Hi, Having some trouble with a lounge floor and a bit stumped on where to go next, hoping for some advice and opinions. @ fair bit of context needed so tried to bullet point it! House originally built in 1970 with parquet floor (usual bitumen underneath). During renovations, we installed carpet over the parquet floor, the underlay we used had a built-in DPM (Wilson's plushwalk). Realise this wasn't necessarily the best idea! About 12 months after the carpet went down, the parquet started to click, eventually rising, causing the carpet to lift in one area. Removing the carpet showed the parquet had popped, presumably through moisture causing expansion. A separate section of the floor had developed mould. We removed the parquet and used a hygrometer to measure the humidity in the floor, most areas were <70%, but one area where the mould had developed was >90%. This has dropped, but fluctuates between high 70% and high 80%, even after having a dehumidifier running for a number of weeks. Ruled out leaks and pipework. Walls not affected and reporting normal levels of moisture. Floor is made up of screed, 150mm slab then hardcore. There is a thin polythene sheet between the slab and hardcore but is very fragile - digging a small hole to check for a DPM found this. It's clear in colour and very easily torn. Assuming the problem is environmental, possibly (albeit thin) DPM failure. We don't want/can't afford to dig up the entire slab and install DPM. Would also probably be required to insulate or whatever modern regs state. There wasn't previously any evidence of damp before we laid the carpet. I'm guessing when we didn't have an underlay with built in DPM on top, any residual damp was just evaporating through the parquet. However in this one area (a metre or two squared) the readings are still higher than the recommended 75%. Currently deliberating the following two routes forward.. OPTION 1: Remove bitumen residue from screed, apply moisture resistant screed and use underlay with DPM (spec says this is suitable for floors with up to 90% RH) OPTION 2: Remove bitumen residue, apply liquid DPM, apply screed, new underlay. Concerns with option 2, how to deal with adjoining walls where the DPC is level/below the existing screen level. Sorry for the very long post, any input is very welcome! All trades we've spoken to are a bit stumped and unsure what to advise so we are also a bit stuck. Really not sure if it warrants digging the entire slab up or not. Thanks!
The problem is the carpet underlay causing it to sweat. You need to use a suitable underlay like cloud 9 or crumb rubber/felt. We have always put down Paper felt over wood block before underlay and carpet to stop the wood block swelling. You need the floor to breathe not block it with a dpm.
If the damp is only in one area have you checked the ground outside? Gutters all working? Soakaway and drains ok? You could remove all the wood block and use ardex na, dpm and Na top coat. That will give you another dpm but i would try and find the source of the damp first if possible
Thanks for the response, I've seen the ardex sandwich approach and seems like a common way forward. My only concern is if that just pushes the damp to the walls/other rooms..no damp detected anywhere else downstairs currently. Have also checked outside for anything untoward there RE drainage, gutters all clear. It's really odd as the damp patch is quite central in the to the middle of the ground floor of the house, not near any external walls. It's not over any pipework and mains water/drains etc are nowhere near. We have already removed all the parquet so just got the bitumen mess left behind at present.
Thanks, that was my initial thought. We removed all the underlay and also removed the parquet (so now just bitumen residue remains for the last few weeks). That area doesn't seem to be drying out though as yet, it's still around 85% today for example.
Its not suppose to push that level of moisture anywhere. It will just slow the amount of moisture rising. Unless you have water under the slab, then it will get pushed somewhere
We didn't put any of that in, the house was built in 1970 and this is the first time we've had any problems so dug down to see what's there! Trades who have seen it have commented it doesn't look like what they'd expect, as it's quite a thin plastic and clear not black. It's definitely not resilient as a modern DPM sheet so maybe it's just broken/damaged. I think the biggest unsolved mystery is why only one area of the floor is reading higher on the hygrometer, when the rest of the floor is 70% max. Everything pointed to some kind of pipe leak but there isn't one (exposed some pipe to check, had thermal imaging done etc).
Hi there, Sorry to hear you’re dealing with these flooring issues—it sounds really frustrating! From what you’ve described, moisture seems to be the main problem, likely due to the DPM not holding up as needed. Here are a few thoughts on your options: Option 1: Removing the bitumen residue and applying a moisture-resistant screed along with an underlay that includes a DPM is a solid approach. This should help manage the humidity levels better and protect your new flooring. Since the underlay is rated for up to 90% RH, it should provide the extra protection you need. Option 2: Using a liquid DPM can also be effective, but I understand your concerns about the adjoining walls. Ensuring a continuous and well-sealed barrier around the walls is crucial to prevent any gaps where moisture could seep through. It might require some careful planning and possibly professional assistance to get it right. Additionally, improving ventilation in the affected area can help reduce moisture levels over time. Even with a dehumidifier, enhancing airflow can make a big difference. Since this is a complex issue, it might be worthwhile to consult with a damp-proofing specialist or a structural engineer. They can provide a more tailored solution and ensure that whichever option you choose is implemented correctly. Hope this helps, and I wish you the best of luck in resolving the problem! Best regards, Steve Pro-Fit Floor Coverings
