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The Hygrometer Is For Me A Test Of Faith

I had a couple of technical calls this week, both regarding screeds and underfloor heating installations. In both instances the contractor was told by the screed supplier that they were ‘rapid drying’ products and would be dry within four or five days.

On hearing this ‘claim’ I emitted a load of expletives, which you’ll be pleased to see I’ve not included in this article. One of the following callers asked what kind of test do we, or should we be using to confirmif it really is dry?

Being an ‘old fart’ or a traditionalist if you prefer, I always favour the hygrometer. I’m not alone in this thinking as this is also the advice of the CFA (Contract Flooring Association).

Anyway, the installer said they were considering doing a carbide bomb test, to which I replied that if they performed this test, they would have to go through the full thickness of the screed for the result to be accurate and also to be damn careful not to hit any of the water pipes as they go down. I reiterated that, to my mind, you can’t beat the hygrometer if you need to know the moisture content definitively.

I know this feels like going over old ground again, but this topic of testing does need reiterating. There are a lot of instruments out there from Encountermeters to the Protimeters and whilst these are very useful tools, in my
opinion, for giving a quick indication of the floor’s moisture content, especially if you use them on what you feel are the wet test areas, there really is no alternative to the hygrometer.

I can never fathom why there is a reluctance to use the hygrometer. OK so there’s a bit of faffing about in comparison to other more instant bits of kit, but who are they trying to fool? The purpose of the exercise is to discover if the floor is wet, not to find a bit of testing kit most likely to giveme the reading I would like the floor to give.

If that was the case, we might as well throw all testing methods out the window and either judge by eye – ‘I see puddles it must be wet’ or kneel down and press firmly with our index finger and if it feels dry it must be.

You might as well take this approach to all installations if your goal is to keep trying different methods until
one gives you a reading you want. Seriously – it’s just as accurate!

This takes me back to the rapid drying claims that suppliers put out. Yes, most products will do exactly as they say on the data sheet if installed on the same floor as tested for the datasheet. Datasheet claims are from a perfect world where standard temperatures and conditions apply, where floors are perfectly even across the whole area and where site conditions (oh yes themagain) don’t have to be factored in, and this is before I question the perfection of anyone’s installation techniques.

Claims such as these are only indicative as they give you an indication of side-by-side drying times, but if you really want to know if it’s dry, don’t check the label – test it!

I know and appreciate there are pressures from main contractors to get you moving on a job as quickly as possible, but you should ask yourself who is taking the risk? If pushed I doubt many will indemnify you against problems based on the label on a bucket.

OK I accept too that some blame must stop with the manufacturers who through the marketing department hype often over-sell a product’s capabilities, but we’re smart people aren’t we? We know that the only true measure
of any product’s performance and its characteristics are to test it ourselves don’t we?
Or shall we just take a guess?

John Alcock is technical specifications manager at Bostik

T: 01785 272727

This article has been reproduced from the Contract Flooring Journal website. You can find them online at