Avoiding Roller Lines in Sealers

By Chris Sullivan – ChemSystems, Inc.

Question:

I applied sealer with a roller and ended up with lap lines. How do I prevent these lines, and is there a way to remove them?

Answer:

First, be sure you are using the proper applicator for the sealer type. Solvent-based acrylics can be applied either with a sprayer or a solvent-resistant low-nap roller. Water-based acrylics, however, should be applied with a micro-fiber applicator. And heavy-bodied coatings (such as polyurethanes and epoxies) should be applied with a block applicator or specialty roller followed by a spiked roller for de-gassing.

Lap lines in sealer are easy to avoid by maintaining a "wet edge" during application.

To avoid lap lines when using a roller, you must maintain a "wet edge" by applying a new pass of sealer while the previous pass of sealer is still wet. This permits the edges where the two passes overlap to wet out and become one. Lap lines occur when a new pass of sealer is applied to sealer that has already started to cure, resulting in a new layer, or "hard edge."

Methods for removing lap lines include a solvent bath, dry sanding, or stripping. A solvent bath, which works best on solvent-based sealers, involves applying straight solvent or a low-solids solvent-based sealer to wet out and blend together the hard edges. Typically the solvent re-liquefies the previous layer of sealer and no additional working of the coating is needed. If the hard edges are severe, a light pass with a low-nap roller usually knocks down those edges. Dry sanding is often used on water-based sealers. Use a 200+ grit screen to lightly sand the surface and knock down the lap lines, and then re-apply the same water-based sealer to even out the sanded surface. If the lap lines are severe, you may need to strip the sealer completely and start over.

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