Yes, tile on painted brick is probably a loser. Suggest you take a power sander with about 36 grit to it to cut off some of the paint and level roughness. Then set 1/2″ Hardibacker in place with latex modified thinset and Tapcon screws into the mortar, particularly around the edges. Normally James Hardie recommends screws every 8″ each direction. Make a point of getting the Hardibacker on flat; check with a straightedge.

Ditra is not used much here and I don’t understand the reason for using it anywhere. My favorite tile store lady said dit-what? when I asked her about it, and she has been in the business for many years.

Size of the tile is your call. People are leaning toward larger tiles these days.

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