Tags: #buildingenclosures #buildingenvelopes #buildingmaterials #buildingproducts #buildingscience #hygroscopic #mgo #water

What attributes distinguish ‘quality’ MgO panels from ‘poor’ ones? And what’s the difference between weeping and panel saturation?

Effects such as panel weeping, premature degradation, and fastener corrosion are associated with inferior MgO panels. Although much attention is given to free chlorides, this metric alone does not account for the totality of poor performance. For example, the MgO shown here reveals discernable weeping despite having ‘acceptable’ free chlorides as typically measured. 

MgO is hygroscopic. It absorbs water from its ambient atmosphere as also occurs with other hygroscopic materials. And when maintained at high humidity, the board will become fully saturated. This occurs regardless of composition (i.e. chloride versus sulfate).  The water seen is the water expelled from a fully saturated board. 

Weeping, on the other hand, has a discrete expression seen here as water droplets in association with open surface pores. The remainder of the board may or may not be fully saturated. Let the pools evaporate and aggregates of salts stand where pools once formed. 

My journey begins into this fascinating world of MgO.