Gaps between floor boards or parquet flooring - cause/cure
Rotted wood flooring
Scratched wood flooring
Stained wood flooring
Questions & answers about the diagnosis & repair of wood floors
This article explains types of damage that occurs
on various types of wood flooring in buildings, and we
describe repair approaches for various wood floor damage.
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Our photo at page top shows cupped wooden strip flooring and an easy way to detect this condition..
Buckled wood flooring due to leaks or high moisture
This 1940's wood floor buckled severely because of wet conditions in a gymnasium after the roof leaked.
But even if a building is not subjected to flooding or wet floors, if the wood floor was installed without adequate clearance around its perimeter buckling can occur when moisture increases in the building.
And as we discuss at FLOOR, WOOD MOISTURE, a successful wood floor installation requires that the wood flooring be acclimitized and at proper moisture level in the building before it is installed.
Very large wood floors (such as in this gym) may need an inch or even more of side clearance at the building walls - a detail accomplished by building out floor/wall baseboard trim if necessary, or in the case of newer products, by the combination of clearance gaps and a floating floor design.
Cupped Wood Flooring - Causes & Cures
Compare our photo at left of concave (curved down) cupped wooden floorboards with the convex (curved up) cupped floor boards in the photo at the top of this page.
At left you can easily see the concave cupping of the floor at left by looking at our flashlight beam across boards in the upper portion of the photo. (The center of concave cupping is down and edges of concave-cupped floor boards are raised - think of "cave" as "caving in" if you want to remember this distinction.)
Diagnosing why a wooden floor has become cupped is an important step in correcting the problem, since we need to identify and correct the moisture source.
There are exceptions, but in general a board swells on its side that is most moist. So on an interior floor like the one shown at left, the fact that the center of the floorboards is cupped "down" we infer that it is the down-side of these boards that is more moist than the finish side facing the room. We find this condition in homes with finished wood flooring installed over a damp or wet basement or crawl space.
At our page top photo the finish floor boards seem to be cupped "up" - suggesting that this floor has been wet from above.
If the floor board cupping is minor and hard to see, you might decide to just address the moisture problem and leave the floor alone. It won't recover, but it the floor should not get worse. How would we repair a badly cupped wooden floor? Sanding the floor flat is an option unless the boards have not only cupped but come loose from the subfloor. In that case floor replacement may be necessary.
Cause of Outdoor Deck Board & Stair Tread Cupping & Shelling - Bark Side Down Advice for Decks & Steps
Indoors we find that floor boards tend to cup so that the concave side of the board is towards the floor's more dry side, and the convex side of the cupped or curved boards tend to be facing the floor's more wet side.
Apparently when a wooden board has uneven moisture content across its thickness it will tend to expand more on its more wet side, causing that side to "arch" or become convex.
But outdoors where despite temporary wetting from rain, deck boards and wood step boards open to air on both sides ultimately have a uniform moisture content across the board's thickness.
In this case experts expect an outdoor wooden board to naturally curve towards the "bark" side of the wood. As Steven Bliss asserts, "always install trim [and outdoor deck boards and stair treads] “bark-side
down,” since the annual rings try to straighten as the wood
shrinks."
If you click to enlarge the photo at above left you might notice that the two most-rotted deck boards (photo center) were installed with deck boards cupped upwards or "concave"; you can also plainly see the end grain in the two 3x12's forming the deck girder (photo lower center). You'll see by the wood end grain pattern that the girder right-hand board has it's "bark side" facing right, and the left hand board has its "bark side" facing left. Both of these boards curved towards the "bark side" - a good example supporting the "bark side down" wisdom when building an exterior deck or stair.
Cupped ramp boards (or deck and platform boards) hold water and form algae or ice more quickly than boards that drain properly. They sometimes rot faster too, as we show in our photograph. Look at the end-grain of any deck, ramp, or wooden walkway board and notice the curved lines that mark the winter wood layers of the tree from which the board was cut. If these lines arch "upwards" when the board is placed, most boards will also be curved upwards (convex) and will drain better. But before nailing a deck or ramp board in place, look at the board surface itself - sometimes the boards don't follow these "cupping rules".
