Concrete and Your Home by the Barrie Building Inspector
Tarion reports that each year a significant percent of basements are constructed with serious defects. At the same time, home buyers are demanding a higher standard of quality workmanship and moisture control than ever before. Part of this is due to consumer education by Home Inspections, TV Programs and articles on poor workmanship.
Concrete is basically a mixture of cement, water and aggregates. The paste, formed by cement and water, coats the surface of sand and stone, binding them together, to form concrete.
ASTM’s cement and concrete standards are instrumental in the evaluation and testing of concrete, cement, and aggregates. Concrete can have different properties depending upon the mixture that is used in creating it, which contains cement, chemical admixtures, and aggregates. These ingredients are mixed with water to create concrete which is used as a primary construction material in buildings.
One simple on site test typically performed in the concrete slump test. The slump test measures the consistency of the concrete in that specific batch. This test is performed to check the consistency of freshly made concrete. It is used to indicate the degree of wetness. Workability of concrete is mainly affected by consistency i.e. wetter mixes will be more workable than drier mixes, but concrete of the same consistency may vary in workability. It is also used to determine consistency between individual batches.
Regular concrete, such as used in residential construction, has a compressive strength rating, varying from 10 MPa (megapascal) to 40 MPa (5800 psi). Concrete cures for a period of 28 days when it will reach approximately 90% of its final strength. Controlling the moisture during the first three days is critical to preventing cracking and shrinkage. Allowing the moisture to evaporate too quickly can cause tensile stresses which can result in more shrinkage cracks. Keeping concrete damp during the curing process minimizes cracking. Spraying water over concrete and covering with plastic sheeting are two common methods used for residential construction. Concrete can continue curing and increasing in strength for up to 3 years.
Air entrainment is recommended for nearly all concretes, principally to improve resistance to freezing when exposed to water and deicing chemicals. Air-entrained concrete contains billions of microscopic air cells per cubic foot. These air pockets relieve internal pressure on the concrete by providing tiny chambers for water to expand into when it freezes. Air-entrained concrete is produced through the use of air-entraining portland cement, or by the introduction of air-entraining agents, under careful engineering supervision as the concrete is mixed on the job. The amount of entrained air is usually between 4 percent and 7 percent of the volume of the concrete, but may be varied as required by special conditions. Entrained Concrete
Chemical admixtures are the ingredients in concrete other than portland cement, water, and aggregate that are added to the mix immediately before or during mixing. Producers use admixtures primarily to reduce the cost of concrete construction; to modify the properties of hardened concrete; to ensure the quality of concrete during mixing, transporting, placing, and curing; and to overcome certain emergencies during concrete operations.
Your finish of the exterior of your basement determines the amount of MPa required by the Ontario Building Code. Most modern homes have a damp-proof coating, which was installed to meet local building code requirements as the home was being constructed. This is usually a tar or asphalt based product applied to the exterior or your home. This product is not to be confused with water proofing, which is a completely different process. Damp proofing allows the concrete to cure without moisture entering during this process. Many damp proofing will fail after a couple of years and if basement is subjected to high water table, will most likely leak in some form.
Many new home buyers confuse the dimple wrap placed around most basements as a water proof membrane. The dimple design of the wrap creates an air gap between the membrane and foundation wall so exterior drainage water or damp/wet earth is never in contact with the poured concrete or cement block foundation wall. Instead water will be drained to the weeping or drain tiles, leaving the foundation walls dry.
Many new home builders will repair any significant cracks by injection of foam or epoxy. Having a Pre-Delivery Inspection can identify these issues that you may miss and usually once that window of opportunity is missed, your on your own. Tarion will not require builder to repair crack unless it is wider than 1/2 inch or water is entering home. If you are in the Barrie area, call the Barrie Home Inspector, to accompany you on your Pre-Delivery inspection. It’s your Peace of Mind that is at stake.
Many custom home are using ICF building process to construct their foundations Insulated Concrete Forms may use polystyrene blocks or panels as the formwork into which reinforcing steel and concrete are placed. These polystyrene forms are left in place to give your home an exceptional R-value. Their history dates back to the period after World War II, when blocks of treated wood fibers held together by cement were used in Switzerland. Some of the benefits of ICF construction is the strength, disaster resistant, mold and rot resistant, sound deadening and energy efficient. Some companies refer to the lack of chemicals used compared to wood framing where there may be VOC’s present from glues etc.