Direct weathering, where products or test samples are directly exposed to the weather, is the simplest and most common type of weathering test. Of the various weathering techniques available, only outdoor natural direct weathering testing is “real” in that other techniques inevitably distort the natural balance of the environmental stress factors.
The disadvantage of natural direct weathering is that it occurs in real. However, it is the reference to which all other tests must be compared to and should always be performed to validate results of other testing techniques such as laboratory accelerated artificial weathering.
