Installation systems for tiling and natural stone. Refer to manufacturer’s guidelines. This seems to have been used in abundance before the original screed was put down. Self levelling compound is often known as floor screed or floor levelling compound and is essential for creating an even floor surface in preparation for upper flooring layers. Cement screed. Mark El-Kadhi New Member. We could scrape up the tiles and start again. For unbonded and floating screeds, a DPM may be specified between the base slab and the screed. #1. There are many proprietary screeds on the market and information about these can be obtained from the manufacturer. 5m height allowed under permitted development as possible. not bonded to the base – typically where a DPM is placed under the screed. The idea is that you are to prevent any screed material from falling down any joints and coming into contact with the cold slab. e. Hi guys. Can be used as a Damp Proof. You also should have removed the vinyl tiles before priming and screeding. Is this okay? Or does this present a real risk of corrosion of the frame in the future?that's rising damp mate, need to dig up subfloor new concrete base, dpm leave 30 days then screed and surface membrane that should help fix the problem. If the insulation is flat and supported by the slab, 50mm screed won't crack or - spend the DPM money on a roll of 25mm chicken wire. This allows for the full 5kg or just half to be mixed at once depending on the area to be covered. 1. In this scenario, a rigid foam insulation is usual, and as you’d want the same U value in the roof, we need the same thickness of insulation. What the DPM is attached to can fail. 4. If modified screed is used you can get down to 55mm. Sunny Hampshire. Our quarry tiles were pretty much laid on dirt so there were some big variations in height over the whole kitchen. com. #1. 0113 2455450 sales@rawlinspaints. DAMP PROOF MEMBRANE. Figure 3: Concrete masonry foundation wall and concrete floor. Let the slab dry first. Ask yourself where the gallons and gallons of water in the slab are going to go - apart from potentially lifting the DPM it will come through any defects in the DPM and cause problems. This allows for the full 5kg or just half to be mixed at once depending on the area to be covered. Country. Laying new floor - needs DPM? dunroving Posts: 1,881 Forumite. Yes. Our Liquid DPM can be used on walls under a render to create a flexible waterproof layer. Well, when I did exactly this on my lower retaining wall - a mere footandahalf high - I lined the back with DPM, the stuff you put under screed to seal yer floors from rising damp. weberfloor flex is a self-smoothing floor levelling compound — often incorrectly referred to as a self levelling screed or self levelling floor compound — which can be tiled onto and is an easy screed for applying onto floor substrates subject to some movement, such as wood or underfloor heating. (DPM) between the concrete and screed. 99 Inc Vat. 2 Feb 2010. 12 Sep 2015. I always put the Celotex under the slab to ensure that it doesn't deteriorate between laying it down and screeding. Im not quite sure where my DPC should be going. I will post up a pic of the failed LVT in a minute for you! Screed seems to be getting damper. with the concrete but the insulation. Mobile Sales: 07920 715745. Contact Us. I moved into my new build nearly 2 months ago now and am having quite a few issues. Pro-Screed Gold is suitable for application over most underfloor heating systems. With a laser. Instead of a membrane, use a foam underlayment material which will keep the wood from touching the screed directly (avoiding any moisture transfer) but which will also allow the screed to breathe and thus dry over time. The floor originally had a carpet laid on top of the tiles, when I lifted it nothing felt, looked or smelled damp. It stops around 10mm away from the internal walls in all rooms. Walkable in 6 hours. I would guess, that a standard mix was used, as that would be cheapest, so could assume 1mm per day, but that`s why a test would be needed. Cutting open would void dpm so should be avoided. Under ambient conditions, PALACE 1-COAT DPM is ready to receive a smoothing compound as soon as 4 - 5 hours after application. Complete product range for installation, renovation and maintenance of wood flooring. Country. This allows for the full 5kg or just half to be mixed at once depending on the area to be covered. High quality painting, plastering and drywalling tools. So latex one its more likely the addy will be affected. Floor screed PIR cavity board Lay, level and compact the hardcore in layers (usually 150mm min / 250mm max). Reinforcement to Suspended Floor SlabsClick and buy N-Virol Superseal Plus Damp Proofing DPM Paint which an be used for several applications including damp walls, floors and on basement walls. Any advance on laying 75mm kingspan directly on existing screed with DPM beneath, then laying 18mm T&G moisture resistant chipboard. Guarantees the early laying of all floorcoverings. heated levelling screeds. 