Thinset Under Cement Board- Yes or No?

Using thinset under cement board is a commonly skipped step amongst many contractors.  We've heard of some contractors who have been installing for years and have never used a mortar under the backerboard arguing that if you use the correct screws and enough of them there is no need for it.     However, many manufacturers including, both Durock and Hardiebacker not only recommend that you use thinset under their backerboard, but they specify it and will void the warranty on their product if it's not used.  Proper installation would be to follow the manufacturers installation instructions for applying cement board to a subfloor.  Thinset is going to create a solid surface under tile and prevent flexing that could lead to cracking.  Using thinset between the backerboard and subfloor will create additional strength, fill in any potential gaps that exist and lessen the possibility of movement.   For less than $10/sheet, we highly recommend taking this extra step to insuring your floor will last and stay in warranty.   At Milford Ceramic Tile, we often run specials on backerboard and thinset, sign up for our mailing list to make sure you're taking advantage of these great deals!!

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