Light and moisture-resistance of sealing products

Sealing products for external use, which are directly exposed to the weather, need to remain stable against the powerful effect of sunlight as well as sealing against driving rain. The stresses are different on each side of the building, so the stresses on the South side are especially high, while those on the East and West sides are moderately high and those on the North side can be classed as low.

Polyurethane in-situ foams, also known as spray or installation foams, are generally less stable when exposed to sunlight. After as little as 10 days, severe discolouration starts, generally from yellow to brown, causing embrittlement of the PU material as a consequence. Within 2 - 4 weeks, the material is so severely damaged that it can crumble out of the joint.

As well as protecting against driving rain, level 3 (weather protection) also needs to protect against the effects of light and moisture.

Sealing products which are used outdoors should therefore be checked for their stability against the effects of light and moisture.

In DIN 18542:2009-07, which is responsible for the testing of PU cellular plastic tapes, the testing requirements for exposure classes BG1 and MF1 (directly unprotected external application) also require testing for stability against the effects of light and moisture. This test to DIN 18542 is not required for joint sealing tapes from exposure class BG 2 and multifunction tapes MF 2. This test is omitted for sealing foils since the planning generally requires such products to be covered, e.g. with thermal insulation composite systems or plaster.
 

The following differences should be noted:

• Construction films / fleece films for the external sealing to level 3
  roughly 3 months to maximum 12 months
• EPDM films
  UV resistant according to DIN 7864 T1
• Impregnated cellular plastic tapes BG 1
  to DIN 18542, approved for direct weathering without covering
• Multifunction sealing tapes MF1
  to DIN 18542, approved for direct weathering without covering

Products that are tested in accordance with the relevant DIN standard may be directly exposed to the effects of light and moisture over a very long period without technically breaking down. There may be discolouration / change to the surface (patina) of these products which is not technically harmful.