What Causes this please?

[scotjimland]

At the power station I mentioned earlier, there was a white 'smuts' board in the car park..

This was a 1mt sq. piece of white PVC that was used to measure 'smuts' from the chimney ..

The reason being, we were next to a yacht marine full of expensive gin palaces.. owners of which claimed were being covered in smuts from the power station .. and were making expensive claims for cleaning their boats.. and no doubt having them repainted..

Car owners also claimed, as a result the SSEB installed a 'free to use' car wash in the car park.. !

The OPs photo is exactly how the smuts board looked ... The soot lands, sticks and gets blown by the prevailing wind.. leaving these typical trails

 

[EuroTrotters]

I’ve not been drinking yet,
But do you have a lot of bats in your location

I have similar markings on my roof, and during the summer we have a lot of bat activity and when bats fly out of roast they poo quite a lot, bat poo crumble when dry , if you get a lot of rain it breaks it down and leave a mark on roof,
I have no proof what’s so ever , but that my own thoughts, you may call me crazy ?

Yes, we do have a lot of bats

 

[buzz1]

Wrong time of year now at my location , bats gone on winter holiday now , but bats poo a lot often it on roof mh and cars generally it will blow off if it gets windy as very light and dry .
bat droping are very crumbly and turns to dust when rubbed between fingers tips ( that how you tell difference between mouse and bat droppings)
So when poo lands on the motorhome roof it’s heated up during the day and drys
if it’s touch turns to power, then mixed with rain water leave stains on roof ,
Which does come off with a wax polish .
Still sound crazy ,
I have no other explanation,
Yes I do have a wood burner but it wasn’t in use
Between cleaning the roof last spring till I cleaned it again in October when I noticed the similar marks as yours ?
I must be crazy posting this

 

[IRHP]

Got similar marks, absolute bugger to get off, Elbow Grease works well but worry about the effects of it on gelcoat. Cream cleaner as well but it's a bit abrasive. Neighbour 2 doors down has wood burner.

 

[Ditcha]

Wrong time of year now at my location , bats gone on winter holiday now , but bats poo a lot often it on roof mh and cars generally it will blow off if it gets windy as very light and dry .
bat droping are very crumbly and turns to dust when rubbed between fingers tips ( that how you tell difference between mouse and bat droppings)
So when poo lands on the motorhome roof it’s heated up during the day and drys
if it’s touch turns to power, then mixed with rain water leave stains on roof ,
Which does come off with a wax polish .
Still sound crazy ,
I have no other explanation,
Yes I do have a wood burner but it wasn’t in use
Between cleaning the roof last spring till I cleaned it again in October when I noticed the similar marks as yours ?
I must be crazy posting this

Crazy

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[CAB96]

Pretty sure it's combustion products.

We have 3 white vehicles, all of them had the same markings couple of weeks (months?) ago.

I'm convinced it was the big fire at the industrial unit near B&Q Stockport.

Elbow grease and normal car shampoo eventually shifted it, I didn't want to use anything stronger on our poptop.

 

[TheBig1]

can be chimney smuts or even diesel smuts if you are near a motorway/main road. The difference is one leaves a sticky residue that burns the paint, the other a greasy residue that washes off easy with soapy water. Commonly we see traffic film causing black streaks by the windows etc, but we are right by an airport

 

[BOOMEL]

I have black spots on the mastic on the roof and around the vents it is crumbling a little bit. I have tried silky, what sorts this out?

 

[TheBig1]

I have black spots on the mastic on the roof and around the vents it is crumbling a little bit. I have tried silky, what sorts this out?

If it's crumbling, it is dried out and nothing will revive the exposed area. it needs cleaning off and a new bead of sealant applied round the vent