Tags: #buildingscience #gypsum

Adhesion to gypsum facers is only as good as the facer’s embedment. In other words, even the highest bond strength between coating to facer or membrane to facer means nothing if the facer itself delaminates from its gypsum core.

High facer bond results from deep embedment; but this also leads to gypsum bleeding through the facer which presents adhesion challenges for WRBs, flashings, and roof membranes. Conversely, embed too shallow and the facer sits on top of its substrate where it’s inherently prone to delamination. Add moisture to the equation and we see delamination reduced by 50 to >90%.

Shown here are three glass facers from different batches of the same product. Specimen 1 shows deep embedment. This is ideal for some coatings and adhesives but challenging to others (e.g. acrylics).   Specimens 2 and 3 exemplify poor embedment with bond strengths <1 psi – well below industry criteria such those used in evaluating WRB adhesion (i.e. 16 psi). While tapes, WRBs, and roof membranes may adhere perfectly well to the facer, the facer itself readily delaminates – something that receives little attention.

It’s more complicated than embedment alone, the role or gypsum admixtures, gypsum density at facer interface, and glass coatings also play important roles.