Bark side up or down on exterior wood decks & stairs:

This article series explains the causes of cupping in wood boards & wood board right side up advice for steps, decks, ramps: this article explains the causes of wood board cupping and gives advice concluding that unless a board is already badly cupped or has a "bad" side, when construction of outdoor decks and wood stairs you should place boards with "bark side DOWN" - that is pith side (tree center side) of the board facing up.

We include a warning about "shelling" damage on decks and steps - a phenomenon that occurs more on the pith side of boards.

Page top photo: in this wood-framed wall the top plate has been nailed "bark side up" - which matters much less in wood frame construction that will be covered by final building roofing and exterior walls.

In framing walls, our opinion was that all else being equal, we'd nail the top plate or sole plate of a wall with its arch "up" or "convex" simply because it was easier to nail the edges of the board down to the studs below.

There has been plenty of argument about bark up vs bark down. Field experience, FPL experts, and further discussion here all agree that because a bark-side-down deck board tends to arch upwards or actually to flatten as the wood dries, "bark side down" is the usually the best practice when building wood decks, steps, ramps, platforms.

Really? Well not always. We make an exception when flooring a deck or porch, especially outdoors, if a board is already so extremely cupped that it's not likely to flatten out if nailed with its cup facing up. We flip those boards over so that their high arch is "up" regardless of where the bark side is found.

Cause of Outdoor Deck Board & Stair Tread or Wood Trim Cupping & Shelling

Why Boards Cup in the First Place: moisture differences dominate wood board cupping

Which side should go "Up" when placing wood deck boards, stair treads?

The two fundamental factors affecting wood board cupping are moisture differences across the thickness of the board and inherent properties of the wood cells and cell distribution patterns that comprise the board.

Our photo above shows a pre-cut treated wood deck stair tread board. Although we see grooves cut by the manufacturer to serve as a walking surface (facing up in the photo) the board has cupped its outer edges upwards towards the bark side of the tree.

This cupping pattern shown above is consistent with the prediction of wood experts (wood tends to cup towards the "bark side" of the tree and incidentally, shows that this stair tread board is going to tend to hold water, grow algae, form ice, or otherwise be less safe than a board whose center had arched upwards. In use, if the upper surface of this board is usually wetter than its underside, it may tend to flatten out.

The extent to which an individual board will cup depends on those two sources of cupping movement combined with the wood grain pattern of the individual board:

Flatsawn boards like the one above will cup more than quarter sawn boards, and board cupping also varies by wood species, where the board was cut from the tree, and also by variations in the installed location and position of the board with respect to weather, rain, ground moisture, wind drying, sunlight and other factors.

Photo: Paul Galow's deck guardrailing top board, cut from near the heart of the tree, is almost quarter-sawn, and has still cupped significantly towards the bark side - the under-side of the board in this case.

Depending on from where in the tree a board is cut and whether it is flat sawn or quarter sawn, the board's future weather and water exposure, it may absorb more water in its wider, center tree-growth rings, expanding more in the center, tending to "cup" (towards the bark side) and so if the board's bark side had been "arched" upwards, it might flatten out.

Article series contents

• BARK SIDE UP or DOWN on DECKS & STEPS?
  • BOARD CUPPING CAUSES
  • ANSWER to BARK SIDE UP or DOWN - separate article
  • BARK SIDE UP ARGUMENT - separate article
  • BARK SIDE DOWN ARGUMENT - separate article
  • WOOD CUPPING vs WET SIDE - separate article
  • CUPPED BOARD HAZARDS
  • SHELLING BOARD SURFACES
  • IPE DECK BOARD CUPPING
  • WOOD FLUORESCENCE TESTS

If you're unsure about the how the wood grain will show up in different lumber saw-mill cutting methods, see the definitions of "flatsawn" or "flat-sawn" or "plain sawn" boards or lumber given

at LUMBER SAWING METHOD DEFINITIONS

Definition of Concave vs Convex Board Shapes

If you're not sure about cupping direction or the definitions of concave and convex, this U is concave (think "arch down" or think "fruit bowl") and this n is convex (think "arch up" or think "rainbow") - courtesy of James MacQueen Contractors cited below.

A concave board has its outer edges curled upwards while a convex-cupped board has its outer edges curled downwards.

Flat-sawn boards cup more than quarter-sawn boards.

Wood Cupping & Uneven Moisture Content

Above: this ground-level deck board on an entry to "the Green Cabin" in Two Harbors Minnesota, is one of several that was nailed bark-side up and has cupped further so that in 2022, sixteen years after it was first nailed in place, the board is cupped enough to hold water after a rain, encouraging more algae growth and ultimately, rot.

