Why Were There Bumps in this Waterborne Finish?

Daniel Boone Headshot

At a seminar for Golden State Flooring in South San Francisco, Calif., I was asked a question about bumps in a water-based finish. The bumps were only in one room in the house, which was the starting point of the last coat of finish. As I got all the details on how the job was sanded and finished, as well as all the products and procedures that were used to complete the job, I realized there were a lot of things that had been overlooked. When I looked inside the contractor's work van, I found a number of things that could have caused the bumps.

PROBLEM #1:

The water-based finish pad that was used for the last coat of finish had also been used for all coats, including the sealer. This creates big problems when finishing a hardwood floor. Most water-based sealers don't mix with water-based finishes (always check the manufacturer's recommended finish procedures). Also, the pad was not cleaned but placed in a pad container filled with water, and the water had not been changed between the different finish coats.

THE SOLUTION:

It is to your benefit to keep a separate pad for each coat of finish, i.e. first coat, second coat, etc. This prevents trash and contaminants from being transferred from one coat to the next. For example, when you use a lambswool pad on the first coat of polyurethane — with either a natural or stained floor — the pad will collect small pieces of wood fiber or splinters that are impossible to remove from the pad. These splinters will eventually end up in the second or third coat of finish,causing bumps or blemishes in the last coat.

PROBLEM #2:

Dirt and other contaminants were tracked onto the job and into the finish.

THE SOLUTION:

Keep your truck and equipment clean. Remember, always vacuum or blow off all machines and tools before entering the job. Most jobs with finish problems are created by not taking the time to clean the area from the truck to the door.

The buffer is the last machine that's used on a job, whether you are screening bare wood or preparing the finish for another coat. Even if you are using a dust-containment system, the buffer and buffer parts should always be kept clean. If dust from a previous sanding job is transferred to a job that will be coated with a water-based finish, it may cause bumps or roughness in the finish. Also, the pads that are used to back a screen collect dust and debris, and they lose small fibers when they are damaged. All of these things contribute to finish problems.

When finishing hardwood floors in an uncontrolled environment, it's always best to spot potential problems before they occur. Remember that you are the professional who was hired to do the job right the first time. Putting all procedures on paper and making them known to the homeowner or general contractor will make things go more smoothly on the job. We all know it's almost impossible to keep people and other trades off our beautiful wood floors, but it should be made clear how important it is to keep the job clean.

MINIMIZE YOUR CHANCES OF FINISH CONTAMINATION

• Use the appropriate applicator for the finish you are using. (Follow the finish manufacturer’s recommendations.)• Don’t use the same applicator for the second coat that you used for the first. It’s best to have one applicatorthat you always use for the first coat, another you always use for the second coat, and so on.• After each use, clean and store applicators properly. Proper cleaning and storage will vary, depending on the type of finish used. Follow the finish and applicator manufacturers’ recommendations.• Sweep and vacuum the floor thoroughly before beginning to apply finish.• Sweep, vacuum and tack the floor between coats.• Avoid tracking dirt and other contaminants onto the floor. One way to do this is to change shoes as you enter the job site. Some floor finishers put cloth “boots” over their shoes before entering the job site.• Keep your truck and equipment clean.

 

NWFA’s Director of Technical Training Daniel Boone and the rest of NWFA’s expert staff are available to answer members’ technical questions. Call 800/422-4556 (U.S.), 800/848-8824 (Canada) with questions or 314/391-5161 (local and international) to get membership information.

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