Caulking and Sealants 101
The purpose of Caulks and Sealants in a home is to bridge the gap between two building materials in order to provide a seal. The presence of this seal will prevent seepage of water and air; whether to keep the cold out around your windows or to keep the water inside the shower. The question is; which caulks or sealants work best for the job at hand? When you visit the caulking aisle, there is enough choice to make your head spin. It used to be quite simple; silicone was the wonder-seal. Two problems; it doesn’t adhere well to wood and when it came to painting, the paint would not adhere to silicone. Then came along latex caulking, easy to use and cleaned up with water. The problem with the first latex products was that they did not perform as well as silicone does. Now, we have both products and everything else in between.
First thing to consider
Most products perform well when they are used in applications for which they were created. Not doing so, is the primary reason why most sealants fail. The second is inadequate surface preparation prior to application. Before making your selection, consider what materials are to be bridged, how much movement will there be in the joint and what type of environmental conditions is the sealant going to be exposed to?
Selecting your sealant
Water based sealants are very easy to use and have many applications. These sealants are ideal for filling fine gaps in trim work. They will adhere to most building materials and can be painted. They produce very little odor and are non-toxic. These latex products are perfect for interior applications. When our demands increase, the high performance latex products rise to the occasion. These premier latex products, like Dynaflex 230 from Dap, can be used for interior and exterior purposes and some of them even have antibacterial qualities that makes them suitable for kitchens and baths. The key is to apply these products in ideal conditions prior to exposure to the elements. A warm dry environment will ensure that they cure properly and perform as promised.
Silicone based products continue to have remarkable performance. They stand up to extreme weather conditions, resist mold and mildew growth, have tremendous flexibility and can be applied at virtually any temperature. Silicone does have an odor; however, it is non toxic. It adheres extremely well to most tiles, glass, plastics and metals. Silicone will not adhere well to cured silicone and for this reason, it is very important to prepare and clear any surface from old caulking prior to applying new.
Polyurethane products are generally more difficult to work with because they are harder to apply and require solvents to clean up. They are toxic and should be handled appropriately. However, when it comes to outdoor performance, they deliver. These sealants have a high abrasion tolerance, they remain flexible and they can be painted. They are ideal in high traffic applications and hold up well around doors windows and siding.
Butyl or Rubber caulking work well in applications where shear strength is required. Shearing occurs in joints where two materials overlap each other. Roof flashing, siding and evestroughs are areas where Butyls are the best choice. These sealants remain soft and can stretch with the joint. They have resistance to moisture and as such are ideal for foundation repairs or anywhere sealants are required below grade.
Elastomeric Caulks can be used in interior or exterior applications and have great adhesion to almost all surfaces. Some, depending on manufacturer, will stretch 200% or more. These sealants can be applied in most weather conditions and can be painted once cured.
Applying the caulking
Once you have selected the correct sealant for your application you are ready to begin, or are you? The performance of the caulking and the success of your project rely heavily on the process of application. There are several things to consider. First; like any home improvement project, preparation is vital, you must have clean surfaces for proper adhesion. All loose paint, old caulking, dust and dirt must first be removed. Some caulks require certain temperature and humidity conditions; ensure your settings are suitable. Next, remember that caulking is not recommended for filling gaps over ½” wide. For it to perform best when bridging gaps, it must bond on only two sides of the gap.
That is why a “Backer Rod” is placed into the gap first and then the caulking is applied. The Backer Rod is a polyurethane foam rod and the caulking will not adhere to it, therefore it only bonds with the two materials on either side of the joint.
Finally, know that caulking bonds best at 90 degree angles. Feathering the edge of the bead by running your finger over it will produce a weak bond, allowing moisture and dirt to penetrate under the feathered edge. That’s why most caulking projects in showers and baths don’t last long before mold and mildew begin to grow “under” the edge of the caulking.
Using tape, such as green painters’ tape, to border and outline your caulking joint gives you a straight bead once the tape is removed. Remember that the tape must be removed as soon as the caulking is applied and smoothed out. If the tape is left too long, the sealant will begin to cure and will pull apart when the tape is removed.
More importantly, once the tape is properly removed, it results in a 90 degree bond between the sealant and the substrate due to the thickness of the edge of the tape. This 90 degree joint, as small as it may be, is a much stronger joint and will hold up to much more abuse from everyday use and cleaning.