Other boards of this deck that rotted before their sisters are illustrated

at ANSWER to BARK SIDE UP or DOWN

We think that an on-ground or close-to-ground deck board stays wet longer on its under-side so may tend to cup up regardless of bark position. Below we explain why.

Two wood board cupping truths that individual boards may not always obey:

1. The wet side of of a wooden board tends to expand more than its dry side.
   
   The "expanding" side, by getting wider, will tend to curve or cup such that the center of that side arches or becomes convex.
   
   The moisture level may, in some boards, overcome the effect of the natural cupping towards the bark-side - point 2 below.
2. Flatsawn boards tend to cup (form a concave or bowl-like surface) towards the bark side.
   
   The bark side tends to cup "towards" the outside of the tree or in the "bark" side direction.
   
   So if a board is installed "bark side down", the bark side of the board tends to form a "cup" with an "arch" facing "up".

The moisture variation contribution to wood board cupping occurs because 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 while the opposing side becomes concave or "cupped".

Outdoors, where despite temporary wetting from rain, deck boards and wood step boards are open to air on both sides, some, including chemists at the US FPL, are of the view that these boards will ultimately have a moisture content within 2% of uniform across the board's thickness. [38]

My view is that moisture content will vary across an outdoor deck board's thickness over time as a function of rain, snow-melt, or construction over wet, poorly-ventilated crawl areas. That is, a low deck's under-side may remain more-wet longer than its upper surface.

Wood Cupping & Tangential Wood Shrinkage

This moisture difference seems to dominate wood board cupping outdoors or inside even though wood experts often describe a different effect: tangential shrinkage and movement that leads the outer edges of flatsawn boards to cup towards the outside of the tree (towards the bark) and away from the heart, adding that the smaller the original tree and the closer to the tree's heart from which a flatsawn board was cut the more extreme will be its tendency to cup.

That wood board cupping is an old and long discussed topic is evident from US FPL citations such Clarke (1930) in the U.S. alone.

Finally, Cloutier et als (1997) noted that during wood drying, water conductivity was generally higher in the radial direction than in the tangential direction which, along with the presence and structure of ray cells in wood fibers, may help explain the actual mechanism wood board cupping that is either absent or confusing in most articles on this topic.[7]

A restatement of tangential wood shrinkage that may be more clear is to pose that wood shrinks more along the circle of its growth rings than across the thickness of the board.

By examining the end-cut of a flatsawn board, you will see that one side of the board will show longer arcs of growth rings (the side closer to the bark side of the tree) while the other side of the board (closer to the tree heart) will sport shorter arcs (growth rings).

Location & Length of Growth Rings May also Help Explain Board Cupping - re-stating Tangential Shrinkage Movement

Our end grain view of a flat-sawn board shown above suggests a third possible source of wood board cupping: the pattern of growth rings through a cross section of the board.

In this photo (above), the long arches of growth rings would also roughly map the round tree shape from which the board was cut.

The winter wood (more dense) is marked by the darker growth rings in the board. The wider gaps of light colored wood are summer wood, a less dense growth of cellulose cells.

Cross section cut of lumber shows growth rings & maps the bark side of the tree, predicting the cupping direction

The long arcing of winter wood (red arrows) occur in the center of the board and arch upwards towards the bark side of the tree.

The thicker rings of growth wood, aka "summer wood" are marked by blue arrows in our photo below.

The darker, thinner lines in our illustration above are also marking winter wood growth rings but notice that in a flat-sawn board these lines occur nearest to the edges of the board and that they also represent the typical end-grain of a quarter-sawn board illustrated below.

As we know that more shrinkage occurs across the width of a board through the flat-sawn long-growth-ring arcs (red lines) than will occur through the quarter-sawn end grain portion of the same board (blue lines) we thus have a third source of board cupping:

More shrinkage (as wood dries) wants to occur in the center of the board than in its edges. But how would this pattern explain the direction of cupping?

Notice that the longest red arcs are towards the upper or bark side of this board?

More shrinkage around the growth ring or arc line means more shrinkage where these lines are longest in the board - the upper center board surface in our photo will shrink more than both the board edges and more than the lower board center surface, thus tending to curl the board's outer ends upwards.

Wood Cupping Develops a "Set" in Boards

Ultimately boards that have cupped due to these moisture differences develop a "set" and remain cupped even when the boards have dried.

You can observe this dramatically in an interior wood floor that has been flooded, then dried. Boards will remain cupped.

