Laying outdoor vitrified porcelain tiles - Porcelain tile question

[0898andy]

I have an old outdoor patio with tiles laid on mortar beds on top of a 6 inch concrete pad. I want to replace the old concrete tiles with vitrified porcelain tiles I've purchased. Can I remove the old tiles and tidy the concrete dabs/pads down to the original concrete pad and lay the porcelain onto the concrete pad ? or do I need to removed the concrete pad and lay new substrate ? The pad is sound and solid it just has marks from the old dabs of mortar from the original tiles. This is the North UK.

[dig dug dan]

Sounds like you will have an ideal base to lay onto there. As long as you can bet enough fall assuming the base is level?

[Tony McC]

You need to consider the levels: would overlaying the existing raise the poaving to less than 150mm below DPC?

[0898andy]

Cheers for the replies.

The slab is 150 below DPC and level , the old flags were above this by maybe 40-50mm and sloped away from the house. So I'd be replacing to a similar height and fall. Had no issues with the old pavers and damp.

Am I correct in saying I can use a normal mortar bed 15-30mm and bond the back of each porcelain tile with a slurry bonding type product ? The reason I ask is I'm wondering if I should use a glue type product onto concrete base ?

Cheers
Andy

[dig dug dan]

From memory, and tonymc may well correct me as I dont bet involved in this stuff much, but you almost lay it on a tile adhesive as if you were doing a kitchen floor, assuming the concrete base is flat. You then wont come to as high as you were before against your damp

[Tony McC]

Yeah - you'd be better off with an outdoor grade tile adhesive.

Build-up levels, if necessary, with a mortar screed (6:1) but the tile adhesive gives much better results.