Blind Side Waterproofing

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Author Message Ruppert Rangel, AIA CCS Senior Member Username: rangel Post Number: 17 Registered: 08-2006 Posted on Tuesday, July 22, 2008 - 05:20 pm:    Does anyone have experience with Grace "Preprufe" waterproofing used below grade under concrete slab? This product seems to eliminate need for mudslab. William C. Pegues, FCSI, CCS Senior Member Username: wpegues Post Number: 734 Registered: 10-2002 Posted on Tuesday, July 22, 2008 - 10:06 pm:    Ruppert, Yes, a good amount of experience. I have one project that did a full vertical and under slab application and the building has been completed and occupied for close to a year now (office building with the project name "20 M Street" - the first project in DC to receive certification from USGBC for Gold LEED new building construction). Mostly here in DC the typical practice is to do only vertical waterproofing and use subsurface drainage and sump pumps. Strange, but, whatever. I have other projects which just did the vertical. Also, our office standard practice now is to use this at elevator pits (under pit bottom, vertical sides and out under the slab of the building 6 feet). Not a lot of product in that application, but, gets a really nice dry pit. Grace's technical group is typically very involved if you need them, we had one project where they assisted in detailing with the structural engineer for caisson construction and how the waterproofing worked. You are correct in that you don't need a mud slab. Unlike bentonite, you don't have to worry about the soil subsiding under the slab over time. The Preprufe forms a bond to the concrete. If you can manage to pull it apart, chunks of concrete will pull free still stuck to the membrane. This was also used on a building at Georgetown University where it was underslab and vertical on walls. I went on a site visit on that one with the Grace reps. So, got to see it going up. I think that building was completed 4 or 5 years ago. It is more forgiving to irregularities in the substrate. Sometimes you still have to prep the substrate to provide bearing behind it, but its just more forgiving. It will cost a bit more than standard bentonite. However, if you were to use the CETCO Ultra version of their bentonite systems the prices are very competitive. If there are other questions you want to ask here, no problem, or contact me by email wpegues@wdgarch.com William Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 285 Registered: 10-2003 Posted on Wednesday, July 23, 2008 - 11:44 am:    I had a similar situtation to William's on a project in lower Manahattan that went 3 stories below grade. We did a full underslab and blindside vertical with Preprufe. I concur with William's opinion of the Grace tech reps. I have discovered that here in California, because of the earthquake design requirements, we can't put the preprufe under the footings. William C. Pegues, FCSI, CCS Senior Member Username: wpegues Post Number: 737 Registered: 10-2002 Posted on Wednesday, July 23, 2008 - 11:47 am:    Richard, Just as a curiosity, what can you put under footings there? And, what is it about Preprufe that prohibits its use? Thanks! Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 67 Registered: 10-2007 Posted on Wednesday, July 23, 2008 - 12:09 pm:    I believe the concern about membranes under footings in earthquake regions has to do with the fact that the seismic forces are often transfered from the ground to the structure by means of friction between the footing and the earth. Membranes tend to have low coefficients of sliding friction. There are other ways to deal with the interface between the ground and the structure. Typically when a building is deep enough to need full waterproofing you can push against the soil, but this might result in some changes to the design of the foundation. Richard L Matteo, AIA, CSI, CCS Senior Member Username: rlmat Post Number: 286 Registered: 10-2003 Posted on Wednesday, July 23, 2008 - 12:33 pm:    William, I think Mark's reply answers your question pretty well. It has to do with the friction between the footings and the soil. We are not permitted to put any type of membrane between the footing and the soil, not just the Preprufe. Mark Gilligan SE, CSI Senior Member Username: mark_gilligan Post Number: 68 Registered: 10-2007 Posted on Wednesday, July 23, 2008 - 12:47 pm:    Richard The question is then how are you resolving your waterproofing issues? Do you have positive water pressure or is your concern related to concern about moisture in the ground? If the concern is about moisture then it may be reasonable to use Xypex in the footings and a membrane under the slabs. If you have to deal with water pressure have you looked at alternate structural systems that would allow the foundation to be wrapped with waterproofing? William C. Pegues, FCSI, CCS Senior Member Username: wpegues Post Number: 738 Registered: 10-2002 Posted on Wednesday, July 23, 2008 - 02:16 pm:    Mark's last post gets to the question I was going to expand to. Just what is done when you are below the water table dealing with hydrostatic pressure.