Next: see ANSWER to BARK SIDE UP or DOWN

Hazards Caused by Cupped Wooden Deck Boards or Stair Treads

Poor drainage of upwards-cupped wood boards

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.

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 the visible curves (the darker colored latewood or winter-wood growth rings) are positioned such that the "cup" formed by these arcing lines is facing upwards - that is the convex side of the board and arcs faces up (opposite of the board in our page top photo) - then these boards that are cupped upwards and will drain more poorly, stay wet longer, rot faster, and in freezing climates are going to stay icy longer.

Watch out: Wetter boards also collect more algae and are a serious slipping hazard, especially on decks and stairs.

Watch out: Use common sense. Especially with pressure-treated wood that may have been soaked unevenly, boards may be quite warped when you are using them in construction. Before nailing a deck or ramp board in place, look at the board surface itself - sometimes the boards don't follow these "cupping rules".

Also see DECK & PORCH CONSTRUCTION.

Shelling Damage to Walking Surfaces on Wood Decks & Stairs

Watch out: As we introduced above in our US FPL quotation, on wooden decks and stair treads, a defect referred to shelling can occur with the bark side down method as this position tends to leave more poorly penetrated (by preservative) heartwood exposed to sun and weather.

Shelling is a term used by some builders to refer to the loss of portions of a board surface as late 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.

For another safety tip when building wooden stair treads using 5/4 deck boards or 2x lumber, avoid using boards whose edge that will form the stair tread nose is, by inclusion of knots, chips, or other defects, likely to break away or form an uneven stair tread nose.

Uneven or irregular or chipped stair tread noses are another trip hazard.

See STAIR TREAD NOSE DIMENSIONS and

see SLIPPERY STAIRS, WALKS, ROOFS for details.

Bark Side Up or Down for Stacking Firewood?

Above: in Nancy and Edna's New York woodshed, the firewood is stacked with bark side up and down and mixed (left side of photo) but as the wood is reasonably-protected from the weather its position is of less concern.

The New York Times reported (February 2013) that the bark-side up or down debate rages unresolved in a related venue, the stacking of firewood by Norwegians.

People appear to be split 50:50 about whether it's better to stack split log firewood bark side up or down.

Having heated my home for years on firewood alone [DJF], and split and stacked a lot of wood, it's easy to understand the argument. [39]

These firewood logs are stacked roughly bark-side up and would, exposed to some wind-blown rain entering this open firewood shed, be a bit better at shedding water without soaking the wood. Stacked in the open this would be perhaps more important.

Bark side up: sheds water better, so we fantasize that the wood will dry out better stacked in that position. But bark side down exposes the two split sides of a roughly triangular split firewood log or a semi-circular split half-log to having its freshly cut and split side up and possibly exposed to more airflow.

Above: smaller-diameter round log firewood that has not been split can be stacked without worrying about "bark side up" - but of course will also dry out more-slowly than if it had been split.

Which did I find was better? Neither. What was more important was to cover the top of the woodpile to keep the whole thing dry. Stack the firewood so that it has good air circulation, and cover the top of the woodpile.

That made more difference than anything else ... except ... I found putting bark side down on the very first course of logs laid on the dirt seemed to invite bugs into my woodpile about 8% faster than if I stacked wood in the other orientation - for the first course.

Watch out: the slipperiness of a ramp varies enormously depending on what is on its surface, including algae, sand, dust, dirt, water, snow, ice, and even some add-on walking surfaces and paints.

At SLIPPERY STAIRS, WALKS, ROOFS we discuss the SCOF (static coefficient of friction) for wet algae-covered surfaces.

IPE Wood Deck Board Cupping

Reader Question:

Three months after constructing a new Ipe deck some of the boards became cup shaped (see enclosed photos).

Soaking two pieces of the leftovers resulted in one of the boards sink and the other float.

Can this 'experiment' prove that some of the boards are not Ipe?
Awaiting your expert advice. E.T. by private email 2016/01/18

Reply:

My opinion is that IPE, described by IPE Depot as " Ipe Decking. Ipe is an exotic hardwood that is naturally resistant to rot and decay, is 8 times harder than California Redwood, and is guaranteed for 20 years without preservatives!" - http://www.ipedepot.com/compare.htm

Should not usually float. A cubic foot of water weighs about 62.3 pounds. According to IPEDepot, a cubic foot of IPE weighs 69 pounds - it would sink in water.

However as this is a "natural" product, I would not assume that all IPE boards are absolutely uniform in density or weight. So some boards or board cutoffs may be a bit under-weight.

