What is sapwood?
Sapwood is the outer, youngest part of the wood in a tree trunk, directly beneath the bark. In the living tree, sapwood transports water and nutrients. Towards the centre, the sapwood gradually changes into heartwood, which no longer has a transport function. In many species, such as oak, pine and larch, the sapwood is clearly lighter in colour than the heartwood. In other species, such as spruce, the difference is barely visible to the naked eye.
Properties
- Low durability. Sapwood contains sugars and starch, but lacks the protective substances found in heartwood. Under the European standard EN 350, the sapwood of all species is regarded as not durable, even if the heartwood of that species is durable.
- Susceptible to insects. Woodworm (the larva of the common furniture beetle) and powderpost beetles mainly attack sapwood.
- Easy to treat. Sapwood absorbs liquid better than heartwood. In pine, a preservative penetrates the sapwood well during vacuum-pressure impregnation; the heartwood absorbs much less.
- More movement. Sapwood is often wetter and can shrink and swell more.
Application
- Exterior work: order sapwood-free. If you use a durable species untreated outdoors, such as oak or larch, order sapwood-free timber. Sapwood in a durable species rots just as quickly as non-durable timber.
- Or have it treated. For pine in exterior applications, impregnated timber is common; the sapwood is then actually the well-protected part.
- Treat cut ends. After cutting impregnated timber, untreated wood is exposed. Treat the cut as advised by the supplier.
- Check old timber. When altering old joisted floors, check the sapwood edge in particular for flight holes and bore dust.
Common mistake: using oak or larch with sapwood for a fence or cladding on the assumption that the whole board is durable. It is precisely the sapwood edges that rot first.
Related terms
- Wood species
- Durability class
- Impregnating
- Wood rot
- Insects in wood
- Heart side of wood
- Pressure-treated wood
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