Cleaning immovable stains from a windscreen

[alangraham]

Can anyone suggest a method of cleaning immovable glass stains from a windscreen? The vehicle has been stored in a large underground car park from which drips from a concrete ceiling have left droplet marks. So far I've tried a proprietary glass cleaner, neat vinegar, white spirit, a potato cut in half, meths, and petrol. None of these have even softened them. You'd think the stains were in the glass itself. Whatever's in this concrete roof has really messed up the glass but the odd thing is that the paintwork doesn't show it at all.

[cleverusername]

Effectively you have a stalagmite forming on your windscreen, the water is picking up substances from the concrete and then they are being slowly deposited on your glass.

Good news is I don't think it will eat through the glass. In theory a strong enough acid should eat away the concrete, if left long enough. You could try making a well with plasticine round the stains and leaving the vinegar on for longer to dissolve it.

However I suspect you might need a stronger acid. Phosphoric acid and trisodium phosphate are used to dissolved unwanted concrete from building work. Sometimes muriatic acid, hydrochloric acid, if they don't work. However we are beginning to talk about fairly nasty chemicals that require proper health and safety equipment.

I work as a lab tech, so I know that those chemical won't affect the glassware we have in labs. No idea if a Dolly windscreen would resist them. I am certain your paint wouldn't. So if you go down that route, testing the effects on an old damaged screen would advisable and properly protecting yourself and the rest of the car would be a must.

[dollyman]

This stuff works and its cheap https://www.ebay.co.uk/itm/JEWELLERS-RO ... xyHntSZAVT

Tony.

[80Sprint]

Buy the pads you put on a drill with some cutting compound. I had a big wiper scratch and it came out with that. Should help with your issue. Available on e.bay.
Don't get the pad too hot or the glue on the pad will loosen.

[alangraham]

I tried the jewellers rouge. It's messy and required a lot of elbow grease but it's worked. Thank you Tony.

[dollyman]

I tried the jewellers rouge. It's messy and required a lot of elbow grease but it's worked. Thank you Tony.

I thought it would, as i have used it myself many years ago I forgot how messy it was so appologies for that.

Tony.

[cliftyhanger]

Brick acid (hydrochloric) acid won't harm the screen. And will work nice and quickly. But plenty of other acids will work, though propbably take rather longer. Vinegar will eventually do the trick I would think. The plasticine/blutack well is a good idea, covered with clingfilm to stop evaporation and left for a while should do the trick.
Paints are remarkably resilient to acids/alkalis, but washing off ASAP is a wise precaution.

Polishing off a deposit from concrete is likely to be very hard work, it will be almost as hard as the abrasive you are using and you may end up scratching the screen as teh deposits break away and do damage as they are moved about.

EDIT a bit of research (slow day here) suggests the staining may be caused by Silicic acid etching the glass, in which case polishing the mark out is the only option.

[tony g]

The brick acid muriatic/hydrochloric must not be kept anywhere where you dont want things to rust. If left in a room/shed with metal objects they start to rust. In a sealed container is ok but if youre soaking something it needs to be somewhere else

Tony