Gibson (2000) points out that IPE is actually a broad term for a number of similar wood species. And White (2007) points out a range of densities among woods classified as "IPE". So your particular IPE deck boards may be less dense.

Furthermore, any natural wood deck board is exposed to cupping if the moisture differences across the board are significant.

Cupping will usually show the concave side of the cup facing the more dry side of the board - which is usually "up" on a deck.

Boards can misbehave and cup "backwards" for other reasons as we discuss ad-nauseum in our articles on deck board cupping beginning at the top of this page.

I'd look into the cause of cupping rather than thinking that if you'd had "better or more real" IPE no cupping would have occurred.

Watch out: there may be environmental and protected wood species issues with exotic woods used in decks or other construction. See Gibson (2000) who discusses chain of custody certification for IPE wood sold in the U.S.

Reader follow-up: Use fluorescence testing to identify IPE wood boards?

Thank you for your detailed answer with the valuable information.

It appears that the 'soaking test' is not absolutely conclusive to determine the exact identity of the boards.

Will the 'fluorescence test' (as described in links given below)

http://www.wood-database.com/wood-articles/fluorescence-a-secret-weapon-in-wood-identification/

Excerpt:

WATER EXTRACT FLUORESCENCE

Also, another trick to do with a blacklight is what is called water extract fluorescence and ethanol (alcohol) extract fluorescence.

Some woods, while they don’t physically fluoresce under a blacklight, will have very bright reactions when wood shavings and/or sawdust is mixed in a small vial or other clear container and held up to a blacklight.

An excellent example of this is Wenge: the wood doesn’t fluoresce, but something as simple as wiping the surface with denatured alcohol will serve to draw out and concentrate the heartwood extractives, and reveal a bright green fluorescence.

The proper way to test for this is to take some small shavings (or sawdust) and place them in a small glass vial with either water (for a water-extract test), or denatured alcohol (for an ethanol-extract test).

Alcohol typically results in faster, more vivid, extract fluorescence than using simply water, but water extract tests can be useful when some woods are known to not produce a water-extract fluorescence color, such as Brazilian Rosewood.

http://www.wood-database.com/lumber-identification/hardwoods/ipe/ [dead link 2024-06-22 - Ed]

http://www.wood-database.com/lumber-identification/hardwoods/cumaru/) / [dead link 2024-06-22 - Ed] be conclusive? - E.T. 2016/02/16

Reply: apparently not

I have not found IPE listed among woods that are easily identified with fluorescence testing. (Dyer 1988, Sum 1991, Pandey 1998, et als cited below).

Have you gone to the supplier of your wood to ask for documentation of where the wood was purchased and where it was harvested?

Wood Properties & Wood Identification

In this illustration, adapted from the cover of Hoadley's book cited just below, our yellow annotations point out some of the features of wood using Hoadley's cross-section of a tree.

[Click to enlarge any image]

• BLACK LIGHT & UV LIGHT USES web article at InspectApedia.com
• Donaldson, L. A., and K. Radotic. "Fluorescence lifetime imaging of lignin autofluorescence in normal and compression wood." Journal of microscopy 251, no. 2 (2013): 178-187.
  Abstract:
  
  Wood cell walls fluoresce as a result of UV and visible light excitation due to the presence of lignin. Fluorescence spectroscopy has revealed characteristic spectral differences in various wood types, notably normal and compression wood.
  
  In order to extend this method of characterising cell walls we examined the fluorescence lifetime of wood cell walls using TCSPC (Time-Correlated Single Photon Counting) as a method of potentially detecting differences in lignin composition and measuring the molecular environment within cell walls.
  
  The fluorescence decay curves of both normal and compression wood from pine contain three exponential decay components with a mean lifetime of τm = 473 ps in normal wood and 418 ps in compression wood.
• Lifetimes are spatially resolved to different cell wall layers or cell types where individual lifetimes are shown to have a log-normal distribution.
  
  The differences in fluorescence lifetime observed in pine compression wood compared to normal wood, are associated with known differences in cell wall composition such as increased p-hydroxyphenyl content in lignin as well as novel deposition of β(1,4)-Galactan.
  
  Our results indicate increased deposition of lignin fluorophores with shorter lifetimes in the outer secondary wall of compression wood.
  
  We have demonstrated the usefulness of fluorescence lifetime imaging for characterising wood cell walls, offering some advantages over conventional fluorescence imaging/spectroscopy.
  
