New Zealand Guidelines for the Management and Removal of Asbestos 3rd Edition
SECTION 5: IDENTIFICATION, ASSESSMENT AND CONTROL OF ASBESTOS IN BUILDINGS
5.4.2 Enclosure
Enclosure is the placing of a barrier between the asbestos-contaminated materials and the surrounding environment. Enclosure of asbestos-contaminated materials is particularly suitable where the material or its protective coating is liable to mechanical damage.
An example would be building a box enclosure around exposed asbestos-lagged steam pipes.
A suspended ceiling cannot be considered as an enclosure if any type of work, routine or otherwise, is performed above the suspended ceiling or in the space between the suspended ceiling and the reinforced concrete slab or ceiling proper. Refer to Section 7 of these guidelines for further information on enclosures.
5.4.3 Encapsulation or Sealing
NOTE: Encapsulation of friable asbestos materials is restricted work and may only be carried out by a person holding a certificate of competence for restricted work or by a person under direct supervision of a person holding such a certificate.
Encapsulation involves coating the asbestos-contaminated materials with a product that usually penetrates to the substrate and hardens the material. Where there is no substantial penetration of the substrate and the coating just provides a protective barrier impermeable to asbestos, the process is usually referred to as sealing. Both encapsulation and sealing are restricted work under the Asbestos Regulations (refer to section 4).
Encapsulation or sealing is not considered an acceptable alternative to repair or removal of severely damaged asbestos-contaminated materials. Sealing would be inappropriate where the sealed asbestos is likely to suffer mechanical damage, for example, through impact, drilling or sanding.
For large areas, the cost of encapsulation or sealing may approach the cost of removal. Any eventual removal may be more difficult and costly. Continuing assessment will also be required if the encapsulation or sealing option is taken.
Not all paints and other surface coatings on the market are suitable for sealing asbestos-contaminated materials. In particular, the sealant should not increase the fire hazard properties of the material being treated. If the insulation is poorly bonded to the substrate, the application of a coating may result in large sections of the insulation material breaking away from the substrate. The surface to be encapsulated or sealed should be cleaned with a vacuum cleaner to remove all debris and dust particles to ensure good adhesion of the coating to be applied.
5.4.4 Coatings for Encapsulation or Sealing
Both water-based (emulsion) coatings and solvent-based coatings may be used. These may be pigmented or clear. Pigmented coatings, contrasting in colour to the asbestos insulation, will be useful in situations where the asbestos may be subjected to mechanical damage. Damaged areas will be shown by a colour difference, making location of these areas for subsequent repair work relatively simple. Pigmented coatings will also allow easier detection of areas where the coating may inadvertently be absent or is too thinly applied.
Application of coatings must be by airless spray. Operating pressure should be kept as low as practicable to avoid creating high levels of asbestos dust when the coating material impacts with the surface of the asbestos insulation. Coatings should not be applied by roller because the suction effect arising from this method of application can cause the asbestos insulation to be removed.
To seal asbestos insulation effectively it is usually necessary to apply several coats of the sealing agent. The first, and possibly all of the coats applied, may need to be diluted to achieve good penetration of the insulation.
Before sealing any asbestos materials, a thorough clean-up of the surrounding area with a vacuum cleaner should be undertaken to remove any asbestos-containing dust.