A process in wastewater treatment where metal screens are used to remove large objects and chunks of debris.
Types of Pre-Treatments
Poured Slab – This is for a building that sits flat on the ground, typically on a concrete slab. A termite technician will measure the area (usually from the plan) which is to be covered by the structure (with concrete, including masonry blocks and/or support columns, if applicable). Ideally, the termiticide will be applied to the sub-floor before any concrete is poured. Most termiticide labels require the application of one gallon of dilute termiticide per 10 square feet of slab area (around 5 litres per sq m).
Americans don't seem to have generally caught on to the use the concrete slab as part of their barrier system. Termites cannot chew through a properly built, modern, reinforced and cured concrete slab. However, in spite of this, if the sub-slab soil is not treated prior to the concrete pouring, the slab is then drilled, following the label directions, adjacent to the foundation/ perimeter, support columns and other critical areas, and then the termiticide emulsion is pumped into the soil with a laterally-dispersing hollow rod. The label-specified volumes and concentrations vary across the brands, but usually require 2-4 gallons per 10 liner feet (about 2 to 5 litres per metre).
Crawlspace Foundations - A suspended floor (often timber) is built with a sub-floor air gap. In the USA, this gap is typically tall enough to allow a technician to crawl beneath the floor, hence the term 'crawl space'. Treating a crawlspace involves the placement of a chemical to the soil so as to provide as close as possible (to a but never quite) continuous chemical barrier on both sides of the foundation. The outside perimeter of the foundation is treated at the footer level. The application rate is usually 4 gallons per 10 linear feet (about 5 litres per metre). If the foundation consist of hollow blocks, an additional 2 gallons per 10 linear feet is often required. Other structural elements of the building must also receive treatment in the soil surrounding them - support columns, porches, plumbing penetrations and other critical areas. This rather haphazard approach is much less certain than the highly detailed application specifications used in Australia's Standard 3660.1
Basement Foundations - Americans seem to like building basements of hollow concrete blocks. These are an ideal way to attract termites as the hollows allow for easy termite access and help to store water for their use. Treating the soil around these structures is difficult, but much easier during construction than after. The termite pre-treat of a basement seeks to create a continuous chemical barrier on both sides of the foundation. The treatment guidelines are very close to the “crawlspace” requirements, but extra drilling of masonry voids near the footer is usually done. See. Ideally, a basement would be made from void-free solid poured concrete and the termite entry points then reduced to just the joints (which can be blocked with a termite-resistant sealant), however this is not yet popular in the USA. Trying to create a barrier in hollow masonry by drilling into it and flooding the voids is at best wishful thinking. The termiticides will not fully penetrate the mortar and many entry paths usually remain. Any exclusion of the termites is usually attributable to the termiticide placed around the exterior walls, however even here, the settling of loose fill can create voids through which termites can easily pass.