Second apply a very thin coat of thin set mortar filling in the current grout lines.
Tile over tile thinset.
Or larger and even more important when you re tiling over tile.
You can put new thinset on top of old but only if.
Thinset with large amounts of latex added are used with glass tiles which are unable to flex on their own.
This could lead to difficulty getting the new tiles level and fully supported by the new thinset.
Epoxy tile adhesive may bond with almost anything and requires special solvents to remove.
If this is not a good idea i can just pack the thinset thicker in that corner at the time that i lay the tile.
Without a somewhat smooth surface it will be difficult to properly trowel out new thinset.
You can tile over exiting tile with latex modified thinset mortar but the bond might not be as sound as.
You can add extra thinset under your new tiles if needed to ensure they re level.
Others prefer to use a larger notched trowel 1 2 x 1 2 in to apply the thin set.
The modified mortar creates a stronger bond between the surfaces.
If the substrate and thinset is solid then you can go over the top with new.
Complete adhesive coverage is critical on large tiles 12 in.
As you re installing your tiles use a level to make sure the new floor remains even.
Ideally tile should be installed directly on top of a surface like cement backerboard which is stable.
So in short you can tile over tile as long as you re working on a fairly sound surface.
How to install tile over old thinset grind it down.
The big issue is going to be the smoothness.
The surface of the existing tile should be free of mold and mildew completely level including grout and.
Then i will mud with thinset and lay tile.
Working in small sections spread the thinset over the existing tile using a notched trowel.
Thinset with small amounts of latex added are primarily used for large format tiles and stone tiles to help absorb flex from floors and walls.
Tile needs a smooth level surface to be installed on.
This is a bonding mortar with either a latex or polymer additive.
However it may be worth noting that you may need to wait a little longer between laying the tile and grouting to allow the thin set to properly cure.
Some installers prefer to flatback each tile with the flat edge of the trowel before applying the tile to the combed thin set.
Position your tiles according to the layout you choose.
When laying tile over tile it is best to use a modified thin set.
If all your talking about is 3 16 then thinset is a good solution.
First clean and then sand the surface of the old tile until it feels rough.