How to Improve Adhesion of Polyurea Coating Lining and Lining Systems
The best solution is common sense, “you are only as good as what you are sticking too!”by Dudley J Primeaux II, PCS, CCI
Apr 29, 2011
AUSTIN, Texas – April, 28, 2011 – Polyurea Coatings and Linings: How to avoid a “Sticky Situation.”
During the January – February 2011 SSPC Conference in Las Vegas, Nevada, polyurea technology was a main item of discussion. In addition to the dedicated session, “A Sure Bet with Polyurea Technology,” there were also several Committee meetings with documents / standards in the works. But one thing was really bothering me and that was several comments related to poor adhesion issues that had been experienced by several facility owners when the technology had been used in their locations. Well I really thought that we had gotten past all that………
I will admit that when the technology was first introduced back in the late 1980’s, one of the big challenges was adhesion of the applied polyurea coating / lining to items we wanted it to stick to, as opposed to things we did not want it to stick to. Some of the first commercial applications were of the adhesion challenged standpoint and unfortunately many failures did in fact occur. Now while this may have been primarily due to incomplete or even non-existent surface preparation, much was formulation related.
You see because the polyurea technology sets / gels so quickly, it is difficult to properly “wet” the surface. Now couple that with poor surface preparation, or even spraying over water or ice, you have a recipe for disaster! Ah you all remember the original Texaco Chemical Company video on The Polyurea Technology from 1990? Yes there it was for all to see, spraying over water and ice! But what many don’t remember is the voice-over explaining the reason for this to show water and ice (cold) does not interfere with the reaction, as compared to polyurethane technology. When many companies copied this video for their company use / promotion, this voice over (explanation) was left off, so many thought it was OK to do this. I can’t tell you how many failed projects I have been on where applicators have applied the polyurea over water because they saw in a video and training that this was OK to do.
So that is why much research and development was done over subsequent years to make the polyurea a coating / lining technology, rather than an interesting or Entrepreneur’s Dream Material. This work has relied on conventional additives that are commonly used in other coating system technologies, as well as special primer developments to enhance adhesion. But the best solution is common sense, “you are only as good as what you are sticking too!”
OK, so back to the point of this story, adhesion. Surface preparation of the substrate is imperative and must be accomplished. For this, we look to industry standards and follow what is taught to us by SSPC / NACE / ISO. Why re-invent the wheel? These are out there and must be followed. In addition to cleaning, you must also create a profile so as to achieve mechanical adhesion / locking to the substrate if you will. The required profile should be specified. Also, your polyurea system supplier will communicate with you on the best procedure to utilize for their material, but you must follow and do it.
But you know we sometime forget that the “substrate” can also be applied primer, or a base coat of the polyurea system. Surface preparation and care here is also very important. And in the case of primers and applied polyurea, there is a very important item called re-coat window. This is the time in which a polyurea can be applied to the primer or first coat of polyurea and still expect adhesion / performance. For a primer, if you coat over too soon, the primer may not be cured properly and blisters will result. If you apply a second coat after this re-coat window, then poor adhesion may result.
Also, re-coat window is affected by ambient temperature. For example, a given primer system may have a re-coat window of 24 hours, at 75°F (25°C). But the same primer, if used at an ambient temperature of say 100°F (38°C), the re-coat window may only be 4 hours. That means you must coat over within the 4 hours after application or chances are the applied polyurea will peal from the primer. Seek advice from your supplier as to real re-coat window times for both primer and polyurea system being used. Don’t guess around with this. All polyurea systems are different from this aspect.
So what do you do if the re-coat window has been exceeded? Well you need to abrade the surface to cut the gloss / hard surface, wipe with a good solvent and then apply the polyurea to the confines of the prepared area only. Now be careful here, wipe and flood are not the same! I can tell you a horror story about a project where the contractor was going to be smart and flooded (dumped a 5-gallon pail) the floor area of the applied layer of polyurea with a strong solvent and used a mop to work in. Not a good idea (and safety issue here), but at least that complete applied layer was then easy to remove and start over. Wonder what that cost was????
Now I have commonly heard that before a second coat of polyurea is applied, wipe the surface with denatured alcohol. Well, if you look at most suppliers Product Data Sheets, a common aromatic polyurea system will hold up to alcohol in a splash / spill application. So the alcohol does nothing to activate the surface, well maybe remove any oils or contaminants that may be present. Use of denatured alcohol is not a good practice. One must use a stronger solvent to activate the surface. Seek direction from you supplier!
So yes, an applied polyurea system will bond to various substrates. But the systems MUST be properly formulated for this and proper / complete surface preparation is required! Attend a training school, this is all covered in detail and will insure successful application work.
About the Author: Dudley J Primeaux II, PCS, CCI:
Dudley is active in NACE, SSPC: The Society for Protective Coatings and Past-President and past-member of the Board of Directors of the Polyurea Development Association (PDA). He has also completed the SSPC-PCS, Protective Coatings Specialist and CCI Concrete Coatings Inspector certifications. He is named inventor of 26 US Patents and 8 European Patents on polyurethane and polyurea foam applications as well as polyurea spray elastomer systems/applications. He is an accomplished author having over 50 technical publications relating to the polyurea elastomeric coating and lining technology, performance testing and inspection, as well as several chapters in SSPC delivered book publications. His publications also include work on firearm collecting and histories, family genealogy / history and hunting adventures.