Waterstop for Elevator Pit in Dry Soil

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Author Message Liz O'Sullivan Senior Member Username: liz_osullivan Post Number: 160 Registered: 10-2011 Posted on Wednesday, October 01, 2014 - 04:24 pm:    Progress drawings indicate a bentonite waterstop at the elevator pit. My understanding is that bentonite and other hydrophilic type waterstops can be ineffective unless they stay wet. The soil is dry, and groundwater is deep - reportedly 75 feet deep. I'm thinking I should suggest a flexible rubber or PVC waterstop instead. Any thoughts? Dave Metzger Senior Member Username: davemetzger Post Number: 540 Registered: 07-2001 Posted on Wednesday, October 01, 2014 - 04:40 pm:    I think this is more of an issue for negative side bentonite waterproofing. Bentonite waterstops are completely encased with concrete, which will have some residual moisture. However, it's a good question, and if other 4specs contributors have contrary experience I'd be glad to learn differently. Nathan Woods, CSI, CCCA, LEED AP Senior Member Username: nwoods Post Number: 601 Registered: 08-2005 Posted on Wednesday, October 01, 2014 - 05:05 pm:    Put a camping tent down on dry soil, peel it up the next and the soil is wet underneath it. I've never had any issues putting Bentonite down against the soil and casting the elevator pits against them. This is cheaper than over-ex'ing the pit, board forming and casting the pit, then spraying it, then backfilling. ken hercenberg Senior Member Username: khercenberg Post Number: 829 Registered: 12-2006 Posted on Wednesday, October 01, 2014 - 07:01 pm:    Dave, I think you are correct. Liz, why not use a negative side product like crystalline? Used on hundreds of jobs with no problems. Lots of good products. I like Aquafin. Mark Gilligan SE, Senior Member Username: mark_gilligan Post Number: 686 Registered: 10-2007 Posted on Wednesday, October 01, 2014 - 10:26 pm:    Waterstops should be coordinated with the structural engineer on the project since there can be detailing issues. Rubber and PVC water stops can lead to local voids. I know of one contractor who does injection systems that likes them because they inevitably leak and require the use of his services. I would like more clarification on your claim that bentonite waterstops can be ineffective if not kept continually wet. If a dry waterstop is subject to moisture it will expand thus preventing the future flow of water. I would expect that elevator pits could accommodate some minor leakage with no problems. Liz O'Sullivan Senior Member Username: liz_osullivan Post Number: 161 Registered: 10-2011 Posted on Wednesday, October 01, 2014 - 10:37 pm:    Mark, very helpful, thanks. I had heard that bentonite can shrink if it dries out, and cause gaps that rapidly rushing water can get through before the bentonite has a chance to swell again, but you're right, the elevator pit could surely take minor leakage without any problems. The structural engineer struck through all waterstops in the draft spec I sent, and has none on the drawings. Architectural drawings call out a bentonite waterstop in the elevator pit. I wanted to make sure that was ok before I went back to structural to explain why I was putting waterstops in the spec. Richard Gonser AIA CSI CCCA SCIP Senior Member Username: rich_gonser Post Number: 79 Registered: 11-2008 Posted on Thursday, October 02, 2014 - 12:23 pm:    It doesn't appear that you're going to have any issue of hydrostatic pressure. Based on your description of a water being down 75 feet, the waterstop would appear to be irrelevant. FYI; I have seen the water table in my area change by 20-30 feet. So a quick discussion with the geotech might shed more light on your risk assessment. If all you have to deal with is vapor transmission, another very simple thought would be to use the under slab membrane as the liner against earth and under the footings. Question: Is the pit anywhere close to the exterior of the building where irrigation or other water sources could cause a issue? Sheldon Wolfe Senior Member Username: sheldon_wolfe Post Number: 794 Registered: 01-2003 Posted on Thursday, October 02, 2014 - 11:15 pm:    Bentonite expands when wet, shrinks when it dries. If exposed to water again, it will again expand. Unconfined bentonite probably won't work after it dries, which is why the at-grade details for waterproofing are important. As a waterstop, it's completely encased, so there should be no problem. Unless, of course, the contractor doesn't install it properly. I saw a project in which an entire line of bentonite waterstop blew the concrete apart because the waterstop was placed too close to the face of the wall. Chris Grimm, CSI, CCS, SCIP, LEED AP BD+C, MAI Senior Member Username: chris_grimm_ccs_scip Post Number: 279 Registered: 02-2014 Posted on Thursday, October 09, 2014 - 12:40 pm:    Regarding bentonite in general (waterstops may be different because of the excellent confinement), I often suggest for designers to read the limitations on the manufacturer's product data. That pretty much says it all, so I don't have to. I wonder how many of the successes with bentonite even where there are voids and it dries, are simply because they got lucky and it stayed dry, or was confined enough it didn't crack too much. Good points here about when the water table or some surface water event brings about changes. 20-30 feet, wow Rich I will have to remember this one! It comes down to the value of the contents of the building, the potential of damage, and the difficulty of access for repairs. Some owners will prefer the cost savings where there is minimal risk. With crystalline waterproofing, it may not respond well in joints and cracks. On a project I helped research a process of deeply routing out the joints and filling with dry pack between pit floors and walls (they had planned to waterproof integrally and do in one pour but they forgot the WP and did it in two pours for pit floors and then walls). It turned out to be an arduous process in such a cramped work space and they decided to use a tank liner product last I heard, which may have been workable in this case because they were sewer ejector pits so it was positive side WP actually here. Other issues I recall were that reinforcing had to be designed much closer for crystalline to work because the concrete must never crack; it was not designed nor installed with that spacing -- and the inlet and outlet pipes in this case needed special attention with sealants or they would leak at the pipe connections even if the waterproofing were perfect. Crystalline might work well if all those other factors were addressed or not present in the application.