Are polyurethane membranes and water-based membranes compatible?

Every day, we come across situations where moisture-cured polyurethane membranes are used but they're used with water-based systems, either on top of a water-based system or a water-based the system being applied over it and there are issues with it. Moisture-cured polyurethane membranes have got a field and a market but what goes wrong when moisture cured polyurethane membranes and water-based systems work together? 

The reality is it's not about the quality of the membrane, which we might witness sometimes during the testing. But is the nature of it being a solvent-based and more importantly due to the isocyanates present in it which evaporates through them during the curing phase.

This can be explained through a generic aspect which is that the solvent-based products cannot be used with acrylic paints or water-based paints. So, if the membrane is water-based in nature, particularly in wetter applications, the properties will react the same and will be incompatible.

The problem is that when you're tiling over it, in a wet area, you're going to see a separation over time. People like PU membranes because it gives them a nice heavy build film, particularly in the winter months. They tend to go with one heavy coat on the floor knowing that they're putting a floating screen or a slip shin on the membrane before they put their screen down to get the adhesion on it. This still works but when it comes to the wall tiling, the wall membrane that needs to directly adhere can't use PU membranes with direct sticking as it leads to a tiling problem.

This is because the tiles have bonded to the water-based membrane but that the specific water-based membrane is compromised or could be compromised where it joins the PU system.

There are water-based systems on MS coatings but MS coatings are not used in Australia for its cost factor, compared to the PUs which are the lower end of the market. But the only concern is that we're getting water-based membranes that are being used and that's where they are failing.

Over the years, by trying on different samples, Gripset has noticed that when a primer is applied over the solvent-based membrane, it gives great results i.e. great dry adhesion. Even, in the case of the PU membranes, the longer the PU membranes are cured, the better adhesion of the water-based system on top of it is witnessed. There's no doubt about that. However, the big issue is its wet adhesion. What happens with wet adhesion is that when you get water that runs near the edge of the water-based membrane or the PU membrane between the integration of the water-based to the solvent-based the system you get a capillary reaction with water which gets under that film edge and it peels off.

Advice For Contractors Out there!

There's a need to be a different way and a better way out there. We turn this blind eye to this in our industry, like out of mind out of sight. What tends to happen is we address it once the problems evolve.

There is a way that moisture-cured PU membranes can be used on site. However, if it is going to be utilized where there is a direct adhering of the tile on top, there is going to be a need to use something that actually is not a bond breaker but something that's actually going to act as an isolator between the PU membrane and the tile bed. There is a need for acceptance to learn that the answer is still not the water-based membrane. So, to successfully waterproof with PU membranes, the point you need to remember is to waterproof right to the floor area.