Frequently Asked Questions

Kiln dried against air dried

Kiln drying is used to make wood more stable by changing its dimensional properties and to prevent further moisture loss relative to the application. Hardwood flooring in the United States is typically dried to a moisture content of 6 to 8 percent, and cabinetry, furniture and trim can be drier still. What matters outdoors is the moisture content of the wood and whether the wood is susceptible to moisture gain.

All air dried and green lumber shrinks as it loses moisture, and tropical hardwoods are no exception. The dimensional change can be considerable relative to the moisture content of the wood, the climate and the time of year the deck is laid; 5/4 stock at a full inch shrinks more than 3/4 inch stock because of its mass. Acclimatising wood on site does not remove that loss, because how the stack is built, the temperature, the air flow and the relative humidity all bear on it.

After installation, an extremely dense hardwood such as Ipe will not gain a significant amount of moisture, so it does not expand. It loses the moisture already in it, and does not take moisture back.

Where a product is installed with a pre-determined gap, the moisture content has to be at or near the level it will settle at. With pre-grooved decking on hidden fastening the gap is roughly one eighth of an inch, and air dried pre-grooved stock will shrink and widen it until more of the clip is visible. Kiln dried pre-grooved decking is taken to roughly 13 percent, close to where the wood would settle. Tongue and groove porch flooring has no intended gap at all, because it is laid tight and should stay tight; air dried porch flooring shrinks after installation and opens a small gap between every plank. Kiln dried porch flooring at 12 percent does not shrink under a roof, although outside edges and corners in prolonged sun can lose a little more.

Do jig-driven and clip fastening systems work with Ipe?

Provided stainless screws are used, these systems will hold in Ipe. The difficulty is the starting gap: both leave a wide opening that becomes wider still once the board shrinks. Published minimums for these systems run to a quarter of an inch and three sixteenths of an inch, where air dried Ipe decking is set with a one sixteenth inch gap precisely because further shrinking is expected.

Is Cumaru better than Ipe?

Both are highly dense South American hardwoods and share similar properties for durability and longevity. Cumaru has two distinct varieties, red and yellow, and most mills do not separate them in a shipment, which can leave a bold and unattractive variation across a deck. Ipe has more varieties, and its colour range runs from light blonde to nearly black, often taking in green and orange; procuring from specific regions where fewer varieties occur is how that band is narrowed to a darker, more uniform colour.

Ipe is often shipped air dried and stays very stable through moisture loss, with no grain raise and slight surface checking. Cumaru is often shipped kiln dried at around 15 percent because stability demands it, and it can still move with further moisture loss, raising grain heavily and checking severely in a way that cannot be repaired. Raised grain is uncomfortable underfoot, and sanding does not stop it returning.

Is Massaranduba a good decking product?

Massaranduba, sold as Brazilian redwood, is a highly dense South American species slightly harder than Ipe on the Janka scale, with a deep red colour, and it is often imported for interior flooring. As decking it is extremely unstable both air dried and kiln dried: it moves extensively after installation. It is also marketed as Abaco decking.