Premium tropical hardwoods such as Ipe and Cumaru have earned their reputations as exceptional decking materials because of their density, durability, natural resistance to decay, and ability to perform in demanding exterior environments. Those qualities do not mean, however, that the boards arriving at a job site should be treated like completely finished, manufactured products.
Wood remains a natural material. It contains moisture, responds to its environment, and displays characteristics created by the tree’s growth and the way the lumber was sawn and milled. Some of the questions we hear about tropical decking are therefore less about defects in the material and more about understanding how dense hardwood behaves.
At J. Gibson McIlvain, we have always believed that informed customers are better prepared to get the performance they expect from premium lumber. In Part 1 of this Tropical Decking FAQ series, we’ll address two questions that can arise before and during installation: why a new tropical hardwood deck may have rough areas and why even a dimensionally stable species such as Ipe can sometimes warp.
Why Does My Tropical Decking Have Rough Areas?
Ipe is exceptionally hard and dense, which is one reason it performs so well as an exterior decking material. That same density can make certain portions of the wood more difficult to machine to a perfectly uniform surface.
The way a board is sawn also influences what appears on its face. Quartersawn and vertical-grain material can expose medullary rays, which are structures within the tree that transported water and nutrients radially while it was growing. These areas can be denser and may not machine exactly like the surrounding wood. As a result, portions of a freshly milled board can sometimes feel raised or rough even though the lumber itself is sound.
This isn’t unique to Ipe or tropical hardwoods, but the density and hardness of species such as Ipe can make the difference more noticeable than it would be with softer decking materials. A rough area associated with grain structure is therefore not automatically evidence that the board is defective.
Tropical decking should also not be thought of as a furniture-ready finished product when it arrives. Ipe decking is typically surfaced on four sides and eased on four edges, and boards may also be grooved when a particular hidden-fastener system requires it. The lumber will still go through transportation, handling, job-site storage, acclimation, cutting, and installation before the deck is complete. Minor surface imperfections can be addressed during the normal installation and finishing process.
When sanding Ipe or another dense tropical hardwood, work with the grain and avoid unnecessarily aggressive sanding that could create an uneven appearance. The objective is simply to smooth raised or rough areas and prepare the completed deck surface appropriately.
If Ipe Is So Stable, Why Are My Decking Boards Warping?
Ipe is considerably more dimensionally stable than many other decking materials, but stability should not be confused with an inability to move. All wood exchanges moisture with its surrounding environment, and changes in moisture content can cause boards to expand, contract, cup, twist, or otherwise move.
When an Ipe deck develops movement problems, it is therefore important to look beyond the species itself. Moisture content at installation, job-site acclimation, exposure to sun and rain, ventilation beneath the deck, board spacing, fastening, and overall deck design can all influence how the lumber behaves.
One particularly important distinction is the difference between lumber prepared for exterior decking and lumber dried for climate-controlled interior use. Exterior Ipe decking is generally supplied at a higher moisture content than the roughly 6–8% material appropriate for many interior applications. Depending upon the material and drying process, exterior decking may be air dried or kiln dried, but it is commonly supplied within approximately the 12–18% moisture range.
That higher moisture content is intentional. Exterior decking is going to live through rain, humidity, direct sunlight, temperature changes, and seasonal shifts throughout its service life. Drying an exterior board to the much lower moisture content appropriate for an indoor environment can create a large moisture differential when that board is placed outside and begins adjusting to its surroundings.
The objective is not to prevent Ipe from ever gaining or losing moisture. That isn’t realistic with any wood. The objective is to begin with appropriately prepared material and install it in a way that accommodates the normal movement that will occur throughout the life of the deck.
Give Ipe Time to Acclimate Before Installation
Even properly dried decking needs an opportunity to adjust to conditions at the job site. Ipe may have been milled in South America, transported by ocean freight, stored at a lumber yard, shipped across the country, and then delivered into a climate very different from the one it recently experienced. Installing the boards immediately upon arrival can lock them into a rigid structure while they are still adjusting to their new environment.
Acclimation allows some of that adjustment to occur before fastening. The lumber should be kept out of direct sunlight and stored so that air can circulate around the boards rather than leaving the material tightly wrapped or stacked in a way that traps moisture.
There isn’t one acclimation period that is correct for every project. Climate, season, board dimensions, storage conditions, moisture content, and the difference between the material and its destination environment can all affect how much time is appropriate. What matters is giving the decking sufficient opportunity to approach equilibrium with the conditions in which it will be installed.
This is also why measuring moisture can be more useful than relying solely on the calendar. The goal is not simply to wait a predetermined number of days; it is to understand whether the lumber has had a reasonable opportunity to adjust before it is permanently fastened to the deck structure.
Sunlight and Uneven Moisture Exposure Can Affect Board Movement
Direct sunlight deserves particular attention because it can heat the surface of a deck considerably and accelerate moisture loss. A board exposed to intense sun on one face while the underside remains cooler and more humid is experiencing different conditions across its thickness.
Deck design can either help or worsen this situation. Adequate airflow beneath and around the boards allows moisture changes to occur more evenly, while inadequate ventilation can contribute to different moisture conditions between the top and bottom surfaces. Ground-level and other low-clearance decks deserve especially careful consideration because airflow may be limited.
Proper board spacing is also part of moisture management. Gaps allow for drainage, airflow, and dimensional movement as environmental conditions change. The appropriate spacing should reflect the condition of the lumber at installation and the climate in which the deck is being built rather than relying blindly on one spacing measurement for every project.
Ipe’s natural stability gives a well-designed deck a considerable advantage, but good material cannot compensate indefinitely for conditions that repeatedly expose opposite sides of a board to substantially different environments.
Seal Freshly Cut Ends
The end grain of a board exchanges moisture much more rapidly than its faces. When an Ipe decking board is cut to length, the newly exposed end can therefore lose or absorb moisture faster than the rest of the board, increasing the possibility of end checking.
J. Gibson McIlvain end-seals Ipe decking to help protect boards during transportation and acclimation and recommends resealing freshly cut ends during installation. A wax-based end sealer such as Anchorseal, or another product appropriate for the application, slows the rate of moisture exchange through the end grain.
End sealing does not make the wood waterproof, nor is that the objective. It simply moderates how rapidly moisture can enter or leave through the exposed end grain, reducing the abrupt changes that can contribute to checking.
Successful Ipe Decks Work with the Wood
Many installation problems associated with tropical decking can be reduced by recognizing that even an exceptionally dense and stable hardwood remains a natural material. Ipe will respond to moisture, temperature, sunlight, airflow, and seasonal conditions throughout its service life. Proper preparation and installation are intended to accommodate that behavior rather than attempt to eliminate it.
Before installation, give the decking an appropriate opportunity to acclimate in shaded conditions with good airflow. During installation, account for drainage, ventilation, spacing, fastening, and the moisture condition of the boards, and seal freshly cut ends to help reduce rapid moisture exchange through the end grain. Minor rough areas associated with Ipe’s grain structure can also be addressed as part of preparing the completed deck surface.
These practices help the material do what Ipe is capable of doing exceptionally well: provide a durable exterior surface that can perform for decades when the entire deck is designed and installed with the characteristics of real wood in mind.
Continue with Tropical Decking FAQs: Installation, Part 2.
