Hardwood Flooring Filler
Different Types Of Filler. Prefinished Floors
It is important to know what type of filler can be used with 
prefinished hardwood floors. Considering the floor after installation is the final product, some types of filler cannot be used, specifically those that are not water based or acrylic. Fast drying alcohol based fillers evaporate quickly. Often what happens is a residue gets left behind that bonds to prefinished floors and cannot be removed safely.
See our video on floor filling with unfinished floors
Some prefinished flooring manufacturers offer their own proprietary floor fillers that come in smaller tubes. They
work well for smaller projects and filling minor gaps like the one shown, but let‘s say you made a mistake and bought a great price reduced hardwood but nobody told you about the gaps you may be faced with. Yup, you’ll find this is quite common with lower priced prefinished hardwoods.
Minwax, Woodwise Filler
If the manufacturer does not provide a filler, the most accessible product one can use is made by Minwax, found in every big box store. This water based wood putty is offered in nine different hardwood tones. Woodwise, a product many professionals use offers a similar product, but in sixteen colors including harder to find Brazilian Cherry and bamboo colors.
For larger problems I’ve found the Pergo laminate sealer effective. Priced at about nine dollars a caulk tube, you should be able to buy it off the shelf at any big box store. The makeup is practically identical to what some hardwood floor manufacturers offer. Acrylic water based and it comes in four or five colors. The products mentioned do have some elasticity to them, however do not be surprised if the filler gets squeezed out during periods of higher humidity.
That’s one of the biggest problems with filling cracks in both prefinished and unfinished floors. Typically during colder months heating systems dry out the environment to the point floors begin to shrink and gaps appear. This is a natural event and can be controlled with a humidification system. Conversely, during periods of
higher humidity, or when doors and windows are open in the warmer summer months, cracks close up and the filler often gets pushed out.
Unfinished Floors - Being Refinished
The same holds true with unfinished floors in regards to seasonal changes. Most finishers will trowel fill the cracks after the first rough sanding pass with the drum sander. These fillers don’t have the flexibility like the ones mentioned above as they dry hard.
Maybe you’re thinking why use it if the filler is going to pop out anyway? Fillers actually encapsulate or protect older floors being refinished. Essentially, older cleaning agents or waxes often seep into the cracks over the years. This can create bubbling or a fish eye effect as they can react adversely with new finish applications.
Trowelable filler that many professionals place confidence in with unfinished floors include Woodwise, Bona Pacific and Timbermate. These products come in quarts, one gallon and 3.5 gallon containers and can be found at many local flooring supply houses. Woodwise also offers smaller packages in three and seven ounce jars.
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