Power troweled concrete- friend or foe?

Here’s a question- if you’re a flooring installer, do you get to make recommendations to your client before the concrete is even poured?

In a perfect world, you would be able to sit in on the discussions between architects, construction heads and specifiers and talk about the concrete stuff. Then you’d know that, by the time you’re called in to lay the floor, the concrete surface is all ready for you and requires minimal preparation for you to do your stuff.

But it’s not a perfect world. You know that the concrete folks have recommended nice water content in the mix to ensure high-strength curing, and a power-trowelled finish to ensure it’s smooth to touch and pleasing to the eye. And somebody’s paid for all that.

Then you arrive. You have to enlist some expensive and time consuming grinding to a specification which gets rid of that sexy power-trowelled surface, because there’s no way your adhesive is going to bond to that. In fact, neither will your moisture suppressant/ mitigation product, when you find that the tight, smooth, power-trowelled surface has prevented the slab from drying much, if at all.

And you have to pay for that.

Wouldn’t it be better if neither needed to be done at all? Somebody would save a lot of money, and whoever advised them to save that money would be quite the hero.

Excessive power trowelling is the bain for flooring contractors. Not only does the “tightened” surface restrict a good drying rate for the whole thickness of the slab, it’s also another reason why capacitance Moisture Meters’ surface readings cannot be relied upon. The less-open and porous nature of the first few millimeters will generally read low. Couple that with a low drying rate, the moisture deeper in the slab will tell a very different story.

Here’s another tip: Grinding ain’t grinding. A surface grind to remove the “feathery” imperfections which can be left from a myriad of other trades or levelling compounds added to the surface- isn’t necessarily going to open the pores of the surface as required. Some homework is required on the specification of grinding!

It might not be possible to have input into the entire building process, to the extent of requesting a desired finish of concrete. However, as major projects are becoming more professionally managed, those at the “end” of the process (such as the humble flooring installer) are more increasingly consulted. If you’re lucky enough to be one of them, make the most of it and put in your two bobs’ worth on power trowelled finishes.

Of course, this is not to blame the concrete guys. They are asked to produce a flat, smooth surface and the power trowel process is the best way to do it. If they under-do it, the job may not be accepted. They trowel as much as possible, “just to be sure”. It’s the specifiers, architects and project managers who need to be fully aware of the pitfalls for the flooring professionals.


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