Repairing Cupped Floorboards
- CSI Division:
- Division 9 - Finishes
- Wood Strip Flooring
- Last Modified:
Technical Procedures Disclaimer
Prior to inclusion in GSA’s library of procedures, documents are reviewed by one or more qualified preservation specialists for general consistency with the Secretary of Interior Standards for rehabilitating historic buildings as understood at the time the procedure is added to the library. All specifications require project-specific editing and professional judgement regarding the applicability of a procedure to a particular building, project or location. References to products and suppliers are to serve as a general guideline and do not constitute a federal endorsement or determination that a product or method is the best or most current alternative, remains available, or is compliant with current environmental regulations and safety standards. The library of procedures is intended to serve as a resource, not a substitute, for specification development by a qualified preservation professional.
We’ve reviewed these procedures for general consistency with federal standards for rehabilitating historic buildings and provide them only as a reference. Specifications should only be applied under the guidance of a qualified preservation professional who can assess the applicability of a procedure to a particular building, project or location. References to products and suppliers serve as general guidelines and do not constitute a federal endorsement nor a determination that a product or method is the best alternative or compliant with current environmental regulations and safety standards.
- This procedure includes guidance on repairing cupped floorboards.
- 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:
- Convex cupping ("crowning"): When the center of
- the board is higher than the edges of the board.
- Concave cupping: When the edges of the board are higher than the center of the board.
- 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.
- See 01100-07-S for general project guidelines to be
- reviewed along with this procedure. These guidelines cover the following sections:
- Safety Precautions
- Historic Structures Precautions
- Quality Assurance
- Delivery, Storage and Handling
- Project/Site Conditions
- Sequencing and Scheduling
- 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).
- National Wood Flooring Association
- Moisture Meters: Moisture Register Products Div.
Aqua Measure Instrument Co.
- Delmhorst Instrument Company
E, Towaco, NJ
- Lignomat USA, Ltd.
- Wagner Electronic Inc.
- Hygrometers and Sling Psychometers:Fisher Scientific
- Forestry Suppliers, Inc.
- Wood screws
- Soap or paraffin to lubricate screw
- Commercial wood putty
- Headless steel pins
- Wood floor refinishing materials (see 06400-10-R)
- Clean, white towels
- Clean, potable water
- Moisture meter or sling psychrometer
- Floor refinishing equipment (see 06400-10-R)
3.01 ERECTION, INSTALLATION, APPLICATION
- Correct moisture levels by removing the source of excess moisture.
- Use a dehumidifier or check outside drainage to see that water is draining properly away from the building.
- Regrade if necessary.
- Allow the boards to dry out (this may take several weeks or months).
- 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 environment.
- If the cupped boards dry out, they should return to their normal position.
- If the boards flatten when fully dried, resecure loose boards to the subfloor.
- For floors installed using nails:
- Check for loose nails. These may be quickly located by identifying squeaks in the floor or loose boards.
- Face-nail loose boards or refasten with wood screws. See also 09560-04-R for guidance on silencing squeaking wood floors.
- For Floors Installed Using Mastic:
- 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 probably lost.
- 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.
- Fill cracks with commercial wood putty. See 09560-02-R for guidance on repairing small holes and cracks in wood floors.
- 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.
- Reapply surface finish.
- If the floor remains cupped after drying, it must be completely resanded and refinished (see 06400-10-R for guidance).
NOTE: Be sure to fill cracks, check fasteners and make any repairs before sanding.
- 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.