LVL Handbook EUROPE

7. DURABILITY

Figure 7.4.

Pressure-impregnated LVL-C beams.

resistant to strong acids, but its resistance to bases is good.

Lignin, on the other hand, is easily dissolved in bases, whereas

it is resistant to most strong acids. For these reasons, wood is

quite resistant to moderate chemical effects.

LVL has good resistance to mild acids and acid salt solutions.

Alkalis, however, cause softening of the wood. Direct contact

with oxidizing agents such as chlorine, hypochlorites and ni-

trates should be avoided.

Wood is generally quite resistant to organic substances.

However, organic solvents such as acetone, benzene, alcohol

etc. dissolve resins, fats and waxes, causing similar effects to

water, i.e., producing swelling and a slight reduction in strength

properties. Petroleum oils have no effect on strength properties

but cause discolouration.

Chemical resistance can be improved with various types of

coatings

7.4 CHEMICAL WOOD PROTECTION

7.4.1 Surface treatment

LVL can be protected against temporary weather exposure by

surface treatments that repel rainwater, and therefore reduce

the amount of moisture absorbed by the product, but allowwa-

ter vapour movement to and from the product. This improves

dimensional stability and reduces swelling of the treated LVL

product during the construction time.

Use in high relative humidity conditions may result inmould

growth on the surface of structural LVL products. If the prod-

ucts are exposed to outdoor air humidity conditions (e.g. struc-

tures in unheated spaces) or wetting during the logistic chain

and construction time, a brushable or sprayable treatment

should be applied on the surface of the LVL components to

reduce the risk of mould growth. In some cases LVL compo-

nents are treated at the factory, but the default practice is for

treatment to be done during offsite production of timber ele-

ments or on the construction site. If there is mould growth on

the surface of LVL products, the mould must be removed, e.g.

by sanding, before closing the structure.

The surface treatments do not affect the product’s strength

properties, but their compatibility with end finishes, such as

paints, shall be verified separately

28, 43

7.4.2 Pressure impregnation

Pressure impregnation of spruce softwood LVL is possible

when the impregnation process is tailored for it. Due to di-

mensional changes due to moisture and to achieve the required

retention level of the water-based impregnation agent, it is rec-

ommended to use only LVL-C for impregnation. For beam-size

products with a width of max 600 mm, a retention level similar

to the AB class used in the Nordic countries can be achieved.

It is also possible to impregnate panel-size products, although

the retention level in the core area is lower.

Applications for pressure-impregnated LVL-C include terrace

and balcony structures, balustrades, stairs and piers where the

products are not in direct ground contact (= Use class 3.1 con-

ditions).

AB class impregnation agents are aggressively corrosive and

therefore only stainless steel connectors should be used in

structures made of impregnated LVL.

The surface of pressure-impregnated LVL is rougher than

regular LVL. The impregnation and drying processes cause

swelling and shrinkage, which open some of the peeling cracks

in the surface veneers. Local cracking around knots and minor

separation of scarf joints in small areas of the surface veneer

might occur.

Impregnated LVL products swell in the process and their

equilibrium moisture content and specific weight are a cou-

ple of per cent higher than untreated products. The increased

weight shall be taken into account, but otherwise structural

design shall be made with the nominal dimensions of the prod-

uct with the strength and stiffness reduction factors according

to service class 3 of Eurocode 5. In some countries additional

reduction factors given by their national requirements shall be

taken into account

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