Greetings MAXJR758 and welcome to the community.
Remodeling a 1950s house? I’m sure you are finding some interesting things
Being that you havn’t specified what type of tile you are putting down I’m going to assume that you are refering to the ceramic tile.
To prep for the ceramic tile you would need to measure a deflection of the floor first and at the end of this post I’m going to attach a link to one of mine previous posts that explains in detail how to do so.
Once you measure deflection of the floor you can proceed with a recommended sheathing and prep for the tile underlayment.
Recommended sheathing (plywood) can be anywhere from 1/4" to 3/4" and it needs to be glued and nailed down over your existing pine decking.
From this point with plywood nailed down you will have two options to proceed with:
First option would be to use cement board underlayment.
Cement board underlayment or (CBU) comes in three different thicknesses 1/4", 1/2" or 5/8" of the inch and you can use any of these to bring your floor up to the desired height.
Why do you need a cement board underlayment?
Basically CBU is the sheet of underlayment with an exposed aggregate that serves
as the adhesion material for the tile ceramic tile thinset.
Cement board and Hardie do not significantly help with a structural performance of the floor and it need to have a firm surface to be installed on.
That’s why deflection need to be measured like mentioned at the beginning of this post.
You second option would be to use Ditra underlayment instead of CBU.
Please refer to this LINK for additional info and installation instruction on Ditra and CBU.
Hope this helps and keep us updated.
George
