Photo 1: This is a maple border and white oak field. Note the light colored maple filler compared to the oak colored filler at the bottom of the photo. The gaps at mitered joints in particular required filling.

Photo 2: As the filled gap widened, the filler broke in a jagged pattern. Filler and gaps in this maple floor are a prominent feature and require additional repair. In this case board replacement or slivering can be options.

Gaps in wood floors are one of the issues that most often create call backs for a wood flooring installation. The other most frequent issue is cupping, but that is for another day. So how do we address the gapping issue? Gaps that are strictly seasonal, that is they generally appear in the winter or heating season and close in the summer, require no repair or remediation. If these types of gaps are filled in the winter, cupping can result as the flooring expands from summer humidity.

So, how to fix gaps?

There are basically three fixes:

  • Fill the gaps with commercial wood filler.
  • Take up board or boards and reinstall the boards with no gaps.
  • Fill the gaps with the same species of wood slivers.

Photo 3: This filler actually was squeezed from the gap as the flooring tightened during the summer. The original gap was likely 3/32”.

Filling gaps with wood filler.

This is probably the most common type of repair, but it has its limitations. Small gaps lend themselves to application of filler. This is done most often during the sanding process for finishing or refinishing a floor. (Photo 1) The basic instructions are:

  • Use a filler color that matches the general color of the unfinished wood. If a different basic color is used and the flooring is ever refinished, the color may interfere with the new color choice. An exception is with wood species that change color with age. Use the filler color that is expected as the wood ages. Domestic cherry and tropical hardwoods fall into this category.  Force the filler completely down into the gap to the tongue level of the flooring. (Photo 1)
  • When applying filler, fill the gap completely and force the filler to the tongue level. Inadequate filler application results in the filler breaking away and becoming an unsightly, jagged, partially filled gap. This can be worse than the gap itself. (Photo 2) Gaps to 3/64” wide and less are filling candidates. Yes you can fill larger gaps up to 3/32” but at this point the filler itself becomes noticeable and the likely-hood the filler will come out is increased. (Photo 3)
  • Also when filling a larger gap, applying the filler and letting it dry then refilling is required, since the initial application will shrink and not completely fill the gap.
  • When applying filler, wipe up the excess filler as much as possible. Too much residue can interfere with sanding causing dips and waves as the wheels rollover the bumps.
  • Filling the occasional gap in a factory finished floor is also considered acceptable. The filler should match the basic finish color. It should also have a sealer/finish component mixed into the filler or have finish applied after it has set, since normal use will prominently soil any filler that remains unsealed.

Photo 4: A water leak caused the flooring to expand cup, slightly buckle and gap along this window. The repair was to replace this area. This was a tough repair as the flooring extended around the door jamb and under the marble hearth.

Take up boards where gaps are located and replace without gaps.

This is generally a less frequent option and is normally used in severe cases after such events as water damage. Flooring subjected to such conditions is also generally loose and noisy and needs refastening. The flooring near a wall line or associated with a doorway is the most often area involved. (Photos 4 and 5)

What are the basic rules for this repair?

Photo 5: Replacement boards were tongue and grooved at the ends, and where necessary a spline was glued in place. This is especially critical in traffic areas such as this doorway.

  • Properly acclimated flooring should be used. That is, the replacement flooring should be at the average moisture content of the surrounding flooring. This requires checking with a moisture meter.
  • A good choice for the replacement flooring is the already installed flooring. This should already be acclimated to the site if the moisture issues have been addressed and the flooring has gone through a heating season.

  • Photo 6:  The bottom hollow back, tongue and groove edges are cut from the original flooring to produce slivers with uniform height. Note the angle of the cut edge producing the slivers is about 7-8 degrees.