Outdoors where a wooden board has both sides exposed to the weather (and to roughly the same moisture conditions) as it dries from its original green state a wood board will cup away from (trying to straighten) the curve of the wood layers that comprise it.
(Sketch courtesy S. Bliss, Best Practices in Residential Construction.)
For this reason when building a deck we like to look at the end grain of the wood and install deck boards with the "bark side" down so that cupped boards won't form puddle-collecting dips on our deck. See DECK & PORCH CONSTRUCTION.
But look at your actual individual boards or stair treads when you are building an outdoor structure. If we are installing a deck board that is already rather cupped, we install it with the convex or "outward curve" side facing up for best drainage.
Watch out: On wooden decks and stair treads a defect "shelling" can occur with the bark side down method. Shelling is a term used by some builders to refer to the loss of portions of a board surface as llate wood growth (the outer surface of the tree and thus the "bark side" of the board) separates from early wood growth (the inner portion of the tree or the tree-center side of the board).
Shelling is reported to occur more often in lumber made from Douglas Fir and Southern Pine. When building an outdoor deck wooden stair tread, it is a good idea to avoid using boards with questionable, likely to separate, portions of their upper surface. Shelling may be less of a problem with wood trim that is to be placed vertically and kept painted or sealed.
Gaps Between Wood Floor Boards & in Parquet Flooring: Cause & Cure
Gaps between wood floorboards may occur for several reasons, but the common underlying cause is a moisture problem.
Installing wood flooring before it has had an opportunity to acclimate to the indoor moisture level of its new home often means that too-moist flooring was nailed in place, later shrinking as building heat further dries the wood.
The gap between the flooring shown at left is viewed from the under-side of the floor of an older building. This is a ship-lap joint whose boards have separated about 3/16".
Gaps can also appear between sections of a wood parquet floor, as shown in our photo (left).
Do not rush to fill in gaps like this in wooden floors. Particularly in the case of wideboard flooring the width of individual boards increases and decreases seasonally as building indoor moisture levels increase (typically in the summer) or decrease (typically in winter).
If you fill the gap between floor boards in the dry (wide gap) season, when the building moisture increases and boards swell the swelling floor boards will push against the gap filling material, actually crushing the edges of the floor board.
Then when the building dries out again a new gap will appear. Or in extreme cases the floor may buckle in damp weather. In either case, it's better to just vacuum out the dust and debris and leave these wideboard floor gaps alone.
At Wood Floor Types where we illustrate a restored and re-finished wide-board floor in an 1860's home, if you click and enlarge the photo you'll see that we left the flooring gaps open. In fact during restoration we sometimes have to pick out putty or other stupid crack fillers that someone has applied earlier.
Gaps and shrinkage damage to wood floors installed over radiant floor heating systems
A common complaint we've investigated is shrinkage gaps in wood flooring installed over radiant heat tubing.
The underlying cause may be flooring that was too moist at installation (see above), or operating the heat at a higher than recommended temperature.
In the gapped wood floor over radiant tubing shown here, the owner, attempting to eliminate a smell associated with the radiant heat tubing, ran the heating system at high temperature, perhaps contributing to this floor gap problem.
Pet urine stains on wood floors - pet stains can ruin wood flooring. Stains are deep enough into the wood that almost no amount of sanding will remove them.
We have had some wood floor stain removal success by careful, by-hand bleaching combined with sanding, followed by careful blending of hand-mixed wood stain products to return the color of the wood floor section to that of its neighbors. See Black Flooring Stains from Animals for details.
Nail & moisture stains on wood floors - Where small black stains developed in a wood floor in a 1920's bungalow that we restored (our lab and office) we had great success by combining sanding with spot bleach using a Q-tip to lighten the black spots where in prior years moisture had caused bleed and corrosion staining around those fasteners.
Any exposed nails were set into the flooring before sanding. After sanding we sat with a q-tip and a damp cloth, dabbing and bleaching black spots, wiping and washing off the bleach when the stain was light enough - thus avoiding over-bleaching the floor. We mixed wood stain products to bring the color of the stained-bleached spots back to the surrounding flooring.
Surface Scratch Repair on Hardwood Flooring
Here is a long strip solid oak wood floor that's shows ugly but fairly superficial scratches. To make this 1970's strip oak wood floor look perfect, sanding and re-finishing may be necessary.