  For example, we have measured significant changes in fluorescence lifetime resulting from changes to lignin composition as a result of compression wood formation that complement similar changes in fluorescence intensity.
• Dyer, Stephanie T. "Wood fluorescence of indigenous South African trees." IAWA Journal 9, no. 1 (1988): 75-87.
  Abstract:
  
  The fluorescence characteristics of South African hardwoods and their extracts were studied to determine their value in wood identification.
  
  Heartwood specimens and water and ethanol extracts of altogether 179 species representing 108 genera and 46 farnilies were exarnined in longwave ultraviolet light. Additional tests were conducted for the presence of Aluminium natural saponins.
  
  The findings of this research correspond with the current knowledge on wood fluorescence. The families Leguminosae, Rutaceae and Anacardiaceae showed positive fluorescence for the majority of their species.
  
  Platylophus trifoliatus is the only indigenous species with a positive reaction to the test for Aluminium. The froth test for natural saponins in wood has variable results, restricting its significance in wood identification.
  
  These results show that fluorescence is a useful characteristic in wood identification and may be applied as a rapid and easy test to verify certain identifications.

• Edlin, Herbert Leeson. "What wood is that?." Viking Penguin, (1969). ISBN 0-670-75907-4 [copy on file - Ed.]
  
  A manual of wood identification for the most important timbers on the British market. The keys are based on those of Schwankl [cf. F.A. 17 No. 3189. KEYWORDS: wood anatomy \ Wood identification
  
  Excerpt: Though all wood is basically similar, every fragment shows the variability found in all natural materials. No two pieces of wood in the world are exactly alike.
  
  This gives timber its unique fascination, for no other common substance shows patterns and properties peculiar to each piece. At the same time it makes identification tricky.
  
  You have to learn to isolate those features that are characteristic of a certain timber from others that many kinds of wood can share.

Mr. Edlin's wood identification guidebook includes actual samples of wood, as we illustrate just above, adding our own addition of Hickory flooring. - Ed.

• Guzmán, JA Silva, H. G. Richter, R. Rodríguez Anda, and FJ Fuentes Talavera. "Wood fluorescence of commercial timbers marketed in Mexico." IAWA journal 29, no. 3 (2008): 311-322.
  Abstract:
  
  A market survey conducted in Mexico yielded 579 wood specimens attributed to 92 genera belonging to 40 families. The fluorescence characteristics of these timbers and their extracts were determined.
  
  Additional tests were conducted for the presence of natural saponins and aluminium. The combustion behavior (burning splinter test) was also studied.
  
  The results obtained largely concur with information on wood fluorescence and other physical characteristics published earlier. The families Fabaceae, Anacardiaceae and Rubiaceae showed positive fluorescence for a large number of genera or species. Vochysia was the only genus with a positive reaction to the test for aluminium.
  
  The froth test for natural saponins can contribute to wood identification in specific cases. The results of the burning splinter test are unambiguous only as regards the difference between charcoal and ash; ash characteristics (consistency, color) are difficult to interpret and their successful application in wood identification considered doubtful.
  
  The use of fluorescence and other physical features can be a very useful adjunct to the classical methods of wood identification in specific cases arising from the market situation and may be applied as rapid and easy tests to verify certain identifications.

• Hildén, Lars, Geoffrey Daniel, and Gunnar Johansson. "Use of a fluorescence labelled, carbohydrate-binding module from Phanerochaete chrysosporium Cel7D for studying wood cell wall ultrastructure." Biotechnology letters 25, no. 7 (2003): 553-558.

• Hoadley, R. Bruce. Understanding wood: a craftsman's guide to wood technology. Taunton press, 2000.
• James MacQueen Building Contractors Ltd, 6A Drynoch, Crossal, Isle of Skye, IV47 8SP UK, Web: http://www.skyebuilder.co.uk Tel: +44 (0)1478 640292 Email: email@skyebuilder.co.uk
  
  Note regarding the terms "rainbow" & "fruit bowl" for describing wood end grain direction:
  
  We first heard this helpful and creative use of 'rainbows and fruit bowls' from the Hulu series, "Impossible Builds". In 2018's Season 1, Episode 2, team build supervisor, Dave, from James MacQueen Building Contractors Ltd. on the Isle of Skye, described his use of this phrase in teaching his crew which way to turn the boards as they assembled the timber cladding (siding) for the "House on the Moon" they were building on the Isle of Harris.

• Laslett, Thomas. TIMBER and TIMBER TREES [PDF] Macmillan, 1894.
  Preface excerpts:
  
  A HANDY-BOOK on Home and Foreign Timber, for ship and house building purposes, is, in the opinion of many, much required.
  
