Is tilebacker board waterproof?

[xerxes]

I had a delivery of boards recently and included a couple of tilebacker boards for a job I'm doing soon. With one thing and another, the tilebacker had to wait outside while I did other things.

This morning I went out to cut them to size and found they were like wet sponges, weighed twice what they had on delivery and had all the strength of wet newspaper. I was able to cut one vertically using a Stanley knife. The second was a little drier and I scored it, then asked a passing builder on site to help me lift it onto a bench, carefully, so that I could finish cutting it. It fell in half, and not along the score line.

I often use cement-based building board (Viroc) and am used to being able to leave it out in the rain until I need it; offcuts left outside are usable after a year or two. How can a waterproof board disintegrate so easily? Why did I pay extra for it?

And do I stand any chance of fixing it flat to levelled battens? At the moment it's indoors in the dry, but horribly bowed.

 

[noseall]

'aqua board' is the product we tend to use.

it is not waterproof but that it does not break down when constantly subjected to water. unlike regular plasterboard.

for a product to become unstable when wet seems like a rather unsuitable product to use as a tile backer!

 

[gcol]

One thing for sure is that tile backer board is NOT waterproof in as much as it will soak up moisture, but will not turn to mush when it does. There's nothing to say that when it is waterlogged that the extra weight involved won't cause it to collapse under its own weight.
Personally, I wouldn't waste my time with tilebacker board. Plasterboard painted with a tanking (proper waterPROOFING) solution is bombproof. I'm getting fed up with saying this.

 

[xerxes]

Thanks for these replies. I guess I've learned an expensive lesson.