The Fundamentals of Sanding Wood Floors – Part 4 Filling and Fine Sanding

Whether sanding a new floor or refinishing an old one, many situations call for filling the gaps, nail holes, and voids in the floor. Now that you are done flattening the floor, vacuum and fill it as needed. There are five options: the first one is to full trowel the floor. That means on your knees using a trowel (that be flexible or not) to spread the filler. Pre-mixed fillers come in different colors to match the wood you are filling and tend to do a good job of accepting traditional stains. When you full trowel a floor it is important to push the filler into the voids, simply bridging the filler over the gaps across the floor as fast as possible isn’t fulfilling the purpose of trowel filling. Let the filler completely dry before sanding it off with a finer grit.

Your second option is to spot fill the floor. Let’s say that the floor is very tight with minimal gaps, or a rustic floor that the homeowner doesn’t want filled – why would you full trowel it with filler? When spot filling, I prefer a patch product, not a product designed to be full troweled. These products are thicker and tend to dry very hard. Using a putty knife walk the floor and spot fill any end joints, nail holes and other areas that need attention. Let the filler dry and sand the same as above.

Your third option is to make your own filler. Old school products like Wood Flour Cement and mixing compounds are still available and have their pros and cons. Making your own filler is simple: use fine dust from edging or multi-disc machine (usually 80 grit or finer) and mix with the flour cement or a mixing compound. Trowel or spot fill the floor as needed. Keeping in mind these products dry very hard and can be more difficult to sand off. The pros of making your own filler:

  • Exotic woods like Jatoba (Brazilian cherry) will change color quickly, so using your own filler ensures that the filler will change color along with the wood. When using a latex based pre-mixed filler with light-sensitive species, as the floor changes color, the filler remains leaving a distinct variation between the two.
  • We do a lot of top nail floors in the Bay Area, California. WFC is the only way to go for us so that we can get a flat surface over the entire floor. With so many nail holes (2 nails in each 2” board every 6” -7”) in the floor, the filler must be hard enough so it doesn’t dish out under the belt sander and the fine sanding machines
  • Sometimes a pre-mixed filler in the color you need isn’t available. Being able and knowing how to make your own is a plus
  • Plus it dries super fast and extremely hard.

The cons of making your own filler:

  • Some versions can be highly flammable and can have a strong odor. Ventilating the house is often necessary.

When sanding the filler off the floor, you have two options:

  1. Use the big machine with a finer grit.
  2. Use a multi-disc machine, a buffer with proper attachments and/or other sanders now available on the market.

The idea of sanding the filler off is to remove the scratches from the last pass.

If using the big machine, go with the direction of the floor. If using any other machine, follow manufacturer recommendations.

When you are done with the field, work your way around the edges and scrape the corners.

Next time we will discuss how to use the edger and how to use a scraper.

Be safe.

Avi Hadad is the owner-operator of Avi’s Hardwood Floors in the San Francisco Bay area. He can be reached at

Technical Editor Note: Be sure to follow NWFA Sand & Finish Guidelines for specific details on this subject. Five options: grain filler, spot filler, trowel filler, touch-up putty, and hard wax sticks.

3 thoughts

  1. I have used a variety of products, I am in Michigan btw. Much of the gaps are related to humidity summer vs. winter. Is there a product that is durable and can handle the changes summer to winter and won’t flake out? I have not found one as yet.

  2. Hello,

    We have sanded our hardwood floor to get rid of some stains and rough areas. Most of the stains are gone but now we have tiny staple holes everywhere.

    It looks horrible and our contractor says no way to get rid of them. Are we missing a step or a point or is it something normal( as they claim) ?

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