Poly bubbles in your oil-based wood floor finish are a dreaded issue and almost impossible to repair. The good news is that they can be avoided with some care and attention to detail.
A few key points to summarize what we will soon get into with more detail: if the floor is not sanded to be completely smooth and flat before you start your application, if your finish application is too thick, and/or if you rush through the process, you will most likely have to deal with poly bubbles and numerous other problems, and the callbacks will surely follow.
The best way to fix such problems with your finish is to make sure you’re doing things right the first time! So here are some tips to prevent poly bubbles from showing up in your wood floor finish:
First of all, make sure the humidity conditions will allow the finish to actually dry before you start the job. If the relative humidity is too high, the finish might not dry properly, essentially sitting as a puddle on top of the floor, and all of your efforts beyond this point will be as good as moot. Acceptable relative humidity conditions for most oil-based poly finishes is usually up to 78 – 80%, but check the specifications from the manufacturer of the particular finish you are using.
Sand the floor with an aggressive grit to get the finish off if you’re refinishing, or to smooth out the boards if you’re installing a new floor. Make sure to vacuum thoroughly in between screening the coats of finish. We recommend a piece of equipment like the ProTeam MegaVac. Make sure that when you’re sanding, your buffer and sander are hooked up to a powerful dust containment system (DCS) as well to ensure that you end up with the smoothest finish possible. Leftover dust can cause a number of problems.
Try troweling your first coat to make sure you start off right by applying a thin coat. (Note that you should only use a trowel if the finish manufacturer approves of this application method.) Most oil-modified polyurethane finishes call for three coats for best results. Note that using a lamb’s wool applicator can make it trickier to apply a thin coat of finish, but if that’s your preferred method for applying oil-based hardwood floor finish, you can certainly use it.
The key is to make sure you’re applying thin coats of finish. This usually means no more than 800 sq. ft. per gallon of finish.
Make sure that each coat is dry before applying the next. If you’re unsure whether it’s fully dry yet, try screening a small area with a wood floor buffer. If the finish starts gumming up, stop and wait 24 hours to apply the next coat. Similarly, when working with stains, make sure the stain dries fully before starting to apply your finish on top. Most finishes require 24-72 hours to fully dry. In many cases, the finish won’t stick to the stain if the stain is not yet fully dry. Try ventilating all coats with a large box fan about 4-5 hours after the finish is applied to facilitate the process.
Screen the floor in between coats while taking special care not to go too deep. Screening is crucial to ensure that the next coat of finish will stick to the previous coat. Once the finish is dry and ready to screen, tack the floor with a slightly damp rag to get up any fine dust that the vacuum left behind before proceeding.
For the second and third coats, try applying with a natural bristle brush (specifically designed to apply finish) attached to a long pole. Browse our selection of natural bristle brushes. Feather your coats of finish to ensure that they are thin enough and to avoid puddles.
Applying your finish with a natural bristle brush will be more time-consuming than using other application methods, but this is a great way to avoid creating poly bubbles.
Note that using overhead lights while applying the finish and coating the floor at night are not good choices because they won’t provide you with an accurate view of what’s going on. You have to look at the finish through the sunlight filtering through the window for the most accurate view of what’s going on as you’re applying it.
The key throughout this process is to apply several thin coats of finish to build upon one another, rather than applying thick coats of finish. This is your best bet to avoid creating bubbles in your wood floor finish!