ÐÇ¿Õ´«Ã½

It is difficult to imagine a building today that does not include sealants somewhere, be it a basic home or an ultra-modern, high-tech complex. However, placing sealants on the external envelope of a building introduces a relatively short-life component into a part that may have a design life of between 60 and hundreds of years. Sealants are also critically reliant on correct application to maintain their performance and achieve long-term durability.

The problem
A sealant may have several functions but its main job is to allow some movement to take place at junctions while keeping water and wind out of the building. Typically, sealant is applied around openings, such as windows and doors; to movement joints in long runs of walls; and where dissimilar materials meet.

If you get it wrong, you risk premature failure or damage to the components of the building around the sealant joint due to damp penetration. There is also a risk to the health of the occupants where damp encourages internal growth of fungi and mould.

Replacing sealant is not a cheap option, as it will invariably include scaffolding. In addition, there may be considerable work involved in removing existing sealant and making good the joint for a new application. Clearly, the onus is on the designer and applicator to get it right first time.

As usual in the construction industry, guidance on good practice is available but spread about several sources. A recent Construction Industry Research and Information Association guide on sealant design, specification and application ran to 200 pages.

What to look out for on drawings

Choose the right sealant for the application, exposure and durability. The Housing Association Property Mutual, an insurer that publishes manuals listing the lifetime of building components, gives frame and joint sealants insurance lives of between five and 20 years. Service lives of 25 years are achievable, it says.

Design junctions to protect sealants from the deteriorating effects of sunlight – for example, lapped joints.

Carefully size the joints and provide full-scale annotated drawings for site staff so they have a sporting chance of getting the application right.

If you get it wrong, you risk premature failure or damage to the components of the building around the sealant joint due to damp penetration

Avoid openings flush with the wall surface. Design window and door openings so they are set back and behind the wall, thus reducing reliance on sealants. This is a standard way of detailing in locations with a severe or very severe exposure.

What to look out for on site

It is essential to clean the substrates on which the sealant is to be applied.

The substrate should be dry before sealant is applied.

Use the correct primer in the correct quantity.

Suitable filler, back-up material (such as closed-cell foam) and bond breakers should be inserted behind the sealant, if specified. All should be installed without damage, twists or breaks, in the correct position.

Apply the correct thickness of sealant – too thick is as bad as too thin.