QUESTION

We are currently pouring concrete for a patio with retaining walls that is being finished with Bluestone tile. My question is, will using Xypex in the concrete help or hinder in regards to preventing Efflorescence?.

ANSWER

Xypex is suppose to waterproof the concrete.  So in theory it should prevent moisture migration in the concrete wall to help reduce the possibility of efflorescence.  You can still get efflorescence from the mortar or thin-set or grout or from the stone itself.

Efflorescence is typically a white stain that precipitates on the tile surface or on the grout joint surface.   Minerals in the concrete, mortars, or stone will dissolve in the moisture; like a salt.  As the moisture migrates to the surface it evaporates that then precipitates the minerals.

Beware that Xpex can act as a bond breaker and interfere with the bonding of the blue stone to the concrete surface.  Xpex requires that the concrete surface be scarified in one way or another so the tile can adequate bond to the concrete.

If the concrete isn't treated with Xpex, we normally apply a waterproof/crack isolation liquid applied membrane that meets ANSI A118.10 and A118.12 designed for this application over the concrete or over the mortar bed if you are floating over the wall to adjust it to be plumb.  This then gives you both a waterproof surface and a crack isolation surface.