Additive chemicals in construction materials are abundant - to resist fire and moisture, repel insects, seal against air leakage or even add to the longevity of a finished surface.

Some older chemical additives can remain active for decades, while others may become relatively inert when they are sealed into a built assembly or as they age.

WOOD PRESERVATIVES

Chemically treated lumber has been used for centuries and is still used today. The preservative added to wood products may allow the material to resist moisture, insects or the effects of weathering.

Common Wood Preservative Types in Older Buildings:

• Creosote: Mostly used for railroad ties and marine applications, creosote is an oily bitumen derived from coal-tar. It is one of the oldest types of wood preservative and is easily identified by its dark brown - black colour and coal smell.
• Pentachlorophenol (Penta): This is an oil-borne treatment, used on telephone and hydroelectric poles, industrial applications, fence posts and highway construction. Penta treated wood has a brownish colouring.
• Chromated Copper Arsenate (CCA): Very recognizable by its green colouring, CCA treated wood was used for everything from wood foundations and poles, to construction lumber and decking throughout the 1970's, '80's and '90's. The treatment is still in use for some applications, but has been ceased for most residential uses as of January 2004.
• Ammoniacal Copper Quaternary (ACQ): The use of ACQ as a wood preservative came about as the use of CCA was decreasing. This treated wood is used for exterior applications - playground structures, fences, picnic tables and decking. The colour can be brown, tan or off-green.
• Borates - disodium octaborate tetrahydrate (DOT): Use of Borate treated wood was common in the 1950's and '60's, though it's use has increased slightly in modern application. Wood treated with borates has a soapy smell and looks crystalline on its surface. It is mainly used to prevent wood-boring insects.

CONCRETE and MORTAR

Ancient structures made of concrete and stone have stood for thousands of years in some parts of the world. The minerals and chemicals used to create mortar, cement and concrete become mostly inert as they cure and age, but there may be hazards when new mixtures are being poured or applied.

Concrete is one of the most durable and long lasting materials we use in modern construction, making it an ideal material for use in building foundations and public infrastructure.

Mortar is a material used to adhere concrete, brick and masonry units together when building walls, foundations and other structures. Once a mortar is applied and dried, it can last for many years unless it is affected by moisture and freeze / thaw cycles.

Important Considerations for Concrete and Mortar:

• One of the main ingredients in concrete and mortar is CEMENT. This additive requires great amounts of heat energy in its manufacture.
  
• Traditional mortar is made of Portland cement, sand and hydrated LIME, or calcium hydroxide. This additive is caustic and alkaline, and may be harmful if it gets on your skin or in your eyes. Always use recommended PPE when working with concrete and mortar.
  
• The fine sand used in mortars and concrete contains crystalline silica. If there is silica dust in the air where work is being done, it may lead to respiratory problems.
  
• Concrete, masonry, brick and mortar is affected by moisture accumulation and seasonal freeze / thaw cycles. This may show up as white, powdery stains called efflorescence or spalling, where chunks of material fall away.
• Concrete has very high compressive strength, meaning that it can handle great loads without failure. However, concrete is not as strong with lateral forces - horizontal and shear loads. Metal reinforcement is required for concrete walls and columns to counteract this weakness. The metal is laid into formwork before the concrete is poured, and may be in the form of long pieces of reinforcing bar ("rebar"), or as welded wire mesh.