  The botanical treatises which are accessible are too strictly scientific in their form and treatment to interest the general reader, and they lack that practical application of knowledge to the wants of the shipwright and carpenter, which it is one of the aims of this book to give.
  
  Hence, I have endeavoured to concentrate into one form all the information which books and long experience -could give, and so to arrange the materials as to make them intelligible and acceptable alike to the master builder and apprentice.
  
  Keeping this in view, I have introduced into the work the substance of a course of lectures on the properties of timber, which I delivered at the Royal School of Naval Architecture at South Kensington and of three other courses of lectures on the same subject, delivered at the Royal School of Military Engineering at Brompton Barracks, Chatham.
  
  Many new descriptions are treated of, and a great number of experiments on the strength of timber are given in detail as well as in the abstract.
  
  Further, there are some useful notes on seasoning timber for use, and the best means to be taken for its preservation.
  
  Public domain, we have deleted some blank pages from the original file found in the Cornell University Library.
• Meier, Eric, "Fluoresence: A Secret Weapon in Wood Identification", [Web article], retrieved 2016/02/17, original source: http://www.wood-database.com/wood-articles/fluorescence-a-secret-weapon-in-wood-identification/
  
  This article includes a table listing wood species and how they appear under UV light. You'll see that while some wood species flouresce, many of that do react with UV light may provide identical result.
  
  For example, these species are shown by Mr. Meier to appear as medium uniform green under UV lighting: Aracanga, Buckthorn, Camelthorn, Greenhart, Machiche, Peroba Rosa, Tornillo, T'zalam.
  
  The article also describes using wood shavings to prepare a water or alcohol extract or tincture combined with UV light to check wood species for fluoresence. - Ed.
  
  Excerpt:
  While certain woods can appear basically identical to one another under normal lighting conditions, when exposed to certain wavelengths—such as those found in blacklights, (which are mostly invisible to the naked eye)—the wood will absorb and emit light in a different (visible) wavelength. This phenomenon is known as fluorescence, and certain woods can be distinguished by the presence or absence of their fluorescent qualities. ...
  
  One of the best examples of fluorescence is found in Black Locust (Robinia pseudoacacia), which is very similar to Mulberry (Morus spp.) in both appearance and weight. But one way to easily distinguish the two is by observing them under a blacklight; Black Locust will emit a strong yellow-green glow, while Mulberry will be non-reactive.
• Pandey, K. K., N. K. Upreti, and V. V. Srinivasan. "A fluorescence spectroscopic study on wood." Wood science and technology 32, no. 4 (1998): 309-315.
  Abstract:
  
  Fluorescence spectroscopy has been suggested as an important tool for identification of timber (Krishna, Chowdhury 1935; Dyer 1988; Sum et al. 1991).
  
  In the present study measurements of fluorescence excitation and emission spectra from solid wood blocks, powder and their extract in methanol from heartwood of Acacia nilotica (Babul),Albizia lebbek (Kokko),Pterocarpus marsupium (Bijasal),Toona ciliata (Toon),Tectona grandis (Teak) andEucalyptus tereticornis (Eucalypt) have been made.
  
  Fluorescence spectra obtained from solid dry wood is independent of excitation wavelength, whereas those obtained from extracts exhibited excitation wavelength dependence indicating presence of many fluorescent chemicals.
  
  The need for systematic study of wood extracts in different polar and nonpolar solvents, which would be useful for purposes of identification of wood species, is stressed.
• Piuri, Vincenzo, and Fabio Scotti. "Design of an automatic wood types classification system by using fluorescence spectra." IEEE Transactions on Systems, Man, and Cybernetics, Part C 40, no. 3 (2010): 358-366.
• Block, Colleen N., Tomoyuki Shibata, Helena M. Solo-Gabriele, and Timothy G. Townsend. "Use of handheld X-ray fluorescence spectrometry units for identification of arsenic in treated wood." Environmental Pollution 148, no. 2 (2007): 627-633.
  Harvard
• Chappelle, Emmett W., James E. McMurtrey, and Moon S. Kim. "Identification of the pigment responsible for the blue fluorescence band in the laser induced fluorescence (LIF) spectra of green plants, and the potential use of this band in remotely estimating rates of photosynthesis." Remote Sensing of Environment 36, no. 3 (1991): 213-218.
• Sum, S. T., D. L. Singleton, G. Paraskevopoulos, R. S. Irwin, R. J. Barbour, and R. Sutcliffe. "Laser-excited fluorescence spectra of eastern SPF wood species. An optical technique for identification and separation of wood species?." Wood science and technology 25, no. 6 (1991): 405-413.
  Abstract:
  
  Use of UV-laser excitation to produce fluorescence spectra for heartwood and sapwood from jack pine (Pinus banksiana), white spruce (Picea glauca) and balsam fir (Abies balsamea) was examined. Spectra were fairly broad without sharp spectral features and overlap of spectra between species was common.
  
