Water and grout, how does it work?

[wedge69]

Just a question of curiosity. I understand that most grout is not waterproof, only water resistent.

So when you are taking a shower for example, what happens? Does the grout absorb water until it is saturated, and then the water gets through to the substrate behind, or once the grout is wet, is the water somehow kept on the surface?

I understand that it is advisable to get the shower area tanked or whatever, but there must be thousands of houses out there that have a shower area that isnt tanked. I for one have no idea what is behind my tiles!

 

[joe-90]

The principle is the same as why cement is waterproof. The water molecule is very large and the matrix bond of grout/cement is very small. This helps prevent the ingress of water but there may be fractures or cracks that the water can enter by.

Most walls aren't tanked.

 

[wedge69]

Ah, ok. That seems like a reasonable enough explaination to me! Thanks.

 

[bathstyle]

The only truly waterproof grout is Epoxy resin but due to human error (in particlar on mosaics) it is very easily to miss out sections.

Also (as mentioned) , grout can crack, so can silicone, this is why we tank.

I always recommend tanking 1m up from the tray/bath, this tends to cost about £25 so worth the extra money for peace of mind.