I’m getting ready to tile a bathroom with a Jacuzzi Tub. The tub has a plywood front and deck framed up and has 3 walls of regular drywall to ceiling (not green board). We are going to use 6x6 tiles about 24” up the walls and on front and deck of tub. 12x12 tiles on floor using modified thinset and Hardie Backer. After reading a few of these forums I believe all you pros and will use the modified thinset and not mastic for the 6x6’s. All right, here’s a couple of questions if anyone could help. I don’t believe I should tile directly to the plywood, use the Hardie Backer or what is the best backer to use around the tub and how to secure it to wood. How about the drywall, any kind of sealer or primer sufficient or should I install some kind of backer board. Last one, will a drywall screw work OK for securing the Hardie Backer to floor.

I don’t believe I should tile directly to the plywood, use the Hardie Backer or what is the best backer to use around the tub and how to secure it to wood.

Hardi or any other cement board could be used and it would still get installed with a bedding layer of thinset and then screwed down to the deck or on the tub shirt, remove the plywood and just use your preference of 1/2" cement board.

It's best to install the tub after the tile, but doesn't always work out that way. If the tub is already set and height to slide th tile under the tub deck is an issue, a membrane could be used over the plywood instead of cement board, either Noble's Nobleseal TS or Schluter's Kerdi. Either one is 1/16" thick or less installed and flashed up the walls around the tub would offer a waterproof seal so even if the caulk joint there should fail, water would never leak behind the tub. If you do have room for cbu on the tub deck, waterproofing it with a roll on membrane such as Redgard or Hydroban would also enable you to flash up the wall/deck intersection. Don't worry if the addition of all this stuff makes the framing higher than the specs for the tub framing as you can always add plywood to the subfloor under the tub to make up the height difference.

With Kerdi, you would install with modified to the tub deck and set the tile with unmodifed. With Nobleseal TS, you would install with modified to the tub deck and in stall the tile with modified. With Hardi, you use unmodified under it and set your tile with modified.

Same for the floor with Hardi, unmodifed under and modified to tape the joints and st your tile.


How about the drywall, any kind of sealer or primer sufficient or should I install some kind of backer board.

Industry standards consider the walls around a soaking tub with no shower head to be considered a dry area. You can give water protection with any of the measures I listed above, but no cbu is needed.



Last one, will a drywall screw work OK for securing the Hardie Backer to floor.

No, you need backer screws, with the Robertson #2 square drive. Sheetrock screws will not like the corrosive alkalinity of the thinset (cbu screws are coated) and the head diameter needs to be a minimum of 3/8". Also, sheetrock screws will break off pretty frequently as they cannot handle the torque needed to countersink into the cbu. Lastly, cbu screws with philips head will handle the torque you need to countersink into the hardi but you will probably snap the tip off the philips bits at a rate of about 1 tip every 7 or 8 screws.

Post back with any other questions you come up with.

Thanks Bljack
I'm liking the looks of the Hydroban, nice video on their web site. Removing front and replacing with 1/2" cement board is great idea and easy enough to do. Can't do much with the deck, will have to cut and fit cement board over the existing plywood. Any advise on filling the gaps I will have between the cement board and tub and how to seal it up?

Thanks again,
KC