  Sample to sample and in-sample variation of the recorded fluorescence spectra was observed.
  
  The fluorescence spectra obtained from heartwood samples of jack pine showed evidence of photochemical bleaching as a result of the multiple laser pulses needed to produce a complete spectrum.
  
  Bleaching may have obscured differences between species. For the mix of species examined no sapwood nor heartwood samples were distinguishable by this technique with the detector used. Use of an optical multichannel analyzer (OMA) could reduce the number of laser pulses needed to obtain an entire spectrum.
  
  Under these conditions it would be possible to determine whether the minor differences in spectral features observed for the different species are more pronounced in the first few laser pulses and if they are characteristic of species.
  
  Certain aspects of the data suggest that with improved analytical equipment UV-fluorescence might prove to be a useful technique for the identification of certain species.

Wood Board Cupping & IPE Deck Board Properties

• "Compare IPE Decking", IPE Depot, Website: http://www.ipedepot.com/compare.htm retrieved 2016/02/09. This company's web page provides properties of IPE wood deck boards and compares them with other decking alternatives including Douglas Fir, SYP or pressure treated pine, California Redwood, Western Cedar, and Philippine Mahogany.
• Fabian, Thomas Z. "Fire Performance Properties of Solid Wood and Lignocellulose-Plastic Composite Deck Boards." Fire Technology 50, no. 1 (2014): 125-141.
• Gibson, Scott. "Choosing Materials for Exterior Decks." FINE HOMEBUILDING (2000): 64-71.
• Mantanis, George, and Charalampos Lykidis. "Weathering test of furfurylated wood decks in a 3-year exposure in Greece."
• Mitchell, Philip H. "Modeling the cupping of lumber." BioResources 11, no. 3 (2016): 6416-6425.
• Shutt, Craig A. "Improving deck safety." LBM J (2011): 26-28.
• Smith, Paul M., and Michael P. Wolcott. "Opportunities for wood/natural fiber-plastic composites in residential and industrial applications." Forest Products Journal 56, no. 3 (2006): 4-12.
• White, Robert H., Mark A. Dietenberger, and Nicole M. Stark. "Cone calorimeter tests of wood-based decking materials." (2007).

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Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

Below: this photo is an Example for other readers - image of IPE Brazilian Walnut is from novausawood.com/

On 2023-06-07 by Wayne Perrier Concerned about Cupping on 5/4x6 IPE decking

hi, I have a deck being built that is 5/4x6 IPE decking and it is slotted on the sides so that a cleat system is used to hold the boards down instead of driving screws through the face of the wood.

The deck builder told me that it was the "nicest" IPE he has ever received.

We have alot of long boards, some 20 feet. the bottom and sides were stained with an oil or solvent-based transparent stain. the tops were left unstained and the idea is to let the boards dry out, come back and sand the tops and then stain it.

We are starting to see cupping -- it's only been installed about a week.

My deck guy says that if we had stained all sides "before letting the IPE dry out" then we would get alot of splitting.

I'm getting worried that the cupping will not go away on its own. Can you advise? It's about a 600 sq ft deck and we've put alot of money into it. Thank you in advance. wayne@perrierfamily.com

On 2023-06-07 by InspectApedia Publisher - IPE decking cupping or warping & checking

@Wayne Perrier,

Thank you for a helpful question about IPE decking cupping or warping & checking.

I'm sorry, but in my OPINION the process you described is almost guaranteed to cause deck board cupping.

You don't say how high above the ground is the under-side of your deck nor do you give country, city, climate, surface runoff conditions or other features that would affect the level of moisture under and around the deck, and I agree that often, once installed and initial drying has occurred, the area under a deck *might* be more-moist than above it - contributing to cupping.,

But in this case, coating one side of a board and then setting it out in the weather pretty much guarantees that there will be significant moisture differences across the thicknesses of the board. Just picture what happens at the first rain! We soak the board but its bottom is sealed - it's nearly a "cup" for holding moisture.

The fact that you said you expected the one-side-coated boards to "dry out, then come bacck and sand the tops and stain it" tell me that the boards were not dry at time of installation and that you coated one side - guaranteeing un-even drying.

