It's raining sand

[Radian]

Only a week ago I finally got around to climbing on our flat roof to clean a Skylight which had a film of fine sand (and algae that grew on it) that got deposited when we had Saharan dust blow our way last year. That's obviously been a cue for more sand to be dumped on us today. 🙄

 

Why does it stick so well? I would have thought it would wash away - the fall on the glass is around 1:60 but it stayed there for over a year, through all kinds of storms. I'm looking up at it now and it's raining quite hard but the stained area I got spotless last week is already looking to be invincibly stained once more. I worry that microscopic scratches left from cleaning the glass are serving as nucleation sites for further staining.

[markc]

Glass is not a smooth surface unless treated with a polymer type coating (self cleaning glass) but on a low angle the volume of water needed to keep sand in suspension would be like a river.

[Radian]

Is there a polymer coating you would recommend?

[markc]

I can’t recommend any post manufacture treatments but you need a Hydrophilic (think that’s the correct term and spelling) coating as this causes the water to sheet and flush debris away with it.

only dealt with panes already treated from the manufacturer

Edited March 16, 2022 by markc

[jack]

35 minutes ago, markc said:

 but you need a Hydrophilic

 

I think the term is hydrophobic.

 

Rain-X for car windscreens is an example.

 

 

[SteamyTea]

51 minutes ago, Radian said:

Is there a polymer coating you would recommend?

Possibly caused by static charge, so just electrify the roof.

 

https://physics.nyu.edu/grierlab/charge6c/

Edited March 16, 2022 by SteamyTea

[ToughButterCup]

Love (phil) it or hate (phobe)  it,   @Radian you're  just going to have to clean the damn windows anyway. Seagull poop really etches windows good and proper

[Radian]

24 minutes ago, jack said:

 

I think the term is hydrophobic.

 

Rain-X for car windscreens is an example.

 

 

It seems that both hydrophobic and hydrophilic properties may play a part in 'self cleaning glass'. Obviously having a hydrophobic surface would mean water chasing away rather than pooling but a hydrophilic surface would also promote complete wetting and allow rain to wash away the dirt leaving a streak free window.

[Radian]

24 minutes ago, SteamyTea said:

Possibly caused by static charge, so just electrify the roof.

 

https://physics.nyu.edu/grierlab/charge6c/

Rainfuel cathode?

[jack]

22 minutes ago, Radian said:

It seems that both hydrophobic and hydrophilic properties may play a part in 'self cleaning glass'. Obviously having a hydrophobic surface would mean water chasing away rather than pooling but a hydrophilic surface would also promote complete wetting and allow rain to wash away the dirt leaving a streak free window.

 

Interesting, thanks.

From Wikipedia:

 

Several techniques are known for the patterning of hydrophobic surfaces through the use of moulded polymers and waxes, by physical processing methods such as ion etching and compression of polymer beads, and by chemical methods such as plasma-chemical roughening, which can all result in ultra-hydrophobic coatings.^[2] While these surfaces are effective self-cleaners, they suffer from a number of drawbacks which have so far prevented widespread application. Batch processing a hydrophobic material is a costly and time-consuming technique, and the coatings produced are usually hazy, precluding applications on lenses and windows, and fragile materials. The second class of self-cleaning surfaces are hydrophilic surfaces which do not rely solely on the flow of water to wash away dirt. These coatings chemically break down dirt when exposed to light, a process known as photocatalysis. Despite the commercialization of a hydrophilic self-cleaning coating in a number of products, the field is far from mature; investigations into the fundamental mechanisms of self-cleaning and characterizations of new coatings are regularly published in the primary literature.

[markc]

3 hours ago, ToughButterCup said:

Seagull poop really etches windows good and proper

So that’s why you get toilet duck but not seagull poop glass cleaner

Edited March 16, 2022 by jack
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