Waterproofing:a guide on moisture diagnosis(3rd part)

3rd part


Read 2nd part here: WATERPROOFING: A DIAGNOSIS GUIDE (2nd part)

LIQUID MOISTURE SOURCES

PRECIPITATION – RAIN PENETRATION (ABOVE GROUND)

To minimize rainwater leaks you need good building design and practices.

Dominant forces are gravity force and wind force.

Although rain precipitation is infrequent and inconsistent it can bring massive leaks and serious damages to buildings and the inside objects. All the same, light but persistent rain can equally induce severe damages.

Flat roofs are very prone to damage due to rain water. Walls receive about the 1/4 of the rainwater quantity.

GROUND WATER SEEPAGE

Water can easily intrude into basements through cracks, gaps and discontinuities on the below ground building envelope.

The best way to prevent this is the efficient management of surface or subsurface water. A solid drainage plan can make miracles.

Water intrusion can originate from high water tables or percolating rainwater runoff.

If discontinuities are not present, the dominant mechanism for moisture movement is capillary suction (or absorption). Rising damp is a form of a capillary absorption. These are molecular phenomena related to water molecules polarization, increased adhesion and cohesion and especially surface tension.

Cracks, construction joints, gaps and pipe penetrations are prime suspects for below ground water intrusion.

INTERIOR LEAKS (PIPES, VALVES etc.)

Maybe this is a purely plumbers domain but a waterproofing expert should easily detect these problems.

Piping leaks can induce real catastrophes. Water quantities from these leaks can reach inconceivable numbers.

Generally these problems are easy to locate. Sometimes, though, when leaks are small, water can travel for considerable distances due to capillary phenomena.

CONSTRUCTION MOISTURE

Construction materials as concrete, renderings, stuccos, wood etc. contain vast amounts of moisture. This moisture is released slowly and gradually and cause higher than normal internal relative humidities for 18-24 months after the project completion (especially during the first winter).

Additionally, during the construction process, building materials are exposed to weather conditions and it’s most logical to store moisture from the environment.

VAPOR MOISTURE SOURCES

People and their daily rituals

Occupants produce through their every day activities high loads of moisture vapor and launch internal R.H. in big heights. We have talked about this subject in other entries. Hereunder we compile the main habits / activities that feed internal Relative Humidity.

1. High occupancy (fewer m2/occupant)

2. Bathing / showering

3. Cooking

4. Many plants

5. Clothes drying inside

6. Floor cleaning

7. Unvented appliances

8. Indoor swimming pools, jacuzzis, hot tubs, whirlpool baths and other similar installations imposed by modern lifestyle and prevailing social trends.

WATER VAPOR DIFFUSION

We have learned that water vapor moves through the building envelope proportionally to pressure differentials and resistance to vapor flow. Diffusion takes place both above and below ground and it’s a much weaker mechanism than water vapor infiltration – exfiltration via convection.

EVAPORATION

Evaporation deserves a separate mention.

Evaporation happens when liquid moisture from wet surfaces is transformed in water vapor. This is the case when air vapor pressure is smaller than vapor pressure of the saturated air in the vicinity of the wet surface.

COMBUSTION

Unvented appliances can induce big moisture loads in the indoor environment.

CONVECTION

Because envelopes are never airtight massive loads of moisture can infiltrate or exfiltrate with the help of air movement.

We have talked about:

- wind effect and

- stack effect.

Water vapor transported via convection is multiple in relation the quantities transported through diffusion.

Air – carried vapor is responsible for serious interstitial condensations.

FEW WORDS ON CONDENSATION

Condensation phenomena take place when vapor-loaded air comes in contact with surfaces at temperature below dew-point.

Condensation is widely misdiagnosed as capillary absorption.

Chris Strogilis