Asbestos in drywall joint compound and plaster

Where the asbestos is

Drywall boards themselves were generally not made with asbestos. The concern is what was put on and around them:

• Joint compound, also called drywall mud, used to fill the joints and cover the screws or nails
• Texture coats on walls and ceilings
• Plaster, in some base coats and finishing coats, and in acoustic plaster
• Patching compounds and fillers

Asbestos was added to some of these products for workability and strength. It was removed from consumer patching products around 1980, though material already sold continued to be used. In practice, walls and ceilings finished before the mid-1980s are treated as suspect until tested.

Because compound is only at the joints, corners and fasteners, a wall can have asbestos in strips and none in between. Renovations add to the puzzle: one room may have been re-boarded in the 1990s while the next is original.

When it matters

Painted, intact walls are not releasing fibres. The risk comes with dust:

• Sanding joints or old paint
• Cutting openings for electrical boxes, pot lights or plumbing access
• Demolishing walls or ceilings in a renovation
• Removing wallpaper where the surface comes with it
• Tearing out wet drywall after a leak or flood
• Drilling many holes

Sanding is the worst of these. It turns the compound into fine dust that spreads through the house and into the ducts.

Hanging a picture is not a meaningful exposure. Planning to gut a kitchen is the moment to test.

Testing

1. Samples are taken through the full thickness of the finish, at joints and corners where compound is thickest.
2. Several samples are needed from different rooms and from any areas that look like later work.
3. An accredited laboratory analyses each layer. Because compound is a thin layer, the lab may report it separately from the board.
4. The result tells you whether asbestos is present and in which material.

Ontario Regulation 278/05 requires owners of buildings other than an owner-occupied private residence to have asbestos identified before demolition or work that may disturb it, and requires contractors to protect their workers. A contractor working in your home is covered by it, which is why a responsible renovator asks about testing in a house of this age.

If the result is positive

You do not have to strip the house. The choice depends on what you are doing.

• No renovation planned. Leave the walls alone. Keep them painted and in repair.
• Small job. Limit the work to what is needed, and have it done with the right precautions.
• Major renovation. Have the affected finishes removed properly before the trades start. It is cheaper than cleaning a contaminated house afterwards.
• Covering. New drywall can sometimes be installed over old walls, leaving the old finish undisturbed apart from the fixings.

How the work is classified

Under the regulation, drywall finished with asbestos joint compound is treated as non-friable material, and the classification depends mainly on the area:

• Removing less than one square metre is generally Type 1 work, with basic precautions: wetting, no power sanding, drop sheets, careful cleanup and suitable respirators where requested.
• Removing one square metre or more is generally Type 2 work, with greater controls, such as an enclosure of plastic sheeting, respirators and protective clothing.
• Using power tools without HEPA dust collection on asbestos material moves a job into Type 3.

Friable plaster, such as acoustic or sprayed plaster, is classified more strictly.

In all cases the material is kept damp, removed in the largest pieces practical, sealed in labelled bags and taken to a licensed disposal site. The area is cleaned with HEPA vacuums and wet wiping, not swept.

Plaster and lath

Houses built before the 1950s usually have plaster on wood or metal lath. Most ordinary plaster contains no asbestos, but some does, and it cannot be told apart by eye. Plaster demolition is very dusty, so testing first is worthwhile. Old plaster walls can also have lead paint on them, which needs its own precautions.

After water damage

Emergency drying often means cutting out wet drywall quickly, before mold starts. In an older house this conflicts with the need to test. A restoration contractor handles this by taking samples at the start and getting rush laboratory results, by drying in place where possible in the meantime, and by treating materials as asbestos-containing if they must come out before results arrive. Tell the contractor the age of the house and of any renovations.

If dust has already been made

If you have sanded or demolished a suspect wall:

1. Stop work.
2. Switch off the furnace or air conditioning fan.
3. Close the room and keep people and pets out.
4. Do not sweep or use a household vacuum.
5. Have the material tested.
6. If it is positive, have the area and, if needed, the ducts cleaned by an abatement contractor.

A single short exposure does not mean illness will follow. Disease from asbestos is associated mainly with heavy or repeated exposure over time. If you are worried, speak to your doctor.

More: asbestos removal and abatement.