Is it okay to have gaps in backer/hardie board when installing tile? I have a contractor replacing some tiles in my tub surround and there are empty spaces where the grout will be going after the tile sets. I'm worried the grout will crack because there is no backer/hardie board behind it.
Amanda, most companies that make ceramic tile backer board recommend that there be 1/8 inch gaps between the edges of each piece when installed. If your contractor has the gaps roughly that size, you should be in good shape. However, if the spaces are considerably larger, there could be a problem.
Also, James Hardie, the manufacturer of Hardie Board, states that the gaps should be filled with the same mortar being used to set the tile prior to any tile installation starting. Once the mortar has been placed between board edges, a 2 inch fiberglass tape should be installed over the gaps. I would think that other backer board manufacturers would recommend the same process to fill the spaces between the boards.
If your contractor doesn't follow this procedure, your concern about the tile grout cracking over the gaps is warranted. There is also a good chance that any problems you may have with the tile in the future wouldn't be warranted by the tile company or the backer board manufacturer.
A reputable tile contractor should know how to install backer board correctly, but if they have any questions, the procedure is outlined in detail on James Hardie's website