Historic Preservation - Technical Procedures
Repairing Small Holes And Cracks In Wood Floors
Hspg Prepared For Nps - Sero
Wood Strip Flooring
Repairing Small Holes And Cracks In Wood Floors
REPAIRING SMALL HOLES AND CRACKS IN WOOD FLOORS
A. This procedure includes guidance on filling small holes
and surface cracks in wood floor boards and filling
cracks between wood floor boards.
B. Cracks the thickness of a dime between floor boards is
not uncommon. In fact, plank boards may expand and
contract 2-1/2 times that distance.
C. Cracks can develop between boards from what is known as
compression shrinkage or compression set. As the wood
absorbs moisture, the floor boards swell. For those
boards that swell beyond their allowable range, the
boards compress against one another and, sometimes,
become damaged. As the moisture level drops, the boards
shrink and a gap develops between the boards.
D. See 01100-07-S for general project guidelines to be
reviewed along with this procedure. These guidelines
cover the following sections:
1. Safety Precautions
2. Historic Structures Precautions
4. Quality Assurance
5. Delivery, Storage and Handling
6. Project/Site Conditions
7. Sequencing and Scheduling
8. General Protection (Surface and Surrounding)
These guidelines should be reviewed prior to performing
this procedure and should be followed, when applicable,
along with recommendations from the Regional Historic
Preservation Officer (RHPO).
A. A wooden floor surface can be either a series of
connected planks or parquet (small wood pieces arranged
in decorative patterns). The wood used is either plain
sawn or quarter sawn. Plank flooring, the more common
type, is assembled by joining: butt joint, tongue and
groove, shiplap, doweled, spline. Wood floors are usually
secured to the under structure by countersinking nails,
blind-nailing, or screwing and plugging.
A. Abatron, Inc.
5501 95th Ave.
Kenosha, WI 53144
800/445-1754 or 414/653-2000
A. Commercial wood putty, colors-in-oil or oil stain pigment
to color putty to match (Abatron, Inc., Allied Resin
Corp., or approved equal) - available in wood tones
B. Wood glue to reattach splinters
G. White wood glue
H. Tissue paper
I. Calcined magnesia
J. Strips of cloth, grey felt weatherstripping or varnished
hemp, marine caulking compound
K. Linseed oil
L. Wood for shims (do not use shingles, they lack
M. Strips of wood for nailing to underside of floorboards or
for filling cracks between boards
A. Small putty knife
B. Brush or sponge to spread pigment
F. Stiff bristle brush
A. Inspect for the signs of decay or insect infestation such
as mold, fungus, bore holes, and sawdust piles.
3.02 ERECTION, INSTALLATION, APPLICATION
A. For Small Holes and Surface Cracks:
1. Fill with commercial wood putty:
a. Stain the putty to match the floor by using
either colors-in-oils or the settled pigment
from the bottom of the stain can.
b. When staining putty to match wood, it is
better to go darker than the wood rather than
c. When filling a hole or crack, add filler in
layers and allow drying time between layers.
2. If a floorboard is splintered, glue the splinter
down and fill the crack.
3. If damage is such that it cannot be successfully
filled and the board is relatively easy to remove,
turn the board over rather than replacing it. The
new surface should be sanded to match surrounding
boards and may need to be shimmed to make it level
with the existing surface.
NOTE: THE FEASIBILITY OF THIS METHOD OF REPAIR
WILL DEPEND UPON THE ORIGINAL INSTALLATION SYSTEM
AND THE APPEARANCE OF THE UNDERSIDE OF THE WOOD
B. For Cracks Between Floorboards: In general, it is best
to leave cracks between boards alone. Gaps often
diminish as the boards expand in more humid seasons.
However, there are several methods for filling cracks
between floor boards:
1. If small, they can be covered with a new floor
finish. If the underside of the floorboards are
exposed, nail strips of wood to the underside of
2. Fill with a paste filler (made by user):
a. Mix sawdust with varnish, shellac or white
b. Mix tissue paper, glue size, and calcined
magnesia to a mass like putty.
c. Press mixture into crack using putty knife and
finish smooth so it is level with the floor
3. Fill with a fibrous filler (made by user):
a. Soak cloth strips in linseed oil or glue, or
use strands of hemp rope (grey felt
weatherstripping may also be used, but is not
as stainable as hemp rope).
b. Pack cloth strips or strands of rope (in
layers, if necessary) into the crack using a
screwdriver or putty knife.
c. If desired, stain the filler material to match
4. Fill with caulking compound:
a. If the floor is to be painted, use marine
caulking compound to fill the crack. It will
expand and contract with the wood and the
paint will hide the color difference.
b. Carefully mask the area before caulking.
c. Fill crack using a caulking gun or similar
injection device. It is best to fill the
crack at mid-cycle (in Spring or Fall).
d. Finish the surface level with the floor.
5. Fill with a thin strip of wood:
NOTE: This option is not ideal because it
reintroduces the potential for compression problems
resulting from wood expansion and contraction.
However for large cracks that are hazardous:
a. Thoroughly clean the opening of dirt and
debris using a stiff bristle brush and vacuum.
b. Slip a thin strip of wood into the crack.
Match the depth of the surrounding floor and
stain to match.
c. Nail or glue the strip to only one side of the
crack to allow for expansion and contraction.
C. In extreme cases, the floorboards will have to be taken
up and reinstalled (see 09560-01-R, "Replacing Damaged
Floorboards" for guidance).
END OF SECTION