If you have sealed the slate you will need to strip it first. I guess you have not sealed it yet so mix 50% vinegar with 50% water. If the water is hard use distilled water. Let it sit, but not dry out for 5 minues or so and then scrub with a nylon brush or a stiff bristle brush. It may take a few applications but it worked well for a friend who had the same trouble with an interior slate floor - by the way, hazy patches on the mortar is common so it's nothing you did wrong.
I have a flag patio and I just added 800 sq/ft. The real trick is to use a brush while the mortar is still fairly fresh (set but not cured) I assume you missed that chance. If this is really just a haze it will wear off pretty fast. Some muriatic acid mixed about 1:20 with water will speed up the process. You are probably going to be wire brushing or chipping out chunks. The edge of a small pointing trowel works pretty good. It won't chip the slate but it will dislodge the mortar chunks
I recently re-grouted (mortar joints) our 1950 slate patio. There are still some hazy patches of mortar on the slate. Is there anything other than scraping or wire brushing it off the slate? I know: should have been neater in the work? but I have this mess now. I have use muratic acid to clean cement before. Just wasn?t sure if there are new products for cleaning cement off slate?
Thanks TP
Yes there are other cleaning agents. Go to a tile supply store and ask for Miracle or Aqua Mix products.
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