Tags: #buildingenclosures #buildingenvelopes #buildingmaterials #buildingproducts #buildingscience #materialsscience #mineralwool #waterresistance

The mineral wool drop test – a simple means for evaluating surfactant release in construction materials. 

Surfactants are substances that reduce the surface tension of liquids. They are released in a variety of construction materials when exposed to water – for example, wood extractives, dyes/inks, alcohols, and plasticizers. When released, all bets are off as to how water-resistive materials will behave.

Porous matrixes with large open pore volumes offer ideal media for assessing suspected surfactant release. The concept is simple enough – water entry thru the porous mineral wool is facilitated by dissolved surfactants. As compared to drop angle measurements, this approach is easier, offers improved resolution, and a better visual depiction. It also offers the added benefits of quantifying absorption rates. In other words, how long does it take for the drop to enter the representative porous matrix?

In this image, I compare dissolved extractives from two thin-mil acrylic coatings. We can clearly see that surfactant release is more pronounced in extractive A than in extractive B. Absorption by extractive A is nearly instantaneous. Full absorption is observed in less than five minutes. 

Test results are determined by material / surfactant type, immersion water volumes, immersion duration, and drop monitoring interval/duration. And, although not shown, water is used as a control to determine subtle effects. I typically perform 12 or 24-hr immersion. Endpoint times are typically one-minute intervals for the first five minutes and then 5-min intervals thereafter. It is important to note that surfactant release rates are highly variable, and I’ve seen significant release following immersion times of less than one hour. So generally, 12 or 24 hours are not necessary, but serve merely as a standard condition. 

In short, this test offers a quick and dirty screening method for surfactant release. It’s fast, easy, and inexpensive.