Shower grout cracking - could be hot water tank?

[Jack Sprat]

Hi

We have a shower that was fitted and tiled about 2 years ago. There are 2 tiled walls, one wall is perfect but the grout on the other wall is cracking really badly and needs to be gouged out and replaced. I noticed that the hot water tank is behind the wall where the grout has cracked, would that be the problem, that the heat from the tank has dried it out? If so, what should I do now? Can I just add some PVA glue to the grout mix before re-grouting or should I introduce a heat baffle / shield somewhere? I'm a novice DIYer and inherited this problem.

Thanks

[BigWallop]

If the water tank is tight against the wall, then just clean out the old grout and redo it all. If you have any room to slide a piece of plasterboard down between the wall and the tank, then it won't hurt to give a bit more protection so the grout isn't damaged again.

But it might not be the heat from the water tank that's causing the problem. If you can check that all the seals around the shower unit are water tight and are not allowing dampness to creep up the wall and making it swell, it might help toward a permanent cure.

[The Natural Philosopher]

I suspect that what is happening here, is that woodwork in the vicinity of the tank has shrunk to a rather lower average humidity than when it was constructed. My house is full of stuff like this: essentially wait till the wood stabilises, and then make good, is the rule.

Provided that wood is ALWAYS exposed to a hot tank, it will simply take up its new dimensions and stay there with little or no change henceforward.

Building timber is usually stored at best in unheated warehouses, and at worst outside in the rain, before being used: the impact of a centrally heated house nearly always causes it to change a bit over he first few months after being built. You may expect about 1% across the grain and about 0.1% along it, shrinkage. In respect of a 2 meter high stud wall, thats 2mm shrinkage. Enough to open up cracks and gaps.

If the wall is blockwork, well that's a different story. Block plaster and tiles and grout are all similar in thermal expansion. so its odd.

[Phil L]

If the tank is in close proximity to the wall, you need to insert some insulation, either polystrene sheet or a tank jacket between the tank and the wall - this should help WRT expansion and contraction.

As far as replacing the grout is concerned, I fear it may already be too late - if the water has got behind the tiles, then the plasterboard will be well on it's way to falling apart....unless it's the rock hard aquapanel, or better still brick/block.

Can you see from the tank side what kind of board has the tiles stuck to it, or is it a solid wall?

[The Natural Philosopher]

Experience says bollocks. plaster can take a good wetting. Its long term soaking that fsk's it.

[Phil L]

And wouldn't being trapped behind tiles in a shower cubicle, and subject to daily drenchings be classed as 'long term soaking'?

[The Natural Philosopher]

No. it tends to go in slowly and dry out as fast as it goes in.

The only place I got degradation was where a pipe came through a tiled plasterboard wall, and the seal wasn't good around it. water dripped down and collected at the bottom of the stud wall and blew the plaster on the OTHER SIDE. It may have done it on te same side as well, but thats all covered by a bath, so I cant see.

I hacked that out and re plastered it. No more problems.