Wood science

An overview of common

terrace woods and their properties

Wood as far as the eye can see

Wooden decking doesn’t just look good. The physical properties of this natural, tried and tested material are also highly advantageous in construction. What’s more, it’s good for the environment.

Wooden decking is technically uncomplicated and can be installed in a very short time. When expertly laid, the decking is insensitive to rain and frost. Whether over soil or a lawn, the ground beneath the decking can continue storing and releasing rainwater without problem. The CO2 absorbed by the wood during its time as a tree remains stored there throughout the service life of the decking. In the event of a fire, its release is carbon-neutral.

When building decking, contractors, planners and architects can choose from a wide range of attractive woods as well as technically modified wood such as thermowood or kebony. As wood experts know, real wood is a natural material which changes its natural colour over the years. It acquires a grey or silvery patina, which for many wood lovers merely accentuates the wood’s inherent beauty even further.

Modified wood and NFC/WPC composites are not natural wood, and due to their different material properties should only be used in accordance with the manufacturer’s instructions.

Which boards are right for me? Your decking will have to cope with mechanical stress and weather of varying intensity, depending on where it is to be installed. Besides visual appearance, different types of wood also have different material properties. The SPAX Board Finder provides a practical overview of popular types of wood and their properties. With its help, you can’t go wrong with your choice of boards!

Please note: In special cases, e.g. rooftop decking or walkways, building consent and compliance with special material standards and care instructions may be required. Get advice from an architect or structural engineer if necessary.

All-rounder with American roots

The Douglas fir originates from North America but has been planted in Europe for over 100 years. Its good machining characteristics, hard-wearing nature and

Douglas fir
Botanical name: Pseudotsuga menziesii
Code according to DIN EN 13556: PSMN
Origin: Europe
Bulk density at a moisture content of 12–15%: 470
Hardness (Brinell) N/mm²: 17
Durability according to DIN EN 350: Class 3
Colour treatment: Suitable (recommended)
Knottiness: Low to high knottiness/radial pattern
Swelling and shrinkage: High
Spiral grain/warping: Low
Wood constituents that cause discoloration: None known
Resin content: Medium
Tannic acid reaction to iron: Low
Tendency to crack: Medium
Machinability: Good
Safety-relevant function: Yes, in Grade 3.1
Remarks: The sapwood content is > 10

Charming European

The European larch is similarly well-endowed with knots, and is therefore often mistaken for the Douglas fir. Since the European larch mostly originates from fast-growing forests, its wood is coarser grained and less hard than its Siberian namesake. Larch wood from high in the mountains is of better quality than larch wood from the lowlands.

Clear varnishes are generally the preferred treatment, so that the larch

European larch
Botanical name: Larix decidua
Code according to DIN EN 13556: LADC
Origin: Europe
Bulk density at a moisture content of 12–15%: 470
Hardness (Brinell) N/mm²: 19
Durability according to DIN EN 350: Class 3
Colour treatment: Suitable to a degree (note manufacturer
Knottiness: Low to high knottiness
Swelling and shrinkage: Medium
Spiral grain/warping: Medium
Wood constituents that cause discoloration: None known
Resin content: Medium to high
Tannic acid reaction to iron: Low
Tendency to crack: High
Machinability: Good
Safety-relevant function: Yes, in Grade 3.1
Remarks: Larch is difficult to paint because of its high resin content, and should on no account be treated with dark varnishes.

Sturdy, good in cold climates

In the north of Russia, icy temperatures predominate for many months. Summer is hot and brief. These conditions result in slow tree growth with fine grains and few branches. Unlike the European larch, the Siberian version therefore provides a hard coniferous wood with good machining properties.

In the north of Russia, icy temperatures predominate for many months. Summer is hot and brief. These conditions result in slow tree growth with fine grains and few branches. Unlike the European larch, the Siberian version therefore provides a hard coniferous wood with good machining properties.

