Wood for exteriors is those types of wood that due to their high natural durability can resist the influence of humidity, pests, and the fact of being constantly exposed to the elements.
If you want to know which are the most suitable woods for outdoor use and what factors can affect or favor their natural durability, continue reading.
But first, visit our blog on wood basics to learn about some technical concepts that you may not be familiar with.
The natural durability of wood is very necessary for exterior wood.
In general, exterior woods are those that, due to their characteristics, are mainly used in the elaboration of garden floors, decking, wall coverings and even furniture that will be most or all of the time directly exposed to the sun’s rays, rain and possible pests.
On the other hand, when we talk about the natural durability of wood we refer to the resistance of this material to degradation agents that can be biotic such as fungi and insects and abiotic such as rain, solar radiation or blows.
Also, it is necessary to clarify that not all woods resist equally; there are some with a lot of natural resistance as Teak wood and, others that are not very resistant as Spruce wood.
The 5 kinds of wood with the greatest natural durability
The following woods are not organized in ascending or descending order; we have included the 5 kinds of wood with the best reputation for carpentry and exterior construction uses, since they are woods that do not need many treatments to be preserved in excellent condition for many years.
1. Teak wood (Tectona Grandis)
Distribution
Although of Asian origin (Burma is the largest producer), this wood is so sought after by wood lovers that there are large plantations in Latin America and tropical Africa, as supply never seems to meet demand.
However, keep in mind that Teak from Asia, that is, from countries such as Burma, India and Indonesia, is considered to be of better quality, although that does not mean that Teak from other parts of the world is not excellent.
With this, what you should know is that the quality of “non-Asian Teak” is usually a little lower (not much) than Asian Teak because sometimes more treatments have to be used to preserve it over time.
However, the final result after treatment provides the same quality.
Perhaps this situation is explained by the fact that non-Asian Teak comes from plantations where sometimes the cutting age of the tree is not respected, so immature wood can be found and that is the reason for the lower quality; but this is not common in the market.
Resistance
This wood is considered by many as the most resistant of all. Its resistance to weathering is such that it needs almost no treatment.
In addition, it has great durability against termites and medium resistance to other pests such as marine borers.
The secret of teak’s great durability lies in the good quality of its heartwood and the oil it produces, which protects it from humidity and solar radiation.
Workability
It is an easy wood to work in almost every way. However, it contains a lot of silica dust, a material that can wear out tools, especially hand and power saws.
There can be problems with the finish of the wood due to the large number of oils it releases, so some varnishes and paints are not suitable, but with the use of solvents the problem can be solved.
Note: silica dust is a compound that in some cases can be dangerous to health because it can cause allergies and respiratory problems, so it is recommended to wear a mask and gloves when working with any wood.
Price
Although Teak wood comes from large plantations (i.e. there is a good supply), it is not an economic wood at all. In fact, it is expensive even in the countries where it is grown because:
- It is a tropical wood (among the scarcest and of good quality and therefore the most expensive).
- It is hardwood.
Color
Sapwood (young wood has no use for timber).
Yellowish white.
Heartwood (mature and more resistant wood)
Golden, sometimes light brown that darkens with the passage of time.
Conservation status
Teak is not environmentally endangered. In fact, it is not even listed by the International Union for Conservation of Nature (IUCN).
Uses
- Manufacture of boats.
- Manufacture of plywood.
- Construction of exteriors (floors, supports, pallets).
- Carving.
- Manufacture of handicrafts.
- Cabinetmaking.
2.Iroko wood (Milicia excelsa; Milicia regia)
Of African origin, Iroko wood is a tropical wood known for its resistance, so much so that some call it “the African Teak”.
Distribution
Iroko wood refers to two species: Milicia excelsa and Milicia regia.
In general, these 2 species are native to the whole tropical region of Africa so they can be found in countries such as:
- Sierra Leone.
- Ivory Coast.
- Zaire.
- Liberia.
- Ghana.
- Nigeria.
Endurance
Iroko wood is very durable; especially resistant to insect attack. However, its resistance to weathering is slightly less than that of real Teak (Tectona grandis).
Workability
Iroko wood is easy to work although its fiber is interlocked, so planing can be difficult.
Also, Iroko contains calcium carbonate, a substance that can wear out tools.
Price
It is cheaper than real Teak so it is marketed as one of its main substitutes.
Color
Sapwood
Pale yellow.
Heartwood
Intense yellow almost golden, although it can darken with time and sun exposure.
Conservation status
Iroko is an IUCN Red Listed species. Its population has declined by more than 20% in the last 30 years due to a combination of deterioration of the tree’s natural habitat and excessive logging.
Uses
- Manufacture of exterior flooring.
- Manufacture of plywood.
- Cabinetmaking.
- Shipbuilding (manufacture of ships and boats).
Note: Iroko wood is considered a sensitizing agent, i.e. this wood can trigger allergies at first contact; but prolonged exposure to this wood will result in stronger reactions and can even become a serious health threat.
