tiling over new drywal mud

Hi,

two questions.
first, I'm installing a new backsplash in my kitchen and one wall I had to redo but to get it straight I had to mud it as you would to finish a wall before painting...so maybe half of the wall to be tiled is joint compound and the other the paper face of the drywall. I will be tiling subway tiles (3by6) and using mastic for the install . before proceeding I would need to prime that wall correct? because of the paperless mud I applied to make the wall flat

secondly, there's a section of wall that has tile now that I will remove. if I can pop the tiles off and scrape the big chunks of mortar off and then "sand" off the remaining ridges can I go over that surface as is with the mastic?

only photo I have of the wall is this one right now (don't mind those cut outs ). The white part on left is fresh compound and the beige stuff on the right the original paper face of the drywall



thanks

 

Best to put on a coat or two of primer, if you ever removed you will be thankful.

Old tile that is removed, if clean surface and not too big of chunks then ok to fill with thin set.

Notice I mentioned thin set, don't use mastic, it's an inferior product, messy, does not grab instantly and in general a PITA.

Seems like everybody thinks it is easier, it's just glue, but just the opposite. I don't recommend pre mixed thin set but I'd go with pre-mixed thin set over mastic.

 

Raw joint compound is powdery, giving it a coat will seal it and give you a better bond with your tile. Use thinset from a powder and not mastic. If your backsplash is near a stove/range the heat or steam from boiling water could cause it to soften again.

 

ok, fair enough, thins set it is!
now, should that be modified thin set or un modified??

 

Unless the tile manufacture states otherwise (which I recall only seeing once) then modified is the norm.

 

thanks Marq1

what's the big difference between the two? there seems to be lots of debate around it, in particular when used with waterproofing membranes such as Ditra (which I'm not using).

 

basically modified is made to adhere to a wide range of products while unmodified is for concrete or mortar beds. as far as ditra, the unmodified between ditra and tile cures faster and more complete, sometimes the laytex or polymers will bleed thru into the grout. now there are special mortars or thinsets especially for ditra and kerdi membranes. lots depend on the tile too..wether porcelain or stone, etc.