Moisture Control
The basic goal of yard drainage is moisture control. Moisture as a key component of natural processes on earth. The important role of moisture in the soil while showing how moisture works to recycle everything back to the soil. How moisture control compliments foundation repair objectives.
Yard Drainage Problems
Examples of yard drainage problems include flooding, erosion, sedimentation, piping, ponding, negative drainage, faulty grade, seepage, soil saturation, soil-moisture fluctuation, excessive humidity, and wicking. These problems can create or aggravate a variety of undesirable soil conditions including soil scars, slope creep, landslide, soil consolidation, soil subsidence, soil shrinkage and soil expansion. In addition, poor yard drainage control can cause erosion, efflorescence, pop-outs, spalling, and cracking of concrete, block, brick, stonework and stucco whether in the form of building foundation walls, concrete slabs, sidewalks, patios, retaining walls, fencing, or other hardscapes.
Adverse yard drainage can also facilitate damage and destruction of metals including reinforcing steel, anchor bolts, post bases, fence poles, wrought iron, aluminum thresholds, window frames, utility enclosures, and gas pipes. Finally, poor yard drainage can provide an environment for pests including moss, mold, mildew, dry rot, mosquitoes, termites, and rodents to name just a few.
Moisture: Agent of Mobility
Moisture is the medium of life and is virtually everywhere in our environment. Moisture is nature’s agent of mobility giving the chemical elements a place and a way to become active and to be modified as they interact among themselves. Moisture also plays an active role in the breakdown and recycling of earth materials. Moisture makes it all happen!
Water is the liquid phase of Moisture. Due to the temperature range on earth, water easily becomes ice (a solid) or water vapor (a gas), assuming quite different properties in each of these three forms. As moisture travels around the “hydrosphere”, changing back and forth between the three states, it molds and modifies the earth. Humans also mold and modify the earth. When we do so, we try to create structures which are durable and stable. The ultimate success of our efforts in this regard will depend largely upon how well we apply our knowledge of certain earth processes. This leads me to a discussion of weathering.
Moisture and Weathering
Moisture plays a key roll in the weathering of rock, eventually transforming solid rock into small particles. When water vapor in the atmosphere condenses and falls on rocks in the form of precipitation, mineral particles within the rock are mechanically dislodged and then carried away by the liquid water. Moisture collecting in tiny cracks in rock will cause pressure within the cracks, breaking the rock when temperatures drop and water expands to become ice.
Our human-made infrastructure is also subject to the cracking and wearing away caused by precipitation. After a few winters, concrete walks and driveways begin to shed their surfaces, exposing and dislodging aggregate and leaving small holes on the pavement surface. These problems can be mitigated through the use of high-quality concrete, the application of protective coatings, and the proper management of yard drainage.
Chemistry Happens
Chemical weathering is an ongoing process in nature, requiring only the daily variations in temperature and humidity to proceed. As the air cools at night, humid air gives up moisture (condensation). As the air warms during the day, moisture evaporates and returns to the atmosphere. Moisture condensing on the surface of rock (or concrete) will dissolve certain chemical compounds which then travel with the liquid water in solution. These dissolved compounds will be deposited elsewhere when the moisture evaporates.
Here is an example of how poor yard drainage destroys concrete: Because of poor drainage, water ponds on the patio after it rains. After the pond evaporates, a white powder appears on the surface of the concrete. This powder is called efflorescence- mineral deposits which are the residue when the moisture evaporates. Nature is turning your concrete into dust.
Minerals in contact with moisture can become hydrated, changing their physical size and structure. When certain chemicals become dissolved, the solution becomes acidic and the weathering process accelerates. Corrosive solutions can easily penetrate concrete, leaching soluble minerals. Minerals in exposed rock or concrete will react with oxygen in the atmosphere (oxidation). When this happens to human-made metals, we call it rust.
Moisture will attack and destroy concrete with reinforcing steel or “rebar” in a process called spalling. Moisture seeping into the concrete will cause corrosion and expansion of the steel. The pressure causes pieces of the concrete to pop out- exposing the rebar and concrete to further damage and threatening the integrity of the structure. Metal pipes and posts which are embedded in concrete are similarly destroyed. These problems can be minimized by keeping all embedded rebar at least two inches from the concrete surface. All exposed metals should be protected from corrosion with proper coatings and maintenance. Equally important, is the control of yard drainage so that moisture does not accumulate around these sensitive areas.
Denver, Colorado
www.danteengineering.com