Grout in between composition shingles?

Hi, I had an inspection today and saw this unusual roof covering system - composite shingles with mortar/grout in between. This seems unusual. Is this a standard roofing system?

Looks like organic fungal type growth. Not sure about the grout. Did you pick at it?


I agree with Brian. Look at all the tree-cover. Was this in a shady area, possibly on the North side of the building? Did you probe it (pick at it)?


Haha, you pick your nose and probe inspection components :grinning:

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There was a lot of tree cover. It was south facing side. If it is fungal what is the recommendation?

Identify, Remove, Prevent Algae, Fungus, Lichens, Moss on Roofs.


1st of all, it is a fungal type growth. But if you are not sure, you can say “organic type substance or growth”.
2nd, it is causing damage such as lifting, loss of adhesion etc. It may be too far gone to be salvaged.

You do not have to make that decision. Report what you observed and recommend evaluation by a qualified roofing contractor.


I agree. It looks like organic type growth…some dried/cracked.


Harland, the tree in your photo is likely the source of the problem. When tree limbs overhang the roof you will get tree sap on the shingles. Sap is the food source for moss an lichen to grow combined with shade and moisture. I typically recommend trimming back any overhanging limbs. Depending on the amount of growth I may add additional comments.


Welcome back to the forum Harald

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I agree, anytime you have overlying limbs and branches over a roof, you will see this type of growth. When left alone for too long, it becomes harder to clean and save the shingles.


Thank you Brian for your advice. Much appreciated.

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Thank you everyone for your input! It is much appreciated! I live in SoCal and it’s the first time I have seen this on a roof.

I agree that overhanging trees are a problem, but that condition is awfully uniform across the roof to be caused by tree sap. Also, it continues on around the corner beneath the overhang. The tree sap I’ve seen under pines often collects under damaged areas (broken branches, etc), so it’s usually kinda spotty across the roof.

During certain times of year, here in the Rockies you can see huge clouds of green pollen blowing across mountainsides. Those shingles don’t look too well bonded. I’m wondering if pollen adhered to shingles sealant strips, with eventual moisture-caused swelling and accumulation of more pollen.