3. Cumaru wood (Dipterix odorata)
Comaru wood is known to woodworkers as “Brazilian Teak” (as you may have noticed, Teak is the standard wood by which durability is judged).
However, Camaru wood has nothing to do with Real Teak.
On the other hand, Camaru wood is extremely hard so it is widely used in exterior applications as this hardness gives it greater strength.
Distribution
This wood is of American origin, more exactly from the tropical regions of South America in countries such as:
- Brazil.
- Bolivia.
- Colombia.
- Guyana.
- Peru.
- Venezuela.
Endurance
Camaru wood is very resistant to weathering and humidity practically does not affect it. Something similar happens with termites and wood-boring insects.
Workability
As such a hard and dense wood, working with Camaru can be difficult, especially when sawing, as the saw blades wear out quickly.
Not to mention silica dust released by the wood, which accentuates the problem of tool wear.
The same happens with gluing, as the silica impedes the action of some glues; in addition, it is necessary to use a drill to make holes for nails and screws, otherwise the wood tends to tear.
Note: often Camaru wood gives off a smell of vanilla, which can help to differentiate it from the Ipe wood.
Price
It is an abundant wood so the price is affordable, which is why it is an economical alternative to real Teak wood which as already mentioned is expensive.
Color
Sapwood
Pale yellow.
Heartwood
Light to dark brown with some purple or reddish tones. In addition, the heartwood fluoresces under ultraviolet light. In fact, this is one of the ways to differentiate it from Ipe wood.
State of preservation
Camaru wood is not listed by the IUCN.
Uses
- Elaboration of floors.
- Elaboration of cabinets.
- Heavy construction (elaboration of beams and supports).
- Dock construction.
- Manufacture of train rails.
- Manufacture of handles for tools.
4. Lapacho or Ipe wood (Handroanthus spp)
Ipe wood is extremely hard and dense and therefore very resistant, so it is widely used in exteriors.
Distribution
Ipe wood is native to warm areas of the Americas. Therefore, it can be found from Mexico to Argentina. Although the tree needs very specific conditions to grow so it is not in high supply.
Resistance
Ipe wood is another very durable wood; it resists very well to insect attack with the exception of some marine borers.
Ipe wood is also extremely resistant to humidity and weathering, which is explained by its high concentration of tannins.
Workability
Like Camaru wood, Ipe wood is extremely hard and therefore difficult to work.
You better have very good quality tools or guess what? They will be dull halfway through the job.
On the other hand, the straight grain makes planing easy most of the time.
Also, due to the tannins, sizing and finishing processes can be difficult.
Price
It is not one of the most expensive woods on the market, but it is not cheap either. Although it is a little cheaper when sold as boards for flooring.
Color
Sapwood
Whitish-yellowish.
Heartwood
It covers all shades of brown (light, dark); most of the time with black stripes all over the surface.
This wood is difficult to distinguish from Camaru wood, although Ipe is usually darker and doesn’t smell vanilla when working with it.
Conservation status
Ipe is not listed in the IUCN, however, its demand is increasing so there is concern about its possible overexploitation.
Uses
- Floor manufacturing.
- Construction of pallets.
- Manufacture of plywood.
- Manufacture of handles for tools.
5. Elondo or Tali Wood (Erythopleum utile Sprangue)
Elondo, also known as “African Oak”, is a very dense tropical wood, but somewhat less hard than Ipe and Camaru.
However, it is harder than Asian Teak.
Distribution
Elondo is native to the African continent. However, it can also be found in Asia where there are plantations.
That’s why this wood is relatively abundant in countries such as:
- Ivory Coast.
- Gabon.
- Ghana.
- India.
- Nepal.
- Pakistan.
Note: Elondo wood coming from Africa is considered to be of better quality than wood coming from Asia. Nevertheless, both varieties are very good.
Endurance
Elondo or Tali is a very resistant wood to weathering and humidity. Its resistance to insects and fungi is also very good. This occurs because this wood has a high concentration of tannins.
Workability
It is generally a difficult wood to work because of its high hardness, but above all because of its high density. Therefore, we find the same problems in all hardwoods such as excessive wear of the saw blades.
In addition, due to the tannins it exudes, many types of glue have no effect. But perhaps the most difficult is planing, as its grain can be very interlocked, which predisposes it to splintering.
Price
It is an expensive wood, even in countries where it grows naturally, so much so that it can equal the price of real Teak.
This is because it is currently in short supply.
Color
Sapwood (young wood has no timber use).
Yellow with pinkish hues.
Heartwood (mature and more resistant wood)
Intense reddish yellow. However, there may be darker or lighter shades.
Conservation status
The Elondo is a species cataloged as vulnerable by the IUCN, which means that it is very likely to be in danger of extinction in a short time due to excessive logging and the deterioration of the tree’s natural habitat.
Uses
Most of the applications of Elondo wood are destined to the exterior, for example:
- Elaboration of decking for floors.
