flooring
We removed a wall to make a kitchen bigger – to use as an eating area.
The kitchen has vinyl flooring, which we are now changing to porcelain tiles.
The way it is now, there is about 1/2 inch rise on the kitchen side.
How can we cover the space where the wall was, so that the floors will be mostly level?
If it's not visible, just got for a manufactured board, e.g. plywood, OSB, etc. For 3cm, you may be looking at two pieces stacked on top of each other. If it's on concrete, install a moisture barrier first. To secure the boards, I'd avoid the temptation to use a Ramset and permanently drive the names into the cement, since the next time the flooring is redone, you can take the opportunity to do it right and pull everything up and go wall to wall. Instead, secure it with a few cut nails. Again, this all assumes that none of this is visible.
(source: jmnails.com)
I'd question how waterproof you need this to be. Will there routinely be water sitting on the floor? If not, you may be over-engineering things.
That said, off the top of my head, one option for waterproofing the subfloor would be to paint on Redgard:
It's a 'paint on' waterproofing membrane that you'd typically use behind tiles on cement board and the like.
Best Answer
My carpenter's solution was simply to bridge the gap with a threshold, with its underside cut differentially to compensate for the difference. Having a clearly raised area between the two, with slopes on either side, is less likely to be a trip hazard than a smaller but sharper transition.