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Silicone vs. Polyurethane Sealant


By VP, Exterior Building Services | June 12, 2013

silicone-polyurethane-sealant-blog-photo-2

This photo shows the negligible impact of weathering on a silicone sealant (left) versus the degraded impact on an organic polyurethane sealant (right) after 3 to 6 years. Photo courtesy of Dow Corning Corporation.

What’s the difference? Why should you care?

The sealant selection process can be daunting. But in actuality, it really is quite simple.

What is a sealant?

A sealant is an elastomeric material that allows for 25% to 50% movement. Sealant is used to fill gaps, to keep water and air at bay, to allow for expansion and contraction of building materials, and to enhance aesthetics. Silicone and polyurethane are two popular types of sealant. Despite their common purpose, there are a few major differences between them.

A Lesson in Chemistry

The primary difference is at the chemical level. Polyurethane is an organic material. Silicone is an inorganic material. The effects of breakdown of silicone and polyurethane depend on the sealant’s chemical makeup.

Why is sealant chemistry important? – UV Stability and Reversion

At this point you may be asking yourself, “why is sealant chemistry important?” It comes down to how the chemistry of each type of sealant performs on a building when it is exposed to UV rays from the sun. In the presence of UV light, an organic material (polyurethane) will eventually revert to its natural state, thus changing properties and deteriorating over time. An inorganic material (silicone) will not.

Lifespan and Full system replacement warranties

While a polyurethane joint’s lifespan is typically 5-10 years, a silicone joint’s lifespan is typically 20+ years. Why is there such a big difference? Simply put, at the end of the day, a silicone joint’s lifespan is longer because, chemically, it won’t break down. Like UV light, temperature plays a role too. Silicone is better suited for temperature extremes. This is especially important in the Mid-Atlantic where we have some of the most dynamic thermal cycles in North America. Changes in temperature cause the joints to expand and contract. Typically, the more flexibility the sealant allows the better. Silicone allows for greater movement if that’s what’s necessary. What does this mean for the owner? For a full system replacement, most manufacturers of polyurethane offer a 5 year warranty. From a silicone manufacturer, you can get a 20 year warranty. The choice comes down to how long you are planning on maintaining the building. Some warranties are transferable to the new property owner.

Cost

We all know cost is a big factor in any decision making process. When deciding between a polyurethane or silicone sealant on a replacement project, you should remember to take a few factors into account. First is the cost of material. Silicone can be up to twice as expensive as polyurethane. Second is the cost of labor. While the initial application process takes about the same amount of time for each material, the frequency in which you will have to repair and replace the polyurethane sealant can be much higher.

Is it possible to transition from polyurethane to silicone?

Yes. However, when replacing existing polyurethane with silicone, great care needs to be made and a lot of extra labor is involved to ensure all existing material is removed.  If the polyurethane is left trapped under the new silicone, it can deteriorate the new silicone over time which can destroy the bond and material. At PCM Services, we always recommend pre-construction mock-ups and testing to determine the level of preparation work required to do the job, to determine if a primer is necessary, and to ensure the aesthetics are acceptable. Many studies have shown that the average typical construction job budgets less than 1% for exterior sealants. And yet, after construction, close to 80% of all water intrusion issues related to the original construction are due to joint sealant problems. There is both a science and an art to successful completion of a functional sealant joint. In the end, it will cost much more to replace the sealant than if it was simply installed correctly the first time.

Why should you care?

You see a crack in one of your buildings. You know it needs new sealant. You meet with a few building maintenance companies and they give you some estimates. Before you jump on the cheapest offer, you may want to know why there is such a large price disparity. What can initially be a cheap, quick fix could ultimately turn into an expensive headache. Choose the right sealant up front and avoid reoccurring repairs in the future.