Tests have been carried out on 22 systems, including one mastic asphalt, four concrete, six polyurethane, three acrylate, and four polyurea. The different materials were applied to sections of car parks located in Kville, Akeshov, which is a suburb of Stockholm, and Baggen, all in Sweden. The samples were also applied to test slabs, which were then subject to scuffing under a modified version of prEN 12 697-50. This test measured the thickness reduction in the coating in millimetres caused by studded tyres.
Edwards said research shows that scuff testing using studded tyres for 60 minutes/ sample is “very promising for testing wear resistance”. She added, “Wear on the studded tyres in the test equipment seems low, and is not expected to have affected results significantly.”.
But Edwards warned that wear resistance is only one of several important functions the coating has to provide. The three parking garages where the different samples are being tested will be monitored for at least five years, from 2014 to 2018, she said.
Karl Wuehrer and Bernadette Gerhartz-Quirin of Covestro Deutschland took a different approach to materials selection, outlining a toolbox that helps determine the correct combination of materials for any particular job.
Making the right choice
The selection tool, called Plasaquick, helps applicators decide on the best combination of amines and MDI for spray-applied polyurea, and polyols for polyurethane and hand-applied polyurea systems. The toolbox is designed for Covestro’s range of Desmodur solvent-free or solvent-borne coatings, and Bayhydur waterborne coatings.
The Desmodur family is designed to work with a wide range of isocyanates, including TDI, MDI, HDI, IPDI and PDI. Bayhydur materials work with PET and ionically modified reactants.
The pair went on to examine the reactivity of the different products in the Covestro range, from very fast-reacting Desmodur VL, which generates a high exotherm with a gel time of a few minutes, through to the slower Desmodur E2683 XP, which has a gel time of approximately two hours.
Aromatic isocyanates based on MDI, including PDI and MDI pre-polymers with isocyanate content of greater than 10%, tend to be brittle, they told delegates. This makes it difficult to measure the hardness of the materials because the needle used to measure Shore hardness destroys the test film.
TDI-based materials using TDI pre-polymers with an isocyanate content of less than 6% produced very flexible coatings, and elongation of up to 800% is possible, they said.
The properties of aliphatic isocyanate pre-polymers depend a great deal on the isocyanate content and whether the film is hard or flexible. It is possible to make materials with Shore hardness of greater than 50 with an isocyanate content of between 18 to 24%.
The Plasquick toolbox they outlined has a wide range of tables and graphs, designed to bridge the gap between theoretical pot life in a cup, and actual working life in an application, they said.
Don’t’ over promise
Overspecifying the finish of a polyurea product to architects and building specifiers can lead to trouble on site, Jos de Graauw of Krypton chemicals told attendees.
He discussed how to produce an acceptable project using a fast-set system. “These will always produce overspray,” he said, “but there are tips and techniques to make the finish look as professional as the material deserves.” De Graauw claimed that small, perfectly sprayed sample pieces, can become a “goal stopper for the actual product itself” on site.
He said this is because handing out smooth sprayed samples can cause arguments on the site over the level of finish that can be achieved in practice compared with the expectations of the specifier, based on a small, perfectly sprayed sample.
To help solve this problem, Krypton chemicals has set up its own education programme which covers basic processes such as preparing scaffolding and masking, how to overlap, and how to apply the perfect overspray.
Courses also include: spraying with and without overspray; spraying polyurea in situ, and spraying different systems.
Blending in
De Graaw said that polyurea has a number of advantages, but when trying to spray an aesthetic surface there are three main criteria to consider. The first is that the system may well be fast set, with a quick reaction; the second area to account for is thermal shock and linear shrinkage; and the third is overspray.
Hospital corridors are a good example of what can be achieved with a single pass, he said. It’s possible to spray approximately 3.5 m. “It doesn’t matter how long the corridor is, this can be done with a smooth surface, without overspray,” de Graauw added. “But, as soon as it needs another pass you willaencounter overspray.” He explained that, done badly, polyurea overspray can lead to stippling, which can vary from fine to coarse.
