A Blindside Waterproofing Primer: Factors to consider when selecting the correct membrane

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Going onsite
All of this is great advice, but it is what occurs onsite that really matters. Waterproofing contractors require good instructions. Installation processes should be clear, easy to understand, systematic, and as simple as possible. ‘Think like a contractor,’ should, perhaps, be the mantra when it comes to product development.

For example, many designers will select material that comes on a wide roll thinking it will mean fewer seams, which are one of the areas of vulnerability on any job. However, wide rolls are hard to kick out as they are heavy and bulky. They get dragged around a lot because installers do not always work in pairs. They are slow to install, and contractors want to finish their work quickly.

There are other various site conditions to consider.

Skill of the installers
It used to be manufacturers required trained certified installers to work with their membrane. This is still true for some products, but many owners are recognizing the best training is done on the jobsite with the people who will actually be doing the work.

Often, the managers receive the training, not the actual workers that would benefit most from the instructions. This requires a manufacturer’s representative to do the training in situ. It is even better if that person is able to communicate well. Regular appearances at the site are the best approach—maybe not every day, but certainly at these critical junctions:

the day the work commences;
the first day the membrane is hung from the backup wall;
the day the detailing starts;
before the concrete is poured; and
during the pours.

One should meet with the representative and anyone else who will touch the foundation wall to iron this out ahead of time. Of course, a consultant can be hired to ‘babysit’ the job, this is not a bad idea if the contractors are unproven and the site is problematic.

Availability and price
There is huge variation in the costs of the different membranes when the variables of the installation are taken into account. One membrane may require expensive tapes; another may rely on preformed boots to cover anchors, while another may require cant strips at every plane change. Sometimes, the expense is worthwhile. Regardless, getting the full story, and finding out if the membrane is available for delivery when it is needed, is the best practice. Supply can sometimes be an issue.

This is a huge subject that requires its own article. Labor and materials coverage gets expensive fast because it means a full-time representative at the site and maybe even regular testing during the install. This is a sticky subject, but it may be better to invest time in good in-situ training rather than long warranties.

Mixing and matching different materials can be problematic and will likely void warranties. Some examples of mismatched products include:

vapor retarders with blindside membranes;
blindside membranes with conventional membranes; or
one manufacturer’s tape with another manufacturer’s transition strips.

There may also be compatibility issues with the pre-applied membrane and surrounding materials, such as the form release on the soil retention wall. Manufacturers should be able to assist.

Other special concerns
There are low-temperature formulations of some products. These will ensure the membrane is still pliable when temperatures fall below manufacturer’s installation recommendations. Similarly, most membranes contain plasticizers that may be compromised by ultraviolet (UV) exposure. One should check the data sheets to ensure the material will not be sitting in the sun for longer than recommended.

Unusual details require the manufacturer’s expertise, or even advice from a waterproofing consultant. The best manufacturer’s representatives will admit when they are unsure and ask for help from the higher-ups.

Finally, no concrete should be poured against a membrane that has not been carefully inspected. Once the concrete is poured, it is virtually impossible to go back and make repairs. Carpenters have a saying: ‘Measure twice, cut once.’ When it comes to blindside waterproofing, a similar maxim might be: ‘Inspect twice, and pour.’      

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