FEELING FLO Rob Speke, technical academy manager at Saint-Gobain Weber, offers advice on
PREPARATION The best way to prepare a substrate is to always remove dust first. You might need to grind or shotblast it depending on how poor the substrate is, so you’ll need a good brush and a hoover to remove dust. Priming is crucial, the substrate will need to be primed at least twice and we always recommend that you brush the primer in. Some people don’t brush, they might use atomisers, but the problem with that is it doesn’t get into the pores of the substrate, which can create a lot of air bubbling. It can also reduce the flowability of any good screed.
You should prime the project the night before you plan on applying the screed, come in the next morning and give it a quick lick over again with the primer – I’d advise using weberfloor 4716 primer, which is an acrylic floor primer for use with all cementitious and hemi-hydrate floor screeds. Then by the time you’ve set up your machine and prepped everything, the primer will have soaked in sufficiently. You shouldn’t really be leaving it longer than 36 hours because then you’re going to have problems with dust particles and people walking over the primed floor.
TOP TIPS Regardless of whether it’s a thin screed, like weberfloor smooth 4150, or a base screed, such as weberfloor fibre rapid 4320, there should be a 10mm soft foam barrier placed around all walls, pillars and columns. This is because in the places where the screed meets another rigid object there’ll be different expansions and this can cause hairline cracking. If you put a 10mm soft foam perimeter barrier around everything, it can help prevent this.
Temperature is critical too; the room you’re screeding must be between 8˚C - 25˚C. High humidity in a room means the screed won’t dry very quickly. Open up a window or a door
34 | SUBFLOOR PREPARATION
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