You can install the dimension stone as well with the underlayment.
Ceramic tile underlay adhesive.
Measure the width of the doorway and halve it.
You need fewer worries about the penetration or leaking of water in your home.
Then mark that distance out from the 3mm mark on your underlay.
Self adhesive tiles some types of resilient flooring including vinyl cork and linoleum tiles are available with self adhesive backing.
Lay the piece of cut underlay on the floor and make it flush to the doorway.
I should add this is not what i would call a hardwood floor quite soft and a bit squeaky.
Draw an arrow onto the underlay to show the direction you need to cut either left or right of the doorway.
Then mark 3mm in from the edge of the doorway.
Exterior plywood is an acceptable underlayment for tile and is preferred to interior grade plywoods because the bonding adhesives used are waterproof.
The mortar permanently binds the tiles to an underlayment which is in turn.
If water seeps through the tile installation to the underlayment it will not cause the wood to swell as happens with interior grade plywood.
The tile is then pressed into place without the requirement of any additional adhesive.
This schluter ditra 1 8 underlayment 323sqft is perfect for ceramic tile.
The key benefit of this underlayment is that this is waterproof.