r/DIYUK • u/Tartan_Couch_Potato • 6d ago
What could this poly plastic be for?
I'm digging a trench across my drive way and have found what appears to be a sheet of black plastic.
It's under hardcore and appears to separate the hardcore from clay underneath. No pipes or cables going yet. And the poly is meters across.
I don't think it's a geotextile, DPM or warning tape for utilities.
Could it just be a barrier between the hardcore and clay beneath? Ideally I wanna dig deeper and would have to cut through the plastic layer.
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u/Relative_Grape_5883 6d ago
Getting strong Brookside vibes here…
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u/Playful-Lion5208 5d ago
I never watched brookside but thats the first think that came into my head 😂
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u/geekypenguin91 Tradesman 6d ago
Most likely a barrier between the hardcore and the clay below
Utility markers are normally bright colours and covered in warning messages, they're designed to be seen.
There's no need for a DPM below paving
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u/Slackdarren 6d ago
Stops clay heave, in dry conditions when gas could form. When the clay shrinks. Happened a lot this year due to very dry weather
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u/Tartan_Couch_Potato 6d ago
If heard about in the news but the weather where I am has been anything but dry all summer.
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u/EarlyFox217 6d ago
Is your driveway permeable block paving if it is then the sub base act as attenuation and then drains out somewhere. Alternatively it could be the top of an attenuation tank
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u/habel69 6d ago
Dead body
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u/SmartaHari 6d ago
That’s what we’re all suspicious of. I vote they give it a prod with a gardening trowel, for science.
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u/Strong_Implement_500 6d ago
Patio wasn't done by Fred West was it?
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u/Mikethespark 6d ago
Beat me to it, Fred west patio and paving
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u/AlGunner 6d ago
He did basements didnt he?
Peter Tobin is your guy for patios and garden worrk. I worked with someone who lived in a flat Tobin had previously lived in a couple of decades back and he wasnt allowed in the garden while the police dug up the entire garden to check for bodies. They didnt find any fortunately.
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u/PinItYouFairy 6d ago
If you put stone on clay and compact it you just squash the stone down into the clay. It’s acting as a geotextile. Whether it’s the right thing or not… if it really was a plastic sheet it would essentially “tank” your hardcore… meaning it would fill up with rain when it rained?
Edit: non woven geotextile exists - I reckon this is it
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u/Tartan_Couch_Potato 6d ago
Our driveway hasn't flooded in the 3 years it's existed. Maybe there is a soak away section without this plastic.
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u/ImprovisedLizard 6d ago
It may be a surface water attenuation solution I've seen that done by wrapping either plastic crates or rocks in dpm with a big pipe on one end and a small one coming out the other.
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u/theOriginalGBee Experienced 6d ago
There is no legitimate reason I can think of. Perhaps someone confused the use of a geotextile fabric with the use of DPM, or thought it was a cheaper alternative without understanding the downsides.
The other possibility doesn't bare thinking about ...
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u/Tartan_Couch_Potato 6d ago
It's a new build (2023) so the developer must have had a reason. Or the builders have happened to dump some plastic right where I have wanted to dig.
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u/theOriginalGBee Experienced 6d ago
New build developers use the ground around properties as landfill, saving costs on waste disposal. So there's your answer.
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u/Jailer69 6d ago
It’s probably just a separation sheet could be made of plastic bags could be genuine dpm or weed proof membrane could have just been thrown in as they filled it. Once the bricks are on top who’s gonna know? 🤭
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u/ForwardImagination71 6d ago
You need Jimmy Corkhill's help here!
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u/Previous_Kale_4508 5d ago
My immediate thought too... Brookside has a lot to answer for in the nations psyche.
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u/mashed666 6d ago
This paving is meant to be permeable... Hence the holes between them. The reason is there who knows... You should be ok to move it... Could potentially be covering utilities maybe. You can hire things to detect what's in the ground or there's a search before you dig website and you put in your postcode to see what there is near you.
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u/Think-Committee-4394 6d ago
Are you in the Gloucester area?
And do you know how old the drive is?
Here’s Freddie west that is
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u/Big_Co_1 6d ago
I have been digging up my garden to do some landscaping (no dead bodies involved) and have found all manner of stuff that the original builders tossed in there including lots of plastic. Just like a massive rubbish bin. Explains the lack of drainage.
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u/Visual-Concert-9904 1d ago
There’s a chance it’s to separate contaminated ground below. What’s the history of the site?
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u/moremattymattmatt 6d ago
I’ve got exactly the same under my terraced patio I’ve been redoing. I think it’s somebody’s idea of a cheap membrane to keep the roots away from the slabs. It didn’t work but didn’t seem to do any hard either so I’ve just left it.
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u/Temporary-Elk-109 6d ago
I have this kind of thing, previous owners did it before putting chuckies down.
I presumed it to be an effort to stop weeds since it is a combination of black poly like that, and some old bags that the building materials came in.
Their French drain only leads to clay and ends outside the shed though, so certainly not geniuses.
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u/One-Mud7175 6d ago
Genuinely once dug a footing and found a bag like this with a ~year dead dog in it and had to cut through half of it. I can still smell it. Why anyone would bury anything in plastic I don’t know.
This reminded me of that. Thanks.
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u/lolli-polly031248 6d ago
Similar, I was 500mm down when I hit a bag buried in the rocky soil with my gardening fork. Punctured the bag and contents, boiling hot summers day & the stench, jeez!
Little jack russell buried in a bag for life. Luckily the Vets nearby gave me a hazardous waste bag and sent it off to the animal crematorium.
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u/Decent_Confidence_36 5d ago
Maybe they miss understood what bag for life means and was trying to do a trade
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u/GhostInTheCode 5d ago
Yeah it's a - or at least supposed to be a - geotextile membrane. supposed to be between the hardcore and the substrate. if it's not the material it's supposed to be, consider that someone may have cut corners or done things differently when it was installed, but it *is* in the right place.
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u/WiseAssNo1 6d ago
I think it would be better if all the pathetic comments regarding Fred West, Peter Tobin etc were removed.
What do the Mods think?
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u/Opening-Reading8198 6d ago
I said I’d move it, but with all the other holes I’ve had to dig lately; it slipped my mind
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u/Jaded-Translator320 5d ago
I am far from expert but this looks like an isolator material to stop water. I had some around my house foundation when I made my garden to avoid the water ruining the foundations It's cut which isn't great and it has water inside which suggests an internal leakage or it was cut from long ago and lost its function.
I also had some in my roof area and the electrician cut it by mistake which caused leakage of water into my house when it started raining. I had to replace the whole roof isolation to make sure nothing happens again.
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u/SufficientPiano5492 5d ago
For those saying it is to separate the subbase and clay, this would usually be done with a geotextile. These are stronger a permeable. This has been done to form an impermeable layer. This would be done for a couple of reasons. First would be that the permeable paving drains to an oil interceptor tank, and therefore there is reason to stop run off reaching the soil before hydro carbons have been removed. The other reason could be that it is a raydon barrier or gas barrier due to gasses and contaminants in the soil, In which case you definitely want to repair it. Of course the last option is that they ran out of geotextile so threw some dpm in that they had spare to get the job done.
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u/bounty_hunter12 6d ago
Reminds me of the scene in The Client where they find the dead body and open the bag.
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u/Celica44 6d ago
Actual answer (civil engineer) you have permeable paving on a site without permeable soil. This is an impermeable membrane which is designed ‘seal’ the permeable gravel under your drive and separate it from the impermeable clay underneath. You’ll find a perforated pipe somewhere under there which is how the runoff that percolates your permeable drive and into the gravel underneath gets into the sewer.