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Posted by Michael Bulatovich on April 17, 2007, 6:14 pm
>> I'm looking for advice on using dimpled membrane products (e.g.
>> Superseal, Delta-MS, etc.) for waterproofing a block basement wall
>> (this is new construction). My foundation contractor thinks it sounds
>> like a good idea, but he insists that I should use it in conjunction
>> with asphalt/6-mil poly applied to the wall so that any water which
>> does manage to get in around the dimpled membrane still won't
>> penetrate the wall. Intuitively, I agree with him that "more is
>> better" when it comes to waterproofing, but I also know that any water
>> that does get into the wall (and inevitably it will) needs a way to
>> escape. If I apply a waterproofing barrier directly to the outside of
>> the wall, that leaves only the inside of the wall for moisture to
>> escape, which, in turn, limits what I can do in the future in terms of
>> insulation/vapor barrier installation. Obviously there are ways to
>> accomodate "breathability" of the interior of the foundation wall, but
>> it seems to me that a breathable exterior is one of the great
>> advantages of using a dimpled membrane.
>>
>> Does anybody here have any direct experience with these products? Are
>> they good enough that I can forego additional waterproofing? For what
>> it's worth, none of the manufacturers' sites recommend anything
>> additional under the dimpled membrane. Then again, they also don't
>> specifically recommend against it.
>>
>> Thoughts?
>>
>> Thanks,
>> Josh
>
> I have used a dimple membrane in conjuction with a peel and stick type
> membrane. My understanding of the dimple membrane is that it doesn't
> actually keep water out, it only provides a drainage plane, in effect
> reducing or eliminating hydrostatic pressure against the foundation.
Exactly right. The water's supposed to run down the inside face of the mat
to the weepers.
> The same thing can be accomplished by backfilling with sand. In order
> to provide drying to the outside, wouldn't the top of the dimple
> membrane have to be vented? Not sure how you would accomplish this
> without having a gap that would eventually fill with dirt/derbris.
Nobody dries the outside of a foundation.
> The type I used (system platon) came with a tapered stip which
> effectively sealed the top of the membrane, so drying to the outside
> would be very limited. I'd side with your foundation contractor and
> use something to dampproof behind the dimple membrane.
Absolutely, except that in certain circumstances waterproofing might be in
order instead. Any water that gets past the membrane will do whatever water
would do if there was no drainage mat: evaporate or leak. You should check
your local building code as I would be surprised if the installation of a
drainage mat exempts you from having to at least dampproof a foundation
wall.
--
MichaelB
www.michaelbulatovich.ca
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