Tips for Applying Marine Sealants

Applying marine sealant is not particularly difficult, but like any other application, it’s important to follow the instructions to get the best results.

Cutting corners or failing to apply marine sealant correctly can lead to bad seals that fail to do what the product was meant to fix. Here are some tips for applying marine sealants. 

Choose the Right Sealant

The right sealant ensures a secure and durable seal, whereas the wrong sealant will spring a leak in no time. There are four distinct types of marine sealant, each perfectly suited to certain jobs, but unsuitable for others. 

These marine sealants are: polyurethane, silicone, polysulfide and polyether. Here we’ll be focusing on only on two: silicone and polyurethane.

Polyurethane sealant provides the strongest adhesive bond of all sealants, but can’t be used on some plastics. This sealant is easily damaged by chemicals (fuel, solvents, bleach), but if a strong bond is required, a polyurethane sealant may be the best option.

Silicone sealant can be used on all materials (wood, metal, plastic), but provides the weakest adhesive bond. This sealant isn’t damaged by heat or chemicals, and if the seal must resist harsh chemicals, a silicone sealant may be the best option.

Prepare the Surface

When using marine sealant, the surfaces to be sealed should be thoroughly cleaned and any old sealant removed, because the marine sealant won’t adhere as well to oily or dirty surfaces

Use a knife or razor blade to cut away debris and old sealant, and use a rotary tool or sandpaper to grind out any debris from nooks and crannies. Once all the debris is removed, clean the surfaces with a solvent to remove any oil or grease residue, then wait for the surfaces to dry before applying any sealant. Consult the sealant manufacturer’s instructions for the correct solvent to use. 

NOTE: It may be necessary to prime and to “key” the surfaces to be bonded by scoring them with a knife or roughening them with sandpaper to help the sealant bond more effectively to the surfaces.

Next, mask off the area around the surfaces that are to be sealed to prevent excess sealant from coming into contact with the adjoining areas.

NOTE: Marine sealant sticks to everything it comes into contact with, so have plenty of rags and solvent ready. Use coveralls and gloves to protect your hands and clothes. 

Let the Sealant Cure

Allow the sealant to fully cure before tightening any mechanical fastenings (screws, nuts and bolts) that secure the surfaces.

Tightening down mechanical fastenings before the sealant has cured will force the wet sealant out from between the surfaces, leaving little, if any sealant left to create the seal. By allowing the sealant to properly cure and harden, the sealant won’t be forced out when the surfaces are tightened again.

NOTE: Curing times may take a week or more. Follow the sealant manufacturer’s instructions for the correct curing time.