In the Netherlands and Belgium a load-bearing structure made of treated wood is often used in a ventilated façade system.

However, the substances that are pressed into the wood are usually very toxic. Although there is sufficient supervision (certification) of the safety of employees in the production of treated wood, there is strangely enough no (or only very limited) control in the use (sawing) and waste phase of treated wood. This is despite the fact that, according to the European directive, impregnated wood in connection with the carcinogenic substances may not come into contact with human skin!

Copper II oxide and chromium trioxide (chromium VI) are often used in the preservation process. Chromium VI is extremely toxic to humans and is internationally known as a class 1 carcinogen. Used substances as tebuconazole and copper (II) carbonate-copper (II) hydroxide are not known as a carcinogen in Europe but in the USA known as a class 2B carcinogen.

This is why the use of treated wood is not permitted or unacceptable in many countries outside the Benelux. The use of treated wood of any kind is highly questionable because structurally very toxic, corrosive, environmentally hazardous and carcinogenic substances are used.

Finally, the one thing you must be extremely careful to never do with treated wood is burn it. Burning treated wood created toxic smoke that can be hazardous to health, so it is advised that treated wood be disposed of through normal waste collection services, unless it is a large amount of timber (where you will have to make arrangements with your council for it’s safe disposal).


Before you start with assembling two materials by means of an adhesive bond, the surfaces must be dry and properly cleaned and degreased first.

Always assume that the surface to be bonded is contaminated and therefore clean both surfaces with TWEHA Cleaner+ and a cloth. TWEHA Cleaner+ is a bonded-cladding-detergent based on Isopropyl alcohol.
Always use a lint-free, non-coloured cloth that does not contain any additives, contaminants or polishes. Clean by rubbing in only one direction, otherwise the contamination on the fabric may end up on the surface again. Never use a cloth several times.
Do not touch the cleaned surface with your fingers again, otherwise skin grease will be on the surface again.
Never use thinner or a gasoline based liquid for degreasing! These are so-called petroleum derivatives and these only make the subsurface more greasy!

If needed roughening ensures that the adhesive can flow in a roughened surface. This increases the adhesion surface and creates a better connection.
Note: the adhesive layer of THEHA Tape will not flow, so when roughening a smaller adhesive surface is created, so, in case of an aluminum framework, never roughen the surface!

Fiber cement: Loose fibers and cement granules
HPL: residue of protective film
Natural stone: sludge or residue from sawing process.
Tiles / ceramics: Cleaners and moisture
Metal: Oil, grease, rust and moisture
Glass: Fingerprints, silicones and moisture
Plastic: Release agents, dust and plasticizers
Rubber: Talc, grease and plasticizers


Before starting check with a peel-of test.


Easily calculate the exact quantity of bonding material required for your project construction by using our free quantity calculator.

The TWEHA Calculator estimates the exact quantity of TWEHA Adhesives required for your building envelope project. It also estimates the number of rolls of TWEHA Tape, the quantity of TWEHA Cleaner+ and other TWEHA products necessary based on standard 600 mm centre-to-centre distance of your substructure. Purchasing slightly more material than the estimated result can reduce the probability of having insufficient resources.


Wind originates due to air movement from high pressure- to low pressure areas. Due to attrition with the earth’s surface (buildings, forests), however, the air movement in the lower air layers will be slowed down: wind speed increases proportionately by height. This degree of increase is again determined by the roughness (construction) of the earth’s surface.
Above sea e.g. a less high air layer will be slowed down. This explains why in the coastal regions the wind blows on average more than in inland areas.
Due to the friction of the air layers, swirls and gusts also occur. Especially in constructions that are sensitive to time-varying wind loads, it is considered advisable to take this into account. Wind nuisance occurs not only within a large complex of buildings such as e.g. the centre of a city, but also in the immediate vicinity of a building.

  • On the one hand, the fact that constructions such as buildings, cranes and towers experience certain wind loads must be taken into account of.
  • On the other hand, one has to deal with the occurrence of wind nuisance, especially in the vicinity of tall buildings.
  • Another important factor that must be taken into account when orienting buildings, in relation to each other and locating the entrances, etc., is the most common wind direction.

The wind causes a load on a structure, where we can distinguish between external pressure (or suction, or friction) and internal pressure (or suction). Local Standards therefore indicates that the most unfavourable combination (s) of simultaneous effective wind loads must be directive in the calculations.

Local Standards (as in Europe the Eurocode 1, the European standard for determining the wind load on buildings (EN 1991 1-4 including the accompanying National Annexes)), are the basis for all your calculations. Depending on, among other things such as geographical differences, the building height and the surroundings, these Standards indicates a value for the maximum ‘Windloads’. In the Eurocode 1 it is a measure of expected value of wind in a storm that can occur once every 50 years.


At the corners or at the edges of a building, the wind loads are much heavier and turbulent than in the middle area due to wind-suction. Therefore Standards provides special calculation rules to determine the width of the strip of the building- and roof-edges on which a heavier and more turbulent wind load occurs.
Standard indicate that the external load must be regarded in a number of situations both in the form of pressure and in suction. A local external form factor expresses the fact that high wind loads can occur in typical local situations. Thus, for example, the load resulting from wind suction often will be normative along the edges of a building.

New buildings to be reconstructed in an already built-up area mutate the wind load on the existing buildings. This all related to the shape and dimensions of the buildings, the mutual distance and the roughness of the surroundings. In such cases the wind load has to be determined by measurements on scale models in a wind tunnel model. This has to be carried out in the so-called design phase so the influence of, and on, the existing surrounding buildings can be taken into account. This is especially for construction engineers and façade builders of importance, but also for owners of buildings where a new building is scheduled nearby.


Tests are an essential part of the TWEHA concept. Our bonding systems are subjected to an intensive internal test program with conditions much heavier than normal use. Please have a look at our survey of tested and approved cladding materials.

Because the reliance in proper functioning of our products is very important, for many years we also have been asking various independent external experts to judge our bonding systems, so by globally executed test programs the excellent quality of the TWEHA glue systems is confirmed.