View Full Version : Slab top-side vapor control — Airspace approach
02-24-2012, 09:40 PM
Read the "READ THIS BEFORE YOU DESIGN,BUILD OR RENOVATE (http://www.buildingscience.com/documents/guides-and-manuals/gm-read-this-before-you-design-build-renovate/view?topic=doctypes/guides-and-manuals)" doc and found above recommendation on page 13 or 19, Or view it here (click me) (http://freepdfhosting.com/f189e71033.pdf). Many of you here, including Dana, seems like "poly + foam + plywood" approach for basement floor. Above approach is "dimpled + foam + plywood".
The dimpled is more expensive than poly. is it worth to spend several hundreds more?
I haven't seen any good science that would indicate a need for dimpled membrane rather than 10-mil poly as a capillary break when retrofitting a slab. The wicking potential of either poly or XPS is extremely small, and no-wicking/drying toward the basement==no mineral depletion of the concrete. The slab itself doesn't "need to dry", and encouraging moisture migration through the slab only degrades it. The additional benefit of having an air-space between the extremely low-permeance non-wicking poly sheeting and the concrete is academic.
Dimpled membranes may be useful under ceramic or wood flooring with NO foam with damp slab, where a rip in a poly sheet might allow some wicking of moisture into the ceramic, staining it. But with an inch of (no-wicking low-permeance) XPS that's not a likely scenario.
If the water table is occasionally high and you regularly get wet spots or efflorescence on the slab, use a concrete sealer on it before the poly + foam.
02-28-2012, 05:20 AM
Do I need to leveling the floor before put poly+ foam?
If you were planning to use a cement based floor leveler it'll bond better and have fewer cracking issues if you apply it to the slab, and not on top of the foam.