Why Is Caulk or ” No More Gaps” Important ?
December 27, 2015
Long considered a carpenter’s best friend for it’s ability to hide inaccurate cuts, no more gaps or “caulk” plays a crucial role in protecting the exterior of a house. The primary purpose of caulk is to provide a water and weather proof barrier. Typically, caulk is applied to joints where two pieces of construction material meet, such as where wood meets wood, or wood meets masonry. To maintain this barrier, caulk should have several key properties: flexibility, adhesion, and “memory”.
Temperature, moisture, and building settling can cause movement in the various components of the structure. Flexibility is important for maintaining the seal during the expansion caused by this movement. Equally important, the no more gaps or “caulk” must ‘remember’ its original shape and return to it when the gap contracts. As with paint, caulks and sealants can be formulated for specific purposes. For example, silicone sealants provide the best adhesion and flexibility; however, they are not paintable, rendering them inappropriate for most applications.
Siliconised acrylic caulks, on the other hand, have a small amount of silicone. The silicone gives the acrylic caulk superior adhesion and flexibility, yet the caulk is paintable. Siliconized acrylic caulks are the best all-purpose sealant. In addition, siliconized acrylic caulks can be cleaned up with water, making them easier to apply and achieve a smooth finish.
While caulk is usually used to seal all exterior joints, caulking certain types of joints can actually cause more problems than it will prevent. Certain types of exterior cladding, for example, are designed to allow air movement between overlapping pieces. Sealing this gap can trap moisture behind the siding, leading to peeling paint, mildewed insulation, and similar problems.
Generally, caulks and sealants are members of one of the following types of chemical families. Like any family, each has strong points, weak points and idiosyncrasies that can make it a very good — or very poor — match for the job at hand.
Polyurethanes: While these reactive- or chemical-curing compounds are difficult to gun and tool and require solvent cleanup, they have excellent flexibility and have good to excellent durability. Some must be applied to a primed surface, but in general they adhere well to a variety of surfaces. They shrink little while curing and can withstand traffic once cured. Even if the surface degrades with heavy traffic, the compound will still maintain an effective seal. They tend to be more expensive than other types of sealants. Once cured, polyurethanes have limited paintability and may react with alkyd- or oil-based paints.
Silicones: Silicones are also reactive-curing compounds, but they offer easy gunning ability. Their jelly-like consistency makes them hard to tool for a nice finish, but they cure quickly and will cure at below-freezing temperatures. Once cured, they are very flexible, extremely durable and resist ultraviolet light degradation. They maintain their properties over a wide temperature range. Most 100% silicone-based compounds cannot be painted. Because they are hard to remove completely, especially on porous surfaces, repairs and future painting can be difficult. New silicone may not stick to old silicone, so proper surface preparation is the key to successful sealant repairs where silicones have been used.
Acrylics: These are the most common in the paint industry and come in a variety of formulations that affect cost, durability and adhesion. They are easy to gun and because they are water-based, they clean up easily. They are low in cost and come in a wide range of performance grades. Typically, the higher the cost, the greater the performance you can expect.
Acrylics cannot be applied in wet or freezing conditions or at temperatures over 100° F. All acrylics are paintable, and no primer is needed before application. Many are available in colors to match substrate, eliminating the need for painting.
Urethane hybrid blended acrylics are at the high end of the acrylic family in cost and performance and can often be used in a variety of applications where a silicone or polyurethane sealant may be used.