Posted by Darrell Nicholson at 03:29PM - Comments: (4)
Application ease is an important factor when it comes to the caulking and seam-filling process, and some sealant/adhesives behave better than others. Among the most desirable traits is viscosity; the ideal consistency should be a paste-like material that can be easily injected into a seam or spread on a piece of hardware.
Of the products we tested for our test of sealants in August of 2010, we found that Sika-flex 291 LOT and 3M’s 4200 Fast Cure had the right consistency to make application a user-friendly experience. They were thin enough to penetrate small seams, but stiff enough to form an even bead.
When applying sealants, surface prep follows the painter’s mantra of smooth, even, and clean. Any contamination—be it oil, wax, or loose varnish or paint—has the ability to nullify the adhesion of a sealant. The prerequisite to a reliably caulked seam starts with the usual scrape, sand, dust, and wash clean.
Most adhesive sealants like well-prepped gelcoat or an epoxy-primed surface, but in the case of the latter, beware of what’s called “amine blush,” a residue that forms on the surface of epoxy resins and primers when they cure. Washing the surface before applying an sealant is a simple cure that removes the adhesion-robbing residue.
All products we tested had the near-magic ability to stick to every place they are not welcome, and attention to detail during the application process is required. Lightweight throw-away gloves, a roll of paper towels, and a paper bag to dump contaminated wipe-off towels into are a must. Work from the top down whether it’s on deck or filling plank seams on the hull. Use masking tape to confine the over-spread and maintain a crisp cut line. All but silicone sealers can be sanded and painted, but the best bet is to achieve a fair, even bead that needs no hiding.
If you’re left with a half-used tube of sealant or caulk, try this preservation method suggested to us years ago by former contributor Dick Wilkens: With a piece of plastic (like Saran Wrap) over your finger, push the sealant back into the tube a bit, leave the plastic in place, and replace the tube’s cap. The plastic excludes the air that usually lets the sealant harden under the cap. According to Wilkens, this can extend the usable life of the product for years.
For more help on selecting an adhesive sealants, subscribers can refer to our August 2010, April 2005, August 2006 and November 1998 test reports online. If you are sealing hatches or ports, you will also want to read our December 2012 PS Advisor column, which introduces some other options for bedding and sealing. There is also our October 2008 test of caulks for teak decks.