RE:waterstoppers in concrete

I have to disagree slightly with Mark on this one. My first option would be ribbed PVC waterstops. With proper detailing, the waterstop does not interfere with the reinforcing. Typically, we use between 3 to 3.5 inches of clear concrete cover for the top steel in the slab. With a 6 inch water stop, this lets the reinf clear the waterstop. I would also recommend the use of shop made fittings for T, L, and X type joints so that only simple butt joints need to made in the field.

Rubber waterstops are much less common, but are available. I believe that the joints are glued rather than welded, but I don't really know.

I'm not a big fan of bentonite strips, but I have often used the hydrophilic rubber strips. There seems to be a war in the swelling strip waterstop arena between the bentonite camp and the rubber camp. I've had reps from both sides tell me that the other does not handle repeated wetting and drying. In fact, I've got an experiment going on my desk right now where I'm testing a hydrophilic rubber waterstop for repeated wetting and drying.

I'll agree with Mark that any waterstop will not work at a crack that isn't at a joint. This gets back to proper detailing and joint spacing. I'll also second the use of Xypex.

--Kipp Martin
Carollo Engineers
Portland, Oregon

>>> Mark Gilligan <m_k_gilligan@yahoo.com> 7/11/2007 10:38 PM >>>
I am not a fan of rubber waterstops. I prefer
creating a good construction joint where the new
concrete bonds to the existing with reinforcement to
keep any cracks small. To this you should apply an
exterior membrane that can bridge the small cracks.
Consider also xypex as an admixture in the concrete to
help seal the cracks.

Since concrete cracks do not always occur at the
construction joints we need a solution that also deals
with the random cracks. Waterstops do not satisfy
this criteria.

Waterstops get in the way of the reinforcing steel and
make it hard to get good consolidation. This is
doubly so if the waterstop is placed in a key. I
believe that this makes the concrete even more porous.

The bentonite strips placed in the construction joint
seem to work and can be accomodated by the concrete.

The one application that I have found where I think
rubber waterstops are appropriate is where the
concrete structures on both sides will move
independently up to an inch or possibly more and where
the inevitable leaking can be drained away on the
inside. One example of this is the joints between
segments in a subway tunnel.

Mark Gilligan

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