bathroom subfloor:hardy board & joist reinforcement

[yule1111]

2 questions:

a) hardy boards are better than durock which is a better replacement for plywood? any disadvantages to hardy boards as the subfloor material?

b) marble floor tiles will be used; supposedly joists need to be reinforced; what is the best way to do that? any neat pictures/websites to demo the reinforcement setup?

Thanks in advance.
Yule

[HJ1]

Yule

Neither hardi nor durock is a replacement for plywood. Cement boards do not add to the structural strength of the floor like plywood does. Cement board's function is to be a good bonding surface for the thinset and tile. You need two layers of plywood and then either hardi or durock. All natural stone installations require two layers of plywood totalling at least 1 1/8" thick, more is always better. Both hardi and durock will work fine after you have enough plywood.

Your joist structure probably is inadequate for a natural stone installation but you need to check. You need to meet deflection of L720. Tell us what you have now. What is the on center spacing of your floor joists, what size are they and what is the unsupported span along the length of the joists? How thick is the plywood, and is it square edge or t&g?

[Bud Cline]

yule1111: "a) hardy boards are better than durock which is a better replacement for plywood? any disadvantages to hardy boards as the subfloor material?"

yule1111, just for the record HardiBacker IS NOT NECESSARILY better than Durock, I don't know where you got that information. It is simply a matter of choice for various reasons but in truth they both perform the same.

NEITHER is it a replacemnt for plywood. They are two entirely different products with entirely different functions.

HardiBacker CAN NOT be used as a subfloor material, never. Hardi is an underlayment material for ceramic tile and stone but can not be used as a subfloor material.

[72chevy4x4]

Is this a DIY question?

[Floordude]

Originally Posted by 72chevy4x4

Is this a DIY question?

It says he is "General" by his title. He definiely isn't a flooring contractor. Maybe he is a painter? DIY his own home... Wait, isn't that the same as a DIY'er??