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Weather testing indicates whether plastering is weatherproof


​In Finland, plastered façades must withstand severe weather conditions: changes in temperature and humidity, rain, wind, sunshine and microbiological stress. Normal wear and tear also occurs. Durable plastering can withstand hits and blows.

Real weather conditions are a true test

VTT Expert Services Ltd tests the durability of façades and their plastering systems under conditions that stimulate actual weather conditions. In weather stress testing, the façade structure is placed between two test environments. One is adjusted to stimulate different outdoor weather conditions, while the other corresponds to standard indoor conditions.

"The testing equipment adjusts the outdoor temperature from -20 °C all the way up to +60 °C. Humidity varies from 50% to 90%. Fans simulate the effects of wind and infra red heating the effects of the sun. Sprinklers are programmed to stimulate actual rainfall. We take regular samples of insulation materials, for example, to see whether they get damp," says Product Manager Pekka Sipari from VTT Expert Services Ltd.

To pass the weather testing, façades and façade structures must perform well in terms of their thermophysical qualities and physical state of moisture and show no signs of damages caused by dampness. Weather stress should also not cause too many changes in the shape of the façade.

Plastering system is more than just a surface treatment

Typical parts of a plastering system include insulation and its fastening, mortars and plasters and the top coating. The entire system is subjected to weather testing. The façade structure as a whole must perform as designed under all conditions to protect the building and keep it healthy.

"Weather stress testing includes tests such as water vapour penetration, water receptivity and water tightness. Water vapour penetration of the exterior surface is a key factor in preventing moisture from accumulating in the structures. Water receptivity and tightness in turn indicate the ability of the plastering to prevent water from entering through the exterior surface," explains Product Manager Hannu Hyttinen from VTT Expert Services Ltd.

"We also test the ability to withstand wind load and freezing temperatures by simulating actual weather conditions in Finland."

Good adhesive and crush strength indicate that plastering can stand the test of time

The key qualities tested on the exterior side include the adhesive and crush strength of the façade.

Adhesive strength indicates how well the parts of the plastering system remain attached. Tests are carried out by subjecting test pieces that have undergone weather stress testing to tensile stretch testing.

A similar test is carried out to verify the product's ability to withstand hits.

"The test mainly simulates damage caused by people, such as throwing things at or kicking the surfaces. During testing, different loads are dropped to the plastering surface from different distances. The results of the test assess the durability of the surface."

Tested products and correct installation provide good results

Using tested and approved products is a good foundation for the implementation of durable and lasting plastering.

"Installation is another important factor alongside good products. Installation according to manufacturer's instructions helps provide good results and ensure that plastering works effectively to protect the building and its health," Sipari sums up.

Choose VTT Expert Services as your expert testing partner

Our expertise and versatile testing capabilities help solve problems related to the functionality of products and production.

With our test equipment, we test different functional qualities of products, such as their durability, strength or acoustic and thermophysical qualities, under different conditions during the product life cycle. Condition testing, such as weather testing, can be used for modelling the long-term effects of temperature, moisture, solar radiation, wear and so on.

Tel.+358 20 722 7070
Fax+358 20 722 7001

Opening hours 9:00 - 11:00 and 12:00 - 15:00, GMT +2 time zone


P.O. Box 47, FI-02151 Espoo, Finland
Tel. exchange +358 20 722 111
Opening hours Mon - Fri 8:00 - 16:30,
GMT +2 time zone
Fax +358 20 722 7001
Contact us

Tel. +358 20 722 7070
Fax +358 20 722 7001
Opening hours 9:00 - 11:00 and
12:00 - 15:00,
GMT +2 time zone