Removing render from windows without scratching

[phykell]

Long story short, a guy came and fitted a new window for us and then rendered over the old tyrolean with sand and cement. Unfortunately he managed to splash the stuff on the new window and didn't bother washing it down. It's now dried and I've tried to wash some of it off but it's scratched the glass.

Can someone suggest how I can get the stuff off without damaging the glass? What about a pressure washer? Or is there something which will dissolve it?

Thanks

 

[masona]

Pilkington Glass recommend using limescale remover

 

[phykell]

Thanks masona I'll give that a go

 

[scolex]

@phykell - did it work? I am in a similar situation - though they renderers managed to get lumps of s&c all over some aluminium windows too....
TIA
S