Re: floor prep for porcelain tile over hydronic heat
Aside from the proper base to apply the tiles the floor structure is just as much or more important.
Many existing floor structures are rarely built for tiles. In many cases they were designed for the minimum standards with considerations only for sheet goods or carpeting or maybe hardwood for the finish surface.
The current thing with new homes is if there are to be tiled floors the floor structure is modified at the time of construction.
The main consideration for tiled floors is the flex or bounce the floor structure has. If there is too much then there is an increased likelyhood of the tiles or grout cracking ----- in which case stiffening the structure maybe in order. This could range from doubling the existing floor joists , adding extra joists between existing , increased blocking.
Another good method , especially with in floor radiant heat , is to use an uncoupling membrane laid on the subfloor first then the tile is adheared to the memebrane. This membrane is designed to provide a movement barrier ( uncoupling ) between the subfloor and the tile.
Ditra by Schulter works very well.
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