The most stable flooring materials in the world
When most people decide to purchase decking material, the first thing they consider is either the look of the wood or its cost. An unfortunately overlooked aspect of flooring material is the structural stability of wood. If you choose an unstable decking material, you risk warping or cracking the deck boards. Warping is the tendency of wooden deck boards to curve inward along their longitudinal edges. Edge checking refers to the cracking and splitting of the edges of deck boards as they absorb and release moisture. Both warping and checking are big problems for the deck owner and can cost a lot of time and money to correct.
Fortunately, the stability of a given tree species is relatively easy to measure. There are certain standardized measurements that are used to determine the mechanical properties of any type of wood, and these properties tell us the stability and durability of the wood in question.
Stability measures
The two main properties used to measure stability are tangential and radial shrinkage. Both radial and tangential shrinkage refer to how much a wood species tends to shrink during the drying process. Radial shrinkage occurs in the direction from the center of the tree toward the bark, while tangential shrinkage occurs tangentially or parallel to the growth rings of the tree. Both radial and tangential shrinkage are measured as a percentage. The lower the percentage, the less the wood will shrink during the drying process and the more stable the board will be when installed.
While radial and tangential shrinkage rates are important on their own, the best way to measure wood stability is to consider these properties together. The smaller the difference between the two measurements, the more stable the wood. For example, if a type of wood shrinks twice as much in its width as it does in its thickness, boards from that wood will warp and bend much more than boards from a wood with a much lower radial/tangential difference.
Stable tree species
Now that we are familiar with how stability is determined, let’s take a look at the most stable types of domestic and exotic wood flooring.
Homemade:
Domestic wood is usually softwood, which means it’s less dense, less hard, and doesn’t hold as much weight. However, that doesn’t mean there aren’t great hardwood flooring options available. Two of the most durable softwood decking options are western red cedar and California redwood.
Western red cedar
Although cedar is a softwood, it is still very stable structurally. Both tangential and radial shrinkage are quite low, and the difference between the two is also very small:
Tangential Shrinkage: 5.0%
Radial Shrinkage: 2.4%
Cedar’s other mechanical properties—strength, stiffness, and density—are also relatively high, making it a durable species suitable for most flooring projects.
California redwood
California redwood is another very stable decking material. Tangential and radial shrinkage values are even lower than Cedar:
Tangential Shrinkage: 4.9%
Radial Shrinkage: 2.2%
Although these percentages are lower than Cedar, the difference is 0.1% greater, meaning it is slightly less stable than the other species – but not by much.
Exotics:
Exotic hardwoods are denser, heavier, and tend to have higher percentages of tangential and radial shrinkage. Does this make them less stable? Not always. Differentials for some exotic cars are lower than their domestic counterparts, making them structurally stronger.
Yep
The percentages of tangential and radial shrinkage of Ipe are much higher than those of Cedar and Redwood; however, the difference is much smaller, making it the more stable wood.
Tangential shrinkage: 8.0
Radial Shrinkage: 6.6%
The 1.4% differential is great and combined with Ipe’s naturally high density, strength and stiffness makes it a natural fit for decking purposes.
Merbau
Merbau is another hardwood with excellent structural stability. The percentages of tangential and radial shrinkage are:
Tangential Shrinkage: 4.6%
Radial Shrinkage: 2.7%
These percentages are quite a bit lower than Ipe’s, and even though Ipe’s difference is only 1.4%, the 1.9% difference is still very good. The low percentages combined with the relatively low differential make this the most stable choice for exotic decking. However, Merbau comes with an unrelated and unfortunate drawback – read on to find out what it is.
Comparisons
For home wood, the most structurally stable option is cedar, although redwood is a close second. For exotics, Merbau is the more stable option, with Ipe decking as a good second choice.
Between Merbau and Cedar, the obvious choice is Merbau. Shrinkage rates are about the same as Cedar, but the difference is much smaller. In addition, the higher density makes the wood more naturally resistant to rot and decay.
Considerations
In addition to structural stability, there are a number of things to consider when choosing the right decking material. Here are some important facts about the tree species mentioned above
- The shrinkage values for cedar and redwood apply only to materials made from pure heartwood. Many manufacturers will include sapwood in their boards, which greatly reduces the stability and strength of the wood. When choosing softwood, check for little or no sapwood content.
- Although Merbau is an extremely stable hardwood, it has one unpleasant quality – it bleeds. When wet, the tannins in Merbau boards will release an intense red color from the wood and can stain any light colored surface. Merbau tannin bleeding can ruin driveways, cars and other living spaces. Merbau decks should be treated with a high quality wood sealer to minimize tannin release. Just to be on the safe side, do not use Merbau over a living space, driveway, concrete slab or carport.
- While structural stability is certainly important, it shouldn’t be the only factor you consider when choosing a decking material. Merbau may have the lowest rates of tangential and radial shrinkage, but Ipe has incredibly high density. This density – which naturally protects the wood from boring insects, mold and weather wear – leads many consumers to choose Ipe decking over Merbau. Ipe also does not leach tannin, making it safe for use on carports and other living spaces.
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