PREFACE

Total waterproofing of basements / foundations is considered by some very experienced professionals as an unattainable objective.

Water, either under its visible liquid phase or under its more mysterious, invisible and unpredictable gaseous phase will sooner or later find its way through foundations in our precious living space.

We will check together five of the most common modi operandi our mischievous opponent uses to achieve its goals.

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Epigrammatic presentation of the 5 reasons for wet basements ' foundations:

 

1. Massive leaks through joints ' cracks - discontinuities

 

2. The role of capillary suction (absorption)

 

3. Condensation phenomena

 

4. Water vapor diffusion through foundations

 

5. Air leakage due to stack effect.

 

 

1.Massive leaks through joints ' cracks ' discontinuities

 

Can you imagine a concrete basement as a monolithic construction? This means without:

- joints

- cracks

- honeycombs

- any construction discontinuity?

No way!

Concrete constructions are built in different phases. Different kinds of joints e.g.

 

Construction joints

Contraction (control) joints

Isolation joints

Expansion joints'

 

...will always break the construction continuity.

 

These joints need utmost waterproofing care and are among the prime suspects for water intrusion in the basements.

 

Many joints can be seen as predermined cracks. We know or we decide their exact position.

This is not the same with cracks that are generally occasional, random and unpredictable.

 

Even if you take the most exhaustive preventive measures, cracks will show up. You can reduce their number and size but you never eliminate them.

Cracks could originate from:

 

* settlement and principally differential settlement

* hydraulic or drying shrinkage of concrete

* constructional errors

* random, excessive pressures on foundations etc.

 

All above causes can be prevented but only up to a point. More or less they cannot be totally controlled.

 

Discontinuities are the number one reason leading to water intrusion in basements / foundations. They need special waterproofing measures which will be analyzed in the near future.

 

 

2. The role of capillary suction (absorption)

 

Moisture in its liquid phase moves through porous building materials from high to low concentration areas. Highly cohesive soils can drive considerable loads of liquid moisture through foundation walls and slabs.

The movement of liquid moisture through the capillary system of porous materials is based on molecular phenomena.

 

Polarity of water molecules make them adhere well on most of the building materials.

It's is this strong adhesion that initiates water movement inside the capillary pores. Adhesion, though, cannot create and sustain massive movement of the water. It is the surface tension of water that involves and sustains the movement which could be an upwards movement against gravity. Each molecule pulls other molecules as if there were links in the same chain.

Put in another way surface tension fights to keep water surface intact and thus helps sustain movement.

Hydrostatic pressure, when present, gives the extra push for the phenomenon to develop. Hydrostatic pressure will second wall pores wetting, acting in this way as a catalyst for the phenomenon evolution.

 

Damp proofing or waterproofing ' depending on the conditions ' could be effective measures against capillary suction.

 

Other possible measures: Granular layers, drainage composites, extruded polystyrene etc.

 

 

3rd reason: Condensation

 

Condensation is described thoroughly in our entry 'THE 4 PILLARS OF CONDENSATION PREVENTION'.

 

Condensation, in contrast with the previously mentioned reasons is an internal phenomenon.

Condensation has unbreakable bonds with dewpointtemperature and not with relative humidity which is a meaningless figure if temperature is not considered.

Condensation is often misdiagnosed and confused with capillary suction (or rising damp).

A well sealed piece of aluminium or polyethylene foil can easily help distinguish between the two.

'Summer' condensation takes place when warm air masses enter basements from the openings and condense on the relatively cold walls.

Interstitial condensation occurs inside the building envelope with the help of vapor diffusion.

 

 

 

 

4th reason: Diffusion

 

Diffusion evolves on a molecular level and has to do with the kinetic energy of the water molecules. These tiny particles pass through the voids of porous materials.

Moisture loads in the ground are almost always heavier than the interior and thus diffusion evolves from the exterior to interior.

Diffusion can have catastrophic results on most floor finishings. Additionally it can feed internal humidity on a continuous basis.

Diffusion can be curbed with the use of appropriate vapor barriers.

 

 

 

5th reason: The stack effect

 

Stack effect in basements is very powerful when they communicate with upper floors. As we have already seen , warm air rises and exlfiltrates at the top of building. A vacuum is created in the basement and air is sucked through discontinuities to equalize the pressure. Air, of course, will bring together considerable moisture loads.

 

 

 

Chris Strogilis

 

Civ. Eng. ' MBA ' DipM

 

About the Author:

Civil engineer with postgraduate studies in MBA and Marketing. christo

Author: Chris Strogilis