Βasements/Foundations Waterproofing:Positive Or Negative Side?(1St Part)

As far as it regards basements/foundations waterproofing there are mainly two different options if you use as main criterion the side on which the waterproofing product is installed:

 a) Positive waterproofing and

b) Negative waterproofing.

 We say that we have negative waterproofing when the water pressure is exerted on the back side of the waterproofing layer tending to detach it from the substrate. This is the situation when we work inside the basement.

Conversely we say that we have positive waterproofing when the water pressure is exerted on the front side of the waterproofing layer and tends to press it on to the substrate.

This is the situation when we work outside the basement or for example when we waterproof water retaining structures as water tanks or swimming pools.

From the above it is more than obvious that positive waterproofing is more desirable since the stress profile it exerts on the waterproofing layers is much more favorable that in negative waterproofing.

 Integral waterproofing is out of the scope of this article. Please check our relevant articles on this website.

 A. Advantages and disadvantages of positive (waterside) waterproofing.

 A1. ADVANTAGES

 1. There is a big variety of waterproofing materials you can opt for.

I mention some of them hereunder:

 * Geosynthetic Clay Liners - GCLs

* antiroot asphalt membranes

* SBS elastomeric, self adhesive membranes (peel and stick membranes)

* elastomeric brushable liquids e.g. based on polyurethane or polyurea resins

* cementitious waterproofing products: rigid/one component or flexible/two component formulae. Conventional or crystalline versions

* asphalt based, conventional, brushable liquid (destined only for damp proofing)

* asphalt based, rubberized brushable liquids suitable for waterproofing purposes.

 2. Positive waterproofing protects both concrete and steel reinforcements from the corrosive action of water and soil chemicals. This corrosive action is especially taxing when there are fluctuations of the water table!

 3. Positive waterproofing protects the structure from freeze-thaw cycles.

 4. We cannot see waterproofing in a vacuum. Waterproofing has to be combined with the necessary drainage measures.

External / positive waterproofing can easily be combined with the installation of a perimeter footing drain.

A footing drain installed in the right way does a perfect job to alleviate hydrostatic pressure!

And if properly protected, it will remain unclogged for decades!

 (end of 1st part)

 Chris Strogilis

Civ. Eng. - MBA - DipM

http://maconwaterproofing.blogspot.com/