Why Are Bubbles Formed in the Epoxy Screed?

At a recent trade show in Dubai, I was surprised to hear from a lot of different visitors (from different countries) complaining to me that epoxy screeds form too many bubbles on the surface. What they meant was that when the screed cures the bubbles leave an ugly looking surface with little holes that is very prone to dirt pick up.
I was surprised that there’s still a lack of knowledge regarding the cause of these bubbles. I am planning a series of articles to help explain from my point of view what causes bubbles and what we can do to avoid them. Bubbles can be attributed to a number of reasons:
1. Problems with the substrate. Usually caused when the substrate Advantages Of Industrial Development is absorbent which leads to air being released
2. Poor application techniques. Most problem associated with bubbles are related to something going wrong during the installation
3. Problems with the actual product. A problem that is growing in importance as many low-cost companies are emerging with questionable product quality
Lets look at each problem separately:
1. When applying epoxy screeds on a porous substrate it’s very important that it has been properly primed and sealed. Bubbles emerge when the substrate is of cheap and porous quality. This is often the case with cement or concrete substrates where the composition of the mortar is not according to standard (for example using an excessive amount of sand or water). The substrate ends up absorbing part of the screed which in turns leads to air being released inside the screed that will lead to holes and huge ugly craters. Often these holes don’t emerge straight away but an hour or two after application.
The solution to poor substrates is to properly seal the floor with several layers of epoxy primer until the surface has achieved a glassy texture. Cost-permitting it is always advisable to apply additional layers on top of the primed surface (whether it’s a simple coating or a screed) before you apply the final coating. A well-sealed and primed surface goes a long way to assuring great results. But what is even more important is to have a decent substrate to begin with.
2. Problems during installation can be attributed to a number of reasons:
When mixing the components that make up the screed (resin, hardener, sand) it’s important to mix at a low revolution. Mixing at high speeds may lead to the material foaming and thus an excessive amount of bubbles emerging. It is advisable to use a mixer with adjustable revolution speed and never exceed 300 rpm. Some installation teams in their hurry to finish quickly, prefer to mix for a short period of time at high speeds. Also after mixing the screed, let the new screed “rest” for 2-3 minutes before applying it.
Most importantly however is what happens when the actual epoxy screed is applied. The use of a spiked roller is essential to properly level and release any trapped air within the screed. This is a process that must be done repetitively. Furthermore the person applying the spiked roller must use spiked shoes to be able to access the entire surface. Many projects fail because the application team did not properly inspect the entire area.
Another issue with installation problems is poor lighting, a common problem when working in underground areas, and/or in facilities that are under construction and proper lighting has not yet been installed. If this is the case, then the installation team must bring its own lighting equipment so that it can properly inspect the entire surface for bubbles as well as other potential problems.
The most sensitive areas for bubble formation are near walls, corners and doors. This is because that these areas are usually not applied with a roller as much as the other areas. Furthermore visibility is somewhat limited because of possible shadows and obstructions. Ensure that one person undertakes to properly apply the roller in all these sensitive areas.
Concluding, in order to avoid bubbles and other problems during installation, the installation team must adopt a strict methodology and a lot of responsibility rests on the project manager to supervise the entire procedure.
3. Problems with the Product. It is important to understand that a properly formulated product does not just contain a resin and a hardener. In fact it is made up of a range of important ingredients that make up the system. Properly formulated epoxy systems contain special additives like defoamers, dispersing agents, and viscosity modifiers. Without these additives the epoxy systems on the market would produce entirely different (and inferior) results. Obviously, all these additives cost money and end up increasing the production cost of the material. Some low-cost producers do not use these additives or limit their composition in order to keep costs down.
Additionally, depending on the product in question, certain de-gassing procedures need to be applied during the manufacturing process in order to remove any air trapped within the product. It is also not uncommon for some formulators to ‘drown’ the system in solvents in order to bring down the cost. What happens then is that during the application stage, the solvent starts to evaporate which inevitably leads to bubble formation as well as shrinkage of the material.
My final word of advice is don’t just pick a product because of low cost. Low cost is usually associated with products of poorer quality. It is Porter’S Five Forces Definition preferable to spend a few extra euros (or whatever your currency is) per square metre to ensure a well executed project and a pleased customer.

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