If that's the primary moisture source (haven't had much rain?) then the boards would be expected to cup or arch "down" as the upper side dried more than the under-side.

But there's an opposite possibility: help me out - and embarrass me if you like - by telling me: are the boards cupped "arch down" or arched (convex or "arch up") ?

If there has been rain, then I would expect the boards to be absorbing more moisture on their un-coated side, causing more expansion of that side, that ought to make them arched, but, then I'm not sure I've got the whole picture here.

Now what are we going to do about it?

Given the cost and trouble involved I suspect you're going to end up trying to protect the deck from rain, let it dry out, and in the driest of your season (where are you ?) if necessary sand or even plane the exposed board surfaces flat, then for heaven's sake, seal all of the board surfaces uniformly.

An alternative would be to dis-assemble all of the deck boards, dry them out in your garage - to below 18% moisture- , then run them through a planer to flatten them out and assure that they are all of both uniform thickness AND that the clip-gaps along their sides are at a uniform distance in the board so that on reinstallation they'll be uniform and flat, stain/coat ALL sides of the boards, and re-install them.

Post some photos (one per comment) to show us what's going on.

For other readers, IPE decking is a Brazilian hardwood, also referred to as Brazilian Walnut. Although this is a hard wood, it's generally expected to air dry rapidly and with only minor checking, warping, cupping, or arching IF your boards are not particularly thick.

Thicker IPE wood such as 4x4 IPE posts or wider IPE boards like a 2x12 IPE are much more prone to cupping and have been reported cupping badly-enough to actually pull deck screws right out of the deck joists below.

Sealing ALL sides of your cut-to-fit IPE deck boards at the same time and staying away from wide boards like 2x12s can minimize the cupping problem.

But

Watch out: if you coat or seal the surface of just one side of ANY board it's going to be more-likely to cup or arch.

IPE Lumber Resources

CHARACTER GRADE IPE DECKING, LUMBER AND TIMBERS [PDF] from Tropical Forest Products, 1-905-672-8000 or 855-344-4500 info@weraetropical.com


Also see the US FPL WOOD HANDBOOK [PDF] that begins discussing IPE lumber on page 2-25.

On 2022-09-17 by Tom Ambalam Do I lay the board with bark side up or down for decks exposed to winter?

I read this article a couple of times but I am confused about the bottom line - on whether to lay the board with bark side up or down for decks exposed to winter.
The article starts with a premise that for decks , bark side should be on top. But the text below is so different.

On 2022-09-17 by InspectApedia-911 (mod) -

@Tom Ambalam,

Thanks, we're reviewing the text and will clarify it.

The topic is confusing and the right answer is found in detail at

ANSWER to BARK SIDE UP or

There we state

For flatsawn boards, if we want to follow the advice of wood experts cited at REFERENCES (https://inspectapedia.com/decks/Wood_Board_Cupping_Answer.php#reviewers) for this article, we'd put the BARK SIDE DOWN when setting deck boards or wood stair treads.

The technical basis and scientific support for bark side down are detailed at

BARK SIDE DOWN ARGUMENT.

BUT THERE ARE EXCEPTIONS to THE RULE:

Our object is for the arch or convex side of the board to face "up" so as to drain better and last longer, but we have seen in practice that sometimes a board doesn't cup the way we expect, so we inspect each board at the time of construction and if it's visibly cupped we will put the "arch" "up" regardless of the tree rings visible on the end of the board.

Thank you for the question; I'm working on the text.

If you return in an hour or more and clear or refresh your browser text you'll see the updated page and we will appreciate any further questions or critique.

DF & AC

...

Continue reading at ANSWER to BARK SIDE UP or DOWN or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• BARK SIDE UP or DOWN on DECKS & STEPS?
  • BOARD CUPPING CAUSES
  • ANSWER to BARK SIDE UP or DOWN
  • BARK SIDE UP ARGUMENT
  • BARK SIDE DOWN ARGUMENT
  • WOOD CUPPING vs WET SIDE
  • CUPPED BOARD HAZARDS
  • SHELLING BOARD SURFACES
  • IPE DECK BOARD CUPPING
• BUTT JOINT CURLING in FIBER CEMENT SIDING
• DECK & PORCH CONSTRUCTION - home
• FLOOR DAMAGE DIAGNOSIS
• SLIPPERY STAIRS, WALKS, ROOFS
• WOOD FLOOR DAMAGE
• WOOD FLOOR MOISTURE

Suggested citation for this web page

BARK SIDE UP or DOWN on DECKS & STEPS? at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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