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A. C. G. C. A. – five sources of moisture in buildings

Richard describes the five sources of moisture in buildings and explains why moisture readings is an art rather than a science.

I’VE been trying to find a five-letter mnemonic that fits with the theme of water. Moist? Humid? Steam? I can’t make them fit. So I’ve had to settle for the bare initials of the five sources of water in buildings that could affect flooring. All have the potential to affect flooring.

A is for ATMOSPHERE. Even on a ‘dry’ day, there’s moisture in the air around us. If it’s cold enough, we’ll see the evidence as our breath turns to steam, or if the outside temperature changes we may have to drive through fog.

Of course, normally inside a building the natural moisture in the air is not a problem. But warm air can hold a lot more moisture than cold air and if the temperature drops the humidity in the air will increase – without change in the actual amount of moisture that’s present – and at a certain temperature the air won’t be able to hold the moisture and so condensation will form. The temperature at which this happens is called the ‘dew point’. Some moisture meters (eg the Tramex CMEx5) show this on the screen all the time, others (eg the Protimeter MMS3) have a menu option to show this.

If you’re ever wondered why manufacturers (and the British Standards) insists flooring should be laid in temperatures above 18deg C, this is the key reason. Finding cold materials hard and brittle is bad enough, but to have condensation forming on the subfloor or the flooring itself can cause problems.

Another reason why I always check the ambient conditions on any job is the flooring itself may be prone to expansion and contraction with changes in humidity. Wood and wood-based flooring and SPC can all be affected. It helps to know whether flooring is in an expanded or contracted condition when considering how big the expansion gaps are around the perimeter.

C is for CAPTIVE MOISTURE. Pipes, tanks, toilets, aquariums. The list of water sources that are intended to be in a building is extensive. As long as the water stays where it’s meant to be, it isn’t a problem. But the floorlayer needs to be aware of its presence. I wouldn’t want to nail through a pipe again (yes, I’ve done it!) and a metal detector is a worthwhile investment. But there are other ways in which captive moisture could cause difficulties.

If I put my moisture meter on the side of a customer’s fish-tank I’d get a wet reading. But as long as there was no condensation on the glass, that water would not cause issues. So the reading would mislead me. But how about if my meter is picking up underfloor heating pipes that are too close to the surface? Or if I’m reading through a surface-applied damp-proof treatment?

The wet readings would be indicating moisture that I don’t need to worry about (unless I’m about to nail, of course). One unrelated thought is that there’s at least one range of SPC flooring that uses fillers that conduct electricity and so will give an instant wet-reading using an RF meter. I’ve learned to check a spare tile, or to hunt for some exposed subfloor (I hope they’ve not put the kitchen on top of a floating floor) to ensure my readings are accurate.

G is for GROUND MOISTURE. Structural damp-proof membranes are a modern invention and many houses built before about 1970 don’t have them. The floor slab is sitting directly on the ground and moisture can rise. Let’s face it, there aren’t many days in the year when you can sit on the grass without getting a damp behind.

In ‘those days’ (and, sadly, I can remember them) homes had open fires and double glazing wasn’t common, so draughty houses vented the moisture naturally. And plastic flooring hadn’t really taken off then, so find a home with a naturally high moisture level in the slab and you’ll be heading for trouble if you lay a waterproof flooring on to it without taking steps to prevent the moisture having an effect.

Simple clues that give away the likelihood of an absent DPM are if the existing flooring is parquet, quarry tiles or mineral tiles (‘Marley tiles’) which all deal with the moisture in a different way.

C is for CONSTRUCTION MOISTURE. Many building materials are applied wet, especially flooring materials like concrete, cement, and anhydrite. These ‘cure’ very quickly – you can walk on them after a few hours. But the excess moisture once the chemical reaction is complete still needs to find its way out of the material.

British Standard gives a ‘rule of thumb’ that it takes one day per mm of thickness for these materials to dry and 1.5 days per mm if the slab is thicker than 50mm. In the past few years it’s become mandatory to include slabs of insulation in a subfloor and this requires a second (and sometimes a third) dpm over the insulation layer to prevent the screed drooping or being absorbed into the foam. This is extending slab drying times and I’ve been finding floors still not adequately dry after two or three years. Moisture measurement is essential.

The other construction moisture issue I’m coming across more frequently is when underfloor heating hasn’t been commissioned before flooring is laid. When it finally gets put on, it forces moisture out of the slab and it can only go upwards.

Builders find it hard to believe a set slab is not dry enough for most kinds of flooring. Showing them moisture readings makes it very hard for them to argue.

A is for ACCIDENTAL MOISTURE. Okay, it might have been easier if I’d used S for spills or L for leaks because that’s what I’m referring to. The water may once have been ‘captive’, but a pipe joint is dripping, a glass has been knocked over or the weather strip on the outside door isn’t a good seal.

In a recent case it was simply messy washing up that ruined a wood floor in front of the sink, but in other cases the source of the moisture was a little more unpleasant. And sometimes it wasn’t accidental, mopping a laminate floor isn’t advisable because it will cause the joint lines to swell.

It has been said that taking moisture readings is an art rather than a science, and with all these factors to take into account, I tend to agree. If you’d like to learn more, The Flooring Industry Training Association (FITA) provides a one-day training course on moisture measurement that you can book onto, or that can be delivered at your company’s premises.
Richard Renouf is an independent
flooring consultant

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