If you

Siberian larch
Botanical name: Larix sibirica
Code according to DIN EN 13556: LAGM
Origin: Siberia
Bulk density at a moisture content of 12–15%: 680
Hardness (Brinell) N/mm²: 19
Durability according to DIN EN 350: Class 3
Colour treatment: Suitable to a degree (note manufacturer
Knottiness: Low to high knottiness
Swelling and shrinkage: Medium to high
Spiral grain/warping: Medium to high
Wood constituents that cause discoloration: None known
Resin content: Medium to high
Tannic acid reaction to iron: Low
Tendency to crack: High
Machinability: Good
Safety-relevant function: Yes, in Grade 3.1
Remarks: Larch is difficult to paint because of its high resin content. The Siberian larch is generally very fine-grained and grows much more slowly than the European larch.

Timeless and tasteful

The oak is popular in Europe for construction, and also satisfies more sophisticated tastes. Tried and tested in house building and furniture since time immemorial, oak

Oak (white oak)
Botanical name: Quercus robur
Code according to DIN EN 13556: QCXE
Origin: Europe
Bulk density at a moisture content of 12–15%: 650
Hardness (Brinell) N/mm²: 23
Durability according to DIN EN 350: Class 2
Colour treatment: Good
Knottiness: Low to high knottiness/radial pattern
Swelling and shrinkage: Medium
Spiral grain/warping: Medium
Wood constituents that cause discoloration: Medium to high
Resin content: ----
Tannic acid reaction to iron: High
Tendency to crack: Medium
Machinability: Medium, pre-drilling essential
Safety-relevant function: Yes, in Grades 3.1 / 3.2
Remarks: When the European white oak is in direct contact with the soil, there are major differences in its resistance to fungi. Knots of different sizes may be present, depending on the manufacturer and quality.

A tough cookie

Bangkirai is a fine-grained Asian hardwood. When freshly cut it has a pale, yellowish brown hue that darkens to medium brown over time. Bangkirai has a moderate tendency to form a spiral grain. Typical pinholes from wood-boring insects are evident from its life as a tree.

Bangkirai has a strong tendency to swell and shrink. Care should therefore be taken to ensure soaked wood doesn

Bangkirai/yellow balau
Botanical name: Shorea spp.
Code according to DIN EN 13556: SHBL
Origin: Southeast Asia
Bulk density at a moisture content of 12–15%: 700
Hardness (Brinell) N/mm²: 26
Durability according to DIN EN 350: Class 2
Colour treatment: Suitable
Knottiness: Low knot count
Swelling and shrinkage: High
Spiral grain/warping: Medium
Wood constituents that cause discoloration: High
Resin content: Low
Tannic acid reaction to iron: High
Tendency to crack: Medium
Machinability: Medium, pre-drilling essential
Safety-relevant function: Not possible
Remarks: Bangkirai may feature so-called pinholes from wood-boring insects. When laying deck boards, it

A tough cookie

Only tough cookies are used in the garden

Cumaru
Botanical name: Dipteryx odorata
Code according to DIN EN 13556: DXOD
Origin: Central/South America
Bulk density at a moisture content of 12–15%: 1000
Hardness (Brinell) N/mm²: 45
Durability according to DIN EN 350: Class 1
Colour treatment: Average (recommended for dried wood only)
Knottiness: Low knot count
Swelling and shrinkage: High
Spiral grain/warping: Medium to high
Wood constituents that cause discoloration: Low
Resin content: ----
Tannic acid reaction to iron: Low
Tendency to crack: Medium to high (pay attention to moisture content)
Machinability: Medium, pre-drilling essential
Safety-relevant function: Not possible
Remarks: Cumaru has an irregular grain orientation, which must be taken into account without fail during installation. The wood must dry slowly to prevent major warping or cracks in the ends and surface.

A gem among woods

In hardness tests, Ipe gets top marks. This wood originates from South America, has low flammability and is especially resistant to rot and pest infestation. These properties make Ipe ideal for decking wood that can withstand the toughest conditions. But ipe also comes top of the class for pond and pool surrounds!

