Surface Energy As It Relates To Masonry

Steven Fechino

Writing this article each month is actually a lot of fun. I get to discuss topics that relate to our trade and allow for the understanding of some really off-the-wall topics or, as someone told me earlier today, some really boring topics. I am a simple person, I like to joke and discuss things on a pretty easy level, so when I discuss topics like today's, I try to explain it how I would be able to understand it. Okay, so far, I have rambled long enough, but if I did not, you may not have invested your time to get this far into the article. Today, I am discussing surface energy and why it relates to masonry, and how it can save you from making costly mistakes.

A big part of why surface energy matters is when you choose sealants to seal term bars, drip edges, end dams and corner pieces to flashings and air barriers. The wrong sealant choice can appear to apply perfectly; however, once cured,  a total adhesion failure can occur, sometimes within 48 hours, and you would never know it because it would be covered, in most cases, with brick.

Surface energy is the ability for something to bond. Here is an example. If you have ever tried to write on plastic Tupperware with a water-based Crayola marker, then you know that the ink will roll up and not stick to the plastic; well, this is incorrect surface energy for the ink to adhere to the plastic.  

Flashings are, for the most part (with several exceptions, of course, stainless steel, for example), all polymer-based materials that can present challenges for common sealants.  

The easiest way to explain surface energy is to say it is based on a number; the higher the number means that compatible products will adhere well, which represents a strong molecular bond. If you have low surface energy, then you have a lower surface attraction for a product to bond. I have an old tractor where the paint is showing wear. When it rains, the hood appears wet for a while; this indicates a high surface energy because the water molecules are bonded better than if the tractor hood had a coat of fresh paint, and that would represent high surface energy resulting in water beading off, a much weaker molecular bond.

Low Surface Energy = Harder To Bond Materials

High Surface Energy = Easier To Bond Materials

As far as sealants go that we use, in order of low surface energy to a higher surface energy required for a proper bond, polyurethane elastomeric, silyl terminated polyether and butyls are in this order. Here is the bottom line, you can believe it or not. Caulking and sealants must be matched to the surface they are being bonded to in order for them to work. It is simple chemistry. Silicones work well on granite, but they do not bond well to Ethylene propylene diene monomer, EPDM as we know it as a flashing, tire tube as we know it as a material.

When resealing a project, let's use a home project; for example, some sealants cannot be used over dissimilar materials. Here is another example of incorrect use of products or incompatible products because of incorrect surface energy at the bond of material. Speaking for a friend, a great guy, I must add, he decided to use Dow Bathtub Sealer around a bathtub that was once sealed with silicone. Being that it was hunting season and the installer was preoccupied with getting into the woods, I may not have, oops, he may not have fully removed all traces and residue of the silicone. The Dow Bathtub Sealant, however, went on the tub very nicely, but the project had to be redone shortly afterward as signs of adhesion failure were apparent because few things can adhere to silicone due to the low surface energy of the product

Primers are sometimes used with sealants; it seems they were more frequent in the 1980s; however, a primer simply can change how liquid bonds to a surface by chemically changing the surface energy of the bonded surface. Primers function in a similar way when used in applying rubberized asphalts to increase the chemical bond of the product.

A sealant can be compatible and still not have a matched surface energy for bonding. It can apply perfectly and still have complete adhesion failure, and the famous statement that it has always worked in the past on everything else will surely get into your pocket sooner or later. 

I recommend that you work with your product representatives to get the proper product for the proper application, and do not count on the project specifications always being correct.