By Rob Paddock
Rob_PaddockIn this article for Paddocks Press, we will be looking at sealants. If sealants were to be personified, they would most certainly be the goalie of a winning team on the soccer field – the ultimate defender.  The main purpose of using sealants on the building envelope of your sectional title scheme is to fill joints and gaps between different building materials and to form a seal that keeps air infiltration and water penetration at bay.

Unlike the striker in a big game (which one might personify as a fresh coat of paint in maintenance terms) goalies receive very little glory when compared to other players. However, should they fail to do their job due to poor performance or a lack of fitness, the team will most certainly suffer a great defeat, even if the teams star performers are still scoring goals.

Whilst sealants might seem like a small detail on the outside of your schemes building, they can contribute to the development of large problems if they fail and allow moisture to get into the walls.

What are sealants?
Sealants are glue-like materials capable of being shaped or formed, and are generally used between different components of the building envelope. Sealants can provide seals around windows, doors and other types of penetrations such as pipes and chimneys. Sealants generally contain inert filler material and are usually formulated with an elastomer to give the required flexibility and elongation. They usually have a paste consistency to allow filling of gaps between substrates. Low shrinkage after application is often required. They quickly cure and transform into a flexible semi-solid material that reduces the flow of water, air and dust.

Sealants can allow for slight movement of different parts of the building envelope caused by changing temperatures, strong winds or humidity. Most building materials joined by sealants will expand when getting warmer or wetter, and shrink when cooling off or drying out. Sealants help to ensure that the building envelope functions properly in these changing conditions. To perform such duties, sealants must be able to:

  1. resist exposure to water, sunlight and temperature variations;
  2. bond to surfaces with sufficient strength; and
  3. accommodate movement of building materials.

Types of sealants

With so many products to choose from, selecting the right building sealant may seem like a daunting task. Applying the correct sealant in the wrong manner, or selecting the wrong building sealant can have serious consequences. The following table is by no means an exhaustive list of sealants available, but will give you an idea of the most popular types of sealants and their specific applications:

Sealant type Features Generally used
Silicone • Life expectancy 10 – 50 years
• Normally used in wet locations
• Strong and flexible over wide temperature range
• Can sustain high movement in the joint
• Adheres to a broad variety of materials, but picks up dust easily
• Poor resistance to tearing or abrasion
Around windows, dryer ducts, pipes
Polysulfide  • Life expectancy 5 – 20 years
• Good adhesion to steel, aluminium and glass
• Can sustain medium movement in the joint
• Should be sheltered from sunlight
In windows, especially sealed insulating glass units
Latex • Life expectancy 5 – 25 years
• Only used indoors
Interior trim (should be replaced if found in exterior applications)  

When choosing a sealant, make sure it has at least the following four characteristics:

  1. Stability over a wide temperature range
    Once fully cured, high-quality sealants perform across a range of temperatures. Select a sealant that functions reliably at temperatures outside your average temperature range to accommodate unexpected temperature changes.
  2. Weather resistance and chemical stability
    UV rays, radiation and weather can cause low-quality sealants to crack, disintegrate and become brittle, compromising the seal over time. Look for sealants with good resistance to these and other erosive factors. Also, some organic sealants react to atmospheric pollutants or chemicals much like iron reacts with water to produce rust. Use a sealant that does not readily degrade after prolonged contact with common elements and industrial chemicals.
  3. Good bond strength
    Good sealants provide durable adhesion to a variety of building materials, including glass, ceramics, wood, masonry, and many metals and plastics. A variety of factors contribute to the bond strength of individual sealants, including chemical composition, cure type and substrate penetration.
  4. Low flammability
    In fire conditions, some sealants are more burn resistant than others. Silicone sealants, in particular, are especially fire resistant.

Some sealants are not compatible with other sealants or with certain building materials and will react to form messy by-products. These reactions can be unpredictable and may impair the intended function of some building components. When changing a sealant type to another, special care must be taken to remove all of the old sealant residue to ensure a good bond.

Why do sealants need to be maintained?
Sealants typically last anywhere between 2 and 50 years depending on the type of product used and the sealants exposure to weather and movement. The bond between the sealant and the substrate can fail, the sealant itself can fail, or the substrate can break. To be effective, sealants rely on both their bond to the building components and their inherent flexibility. Sealants must therefore be replaced when either fails.

Although the use of sealant is inevitable on most buildings, good design tries to minimize the amount of sealant used. So, if you see sealant on your building, you should expect that it is there for a good reason and needs to be maintained.

A relatively small investment in maintaining the sealant will help to prevent damage at a particular location in your building envelope including possible damage to the wall itself. In my next article for Paddocks Press, we will look at how the maintenance of your building’s sealants should be performed.

Article reference:
Volume 4, Issue 12, Page 4.

Back to Paddocks Press – December 2009 Edition