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Paint Geeks: Caulk & Sealant for Healthy Joints

18 August, 2020

Although caulking and sealing are common projects for painters, doing so correctly takes some preparation, skill and knowledge of the types of products to use. Especially for locations with changing seasons, it’s important to select a caulk or sealant that can expand and contract and that provides strong adhesion and superior flexibility for these types of demanding applications. The sealant needs to strongly adhere to the surface and stay flexible to withstand expansion and contraction without cracking or losing adhesion. Look for caulks or sealants that can provide multisurface use, say “siliconized, elastomeric or advanced,” and meet ASTM Specification C920. This testing indicates that they have been proven to provide exceptional adhesion and flexibility.

Caulks typically fail for two main reasons: they haven’t been properly applied or the wrong caulk is used for the job. Preparation is key before beginning any caulk project. If the area where the caulk is to be applied hasn’t been properly prepared, it can lead to failure down the road. Most caulks require that the application area be clean, dry and free of old caulk, dirt and debris. If the area is dirty, the new caulk can’t properly adhere to the surface. Additionally, not applying enough caulk can cause failures, especially with latex sealants that are designed to shrink a little bit after they’ve dried.  If too little is applied and tooled and then the caulk shrinks, it can contribute to cracking and loss of adhesion.

Another issue that can lead to failures is if the joint is too deep or too wide. In this case, the caulk may not dry completely, leading to poor performance. You should always read the label to determine the recommended joint depth and width for the caulk you’ve selected. 

Finally, using the wrong caulk for the job can lead to failure. For example, you wouldn’t want to use a less expensive painter’s grade caulk with low flexibility for a demanding exterior application, such as around a window or entry door. More demanding applications such as these will be constantly exposed to temperature and moisture fluctuations as well as UV exposure. Constant exposure to these harsh conditions can lead to poor performance or shortened product life.

Trained Seals

Caulks and sealants also can be used to provide a waterproof seal between two dissimilar surfaces. Typical applications include filling gaps and cracks, such as between a window and the siding, to keep out water, moisture and air and to prevent damage. Caulks and sealants shouldn’t be skim coated to replace a liquid-based waterproofing coating where such an application is required.

When properly applied, caulks and sealants are designed to provide a durable, waterproof seal. Again, be sure the area to be caulked is properly prepped and cleaned and be sure to use backer rod material if the joint is too deep. Each caulk is different, so make sure to read the label to understand the application recommendations. Higher performance sealants will offer stronger adhesion to a wider variety of substrates and greater flexibility to withstand joint movement. All of those characteristics contribute to a strong, durable seal that will stand up to water and the elements without cracking or breaking down.

The Prime Directive

When it comes to painting applications, a caulk typically does not need to be primed before painting unless specifically recommended by your paint manufacturer. In most cases, the work surface would benefit more from an application of primer before applying the caulk, not after. Most primers are specifically focused on stain blocking and promoting adhesion. Likewise, most primers tend to be low in flexibility – simply put, they do not flex as well as most caulks and sealants. In joints where a significant amount of expansion or contraction may occur, the primer may “check” or crack. For this reason, primers function best when used to prepare a surface to receive caulk or sealant.

The paint-ready time for caulks and sealants varies by product and technology type. Most latex-based caulks and sealants are paint ready in two to four hours; however, there are some latex sealants that are paintable in as little as 20 to 30 minutes, allowing for improved productivity. Hybrid technologies, sometimes referred to as “paintable silicones,” can be painted in as little as 30 minutes, even when applied under challenging conditions.

Polyurethane and solvent-based sealants typically have much longer paint-ready times, some as long as seven days or more. Silicone sealants, on the other hand, are not paintable.

For more information on caulk and sealant products, visit www.dap.com.

By Jennifer Johnson, Group Product Director - Caulks & Sealants, DAP

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