- Exterior carpentry (doors, window frames).
- Wall coverings.
- Manufacture of decorative veneers.
- Construction of docks.
Classification of wood durability
The following chart shows a short classification of woods according to their natural durability; obviously these are not all woods, but they can be useful to give you an idea of which one could be useful in case you are looking for wood for an exterior project.
Factors that favor the natural durability of wood
Natural wood preservatives
Another thing to keep in mind is that the natural resistance of wood is conditioned by the number of resins, tannins, and natural oils present in each wood.
Resin
Resin is a chemical compound produced by conifers such as spruce and pine and its function is to protect the tree from insects since this compound is toxic to them.
In addition, the sticky texture of the resin helps the tree to expel insects that have gotten inside the trunk, trapping them and immobilizing them until they die of starvation.
But the resin not only protects the wood from insects, it also protects it from fungi and even from blows because it can cover wounds present in the trunk so that they heal faster.
Tannins
Tannins are other chemicals produced by trees for their own protection. In fact, it could be said that tannins are the “resins” of hardwood trees such as oak, cherry, ash, and others.
Likewise, these compounds prevent the wood from rotting by protecting it from excess moisture, while keeping pests from eating away at the tree.
Natural oils
Natural wood oils are oily substances that mainly serve as lubricants for the wood when climatic conditions are extreme.
Thus, in times of drought, the oils allow the wood to be moisturized and not dry out.
On the other hand, in very rainy conditions, oils help to control humidity, since their oily nature repels some of the water on the surface of the wood, preventing it from rotting.
Heartwood-sand ratio
The heartwood-sapwood ratio in each species is a determinant of the wood’s resistance. Heartwood is the mature and usable wood of the tree, that is to say, it is the “hard” and “resistant” wood.
Sapwood, on the other hand, is soft and not very resistant. This is because sapwood stores much more moisture than heartwood.
This is why it is almost never used for timber purposes. Therefore, it is not unusual that pests tend to attack this part of the trunk more regularly.
From the above, we can conclude that the higher the proportion of heartwood in a tree, the better the quality of its wood.
Factors that impair the natural durability of wood
Biotic degrading agents
These are fungi and xylophagous insects, i.e. they feed on wood components such as cellulose and lignin.
Thus, keep in mind that the more humidity there is on the wood, the easier it will be for xylophagous insects to digest it, so humidity is always to be controlled.
Therefore, the main problem that these agents pose is that they rot the wood. Thus, in some cases, the rot is visible, while in other cases the rot is internal and can only be seen well when the tree has been felled.
Right now what we want to know about these agents are the ones that cause the most serious functional deterioration of the wood, so they should be the first concern of anyone who has wood to sell or buy.
Abiotic degrading agents
These agents derive from climatic phenomena such as rain or direct exposure to solar radiation.
Therefore, abiotic degrading agents often cause aesthetic rather than functional damage, as they can, for example, discolor wood.
However, that is not to say that abiotic agents do not represent a serious problem, as excessive exposure to sunlight can cause wood to crack when drying naturally, or curve in more extreme cases.
Note: no matter how naturally resistant a wood is, you must always avoid placing it on the ground or anywhere where water accumulates. That’s where there is the most moisture and not all wood treatments or natural resistance can counteract the effects of excessive moisture.
Different uses of outdoor wood
Finally, we would like to clarify that not all outdoor applications are the same. You may have a table made of Teak wood but it’ll last many more years and will be in better condition if you keep it covered from humidity and the sun’s rays.
On the contrary, if you leave that same table completely exposed to water you’ll reduce its useful life considerably.
That is why in Europe there is a standard, the EN-335, which classifies woods according to the degree of humidity they can withstand; this way you know which woods are suitable for exteriors and which are definitely not.
Class 1
These woods are intended for interior use. They are usually labeled as being unsuitable for damp environments.
In fact, the manufacturer will most likely not give you a guarantee if the humidity of the environment where you want to use these woods is higher than 12%.
However, if you have any doubts, ask at the place where you buy the wood.
Class 2
These woods are also designed for interior use; they are a little more resistant but are not recommended in places with humidity above 20%.
Grade 3
Class 3.1
These woods have either been treated or have a medium natural durability so they can be used outdoors as long as they are away from places with high humidity concentrations, such as the ground.
Likewise, they can be preserved in environments with humidity not exceeding 20%.
Class 3.2
This type of wood is for exterior use. Their natural durability is medium or they are durable woods.
However, you should keep them away from the ground or other places with too much humidity. They can withstand environmental humidities above 20%.
Class 4
These woods are durable to very durable. They withstand ambient humidity well above 20%.
Therefore, they can be in contact with the ground or other very humid places.
Class 5
These are all woods considered to be very durable, i.e. they are not affected by humidity.
In fact, seawater doesn’t cause any damage to them and, for this reason, they are used in shipbuilding, i.e. they are used to build ships or to make the floors of docks and harbors.