We are regularly asked whether it is acceptable to broadcast the decorative flake (color chips) into the first coat of a rolled on resin floor coating system?
We have heard that some floor coating contractors are now offering a 2 coat system, where they broadcast, or throw, the decorative chip into the base, or 1st coat, and then do a 2nd coat as a top coat. Some applicators tell customers that they put on an “extra thick” base coat and that this is the same as the 3 coat system that other seamless flooring contractors are offering.
The floor system we recommend is a 3 coat system, consisting of a base (or prime) coat, a 2nd coat into which the decorative flake (chips) are broadcast while the resin is still wet, and finally a top coat. In some cases where the customer wants to have a thicker floor for exceptionally extended durability or to produce a very smooth finish, a 4th coat may be applied.
Having said this, we are constantly reminded that many competitors cut corners and we are aware that a newer trend to cut corners appears to be to eliminate one of the coats and broadcast the flake into the first coat that is rolled out. Eliminating this coat saves labor and resin and results in a much lower cost floor. However, our experience and research leads us to conclude that this "short cut" will produce a floor with adhesion issues which is more likely to pop up or peel off prematurely. Why?
The reason has to do with adhesion and more specifically, surface tension. There are a few very important keys to producing a floor that has good adhesion and which will stay down long term. The first step in promoting good adhesion is to have a properly prepared floor that is clean and free of dust, debris, grease, oil and other impediments to adhesion. In our experience, the best results in this regard are produced by dry diamond grinding the concrete as the surface preparation method of choice.
The next consideration is understanding the chemistry you are using and more particularly the percent solids of the resins you are rolling out. With most solvent borne epoxy and polyaspartic coating systems it is typical to see solids contents in the range of 60% to 100%.
Keep in mind that concrete is essentially a sponge. Meaning it is very porous. And the density of the pores across a slab of concrete will vary. Some like to say the "porosity" of the concrete slab will vary across the slab. To achieve good adhesion, we need the resin to soak into (wet) the concrete (substrate).
Whatever language you choose, it is common when rolling out wet resin to see it absorb at different rates across the floor. Areas where the pores are more numerous will see the resin wetting in (soaking) at a much higher rate. This is perfectly normal. The challenge lies in the parts of the floor that are less porous (more dense), or when you are working with a floor that has much higher PSI concrete. In these areas, we will see the wet resin soaking in at a much lower rate. This can manifest itself in appearance as actually being a "nicer" looking result, but beware. While the consistency of the resin and any pigment in it appear much thicker and more uniform, you might be fooled into thinking you are getting a good result. Again, remember this is the 1st or prime coat. This uniform appearance is caused by the resin NOT soaking into the floor. This is a bad thing. We want the resin to soak into the floor on the prime coat. The job of the prime coat is to soak down into the concrete, fill all the pores, and when it dries, “lock itself” into the concrete for good adhesion. A well applied prime coat will not look good, simply because it is doing what is intended, soaking down into the concrete, not sitting on top. When the prime coat, or 1st coat, looks good and uniform, this is a big warning flag that you are not achieving good levels of wetting (the resin soaking into) the substrate.
When using more expensive resins that typically have higher solids content, this higher solids content can also be counter-productive to this goal of wetting concrete on the prime coat. This is one reason why manufacturers recommend and why applicators will "cut" (dilute) the resin, usually with a solvent such as acetone, particularly for the base coat. By diluting down the percent solids in the resin with solvent, this will help thin out the resin and help the resin soak into the concrete and flow more easily into the small and as yet unsealed pores of the substrate. This process of "cutting" the resin with solvent is especially important when working with more expensive resins that have higher solids content. We typically recommend cutting the resin so that it is around 60% to 65% solids for the prime or base coat. For concrete that has very high PSI ratings and therefore much higher density (the pores are smaller and less in number), we would recommend cutting the resin even more for the 1st coat. Remember, the idea with the base coat is to get the resin to soak into the pores, so that when the resin dries, it will literally "lock into" and glue itself to the ridges and surfaces of the millions of pores in the substrate, producing a floor with optimal mechanical adhesion characteristics. Essentially this acts as the strongest foundation you could hope for when building up a coating system. And your coating is only going to be as strong as the weakest link which is often the base coat.
