How to Repair Cracks and Holes in Floors

Before laying a new floorcovering, it is essential that the existing floor surface is sound and smooth. As well as repairing or replacing floorboards, you may have to fill cracks and holes in wooden floors, and deal with unevenness, and possibly damp, in solid floors. Any faults not rectified will eventually show through the floor covering and may damage it.

Filling holes in timber floors
Nail and screw holes can easily be plugged using a flexible wood filler applied with a filling or putty knife. If the floorboards are to be left exposed and treated with a clear sealer, try to match the wood filler, or stopping, to the color of the surrounding floorboards – so do the filling after any sanding.

Larger recesses can also be filled with flexible filler, but if a knot has fallen out, leaving a large round hole, plug this by gluing in a short length of dowel and planing it smooth afterwards. Select a dowel that matches the color of the floor or stain it once planed down.

Filling cracks in timber floors
You will find two main kinds of crack in timber floors: splits in the ends of the floorboards and gaps between the boards.

A split can often be cured by skew (toe) nailing – that is driving two nails through the end of the board at an angle toward the centre and down into the joist. As the nails are driven in, they should close up the split.

Gaps between floorboards are more difficult to deal with. If they are narrow, flexible wood filler will work, but for wider gaps, you must cut slivers of wood and glue them into place in the gaps. Once the glue has dried, plane or sand the slivers flush with the surrounding floor and stain to match if necessary.

If there are lots of wide gaps between floorboards, a better solution is to lift all the floorboards one by one, starting at one side of the room and working toward the other, and re-lay them tightly against one another. Floorboard clamps will help you do this, as they force a board against its neighbour while you nail or screw it down.

Levelling a wooden floor
Individual rough patches on a timber floor can be sanded down by hand, which you should do after using filler, but where floorboards have become cupped or are heavily encrusted with old paint, grease and polish, the best move is to hire an industrial-type sanding machine and re-sand the floor. Begin with coarse abrasive and progress through to the fine grades, working across the floorboards at an angle. Finish off by working along the floorboards with fine abrasive. Hire an edging sander as well, unless you own a belt sander, because the floor sander will not sand right up to the skirting boards.