Roof slate query.

beyond the blue

beyond the blue

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Neil
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I have a house that has some sort of deposit on one of the roof slates. This is a picture of another house (not mine) that has the same thing but a lot worse. Has anyone any idea what it is?
 

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Could it be old roofing felt melting and dribbling down?
 
Nod said:
Could it be old roofing felt melting and dribbling down?
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How old is the roof? Old roofs dont have roofing felt under the slates they were just torched (sand/cement pointing between the slate and the rroofing lath) to seal the gaps.
 
luthy said:
How old is the roof? Old roofs dont have roofing felt under the slates they were just torched (sand/cement pointing between the slate and the rroofing lath) to seal the gaps.
Click to expand...
I have been up in the loft space and you are correct there is no roofing felt just pointing. So unless there has been a repair at some stage it rules out melted felt.
 
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Its hard to tell from the picis it actually a deposit or could it be the that the slates are breaking down and laminating and weathering.
 
Does make me think of a lichen like growth?

When did you first notice it and has it been 'growing'?
 
As above lichen is common on slate roofs this photo certainly looks like that is what it is.
 
beyond the blue said:
Only noticed it a couple of days ago. I have a guy doing some work on the gutter at weekend so will ask him to knock a bit off with a long stick.
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Looking at the picture again another thing it could be is moss.........AFAIK not uncommonly associated with lichen.

As I understand it, Lichens are seen in isolation but more typically are flat like splashes of paint.

Also, as most moss is green the very pale appearance in your picture is a bit of a mystery?

It will be interesting to see it close up...... especially if he can scrap off a bit including where it is attached to the slate.
 
Not all lichens are flat look at the ones used by modellers to make bushes and trees. Another thought did occure to me however, but it does depend on the age of the roof. Roofs that were constructed before the common use of Portland cement were torched with lime putty or lime mortar. They never set rock hard and allow for some movement. It could be a residue from that finding its way put to the front of the slates and building up over time.
 
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