Bentonite Foundation Waterproofing

The following are images, with accompanying explanation, taken during several site visits to a bentonite waterproofing installation. More background on this type of waterproofing can be found in the textbook, Chapter 2, Foundations, Waterproofing and Drainage, or on a manufacturer's web site.

[Click on images to enlarge.] The foundation is cast-in-place concrete. The geotechnical report indicates a high likelihood of groundwater around the foundation, especially during wetter times of the year. The interior of the basement includes fully finished spaces. Due to the severity of the groundwater conditions, and the sensitivity of the interior spaces, waterproofing and a drainage system are being provided both around the foundation walls and under the basement slab on grade. This article will look at the waterproofing applied to walls, with special attention to the treatment of penetrations in the wall.

In this view, one side of the concrete wall formwork has been erected. Steel reinforcing and form ties are in place, and a collection of PVC pipe sleeves have been installed. These sleeves will be cast into the wall. Later, utility lines of various types (water service, waste, gas, power, etc.) will be installed through the openings created by these sleeves.

The ends of the sleeves are taped off with duct tape to prevent concrete from leaking into the pipes during the pour. Around the middle of each pipe is a bentonite mastic waterstop. These will be cast into the concrete and create a waterproof seal between the concrete and the outside of the PVC pipe.

Here are the sleeves after the concrete has been poured and the forms stripped. Note the rough concrete edges around the outside of the PVC pipes. It's easy to imagine water seeping through this juncture if there wasn't a waterstop part-way in to stop it.

Here is another example of the use of the bentonite waterstop. On this project, waterstops are to be applied at all "cold" joints (where new concrete is cast directly against previously poured concrete) throughout the foundation work, to prevent leakage across these vulnerable locations. Note however that bentonite waterstops are not suitable for use at moving joints.

This view, from the inside of the foundation, shows a short length of utility pipe installed through the PVC sleeve. The outer sleeve can be seen, its face flush with the concrete wall. The inner pipe, which projects beyond the surface of the wall, is the actual utility service line (the continuation of the pipe will be installed later). In between is a mechanical gasket, which when tightened, forms a waterproof seal in the space between the sleeve and the utility pipe.

Here is another view of a partially installed utility line, this time taken from the outside of the foundation wall. Bentonite panels have been partially installed around the pipe penetration. Note the additional layers of waterproofing and mastic applied around this penetration to provide additional protection against leakage.

This image shows an interesting detail at the foot of the concrete wall where it meets the spread footing. Additional bentonite granules contained in a plastic "sausage" are inserted behind the panel. The plastic will dissolve when it first comes in contact with water, depositing a thick extra layer of bentonite at this vulnerable juncture.

This final images shows a section of wall with the waterproofing work almost complete--the top edge of the waterproofing is set to come within six inches or less of finished grade. Drainage panel installation is still in progress, with the upper half of waterproofing yet to be covered. In addition to relieving water pressure against the foundation wall, these panels will also provide physical protection to the waterproofing as the foundation is backfilled. Note the filter fabric facing on the drainage panels. This material prevents soil particles from being carried into and eventually clogging the panel. Note the fasteners used to attach the bentonite and drainage panels to the wall. These powder-actuated fasteners penetrate through both panels into the concrete. When the bentonite first gets wet and swells, it will form a tight seal around these penetrations. Also partially visible at the bottom right of this photo is the trench along the sides of the spread footing, ready to receive perimeter footing drains.
(c) Joe Iano 2003