No one seems to know the answer on how much moisture a surface dpm holds back. Basically because you use a surface dpm to get the job done. So we have set up a test at floorskills. While we are testing the dpm I figured we would do a test with tramex and the new iprobe v the RapidRH system v a hydrobox. Lets see just how quick we can get results between them all. All brand new probes have been used . 9am this morning the starting readings from the hydro boxes is - hydro box on concrete= 65% RH hydro box on DPM = 65% RH tramex cms is reading 5.3 % Probe tests was inserted at 10.15 am . The starting reading was- Iprobe Plug Test = 65% RH RapidRh = 82% (probe was stored in a different area to iprobes so this is why it started off a little higher)
So we are 1hr 30 minutes in to the test. With the Hydro boxes. The results so far (please note that BS standards says a hygrometer test takes 72hrs) Hydrobox on bare concrete = 68% RH Hydro box on dpm = 65% RH The Plug tests have been in for 20 minutes and we have - IProbe Plug test = 98% RH RapidRh = 94% RH
Sorry didnt get time to post up results before i left the other day. Been without internet since also. So the results another 40 minutes later = So we are 2hr 10 minutes in to the test. With the Hydro boxes. The results so far (please note that BS standards says a hygrometer test takes 72hrs) Hydrobox on bare concrete = 69% RH Hydro box on dpm = 66% RH The Plug tests have been in for 1 HOUR and we have - IProbe Plug test = 99% RH RapidRh = 95% RH Tomorrow morning we will have the results after 72hrs which is how long BS standards dictate the tests need to take.
Lets just say i have a reading im not happy with. I started so i will finish! however i have drafted in another couple of tests along with a couple of sub floor experts to challenge the results im looking at. Basically i don't belive what figures im looking at. There is something wrong somewhere. I will put up all the results plus any WRONG results i might be looking at with a explanation of why or what has gone wrong. If i have made a mistake then im sure many others will so i need to give the heads up.
O.K, some more results for you. After 72hrs (BS standards) i was looking at a very worrying result. The results after 72hrs was - Hydrobox on bare concrete = 72% RH (this power floated concrete but has been abraded, this is the worrying result !) Hydro box on dpm = 66% RH The Plug tests have been in for 72hrs and we have - IProbe Plug test = 96% RH RapidRh = 95% RH The results after 130 hrs was - Hydrobox on bare concrete = 91% RH Hydro box on dpm = 67% RH The Plug tests have been in for 130 hrs and we have - IProbe Plug test = 96% RH RapidRh = 95% RH Going back to the 72hr results, if you compare the hydro box reading compared to the plug test, well the hydro box is saying the powerfloated is dry but the iprobe and the rapidrh are saying its very wet ! (sure you can see why i was very worried and still worried by the result) So what went wrong? Well nothing. The hydro box WAS wrong 'sort of'. Actually i would say British Standards was wrong in the amount of hours its says a test takes. (72 HRS) . The tests and other tests to back it up have now been done. The hydro box is now reading 91% RH and climbing every day BUT slowly . It has now been approx 130 hours and the hydro box is still reading low, its almost there but not yet. So what is that telling us? Its telling me that BS standards is wrong in how long it takes to take a RH reading with a Hygrometer hood / box in the test i have done. WHY IS IT TAKING SO LONG FOR A HYDRO BOX / HOOD TO TAKE THE READING COMPARED TO PROBE TESTS? well thats simple, The power floated concrete im testing is very dense and the moisture is taking a very long time to build up in the hydro hood. A less dense concrete would of given results a lot faster, maybe even in 24hrs. Now the problem here is you may of followed BS standards and believed the subfloor was dry. However when you installed the flooring the moisture would now start to build and the flooring would of failed. So take this as a warning, rushing tests with hydro hoods is not the best idea. They can need a lot longer than what BS Standards state in some cases. SO ON TO THE PROBE TESTS, the probe tests read and gave a approximate reading in under 1 hour. However the reading was a little higher than the true reading for the tramex Iprobe( i would prefer it to read high than low tho ) and a little bit lower for the rapidRH. Dont forget the test should take 72HRS tho. After the 72hrs the probes have read spot on. The reason why the probes have managed to give us spot on readings MUCH faster is again simple. A concrete subfloor is always going to be drier at the surface. The moisture is trapped below the surface. The ideal testing depth is at around 40% the thickness of the concrete. This is where the Iprobe and RapidRH sensors was placed when testing. Because of this they could take a reading in a matter of minutes and then needed a few more hours to become stable and get to with equilibrium with the concrete they was testing. Hope this is off help to you all. So
So what your saying is if you recommend a testing method ignoring BS not that we should You would say probes are better ?
Matt, thanks very much for posting these results. I've always had a little concern over the hydro box. Do you think it's time BS re-defined (Perhaps bring up to date) their excepted testing methods? It certainly would appear that way. It's findings like these that should be presented to BSI to spark a review. Out of interest, will you be doing that? To see results like these really knocks confidence in installers when we're getting told to test one way but with an invasive testing method in the background that seems far more accurate. I asked for a second opinion reading from Ardex on a recent installation and they used a humidity probe!
I've had this on the last 2 jobs (both hemihydrate) I've put down a hygrometer. After 2-3 days it was reading around 75%rh but a week later it was up in the high 80s. Luckily most my jobs are not very local and I leave the boxes down sometimes over a month! I was thinking I should take the hygrometers up after 72 hours as that will be the true reading. Obviously not.
On "normal" concrete it should be fine. The test was on powerfloated floors that take at least 10 years to dry (if there's a dpm underneath it). That's why it took longer to reach equilibrium - am I on the right lines Matt?
BS says a hygrometer test that should take a MINIMUM of 72 hrs. A probe test and hydro box both meet BS standards as both are being read with a hygrometer . one being in a box and the other being below the concrete surface. Problem is BS says a minimum of 72 hrs. The word MINIMUM is the key here. A floorlayer reads it as 72 hrs and we are done when a hydro box CAN take a lot longer to read as proven in my tests. How long depends on the density of the concrete.
A probe test IS bs standard providing its result is read in RH.(so a hygrometer probe) Do you think i should report my finding to BS standards? If we was to re-write the standards to each and every test out there then we would end up with a very thick manual. BS Standards will not write a manual to suit every reading device out there. They will simply give a 'maximum' time to take a reading. In other words the test time might end up being changed from 72hrs to 300hrs ! Pooh.. Fan... what do you think ? Personally im leaning more and more to a MC test that is done by scanning the subfloor. Its a instant reading but im yet to see it be wrong. Its a reconnised test in European countries. Maybe we should listen to the our international / european cousins?
Ye on 'normal' concrete it should read perfect in the 72hr guide that is given. Can someone tell me what normal concrete is tho and how do we know by looking at it? Correct, powerfloated can take many years to dry.
