Dry ice blasting for mold in Alberta attics, is it effective?

Dry Ice Blasting for Attic Mould: What Alberta Homeowners Should Know

We found no Alberta or Health Canada guidance on dry ice blasting for mould, or any that rates it against other cleaning methods. Whether any method suits your attic depends on what is causing the mould, how much is there, and what is in the building materials around it. Whatever the method, it cleans; it does not fix the moisture source. Health Canada advises that controlling humidity and repairing water damage promptly is the foundation of any mould fix. If the attic ventilation, vapour barrier or roof is still letting moisture in, mould will return regardless of the cleaning method used.

Size matters before anything else. Health Canada defines small mould as one to three patches each under one square metre, medium as more than three patches or a patch between one and three square metres, and extensive as any patch larger than three square metres. The Canada Mortgage and Housing Corporation says medium areas should be handled by qualified and trained maintenance staff, and large areas by qualified and trained mould remediation contractors. An attic with widespread mould on the sheathing is likely to be in the extensive category.

One issue specific to Alberta attics is the age of the building. The Alberta OHS bulletin ASB004 notes that buildings constructed before 1990 carry a higher risk of asbestos-containing materials, and the Alberta Asbestos Abatement Manual adds that vermiculite attic insulation, including the Zonolite brand, may be contaminated with asbestos. If your attic has vermiculite, Health Canada says not to disturb it or attempt to remove it yourself. Before any contractor runs blasting equipment through an attic in a pre-1990 home, bulk samples of insulation and any suspect materials should be tested. Published Calgary-area lab costs for bulk samples run $65 to $145 per sample. Disturbing asbestos-containing material without proper controls puts workers under the Alberta OHS Code's asbestos provisions, including the requirement that workers hold a government-approved Alberta asbestos worker card to enter a restricted area.

There is no Alberta licence for mould remediation, and no provincial notification requirement for mould work the way there is for asbestos. Alberta Health Services advises that air testing for mould is usually not recommended when mould is already visible; the priority is finding and fixing the moisture source, then removing affected porous materials, which Alberta Health Services says typically require removal rather than cleaning.

When getting quotes, ask each contractor:

• How they will identify and address the moisture source, not just the visible mould
• Whether they will test for asbestos before disturbing any insulation or building materials in a pre-1990 attic
• What happens to removed debris and whether disposal is included
• Whether clearance assessment after the work is done by someone independent of their crew

Published Calgary-area mould remediation costs for a large area such as a whole attic run $3,000 to $15,000 or more, depending on size, access and what materials need replacing.

Start with the contractor's moisture diagnosis, because no cleaning method helps until the source of the water is found and fixed.