slate roofs, worn out slate roofs, types of slate roof wear and damage, and stains or discoloration on slate roofs.

Starting at SLATE ROOF INSPECTION & REPAIR we describe procedures for evaluating the condition of slate roofing. We describe the types of roofing slate, common defects, inspection topics, and some repair tips. This article series assists home inspectors, building buyers or building owners, and roofing contractors in evaluating the condition of slate roofs by providing photos of various slate materials, patterns, defects, and conditions.

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A Photographic Guide to Defects in Slate Roofs

Photo guide to Cracked, Broken Slate Roofing Inspection & Repair

Broken roofing slates

Article Contents:

Cracked, broken slates, probably not leaking but note the diagonal crack in the slate below the course with a missing slate half

Cracked roofing slates

Cracks: Slate crack repair
, copper was slipped up over a slate which had split just below the butt joint of slates in the next course

Photo Guide to Delaminating Roofing Slates

Photo of delaminating roofing slate

Delaminating roofing slate, if the delamination is only in the upper surface layer of the slate the material may have substantial remaining life.

Also ask how many of the roof slates are delaminating at all - note the neighboring slates on this roof are sound.

Repair on loose roof tiles

Surface delamination on slates: Notice the surface delamination on some of these slates. A close inspection is needed to evaluate slate delamination when it looks like this. We need to know if the slate is basically sound, hard, and secured to roof, or if alternatively the delaminations are throughout the slate body, making it soft.

See our photos at SOFT DETERIORATED SLATES where we show close up photos of slate that looked pretty good on the roof but when touched, disintegrated easily

Photo Guide to Slate Roof Flashing Details

Slate roof flashing defects

Flashing: Chimney in the roof valley
, was a probable factor in recurrent leaks in this slate roof

Slate roof with good sidewall flashing to a brick building

Flashing: Slate roof with good side-wall step flashing
, against a brick wall

Slate roof flashing defects-closed valley caulked

Flashing: Suspect copper valley in slate roof
, note the attempt to "patch" the valley with roof mastic - and the cracks in the mastic - this repair is not durable

Photo Guide to Loose, Sliding, Lost Roofing Slates & Slate Nails 

Repair on loose roof tiles|

Nails: sliding slates
, mean the nails are lost - perhaps from corrosion.

Don't underestimate the implication of many slates which have moved only a little bit - all may have lost their nails.

Notice also the surface delamination on some of these slates.

Loose roof slates

Nails: Slate fastener failure
, might be indicated by the slate at right if it is sliding down - can you move it back up?

If you can, this slate has lost its nail and is not connected. Use a slate hook or copper tab to secure the loose slate in place.

Sliding roof slates

Nails: Roof Tiles (not slate)
, repaired using copper strips - the strip ends holding tiles have been bent back by sliding snow - expect movement, leaks, and extensive nail failures.

This defect also occurs on slate roofs repaired using this method. This demonstrates the advantages of slate hooks in lieu of copper strips when replacing lost slates.

Slate damage photo

Slate damage at chimney and lower edge, probable leaks at chimney. Why to the slates seem loose particularly around the chimney?

Often the building framing settles away from the masonry chimney as framing ages, sags, or settles due to shrinkage or later rot or other in-building damage. But the chimney, built of masonry, tends to remain the same height.

On many old houses the framers actually connected roof framing right to the chimney. Later when the building sagged, settled, or moved, the framing pulls away from the chimney causing damage to the roofing slates and flashing, and leading to leaks in this area.

Another common source of slate roof damage around a chimney is wear and movement caused by flashing leaks and, in freezing climates, frost.

Photo Guide to Slate Roof Defects: Mineral Inclusions & Staining in Slates

Mineral inclusions in roof slates

Mineral inclusions
: Slates with mineral inclusions, the wash-out of minerals in some slates can lead to holes and leaks

Mineral inclusions in roof slates can lead to holes and leaks

Mineral inclusions, holes in slates
- the slates with these defects need to be replaced or patched from below with copper panels.

Stains and Wear Indicators on Slate Roofing, a Photo Guide

Stains on roof slates help diagnose their condition and life expectancy

Staining on roofing slates: Slate edges showing moisture absorption, but generally good condition, these slates have a good remaining life

Effloresence marks on slate roofing

White Efflorescence on roofing slates: the white markings shown on these roofing slates, is a mineral deposit left behind as water evaporates. Water penetrating the slate material absorbs minerals and leaves some of them, probably Ca and Mg on the slate surface.