There is also another significant phenomenon occurring when rolling out the first coat that many applicators are not aware of and which is exceptionally important to adhesion and which is the key to why you do not want to broadcast chips into the first coat. And unfortunately, this phenomenon is something that many less professional coating manufactures are not aware of. And that phenomenon is surface tension.
Nearly all of us know intuitively what surface tension is. At some time or another, most of us as children had an opportunity to play with the convex (bottom outwardly curved) surface of a spoon in a glass or bowl of water. We notice that the outwardly curved surface on the bottom of the spoon when dipped slightly into the water and then slowly lifted up will cause the water surface to lift up with the curved surface bottom part of the spoon. We can lift the spoon a ways before we end up breaking the surface of the water and seeing it fall back into its original, at rest, position. The force lifting the water in this case is "surface tension". And this is a very important factor to consider when painting a floor.
Surface tension is a phenomenon that is present whenever there is a thin, wet film, in this case, a layer of wet resin rolled out onto a concrete floor. Every careful, experienced and well educated chemist will consider surface tension when formulating resins. Surface tension is present in any wet film surface, including the wet resin we roll onto floors. If this surface tension is not released or worse yet if it is increased too much, it will prevent the wet resin from properly soaking into the floor. If this happens, when the resin dries, it will not sufficiently soak into and "lock itself into" the millions of pores and surface areas in the concrete itself, resulting in a floor with much weaker adhesion characteristics.
Our resins have additives in the formulation that are specifically designed to release surface tension. Some may call these "adhesion promoters" or "flow and leveling agents". Whatever you call them, they are very expensive and are often times the single most expensive ingredient in the resin. Many competitors and cheaper brands of paint and resins do not go to the added expense or effort to include these surface releasing additives in their formulations.
Now, here is the important part, when it comes to broadcasting chip into the base, prime, or 1st coat of a floor coating. The effect of these expensive additives can be nullified by two things that are totally within control of the applicator. The first is rolling on the base coat too thick. The thicker the wet film, the higher the surface tension will be, making it harder for the wet resin to soak into the floor properly. This is part of the reason why we issue guidelines on how many square feet per gallon we recommend using for each coat of a flooring system, to help prevent the applicator from laying on the base coat so thick as to create too high a surface tension which then defeats the ability of the resin to wick into the floor sufficiently. A second thing at play here is to avoid putting anything on top of the wet resin on the base coat that can act like the spoon effect and which can create added surface tension, such as decorative chips or flakes. You do not want to cover up this first layer of wet film with chips, as doing so will increase the surface tension and the chips will literally pull the resin towards them and also contribute to defeating the ability of the resin to soak down into the pores of the concrete.
In our experience and research, broadcasting chips into a wet base coat can increase the surface tension of the wet resin and diminish the ability of the resin to soak into the floor. Also, many applicators because of experience will feel inclined to roll out an even thicker layer on their base coat when they are only doing one coat and intend to throw chips into it, to make sure there is plenty of wet resin to "glue" the chips into the floor. This is the proverbial double whammy, as mentioned above, because this thicker layer will also increase surface tension which is not desired for the first coat.
From our experience and research, we know that chips broadcast into the first coat will result in areas that easily pull up or peel off because the resin under the chips did not sufficiently soak into the floor. We also see another effect on floors where chips are broadcast into the first coat. Remember that concrete floors are of varied porosity. In areas of much higher porosity, the base coat can soak into the floor so quickly that it leaves a void on the surface so that when the applicator throws the flake, he/she may think the chip is sitting in a sufficient amount of wet resin to "glue" the flake into the floor but in reality, the chip is sitting on mostly bare concrete as the resin beneath it soaked in at too high a rate without the applicator knowing. Covering this up with chips, on the first coat, can hide this and fool the applicator into thinking they got good coverage and hence will have good adhesion when they will not.
Either result can produce a floor where adhesion suffers and where we later see sections pull off in irregular intervals where the resin did not sufficiently soak in and wet the floor, leaving the customer disappointed and the applicator with costly and timely repairs to address.
The best way to avoid these known issues is to not take a short cut and not fall prey to the temptation to broadcast the flake into the first coat thinking that you are saving money. This surface tension phenomenon holds true for any wet film and this applies regardless of the resin system you are using, for example, acrylic, epoxy, polyaspartic polyureas, urethanes, polyurethanes and so on.
© Copyright, 2017, Slide-Lok Corporation.
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