The culprit is lime scale a chalky mineral left behind when the tiles are exposed to hard water.
White residue on slate tiles.
The answer you say you have not sealed the floor yet so by the sounds of it you could still be wiping off the cutting dust residue on the surface of the slate tiles.
But after it dries the white is back.
When you wipe the tile to remove the leftover grout you must rinse your sponge often.
Your suggestions are deeply appreciated.
First take a close look.
If not you re just spreading the grout residue onto new tiles.
Even spilled paint and other residues can be removed using a natural process.
If your slate is looking a little worse for wear do not be alarmed.
White residue on the stone ruins its appearance.
When the tile is wet it looks fine.
There is also a white discoloration in the grout.
This section is also weaker and is beginning to crumble.
You can t see this when the tile is wet but.
Within two day we noticed white picture framing and white discoloration on many tiles.
With the exception of where we mostly stand under the shower head the tiles all have a white chalky coating on them.
I have a slate tile patio on the back of my house.
It has been about a week and the white areas are continuing to grow as does the number of tiles affected.
If the substance can be scraped into shavings it may be an accumulation of cosmetics soaps cleaning products or hard water build up.
The minerals in the water crystalise which results in white residue appearing on the surface of tiles.
I ve tried a multitude of products to clean it off but nothing works.
If it is powdery then it is likely efflorescence.
White residue stains on tiles known as efflorescence white stains appearing on the surface of tiles is caused by water penetration underneath stone or tiles.
These stains usually white but sometimes brown or black can be removed without too much time or trouble.
When done correctly removing scale from the often.
One of the tiles has formed a chalky white section.