Primerless Urethanes

As I was reading a recent post on the glassBYTEs.com™/AGRR™ magazine Forum, I was drawn to a discussion about primerless urethanes. I believe that primerless urethane has a place in the automotive glass technician’s truck or tool box, but as a trainer I don’t typically recommend it as an everyday urethane in the field. Why? Because a primerless urethane requires perfect cleaning and prepping of the glass, and conditions may not always allow for perfection.

Some products state they’re primerless, yet they require the application of a cleaner/preparation material to promote adherence. It would take a major debate between chemists and English majors to define and explain a primer vs. a preparation and a prep from a cleaner. Let’s settle on one premise that is correct regardless, always follow the adhesive manufacturer’s instructions to the letter and without deviation.

The purpose of my post is to make sure that those who chose to use primerless urethanes use them correctly and with diligence and adherence to the idea “cleanliness is next to godliness.” The number one reason for adhesive failure is the improper cleaning of the surfaces. If the technician makes a lackadaisical effort at cleaning the bonding surface of the glass edge and pinchweld area, the adhesive can’t stick to the bonding surface no matter how good the reputation the product has for performance.

The benefit of prime-able urethanes is that the primer acts as a back-up for not-so-good cleaning. Don’t get me wrong, proper cleaning is important for both prime-able and primerless urethanes to adhere. However, primerless urethanes need extra special care in the cleaning process. Any contamination will cause the products to fail and some to fail badly. If you have “some” contamination in an area, it may create a leak problem, but improper cleaning habits with primerless urethane can cause catastrophic failure that could maim or kill people.

So, if you choose to use the primerless products out there, develop the talent and practice the proper cleaning techniques recommended by your adhesive manufacturer. Here are the procedures that feel fit those parameters.

  • Use an approved glass cleaner. One that is free from ammonias, silicones and petroleum additives. Make sure they are free from fragrances and anti-static properties. Streak-free cleaners usually use additives that leave a film that will not allow the adhesives to reach their proper strength requirements.
  • Concentrate on the glass-bonding area. The glass-bonding area is defined as the frit area of the glass or the inside outer edge of the glass surface.
  • Use a foaming glass cleaner. The foaming glass cleaners highlight where contaminants can hide by dissipating when coming in contact with the oils and films on the glass surface. Test the glass by spraying the glass edge with the foaming glass cleaner and look for dissipation. When the dissipation occurs scrub that area and retest the bonding surface.
  • Non-traditional (NT) contaminants must be removed. NT contaminants are the ones that few technicians notice or take the time to remove. These can usually be found around pre-attached mouldings or encapsulation but can also be found right on the bonding edge of the glass. Water and/or glass cleaner may appear to “ball-up” when applied to this contaminant but it may not show itself by dissipating the foaming glass cleaner.
  • Use an abrasive pad or cleaner to clean off the NT contaminants. Some of the major brands of adhesives have products or devices to remove the NT contaminants. Dow offers its Betabrade™ and SIKA offers cleaning pads called SIKA PowerClean Aid. One thing to note on these products is that they remove the contaminants without taking off too much frit paint. The frit protects the urethane from its only enemy, ultraviolet light. So abrasives must be used to remove NT contaminants but they must be used correctly to not remove the frit.

If an abrasive pad like Scotch-Brite is used, then make sure the surface is wet and do not place too much pressure on the surface of the glass. Stop when the NT contaminant has been removed.

  • Clean and dry the surface thoroughly. Make sure all surfaces are clean and dry before installing. If it is your habit to prep the glass before dismantling the vehicle, turn the glass over on your windshield cradle to keep airborne contaminants from falling onto the bonding surface.
  • Use unpowdered nitrile gloves when handling the glass. Obviously, vacuum cups are recommended to set the glass into the opening, but even that requires the use of gloves to guard against accidentally touching the prepared surface and contaminating the bonding area.

Primerless products can be a viable option, but make sure your cleaning procedures are above reproach. Remember that improperly cleaning of the bonding surfaces is the number one reason for adhesive failure. Make sure of your procedures, and develop the habit to make sure it is done right each and every time. In our business cleanliness is next to godliness.