But an alternative to try first is thorough cleaning, perhaps buffing with steel wool, followed by application of a sealant and finish coating. Often superficial scratches in a wood floor disappear from view when the scratched finish coating is restored.
It's usually a better practice to repair a floor with the least aggressive means possible, preserving the material for a longer life.
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Additional technical contributors & reference sources for this article are listed below.
Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.
America's Favorite Homes, mail-order catalogues as a guide to popular early 20th-century houses, Robert Schweitzer, Michael W.R. Davis, 1990, Wayne State University Press ISBN 0814320066 (may be available from Wayne State University Press)
American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, www.apawood.org
Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on Asbestos, Its Industrial Applications, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print).
Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
How could homes be designed and built more efficiently?
What kinds of construction and production techniques worked well and which did not?
How did people use different kinds of spaces in their homes?
What roles did community planning, zoning, and interior design play in how neighborhoods worked?
"
Isham: "An Example of Colonial Paneling", Norman Morrison Isham, The Metropolitan Museum of Art Bulletin, Vol. 6, No. 5 (May, 1911), pp. 112-116, available by JSTOR.
Manufactured & Modular Homes: Modular Building Systems Association, MBSA, modularhousing.com, is a trade association promoting and providing links to contact modular builders in North America. Also see the Manufactured Home Owners Association, MHOAA, at www.mhoaa.us. The Manufactured Home Owners Association of America is a National Organization dedicated to the protection of the rights of all people living in Manufactured Housing in the United States.
Pergo AB, division of Perstorp AB, is a Swedish manufacturer or modern laminate flooring products. Information about the U.S. company can be found at http://www.pergo.com where we obtained historical data used in our discussion of the age of flooring materials in buildings.
Plank House Construction: webslog from plankhouse.wordpress.com/2009/01/25/plank-house-construction/ and where plank houses were built by native Americans, see
Large 1:6 Scale Plank House Construction / P8094228,
Photographer: Mike Meuser
06/12/2007 documented at yurokplankhouse.com where scale model Museum quality Yurok Plank Houses are being sold to raise money for the Blue Creek - Ah Pah Traditional Yurok Village project.
Weaver: Beaver Board and Upson Board:
Beaver Board and Upson Board: History and Conservation of Early Wallboard, Shelby Weaver,
APT Bulletin, Vol. 28, No. 2/3 (1997), pp. 71-78, Association for Preservation Technology International (APT), available online at JSTOR.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
"The Elimination of Unsafe Guardrails, a Progress Report," Elliott O. Stephenson, Building Standards, March-April 1993
"Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
Access Ramp building codes:
UBC 1003.3.4.3
BOCA 1016.3
ADA 4.8.2
IBC 1010.2
Access Ramp Standards:
ADA (Americans with Disabilities Act), Public Law 101-336. 7/26/90 is very often cited by other sources for good design of stairs and ramps etc. even where disabled individuals are not the design target.
ANSI A117.4 Accessible and Usable buildings and Facilities (earlier version was incorporated into the ADA)
ASTM F 1637, Standard Practice for Safe Walking Surfaces, (Similar to the above standards)
American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, www.apawood.org
Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on Asbestos, Its Industrial Applications, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print).
Asbestos Identification and Testing References
Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed
the basis for current work by asbestos identification laboratories.
Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone
ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:
Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
How could homes be designed and built more efficiently?
What kinds of construction and production techniques worked well and which did not?
How did people use different kinds of spaces in their homes?
What roles did community planning, zoning, and interior design play in how neighborhoods worked
"An Example of Colonial Paneling", Norman Morrison Isham, The Metropolitan Museum of Art Bulletin, Vol. 6, No. 5 (May, 1911), pp. 112-116, available by JSTOR.
Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
Slips, Trips, Missteps and Their Consequences, Second Edition, Gary M. Bakken, H. Harvey Cohen,A. S. Hyde, Jon R. Abele, ISBN-13: 978-1-933264-01-1 or
ISBN 10: 1-933264-01-2,
available from the publisher, Lawyers ^ Judges Publishing Company,Inc., www.lawyersandjudges.com sales@lawyersandjudges.com and also from the InspectAPedia Bookstore (Amazon.com)
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