Silicon (notice the spelling difference from “silicone”), is number 14 on the periodic table of elements and happens to be second most abundant element in the earth’s crust. It was first isolated as an element in the 1820’s and has since been used to create products we use in everyday life. It is used in semiconductors and photovoltaic panels. Silicon dioxide, or silica, is used in concrete and in the production of ceramics. Silicon is also used to create silicone, a manmade compound with many applications. It is used in the medical community (think implants) and as a lubricant used in both industrial applications and for food preparation (non-stick cookware). What this article will focus on though is its use in the construction industry, as a sealant.
A sealant is a material used to keep something, (liquid, air, dust, sound and heat), in or out of a joint or opening, it’s a type of mechanical seal. Sealant is often referred to as “caulking”, I’ve also heard “silicone” used as a blanket term when describing a sealant. Silicone is a synthetic or man-made polymer that is one type in a family of many different formulations of sealants. It was first introduced in the construction industry in the mid 1950’s and is still a very popular sealant, even with many other choices available.
The properties of silicone, mostly the good.
Silicone is a type of synthetic rubber made from pure silicone. Silicone sealants can be clear (kind of) or colorants can be added. It retains a level of flexibility and elasticity after it cures. Silicone is non-toxic, making a good choice in food preparation areas. It is tolerant of high temperatures and is resistant to moisture and UV. There are variations in silicone formulas, the biggest being how they cure. Neutral cure silicone tends to bond better to most common building materials. Acid or acetoxy cure silicone is the type that has a strong vinegar smell when using, (it’s made my eyes water on many occasions) this silicone is usually less expensive and tends to cure quickly but the acid can adversely affect some surfaces.
Now for the bad.
Okay, not really bad, but there can be better choices in many circumstances. Most silicones will not accept paint, in some instances, color matching to adjacent surfaces can be difficult. Silicone has a decent bond with good flexibility, but there are newer sealants that perform much better in both categories. We will discuss silicone alternatives shortly.
And this really is ugly and should be a deciding factor when choosing a sealant. Most silicone will not stick to itself, and other sealants will also not stick to it, so if, or more likely, when a joint requires maintenance, all of the cured product needs to be removed from the surfaces. This includes any thin residue left on the substrate, often removal will require one or more chemical or heat treatments with multiple scrapings to remove all the silicone residue. If this is not completed, premature failure of any new sealant applications may result.
The Alternatives-Synthetic Rubber
Advances in sealant technologies continue to improve and alternatives to silicone have been around for a few years. Three of the more common and readily accessible options are Sashco’s Lexel, OSI Quad and DAP’s Ultra Clear. All three manufacturers offer a clear synthetic rubber sealant that is produced using a different chemistry than the traditional silicone sealants.
The benefits of the newer synthetic rubber formulations.
These synthetic rubber sealants are sticky, whereas silicone tends to be greasier. All three alternatives have impressive adhesion characteristics. They bond to most surfaces and can even be successfully applied to damp and wet surfaces. Most hold their seal even when submerged. They are mold and mildew resistant, and paints will stick to the sealant once it has cured. They are more clear than traditional silicone, and because of their solvent base, are freeze resistant with application temperatures as low as 0°F and service temperatures ranges from -40° to +200°F. The biggest advantage of this formulation of sealant is its ability to stretch and move when needed, then return to its original shape. Joint movement of up to 400% can be reached before adhesion or cohesion failures.
A few drawbacks.
No one sealant is perfect for every job, synthetic rubber sealants are no different. Because of their solvent base, the material shrinks as it cures and they do not work well with polystyrene, polypropylene or polyethylene products. There are a few other compatibility limitations, check with the manufacturer’s technical data sheet for more details. Another downside to the solvent base, they have a higher VOC level. This dissipates quickly as the product cures, but application is recommended in well-ventilated areas. Both Lexel and Ultra Clear products can be tooled, OSI Quad does not recommend tooling.
My experience in using these silicone alternatives.
My preference is to use water based or acrylic sealants whenever possible, (they are easier to tool and easier to clean up.) but if I need an increase in performance such as greater elasticity or a better bond, the synthetic rubber products are my next choice. They are very impressive in both how they adhere to other materials and in the amount of joint movement before failure. Because of how sticky they are, they can be a bit tricky to tool and will require something more than water to clean up. You’re going to want to follow the manufacturer’s recommendations in both. There is a sealant option that has a more robust adhesion, polyurethane sealants. This sealant/adhesive technology can be problematic when it comes time to servicing the joint. Polyurethane will stick tenaciously to surfaces, making removal of the product difficult, for this reason, synthetic rubber may be a better choice in many circumstances.
In my opinion, silicone had become the “Kleenex” of sealants, often resulting in the word silicone being substituted for sealant. Something I’ve learned about being in the construction industry for nearly 3o years is product improvement and innovation is ongoing. There are companies out there constantly testing their products against their competitors and trying to improve their products and processes. The sealant and adhesive industry are no different. Silicone was, at one time, the best sealant available for many applications, and it still has many uses, but advancements in the chemistry have shown there are now products that can perform better, especially when the sealant fails, and maintenance is required.