Many slate roofers and slate inspectors assert that as the white stains progress from the edges of individual slates towards their center, one can estimate the remaining roof life. If 50% of the slate remains inside of the white area, the slate may have about half of its life remaining.

We recommend that this condition be confirmed by close inspection as well since other slate deterioration factors could be at work.

Edge of slate shows thickness and layers of minerals

Thickness of Roofing Slates, Close up Photo of Slate Edges in Good Condition

Edge of slate shows thickness and layers of minerals

Slate edge close up
, showing the natural layering of mineral deposits in the original stone

Measuring the thickness of roofing slates after installation

Thickness: Measuring slate thickness
, and close up inspection permits check for slate delaminating and softness

Thin worn out roofing slates

Thin, worn slates, French and conventional pattern
, missing slates, tar patches, leaks. This roof is probably repairable But we 'd need a closer look at those slates to evaluate their thickness and hardness.

White Stains on Slate Roofs

Effloresence white stains on a chimney (C) Daniel FriedmanReader Question: long white roof stains down from chimney

We are buying a house with a slate roof on a six year old home...the roof has long white stains down from the chimney. Looks like it's coming from the flashing around the stone chimney. Thoughts? - Steve

Reply: possible sources of white stains on roofs and buildings

White stains down FROM the chimney? Steve I'm not sure and would need to see some photos (use the CONTACT link found at top, side, bottom of our pages to send me some pix) . Our photo at left shows white efflorescence on the outside of a masonry chimney - discussed at White/Light Stains on Chimneys.

Search InspectAPedia for
Chimney Stains, Discoloration, Leak, Diagnosis, Cleaning & Repair Guide
to see white efflorescence stains on chimneys themselves as well as other types of stains on chimneys themselves (photo at left).

White stains on a roof can be pigment wash down from something above, salts from flashing corrosion, and on slate, white stains that form on individual slates, beginning usually as a roundish spot at the center of individual slates, are a sign of aging and wear.

See STAINS on ROOF SHINGLES for our library of types of stains found on roofing surfaces. There we include this comment

White stains on roof surfaces may be from wash-down of pigments in paint on surfaces above the roof such as a gable end or dormer wall; white or less-black roof surfaces may also be found below copper or aluminum flashing whose salts run down the roof surface in wet weather, preventing algae or moss growth and leaving a white area on an otherwise stained roof surface. Details are at See WHITE STAINS on ROOFS. Our article at ALGAE, FUNGUS, LICHENS, MOSS on SHINGLES includes a photograph of this condition on a wood shingle roof.

White stains on slates themselves (photo at left) as a wear indicator are discussed in the article above on this page.

To diagnose white stains that are on a roof, building chimney, or walls, and specifically around or below a chimney, I'd be alert for flashing leaks - check indoors - and I'd follow the white stains up to their point of origin on the roof to see just what materials are there, for example:

  • A white-painted dormer side or window above a roof section can bleed down white onto a roof surface
  • Mineral salt runoff from some metal flashings, particularly aluminum, may result in a "white" or "clean" area on otherwise darker building roof or even walls below
  • Less often white stains below a chimney could be salts leaching from the chimney interior through the masonry and onto the roof surfaces (more often these are dark brown or black and relate to combustion products)

Finally, I can comment more accurately if I can see some photos of the roof in question. Here are articles on building roof stains:

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Frequently Asked Questions (FAQs) about slate roof inspection, leak troubleshooting, repair or replacement

Reader Question: extent of hail damage to slat roofs

(July 10, 2011) Rich said:

What type of damage would you expect on a slate roof when it is hit by baseball sized hail? The roof was installed in 1955 and the hail storm happened in 2006.


Rich: baseball-sized hail? I'd expect to find extensive broken damaged slates throughout the field of the roof, possibly worse on some roof slopes than others depending on the direction of hail movement and winds. I'd expect sheltered areas of slates that didn't get the hail by direct impact to not show that damage.

Certainly on a 1955 slate roof, chances are that by 2006 there would have been other repairs, and there could be other issues such as with flashings or fasteners.


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