Historic Preservation - Technical Procedures
Repairing Cupped Floorboards
National Oak Flooring Manufacturer's Association
Wood Strip Flooring
Repairing Cupped Floorboards
REPAIRING CUPPED FLOORBOARDS
A. This procedure includes guidance on repairing cupped
B. Cupping of hardwood floors is caused by one side of the
board gaining or losing moisture faster than the other
side. Some cupping, especially in wide plank floors, is
considered normal. It is usually barely noticeable.
More severe cupping is of two types:
1. Convex cupping ("crowning"): When the center of
the board is higher than the edges of the board.
2. Concave cupping: When the edges of the board are
higher than the center of the board.
C. Cupping may result from the inability of moisture to
evaporate through the boards. In the case of concave
cupping, the presence of an impervious surface finish on
the floor may prohibit the transmission of moisture,
causing it to build-up on the back side of the board.
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. National Wood Flooring Association
A. Moisture Meters:
1. Moisture Register Products Div.
Aqua Measure Instrument Co.
2. Delmhorst Instrument Company
3. Lignomat USA, Ltd.
4. Wagner Electronic Inc.
B. Hygrometers and Sling Psychometers:
1. Fisher Scientific
2. Forestry Tools & Supplies
A. Wood screws
B. Soap or paraffin to lubricate screw
C. Commercial wood putty
D. Headless steel pins
E. Wood floor refinishing materials (see 06400-10-R)
F. Clean, white towels
G. Clean, potable water
A. Moisture meter or sling psychrometer
E. Floor refinishing equipment (see 06400-10-R)
3.01 ERECTION, INSTALLATION, APPLICATION
A. Correct moisture levels by removing the source of excess
1. Use a dehumidifier or check outside drainage to see
that water is draining properly away from the
2. Regrade if necessary.
B. Allow the boards to dry out (this may take several weeks
C. Take moisture readings bi-weekly or bi-monthly to
accurately determine humidity levels. Use a sling
psychrometer or digital thermometer hygrometer.
NOTE: DO NOT PROCEED WITH ANY REPAIRS UNTIL THE MOISTURE
READINGS ARE BALANCED BETWEEN THE FACE AND BACK OF THE BOARD
FOR AT LEAST 30 DAYS.
NOTE: FLOORS WITH A SURFACE FINISH WILL DRY OUT MUCH SLOWER
AS THEY TEND TO RESPOND MUCH SLOWER TO MOISTURE CHANGES IN THE
D. If the cupped boards dry out, they should return to their
E. If the boards flatten when fully dried, resecure loose
boards to the subfloor.
1. For floors installed using nails:
a. Check for loose nails. These may be quickly
located by identifying squeaks in the floor or
b. Face-nail loose boards or refasten with wood
screws. See also 09560-04-R for guidance on
silencing squeaking wood floors.
2. For Floors Installed Using Mastic:
a. Check adhesion of floorboards to subfloor.
Walk across the floor and listen to the sounds
made. If a popping sound is heard, or if the
floor sounds hollow when tapped, adhesion is
b. Remove affected boards. Some adhesives such
as asphalt cut-back mastic can be reactivated
by lightly spraying it with kerosene. Consult
manufacturer for recommendations.
Drive headless steel pins through the affected
boards and into a wood or concrete subfloor.
F. Once the floor and fasteners are secure:
1. Fill cracks with commercial wood putty. See 09560-
02-R for guidance on repairing small holes and
cracks in wood floors.
2. Reapply surface finish.
Buff with 00 steel wool, clean and rewax.
NOTE: IF A POLYURETHANE FINISH WAS USED, RECOAT
ONLY IF THE FLOOR HAS NOT BEEN WAXED.
G. If the floor remains cupped after drying, it must be
completely resanded and refinished (see 06400-10-R for
NOTE: BE SURE TO FILL CRACKS, CHECK FASTENERS AND MAKE
ANY REPAIRS BEFORE SANDING.
H. A severely warped or buckled floorboard which cannot be
worked back into place, will have to be replaced, see
09560-01-R "Replacing Damaged Floorboards" for guidance.
END OF SECTION