To prime or not to prime by Jim Cresswell – Mapei
At MAPEI, a constant question we come across is in regards to the application of NIVORAPID.
“Do I need to apply primer”? There are a few different answers to this depending on the application method and the substrate condition.
Nivorapid is ideal for ramping to create flush transitions with adjoining surfaces.
As Nivorapid is high in polymer, and the substrate is free of contaminants (curing compounds) and is porous, it does not require priming, but it has to be worked into the surface. The issues surrounding this is there are different ways an installer likes to apply it…
This is where the material is poured into position and the top is just smoothed over with a trowel or gauging tool. This does not work the material into the substrate and will have poor adhesion which will lead to cracking, drumminess or delamination. If this is the preferred method, the installer should prime the substrate to improve adhesion or simply apply a small amount of the Nivorapid and complete a slurry coat with a trowel, pressing it hard into the floor before applying a large quantity to build up the height.
This is where the material is poured into the area and trowelled into the surface before creating heights. When it is trowelled across the substrate you are pushing material into the substrate which increases the key it needs to bond. Concrete has micro capillaries and when it is forced into the surface it locks the material to the floor. Concrete needs to be open (porous) for this to happen.
The substrate needs to be clean.
All building sites have many different trades working before it is ready for floor coverings and during this time many things contaminate the floor e.g. paint, plaster, adhesive residue and dirt. These contaminants should be removed as they will become a bond breaker between the Nivorapid and the substrate. They can be removed by sanding, grinding or scraping.
The substrate also needs to be porous. More and more these days, slabs are being highly burnished which closes the surface of the concrete. A simple test can be achieved by flicking water onto the surface. If the water beads up on the surface and does not penetrate after 5 minutes it indicates that the substrate is closed. The best action to take is to either use a diamond grinder (9 inch) to treat localised areas or prime with Eco Prim T undiluted or Eco Prim Grip. These primers are bonding promoters. Please note that all surfaces must be clean and free of all contaminants.
1. Clean It – A two minute clean will save a lot of $$ where failure could have been avoided.
2. Work it into the surface – If no primer is available onsite but you have porosity, a two (2) minute scratch coat will improve adhesion.
3. Check the porosity – Simple and inexpensive to do. If you cannot grind it, “prime it” in accordance with the porosity.
This small investment is better than reworking or replacing the flooring.
Editorial by: Jim Creswell
Resilient Products Manager
Mapei Australia Pty Ltd