Outdoor grouting - avoiding white dust due to rain

[DIYNovice1979]

I used some multipurpose white indoor/outdoor floor grout for my paving slabs outside. I did this during a boiling hot day and there was no rain for 24 hours, I also wiped away all the dust leaving a clean finish. However whenever the area gets wet it leaves a thin layer of white dust on the slabs. How can I ensure this thin layer doesn't appear again?

Thanks

 

[Wayners]

White spirit on a rag.
That's how I clean tiles so it dries without dust.
Just try a small section first..

If you keep using water to wash you will get the white powder residue.

If you got any more to do wide masking along slabs. Don't get any trout on them