Just got myself a Hygrometer. When you do a test; we are told to do it over 72 hours. If after say 12 hours, the reading exceeds 75% relative humidity which indicates that a damp proof membrane needs to be applied, is there any need to leave it and continue to the 72 hours, and if so why?
leave it for a MINIMUM of 72hours. Because it has gone up will normally mean a Surface DPM is required, also you need to know its final reading to know what dpm system and how many coats you might need. However the reason you leave it for 72 hrs is so it can equalize. There is plenty of times the hygrometer can read high in first few hours and drop down again. Also vice versa, a hygrometer can read low for first 48 hours etc before it starts to rise.
if you run out of the butyl tape and are in a fix for some, kids plastacene works too so ive been told but not blutac.
Matt what do you do with a modified screed? Like say a 75 mm k screed On the tin it states dries in 7 days! if you put a hydrometer on it,it will still show it's wet, It's a bit like if you put down stopgap 600 thick and test that the next day it will it's damp but fballs say you can lay on it? Only test to make sure is a calcium carbide test, but they are expensive and a pain, Fballs say it's the screed company responsibly to confirm it's ok, but the site want me to agree that is ok? As normal they don't want to pay for DPM if it dosen't need it, Any ideas
Hi Spacey, Headlam got it for me. The yellow one with the dial on top. Cost about £100, and came with a small roll of tape. Is it possible to screed completely level first, then apply D.P.M. Or will the damp cause the screed to fail? Balls say the dried D.P.M. will accept a direct coat of Karndean Skim Coat.
You can screed first if the concrete is ruff so the dpm will go further & you get a better coating but you need to use a moisture tolorant latex & then apply another coat over the top of the dpm !
I have used it under a dpm a few times. No problems. Did have some crack ontop of asphalt last week though? Weird.
I said this a while ago on twitter as on the bag it didn't say moisture tolerant. But it does say on the tech sheets it can be used under a dpm.
We have recently been working on a job with a high moisture reading. (Protimeter Surveymaster) F.Balls recommended removing the bitumen remains, then F77 DPM (new product I think), then Stopgap 300. However, Ardex were happy to recommend a layer of Arditex NA over the bitumen (as long as it was 'sound' and not flaking etc), DPM, then another layer of NA. Customer went for laminate in the end! Mark
