We had a new roof light fitted on our caravan but after a while these strange marks began to appear. The fitter told us it was tree sap as it was sited near trees throughout the summer but I�m not convinced. We�ve tried numerous times to clean it with different methods but to no avail. Any suggestions?
Depending on how the skylight was manufactured, items 'formed' from stock sheet usually have a protective film on them to prevent scratches during processing, it's meant to be removed when the part is put into service.
Yours looks very similar to what happens when that film is not removed and degrades in sunlight, becomes embrittled and starts to flake off in small areas!
When new it's easy to just peel the film off, but once degraded it's much more difficult, and the also degraded adhesive doesn't let go any more! Trying to get it off risks damaging the skylight, given time nature will do the job and it will mostly just 'weather' off! If you can get to feel the surface, your finger tips would be able to feel the 'edges' where the film's started crumbling.
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Thank you. That makes sense. We had considered this as a possibility but the guy who fit it suggested it was tree sap but he hadn’t returned to look at it and we took him by his word. Live and learn.