An essential step in every painting project, caulk application takes more than a strong wrist and a steady hand. Beginning with substrate assessment, followed by proper surface preparation, then skilled application and finishing technique, a successful caulk job should be virtually invisible to the property owner.
Assessing the Situation
Joint size is critical, and most projects present a variety of joint sizes to be dealt with, so more than a single caulk product may be needed. Begin by comparing the joint size to the percentage of movement the caulk you are considering can take. If the joint is greater than 1/2″ deep and 1/2″ in width, it is important to use a backer rod in the joint to maintain the optimal sealant thickness and prevent the sealant from making a three-point bond. Large joints may require the use of elastomeric sealants to stretch and fill the space; typically, ASTM C-920 class sealants are used to successfully bridge large dynamic joints. Caulk or sealant should only be applied at the temperature the manufacturer has recommended. This insures the joint to be caulked or sealed is at the optimum width.
Preparing the surface
Once you’ve determined the correct product(s) for the job, you are ready to prep the surface, which mainly consists of cleaning. Caulking over dirt or dust, or over paint that is not fully attached will not allow the cured bead to adhere, so proper cleaning is a critical step not to be skipped.
If you’re caulking a previously painted surface, remove any peeling or compromised coating. Next, blow as much dust and debris off as you can, and wipe the rest using lightly dampened rags until clean.
If you’re working in a new construction, wipe down baseboards and around joints where drywall dust may have settled. Again, blow as much dust and debris off as possible, then wipe the rest using a damp, lint-free rag.
Regardless of the substrate, never use a soaking-wet rag, as you don’t want to introduce moisture to the surface before caulk application.
Proper caulk bead configuration
It's all in the tooling technique
To begin, cut the tube’s tip (at an angle) slightly smaller than the width of the gap. Avoid cutting the nozzle tip too small to be able to release the yield needed to seal the joint. Practice on a scrap before beginning to assure all is working well. Position the gun so the sealant gets forced into the gap. Pushing or pulling the gun along the surface is acceptable; keep the bead smooth with good contact to the substrate. Run a continuous bead whenever possible and, as a general rule, keep the bead slightly ahead of the tip to eliminate air pockets or overlap that leave an imperfect joint. And take your time; don’t rush this process.
Once the caulk is in place, tooling will improve both surface adhesion and appearance. Be careful not to remove caulk from the joint while tooling or you may leave the bead too small, leading to cracking failure. And never use a solvent when tooling, as that can also diminish the caulking.
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