My foundation is poured concrete and was given the usual cursory damp proofing spray after its construction. However, I insisted that to avoid leaking problems once and for all, that a dimpled plastic waterproofing membrane be applied to the outside of the foundation prior to back filling.
As I understand it (now), there are two types of membrane. The first is a dimpled membrane that is applied with the dimples facing the concrete; this allows any moisture that gets behind the membrane to condense on the plastic and then drain down through the air space to the perforated perimeter drain. The second type has a geotextile sheet bonded to the dimples; this membrane is applied to the foundation with the dimples facing outward, the idea being that soil particles will be filtered out of any groundwater before the water hits the smooth side of the plastic membrane and then finds its way down to the drain tile. My understanding of the difference between the way these two membranes work is good now, but comes a little late. My contractor hadn't used this sort of product before and purchased a roll of membrane with the geotextile attached. He took a guess at how it should be applied ....and installed the dimples against the concrete with the geotextile sandwiched between the plastic and the wall. The foundation is built into a substantial slope and was backfilled for the most part with clean, small rock rather than "fill". The upper side of the foundation (built into the hillside) is about 7 or 8 feet high/deep and this is the section where the membrane was applied. After a year in place I've had no leaking or dampness issues, but I'm just wondering whether to be concerned about the waterproofing membrane having been put on the wrong way around. I assume the textile material being between the foundation and the plastic membrane could potentially block the passage of any moisture travelling between the plastic and the foundation. It would be a massive job to re-excavate and re-apply the membrane as would all have to be done with hand digging.
On a related topic....behind the uphill side of the foundation is a 7 foot masonary (stone) retaining wall, separated from the house by a about a 6 foot space. The retaining wall was built against a fractured rock face after blasting was completed. There were weep holes put at the base of the wall but I don't see evidence of any water coming out of these. However, there is considerable efflorescence evident around many of the mortar joints between the rocks, suggesting that moisture is finding its way through. Is this a concern? I have read that lime leaching out will lead to mortar/wall failure, but I've also been told that the white leachate on a retaining wall is just a "cosmetic" issue.
Seeking "peace of mind" before I actually get to move in to the new house next month ... thanks for all advice.
Posts: 8 | Location: Vancouver Island, British Columbia | Registered: 17 April 2007
whats more important than the membrane is what, and much asphalt etc is directly-applied to walls. It is this mastic that keeps water/moisture out.we backfill w/all gravel,by hand, so 6 mil visqueen is what we (30 yrs)some others have used/applied over the mastic to protect it as we backfill, zero problems.(if waterproofing existing crack,hydraulic cement before applying asphalt & visqueen is best)
dimpled membranes etc can be used when backfilling w/equipment. dimpled membranes can-do allow water BETWEEN the membrane and the damproofing/wall.Visqueen will STICK to mastic/asphalt if applied correctly.If/when cracks occur or with poorly packed rod holes,loose-thinly applied parging(block walls)or thin damproofing breaks down...leaks follow.
apparently they backfilled w/mostly 'small rocks' as you say, much better than backfilling w/crap soil....this will help take the water quickly down to tiles rather than, when backfilled w/clay etc, water building up in clay and taking forever to get down to tiles as clay expands against wall(s)....lateral-soil-pressure. Good thought there on not backfilling w/crap.
Down the road,long as no cracks occur...long as rod holes were packed correctly and the thin damproofing holds up(some deteriorates pretty quick)you should be ok.
If a crack does occur, say a vertical crack in one area of 1 wall, just re-dig this area and waterproof it,the crack. We`ve done it on new homes,no problem. Yes sure, lil bit of pain but done right.
Per retaining wall(s), have seen many...seen some never have problem,seen others bow in, crack(s) occur etc.Seen some w/weeps and some without.Some will crack,bow regardless of any weeps, just like a basement wall can.
http://www.e-o-f.com/foundation.html#WATERPROOFING_PART scroll down to.. 'the waterproofing part'...past the 2 photos 1) 100% ADHESION...gotta stick to wall, NOT merely sit in front of/agst walls...there is a BIG difference. Waterproofing the walls, protecting the mastic w/visqueen etc when backfilling and using gravel to backfill, all works together to help keep water out,off walls.
...in depth investigation into the water penetration problems....multiple wall deficiences were observed, all primarily the result of poor-workmanship
..partially filled collar joints, poorly consolidated collar joint.Removed brick units revealed a completely omitted collar joint...
...the effects of improperly constructed collar joints were two-fold. First, structural integrity of the walls was compromised...Second, compromise of WATER RESISTANCE...the omission resulted in unimpeded water migration into the joint...
-Facial Separation Cracks.. most frequently caused by inadequate tooling of mortar joints during construction....
-Brick Unit Cracking.. cracks of the type evident at the building are typically caused by water penetartion and subsequent freezing and thawing....etc
