I should mention, there was no waterproof barrier put up between studs and cement hardi board. Should there have been??? Will it be a problem without having a barrier between the two, or should coating the hardi board before tiling help any with water getting behind the tile as asked in my original post?

If there's no vapor barrier behind, then there needs to be a waterproofing membrane rolled on the face of it.

Thanks Bill....that's what I figured.

Bill, what is your best recommended product to coat the hardi backer board before tiling?

My husband insists it doesn't need to be waterproofed. He said he installed the cement board according to instructions and nothing said to put up a protective membrane before hanging it (first mistake, in my opinion), but I just learned this. So, I need to convince him that it needs to be waterproofed on the outter side before installing the tile. He can be a stubborn man, but if I show him enough proof from contractors, I can win this one, and save a ton of "potential" headaches later.

Thanks again. Your help is always appreciated.

"He said he installed the cement board according to instructions and nothing said to put up a protective membrane before hanging it..."

Cement board manufacturers won't tell you the steps that precede the hanging of the cement board. Nor will they tell you how to tile over it, or what color grout to use. They'll just tell you how to hang their product. It's all about the liability.

It's up to the installer to know the steps that occur before and after, because with construction varying due to regional code restrictions, etc, often times there's not a "one size fits all solution" for a lot of these construction materials.

No need, if he really doesn't want to. He can instead replace the tile, cement board, studs, and even plywood under the tub in a few years if he'd rather. All it takes is a product like Hydroban from Lowes or Redgard from Home Depot, and a paint roller to coat the cement board, and it's done. No muss, no fuss. That he's debating this is, as the old saying goes, a penny wise, and a pound foolish.

Okay, so maybe I'm beating a dead horse here, but I didn't mention earlier that these words are printed on the Hardibacker board:

Hardibacker 1/2" Wet Area Cement Board
Superior Moisture and Mold Protection

Does that make a different, or still better to apply a waterproofing membrane such as Redgard or the like, before tiling?

Thanks.

Bumping this 'cause it stayed on page two after my last post.

I'm very familiar with Hardibacker's properties. Personally I can't stand using it, but that's beside the point. Waterproof it. End of story.

debi, here's the thing:

True cement board is made of non-organic "ingredients". Nothing cellulose-based, like the paper facing on gypsum board.

Cement board will not degrade when undergoing long periods of water saturation. It will not degrade after repeated wetting and drying cycles like the gypsum core in gypsum board.

So does cement board itself have moisture protection and mold resistance? Yes. Because there's nothing organic in it to feed mold, and there's nothing in it that will degrade from water exposure.

But you'll note that it does not say cement board is waterproof. It's not. Water can wick right through it. And what's on the other side of the cement board? Your house's wood framing.

Again, you'll find manufacturers telling you about their specific product, but they can't say how their product will interact with or protect materials attached to it.

So cement board is essentially not affected by moisture.

Your house's wood framing will be affected by moisture.

Insulation can be affected by moisture.

So you have to decide how to prevent moisture generated by your shower from reaching the wood framing or any insulation within the framing bays. Obviously the tile and grout will shed most of the water. But that's why a barrier of some sort needs to be included before residual moisture and moisture vapor driven through the assemble can reach the wood framing.

There are a lot of people who build incorrectly. Some through ignorance, some through apathy.

Two dollars worth of 6-mil plastic could have solved this before the cement board was installed. You can unscrew the cement board, hang the poly and reinstall the cement board. Or leave the cement board up, mesh tape and mud the seams, then use a topical membrane to waterproof the CBU.

Based on the path this thread has taken, I'll toss this out. When you tile, don't use mastic. Don't use any premixed comes-in-a-tub type of adhesive.

Do you have to use mesh tape, if you use a waterproof membrane? The waterproof seals the seems and its stretchable if there is any movement.

Tape and thinset is required at all joints.