We do a lot of repair work and recently we have had a large rash of calls regarding the waterproofing of exterior elevated patios with brick pavers/stone/tile.  I have seen several cases where the porch is framed out of pressure treated lumber.  A rubber membrane is applied over the plywood sheathing and overlaps perimiter flashing.  A mud bed is installed over the membrane and pavers on top of that.

This is where the problems begin.  First problem is that water is coming through the ceiling below (usually a T&G beadboard) and is rotting it out.  The water stains are only along the exterior edge.  At first I thought that the membrane was applied first and then the flashing was installed improperly and that was where the water was leaking.  After removing several of these patios, it seems the flashing usually appears to be installed correctly – maybe it is not sealed well.  Typically we pull back the membrane, install copper flashing so we can solder the joints then install a new membrane over the flashing and make sure it is sealed well.  Then the old membrane is lapped over the new membrane.  New mud bed, waterproofing and new pavers.  Does anyone else see this and do you have any better solutions?

Next problem:  Apparantly, when water penetrates the pavers and goes into the mudbed, when it comes out near the flashing is carries some salt deposits with it.  Huge stalagtites form around the perimeter and they drip all over everything below.  Very ugly.  Some say this is calcium carbonate (never heard of it).  I also have different engineers saying that it is efflouresence and others saying it is effervescence.  I’ve always believed the first was white powder coming our of bricks taking the lime out of the mortar.  The second I thought was the release of carbon dioxide like when you open a bottle of Coke.  Are these engineers using these terms incorrectly or have I missed something along the way?