0. I've dug down and exposed part of the DPM sheet under the slab so I'm happy using trade plan, turbo then renovation screed. Mine is below the concrete. Onto the concrete. I recently had a new boiler installed and new radiators fitted, and the plumber has cut the old copper. 6. Am hoping for UFH in screed (supplied won't do 50mm, only 65mm). Learn More Damp Proofing 15 Items DPM Handy Pack - 300mu 1200 gauge - 4m x 5m Rating: 2 £17. 65mm Screed. 0. Curing under polythene 12 hrs 12 hrs Drying time to receive finishes - from removal of curing polythene sheet 50mm thickness and 50% RH. floating construction then a second "slip". Hi, Thanks for this, so it sounds like you would normally just overlap (and seal) the floor DPM and one over the threshold which extends to the outer leaf? I've filled the cavity with concrete under the door opening and poured the slab and the screed will go across the cavity to the outside leaf (which has the perimeter insulation to stop cold spots). Curing Under Polythene 12 hrs 12 hrs Drying Time To Receive Finishes - from removal of curing polythene sheet 50mm thickness and 50% RH. 0m is a low density polythene membrane for use under floor screeds which are not subject to hydrostatic pressure, to protect buildings against moisture from the ground. you might just have a low spot along the old wall where the concrete meets the wooden floor. Reinforcement is required when you’re concreting areas that will be subjected to heavy loads, such as garages and car parks. Stack Exchange Network. You should use them to protect all final floor finishes. To remove this type of asbestos containing floor. It is much easier to work on sections of the floor than try to achieve an even finish across the whole floor in one go. The screed will be only ~50 max (not yet dug any up). Many can be used over a variety of existing uneven substrates, using gravity to allow the latex mixture to self-level. 21) Timber block. Price: £4. Information ARDEX DPM 1 C. Ground-bearing concrete floor slabs should be protected against ground moisture by providing a continuous damp proof membrane (DPM). For traditional screed, the usual total will fall within the range £18. Vac up any loose sand once it's set and then tile. 4) at a thickness of 3" inches The guidelines state that a damp proof membrane that is placed under the flooring should be around 1200 gauge and constructed of polyethene. Non-structural floor screeds shall be adequate for the location and intended use, and provide a suitable background for floor finishes. Sealing a patch of DPM around its edge to the old is easy, just use silicone goo. The company keeps abreast of market developments by. AN INTRODUCTION TO. Should I lap DPM under or over Dpc then celotex, then another DPM lapped up the wall with 25mm up stands. Packaging: 25kg bags. would it beneficial to change the floor structure to incorporate circa 250mm of eps insulation under the concrete slab, instead of the 150mm pir above. #1 CGN Screwfix Select andyscotland said: ↑ The concrete slab I poured for my utility room extension is slightly uneven - a small dip into the centre. If the DPM is still wet you should have not tiled over. Replacing over half of your floor will mean you’ll have to insulate to at least 0. top of my concrete slab was about 50mm below DPC, I finished with battens and floorboards. Option 1 is clearly cheaper but as long as it takes a screed floor (says it does) and gets signed off by. Insulation is laid on the concrete and covered with a screed. user contributions licensed under CC BY-SA. Checkatrade offers the following guide: Electric underfloor heating cost. Our Epoxy DPM can be used on concrete floors and fine concrete screeds, of not less than 50mm thick in the case of un-bonded screeds. You adjust the concrete slab to let your. from a purely technical point of view a screed should always be divorced from the substrate by means of an operational DPM. The lower sand ratio means a higher ratio of cement, which gives a stronger mix. Fig. Figure 1: Concrete floor slab and integral footing. Self levelling compound was laid straight on top of the concrete floor (with no primer). above the slab I am having a screed to cover the UFH pipes. Firstly, there was no need to use a liquid dpm if you used underlay with a built in vapour barrier. 00. The only way to tell properly, is to carry out a proper test. A Damp Proof Membrane or DPM is a waterproof barrier that’s introduced between your sub floor and your wood floor. LKAB Minerals +44 (0) 7966 651006. The purpose of DPM. 4 Screed. carpet, tiles etc. #1. . 