Waterproofing:a guide on moisture diagnosis(2nd part)

Read here 1st part: WATERPROOFING: MOISTURE DIAGNOSIS GUIDE (1st part)

 C. SOIL TYPES

Sandy soils are the most desirable soils around basements. They permit rainwater runoff to easily infiltrate and percolate deeply until it meets the water table (e.g. an aquifer).

Silty or clayey soils can trap water pockets (perched water) which potentially can induce hydrostatic pressures.

Some soils are expansive. They may contain e.g. bentonite or montmorillonites mineral with considerable swelling capabilities.

Swelling and especially differential swelling can cause settlements, differential settlements and cracks on foundation walls.

D. BUILDING MATERIALS TYPES

Building materials vary in their porosity and water and vapor permeability.

Additionally there are vast differences in their hygric buffer capacities.

For example a typical construction in Greece with concrete and clay bricks can have 100 times (!) bigger hygric buffer capacity than a construction made of metal and cement boards.

E. BUILDING ORIENTATION

Building orientation will have consequences on the hygrothermal performance of the building envelope.

Some examples:

North west orientation will increase condensation phenomena and decrease drying capacity.

Orientation of long axis of the building toward prevailing winds will increase air infiltration, interstitial condensation but also the cooling effect.

F. HYDROGEOLOGICAL PROFILE

The existence of ground water can exert a dramatic influence on the waterproofing integrity of below grade constructions.

The problem is more serious when the water table is near or higher than the basement floor.

Lack of perimeter drainage or drain tile clogging will further aggravate the problem.

Hydrostatic pressure can exert tremendous forces on the foundation walls. It can induce cracking and then push vast amounts of water into the interior and through the cracks.

The relief of hydrostatic pressure is of prime importance in all waterproofing interventions in basements.

G. USE OF THE BUILDINGS

Use of the buildings is critical from the water vapor production point of view.

Spaces with massive production of water vapors e.g. indoor swimming pools or other sport venues, certain industries (paper, cans, dairies, breweries etc.), collective kitchens and sanitary rooms are prone to surface and interstitial condensation.

These buildings / spaces need strategic use or vapor barriers and thermal insulation to alleviate these problems.

H. CLIMATOLOGICAL CONSIDERATIONS

Climate is one of the parameters that play an important and dynamic role in the way moisture affects buildings.

Strong rain precipitations feed aquifers, raise water tables or create pockets of water (perched water).

Spring thaws are real ordeals for the waterproofing defense lines of basements / foundations.

Roofs and walls are preys to winds and precipitations.

Buildings on the seefront have to face increased moisture, chlorides and strong breezes.

The placement or not of vapor barriers and their exact locations depend on the local climate.

To make a diagnosis on waterproofing issues you have to understand the local temperature and humidity conditions. These will give you the insights you need.

I. BASIC CONCEPTS OF BUILDING SCIENCE

Knowledge of the basic concepts and mechanisms of building science or buildings physics is indispensable for the decipherment of moisture riddles.

More analytically a knowledgeable person in the waterproofing industry should have a firm grasp of concepts as:

- relative humidity

- absolute humidity

- dew point

- condensation (surface and interstitial)

- diffusion

- pressure and temperature differentials

- capillary absorption

- hygric buffer capacity

- vapor barriers

- ventilation (natural and enforced) etc.

Chris Strogilis

Civ. Eng. – MBA – DipM

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