Using The Hygrometry Facility
John Roberts tests the latest Tramex CMexpert 11
LAST month I discussed the various functions of the Cmexpert 11 as applied to surface testing and wood moisture. This month I look at its hygrometry functions.
British Standards advises using hygrometers for moisture testing in screed floors. BS 8201:2011 Annex A now includes the sleeve method. Insert sleeves into the screed after drilling a hole (not with underfloor heating or where pipes are located). Then insert a humidity probe into the sleeve; later connect to the meter.
The test kit described last month included meter, spikes, hammer spikes, three iprobes, laser thermometer and calibration check salts tank for iprobes and a calibration plate for the meter, designed to check the meter’s calibration.
Switch on the meter and press the eight studs on the base. The reference reading should be 4% ± 0.2%. I have used plates on other Tramex meters and they have never gone out of calibration, but don’t take chances!
The salts tanks help checking iprobes calibration. When I received the kit the salts tanks were in the box secured into foam locating holes. First, I removed them and left them in my office to keep them at a reasonably constant temperature.
Ideally they should be out of sunlight and not near any heating (radiators etc). Do the test at around 20degC. To test remove the cap on the tank and insert the iprobe leaving it for at least 12 hours, but 24 hours is better. Meanwhile, keep temperature stable to ensure an accurate check.
To check, attach the Hygro-i interface cable to the iprobe and the meter. Once switched on the screen shows the reading. It should be 75% RH ± 2%. If not, contact Tramex for advice.
Always record the test results, then date and sign the document. Keep it with the kit to prove when you last checked the calibration – information you may need.
Testing for RH readings are easy using the sleeve and hygrohood method. The sleeve is supplied with the kit, but I had to buy the hygrohood.
The sleeve method is preferred on-sites as you insert the sleeve into the screed flush with the surface, preventing accidental moving (or deliberate removal) of the box on top of the screed. The hygrohood (box) helps checking subfloors with underfloor heating and concealed services.
Firstly, seal the hygrohood onto the screed with Butyl tape after removing all contamination that could affect the reading. Insert the sleeve into the screed after drilling a 16mm hole for the 22mm deep sleeve or a 19mm hole for the 80mm sleeve at a suitable depth.
Drill the 22mm sleeve hole to 44mm to allow the seal cap to be inserted into the hole to protect the iprobe and to seal the hole until equilibrium is reach after drilling.
Drill the 80mm sleeve hole to 80mm deep as these sleeves have different cap seals. The depth depends on the screed thickness which may be unknown. Drilling too deep will penetrate the membrane. Most screeds should be at least 45mm thick. You can cut the 80mm sleeve down to surface level once inserted if the depth is less than 80mm.
Open both sleeves at the bottom and insert them into the drilled hole by sliding the sleeve onto the insertion tool. Then push down into the hole, afterwards removing the tool.
Note: Insert the sleeve with the flange end uppermost. I found the insertion tool slides in easily at the flange end, but has a little resistance on the opposite end. Once I’d made a mental note the direction was simple to remember.
The hood has a sleeve inserted so use the Hygroi probe the same as the sleeve in the subfloor.
To insert the iprobe attach it to the insertion tool which has two slots to allow the iprobe to be locked onto the tool. These are mainly for removal as the probe will be below surface level when inserted. But they help to prevent damage to the probe when inserting.
Push the iprobe down to reach the top of the 22mm sleeve or the flange in the 80mm sleeve. When I tested the sleeves placed on a desk it gave me a feel for what to expect.
Allow at least 24 hours after drilling the hole and inserting the sleeve, before inserting the probe. This will allow the hole to equalise as the screed will slightly dry with the heat from the drill. Also during the first few hours it will draw moisture from the surrounding screed.
This tends to stabilise after a few hours although the manufacturer recommends allowing 72 hours. I then inserted the iprobe and re-sealed it with the cap, and left it for at least 45 minutes to reach equilibrium. You can then take your first reading and record the information. Insert the interface cable into the iprobe on top of the meter. When you switch it on you can see the relative humidity, temperature and temperature dew point.
Replace the cap and leave it for a further 30 minutes before taking a second reading. This reading should be within 1% of the first reading, if not leave it for another 30 minutes before taking a third reading. If this reading is greater than 1% difference to the others, investigate further or accept the fact that the screed is wet and consider leaving it for a longer and re-testing or apply a damp proof membrane (not on underfloor heating).
Remember that if a surface within the room is at the same or lower temperature than the dew point, then condensation will occur. This is where you need to use the laser thermometer (part of the kit). Strike the laser onto the surface for the test and record its readings.
The advantage of the sleeve is that, providing there is no surface water from cleaning or other sources, other trades can work over the area without damaging the sleeve.
After finishing the test, I removed the iprobe with the tool. The hood method is similar, although it is mounted on the surface. I have checked these probes against other probes and hygrometers I have used in the past and found them quicker to reach equilibrium and are more accurate.
I have used this kit for a few months and always take it with me to use on every inspection and subfloor survey. It allows flooring contractors to evaluate subfloor moisture to British Standards.
This kit is more expensive than DIY types, but is worth it when considering the costs of failure. Taking and recording readings (with a witness) will help protect you if failure does occur. Remember the readings are at the time you take them.
The instrument will be a better friend if you have all the knowledge to use it. TAOFS offers training in moisture surveying with this and other manufacturers’ instruments. Training can be at one-to-one or group sessions at your premises if required, or a venue to suit.
John Roberts founder TAOFS (The Academy of Flooring Skills) and prominent consultant in flooring. TAOFS offers training in all types of floorcoverings.
This article has been reproduced from the Contract Flooring Journal website. You can find them at www.contractflooringjournal.co.uk.