Unlike other hardwoods, Ipe is not prone to swelling and shrinkage. Water has little impact on it. The risk of cracking and splitting so common in other hardwoods does not apply here. Nevertheless, we still recommend pre-drilling Ipe.

Its pleasantly homogeneous pale to olive brown appearance gives ipe a refined look. There is barely any sign of annual growth rings. When a section is cut through the wood, there may be alternating shiny and matt stripes. This is due to the interlocking grain that frequently occurs in tropical tree species. Occasional yellowish speckles have no influence whatsoever on stability and other technical properties.

If you prefer to delay the bleaching of the olive brown wood to silvery grey, pigmented oil is the answer. Pigmented oil blends with the tree

Ipe, lapacho
Botanical name: Tabebuia serratifolia
Code according to DIN EN 13556: TBXX
Origin: Central/South America
Bulk density at a moisture content of 12–15%: 900
Hardness (Brinell) N/mm²: 48
Durability according to DIN EN 350: Class 1
Colour treatment: Limited/difficult, not recommended
Knottiness: Low knot count
Swelling and shrinkage: Very low
Spiral grain/warping: Very low
Wood constituents that cause discoloration: Low
Resin content: ----
Tannic acid reaction to iron: Low
Tendency to crack: Very low
Machinability: Medium, pre-drilling essential
Safety-relevant function: Yes, in Grades 3.1 to 4
Remarks: There may be considerable differences in colour in a delivered batch. Ipe is especially suitable for dry and sunny spots, as its rate of shrinkage is only moderate and it dries very slowly.

Garapa comes from the South American tropics. Garapa wood is sturdy, resistant to rot and relatively water-resistant

The risk of swelling and shrinkage is low to medium. This wood is slow to release water, reducing the risk of cracking and splitting due to fluctuating climate conditions or moisture. Garapa is therefore often the first choice for decking and pool surrounds.

Garapa is virtually knot-free and therefore has a very uniform grain. When dry, its colour ranges from gold to almond with numerous warm nuances of shade. The relatively coarse surface of the deck boards is polished to create a smooth shine. If you like being barefoot, you

Garapa
Botanical name: Apuleia leiocarpa
Code according to DIN EN 13556: No code as yet
Origin: Central/South America
Bulk density at a moisture content of 12–15%: 700
Hardness (Brinell) N/mm²: 30
Durability according to DIN EN 350: Class 3
Colour treatment: Average, after weathering
Knottiness: Low knot count
Swelling and shrinkage: Low
Spiral grain/warping: Low
Wood constituents that cause discoloration: Low
Resin content: ----
Tannic acid reaction to iron: Medium
Tendency to crack: Low
Machinability: Good, pre-drilling essential
Safety-relevant function: Not possible
Remarks: It initially has a pale, slightly yellowish hue, which rapidly darkens to brown and later develops an attractive grey patina.

One of a kind

Bongossi is a hardy West African. Not only is bongossi wood resistant to pests and fungi, it can also defend itself against seawater and submarine micro-organisms. Even shipworms have no chance with bongossi, especially the kind found in non-tropical waters!

On land, insects both familiar and exotic

Bongossi/azobe
Botanical name: Lophira alata
Code according to DIN EN 13556: LOAL
Origin: Africa
Bulk density at a moisture content of 12–15%: 950
Hardness (Brinell) N/mm²: 53
Durability according to DIN EN 350: Class 2
Colour treatment: Average, after weathering
Knottiness: Low knot count
Swelling and shrinkage: Medium
Spiral grain/warping: Medium to high
Wood constituents that cause discoloration: Low
Resin content: ----
Tannic acid reaction to iron: Low
Tendency to crack: Medium to high (pay attention to moisture content)
Machinability: Medium, pre-drilling essential
Safety-relevant function: Yes, in Grades 3.1 / 3.2
Remarks: Marked spiral grain possible, highly suitable for water features.