External drainage membrane. I have an installation guide. A .pdf that can be printed here. Opens in a new browser tab. A Youtube video here. It is 10 years old so a bit out of date. But it might be useful to you. My membrane is particularly tough, yet cheap. It won't let you down like cheaper membranes. You have to install this membrane before you backfill and you might walk over it, in heavy boots carrying heavy loads, for a few weeks before you complete the task. I was often disappointed that famous brands were wrecked in this same situation where my thicker membrane survives. My membrane costs more to manufacture but I can sell it almost as cheaply as the thinner material sold by others. A tiny bit extra is worthwhile for a product that doesn't need replacing.   Comparison table (data from a few years ago, but I don't expect it has changed): Basement Expert Newton 410 Geodrain Wykamol Geotex Membrane Colour and material Black HDPE Black HDPE Various. HDPE Density 1,100g/m² 740g/m² 900g/m² Material thickness 1mm 0.6mm Stud depth 8mm 9.6mm 8mm Price per m² £4.17 If you buy either Newton 410 or Wykamol Geotex, their instructions tell you to peel back the geotextile filter layer and overlap the studded plastic layers before overlapping the filter layers. A similar product, photo below, has an overlap on the geotextile filter so it definitely seems likely to be easier to install than either Newton's or Wykamol's. But there is no need to overlap my membrane - easiest of all. All the other 3 also sell you a plastic covering strip for the top to stop dirt getting down between the two layers. But the top covering strip doesn't really work across an overlap because the dimples in the two sheets don't marry up well. It is so much easier, and usually much more effective, to put up the studded sheet first then to cover it in full-width (usually 4.5m) geotextile filter membrane, simply tucking it over the top to keep the dirt out from above and having plenty at the bottom to wrap over your land drain all in one go.   Whatever brand you use, if you have the foresight to cast some small pieces of timber batten into your concrete at what will be the top of each row of bobbled membrane, fixing the bobbled membrane and then the filter membrane will both be super-simple and fast. 10m long rolls £75 each. 20m long rolls £150 each. Delivery at cost. No VAT. My rolls of drainage membrane are 10m and 20m long. The full width is 1.9m. This means they each weigh 21kgs and 42kgs. The width with studs is 1.8m. The flat edge at the top means a small overlap to keep the water draining correctly is very simple to achieve - much easier than trying to match up studs in two different sheets. Please Note. You need to buy the filter membrane separately. The non-woven is a lot better because it still works where it is overlapped. But the woven variety does not work where it is overlapped. Woven geotextile filter membrane, which you see in the product data sheet, is much cheaper than the non-woven sort in the picture above. Woven membrane has little gaps in the corners where the weave overlaps. If you overlap woven membrane it no longer filters. It becomes waterproof. This means that you have to take great care with the cheaper variety for your drainage to work. You need much less care with the more expensive sort because two layers of non-woven geotextile membrane still filters and still lets water through. Famous Brand Alternative - Sika. This customer of mine built a basement 2 years earlier while still a customer of Sika and has more recently built a swimming pool in another basement using me. But he still had an external drainage membrane that you see he has begun fitting here. This has non-woven geotextile membrane already fitted. It has extra for an overlap along the bottom but at the ends you have to sort an overlap out yourself. At the very top earth could get in between the filter membrane and the bobbly membrane, filling the drainage void over time, unless you buy more filter membrane to fold over or a special top strip. You can see the drainage pipe around the bottom. The workforce have to find a way to get the water draining down the membrane into the pipe without any chance of dirt getting into the pipe as well, so they have to come up with a solution themselves rather than being supplied with one. I describe how I have learned to sort out these issues very simply in this Product Data Sheet available here to print. Opens as a .pdf in a new browser tab. Imagine that all there is fitted to the wall above is the black plastic with the bobbles facing toward you. Cut a length of filter membrane probably the same length as this wall. Lay one factory-edge on the ground, under the pipe and against the wall. The filter membrane will be 4.5m wide perpendicular to the wall. Cover the pipe in shingle. Wrap the filter membrane up and over the pipe and shingle till you can put clods of earth on the filter membrane to hold it against the wall where the two meet. Lift the remainder of the filter membrane. Fix it to the wall roughly at the top of the black plastic bobbled membrane. Tuck your remaining filter membrane over the top of and behind the bobbled membrane to filter water that wants to get in the top. My guess is that my way will cost a third or less the cost of a famous brand as well as being quicker to fit properly.

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