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The Problem
A few months back, a reputable contractor in our area called and wanted me to look at a job that was giving him headaches. He had just finished recoating a maple floor. Immediately after applying the final coat, he told me he noticed a large section of the floor reacting. Once dry, this section of finish alligatored and peeled badly enough to expose bare wood. The contractor told me he had done everything he normally does for successful recoats.
The Procedure
Prior to even touching the floor, the contractor had gone over many questions and answers with the homeowner—asking about the cleaning history, chemicals used, and the original type of finish used on the floor. Satisfied with the answers, he then lightly abraded the surface and cleaned the floor with a chemically treated tack cloth. Then, the contractor applied conversion varnish using a brush.
The finish went on smoothly as usual, and there were no problems with flow or leveling—until he reached that particular section of the floor. The finish seemed to pull away from itself. He stopped coating immediately. By the next day, that part of the finished floor was alligatoring and showing discoloration.
The Cause
As he and I inspected the problem area, it became obvious that some sort of contaminant had been spilled on that section of floor at some point. Even after his standard recoat prep work, the contaminant had not been neutralized.
Contaminants introduced to open finish and/or contaminants on the floor itself prior to finishing are by far the most common culprits in adhesion issues, even when using an aggressive finish such as conversion varnish. This is especially common in a recoat situation.
How to Fix the Floor
Should a floor have minor alligatoring and peeling issues, the solution may be to simply screen and recoat. When using a finish such as conversion varnish, hand-scraping and hand-sanding prior to a screen will likely smooth out alligatored sections. These steps are usually sufficient, especially if the section is off to the side or near a wall where any sheen differentiation won't be noticeable. However, in this particular scenario, there was excessive peeling down to bare wood, and a simple screen and recoat would not produce quality results. In the end,the floor was resanded to bare wood and refinished.
In the Future
As most contractors will say, a recoat can include enough unknowns to make anyone a little nervous. In this particular situation, the contractor did a good job of doing his homework about the floor before starting.
Let's examine the method of cleaning for wood floor recoats. Rather than using a tack cloth with chemical components, I would advise cleaning thoroughly with the finish manufacturer's specially formulated cleaner. Go over the entire floor with the cleaner several times, rotating in dirt-free rags with each pass. If you can't get your hands on the cleaner, my next choice would be to clean with denatured alcohol. Lacquer thinner is a popular choice for many, but I've found it to be a bit too harsh on some jobs. Be sure to check with your finish manufacturer for acceptable cleaners.
Once the floor has been thoroughly cleaned,examine the floor. If you notice any problem areas,notify the homeowner before taking any further steps. You might be better off resanding. If there are no obvious problems, then abrade the floor according to the manufacturer's recommendations. The type of finish you use will most likely influence how you abrade. Use any bonding additive the manufacturer recommends, as well, as they offer increased adhesion on a recoat and may make the difference between success or failure.
If there are too many unknowns regarding are coat job, the safest bet will probably be a resand and finish. In most cases, sanding to bare wood eliminates the possibility of prior coating contamination.
Remember, not all homeowners may be "in the know" about contaminants when answering your questions. After all, contaminants can range from the obvious (oil soaps) to the obscure (mayonnaise). Your work and reputation are on the line,not to mention the financial burden of restoring aproblem floor. When possible, obtain a fully answered questionnaire about a floor's history,complete with homeowner's signature, before beginning work on a suspect recoat. Worst case scenario if the floor is a complete mess? Walk away—some recoat jobs are just not worth the headache.
Bottom line: Prep the homeowner as much as you prep the floor. Involving homeowners in therec oat process and preparing them for possible outcomes can make a big difference. Case in point: The contractor in this situation earned two paychecks from one floor job.