  • When the existing flooring is used, nails should be clipped off and the boards measured to place like-size boards in the same run. 
  • If replacing an area in the middle of the floor, new slightly wider boards may be necessary as the old boards may not fill the space completely and line up with the existing runs. Reinstalling with some gaps may also be necessary if the repair is during the winter. Tight boards without small expansion gaps can result in area cupping later as summer humidity affects the flooring. 
  • Also light sensitive species will look different from the surrounding older flooring. So it is necessary to set proper customer expectations that the repair will blend over time.

Photo 7: The slivers are being cut. In order to maintain the angle, the stock is turned over for each rip. Also, adjust the fence for wider or narrower slivers as they are made.

Fill the gaps with same-species slivers.

This is becoming a more often used option for repair of gaps. The repair is with the same species so it is not materially different from the existing wood, and a solid properly installed sliver will not break away creating a jagged area during normal seasonal gapping. Larger gaps can also be repaired leaving minimal to no noticeable features, particularly to the casual observer.

Photo 8: The finished slivers should be of different widths to fill the varied gaps.

How to sliver a floor:

  • Cut slivers of different widths and about 1/2 the thickness of the flooring. This allows you to choose a sliver that is right for the gap involved. It is not so tall above the flooring, and during installation will not be too fragile. (Photos 6, 7 and 8)

  • Photo 9: These are gaps that were left after the window repair in Photos 4 and 5.

  • The typical sliver is cut on an eight-degree angle. (Photo 6) Choose slivers that are a similar color and grain pattern of the boards along the gap. This means if the board is a darker heartwood, don’t cut all sapwood slivers.

  • Photo 10: Use a utility knife and thoroughly clean the gap. This can also widen the gap slightly at the tapered ends in order to insert the sliver. Vacuum all the residue from the gap.

  • Clean the gap thoroughly and vacuum out any residue. (Photos 9  and 10)

  • Photo 11: Dry fit the sliver. Be sure to cut to length, as a too-long sliver will break away and not properly fill the gaps at the end.

  • Dry fit the slivers for proper fitting. It may be necessary to cut some of the bottom point off in order to fit into the different width tapered gaps.

    Photo 12: In this case the gap ends tapered to nothing and required the gap be opened with the knife. Also the bottom of the sliver was trimmed where the gap was widest; this allowed the sliver to bend and not break so the fine bottom wedge could fit into the tapered ends.

    Cutting the bottom allows the sliver to bend and not kink so it can be more easily inserted. (Photos 11 and 12)

  • Photo 13: Lightly tap the sliver home. You can use a block of wood but the wider bearing where the ends of the sliver are elevated can break it off. Note the wood glue on the near side. The sliver was glued only on the one side.

  • After fitting, apply wood glue to only one side of the sliver and spread it uniformly. Don’t be overly generous with the glue; a thin coating will be sufficient.
  • Position the sliver in the gap and carefully tap it home. You can use a block of wood to tap with, but a larger bearing tends to bend the sliver and may break it. (Photo13)

  • Photo 14: Score both sides with a sharp utility knife using light pressure. Too much pressure will cut through and pull splinters from the gap requiring additional repair.

  • Take a sharp utility knife and score the sliver slightly above the level of the floor until the excess is cut away. Too much pressure will also break the sliver and likely pull some of it out of the gap. (Photo 14)

  • Photo 15: The result should take care of the gaps and not be noticeable from a standing position. In this case we succeeded.

  • Finish the operation by scraping the remaining excess to the floor level. Angle the scraper and work from the center to the end. This keeps from pulling parts out of the gap.
  • Let all the glue set up before sanding. Also, don’t leave slivers standing in the gap without completing the cutting, as the glue line will be obvious and likely not sand out.

 The result should be a floor with minimal gaps and the repair is not noticeable from the standing position. (Photo 15)

All in all, gaps can generally be repaired with attention to detail and proper craftsmanship. Only the most severe general gapped condition with overall loose and noisy flooring requires replacement of the entire floor.

I would like to thank Wayne Lee with Cardinal Hardwood and Tile, Springville, TN for the help with the area repair and slivering.