Dry grouting - Stains left by white cement on flags

[con]

I've tried to dry grout on a patio of light colour indian sandstone flags. I used a completely dry 3:1 mix of silca sand and white cement to get a suitable colour. Unfortunatly the white cement has left a thin film on the top of the flags making them a very bright colour. Will the white film be weathered off or can it be removed.

I hope that you haven't covered this topic before.

Con :p

[Tony McC]

It will weather away .... eventually, but it could be patchy. If you use an acid-based cleaner, it might affect the colouring of the flags, but just which flags are affected, and how badly is very, very variable.

Lithofin have a product by the name of "Cement Away" that might be more suitable, but again, you MUST do a test first as some sandstones will recat even to this specialist cleaner.

Where you went wrong is in thinking you had a completely dry mix: the sand may have been bone dry, as may the surface of the flags, but there is always some humidity in the atmosphere, and this is sufficient to partially hydrate the fine residue of cement powder that is inevitably retained on the surface of the flag when you brush in.

In your position, I'd be termpted to leave it for this year and re-assess the situation after it's had a winter out in the open.