50mm C&S (1:4) screed towelled smooth. . Stack Exchange network consists of 183 Q&A communities including Stack Overflow, the largest, most trusted online community for developers to learn,. Celotex PIR’s closed-cell, moisture-resistant composition helps to prevent water ingress. Other benefits. – the UK’s leading manufacturer of flooring adhesives and floor preparation products for the contract flooring industry. An ARDEX Damp Proof Membrane will protect the floorcovering. It is not. Damp Proof Membranes. This should be laid on a bedding material such as screed which doesn’t damage the sheet and has fully sealed joints. Wet underfloor heating. Screed & Insulation. The tiler can then latex or screed over the DPM. Our Liquid DPM can be used on walls under a render to create a flexible waterproof layer. above the slab I am having a screed to cover the UFH pipes. Was looking to do liquid DPM sandwich with fball 1200/F77/1200 (or NA/1cDPM/NA but that’s costing another 30% more. This can only normally be guaranteed if its an new build or extension and most houses have been sold, inherited etc. If a screed such as A38 or Topcem was used, this can reduce the drying time, and with A38 this can be just one day. 28 Sandiwch damp-proof membrane. I thought common practice was to tuck the DPM under the DPC, but mine is the other way around: I'm about to start taping the insulation around the studwork and then I'm going. Two coats will provide protection up to a maximum hygrometer reading of 95% RH. someone suggested removing the blocks on the inside along the width of the bifold and screeding all the way to the brick course. He also saw hairline cracks in the top layer of screed in places. #1. ORDER LINE 0800 047 6775. BONDED VERSUS UNBONDED SCREEDS Bonded topping screed installations are the most common as this allows the minimum thickness (15mm) to be applied thus limiting the weight load on the structure. You will need to tear the lot up. The oversite is then constructed internally along with polythene DPM, insulation and floor screed etc. Therfore putting foil faced boards under screed is a waste of time and is the principle reason kingspan make tissue faced boards. #2. 24 h After curing of screedSANS 10400, Part J Floors (which is the SABS “deemed to satisfy” regs) states: “Ventilation of the subfloor space in suspended ground floors shall be provided by means of openings spaced not more than 2,4. For bonded screeds, M-Bond Extra epoxy resin combinedWhen laying self-levelling screed, the thickness varies from product to product, however as a general guideline please find the depths below: Minimum depths are usually 2-3mm, however there are some products that can go down to “featheredge”. 2. Uses/Subfloors:If you have under floor heating, you can use it to dry the screed 7 days after installation and the additional depth, (up to 65mm), becomes less important, But you’re still wasting money on screed you don’t need. We have our sub concrete floor in, and there will be a 1200g dpm, then 100mm insulation, then another dpm and finally 65-70mm screed. Use polyethylene sheeting to create a waterproof membrane to ensure that there is no leakage of the screed when it is pumped in wet. For example, when installing Celotex under floor. I think this is too expensive, so got a quote of another supplier of £2565 plus any potential floor preparation, with latex screen costing £13 /sqm or a feather finish at £2. The screed manufacturer agrees that their screed can receive an epoxy DPM. Changed mate!constructed as a separate concrete (Figure 2) or concrete masonry (Figure 3) perimeter foundation wall with the slab laid later. No this is designed to be used under floor screeds, tiles, render or plaster. 20m2, 50mm = 0. Developer has quoted £3744 for approx. Hence we always say DONT apply a surface dpm to a subfloor subject to rising damp. A Damp Proof Membrane or DPM is a waterproof barrier that’s introduced between your sub floor and your wood floor. So the floor has been there for 70. It needs: 100mm or more of well compacted type 1 MOT, sufficient sand to blind, DPM, insulation, screed. Bostik Screedmaster Rapid DPM is a ready for use; one part, water-based damp proof membrane. Side extension refurb: old concrete slab is uneven with a line of about 10mm difference in heights down middle, and dpm under screed is visibly not 100%, with a few gaps. Yes it is a small breach on regs but would be up to building control to decide. Once set, you can then apply your screed flooring to the DPM base. Labour costs. i'n not farmiliar with wickes dpm and the primer used for professional (if you like) screeds is neoprene. The advantages are the relatively low price of about £12 per square metre in combination with also relatively low installation costs of £8 – £12 per sqm as well as the high load- bearing capacity of cement screed. Discussion in ' Builders' Talk ' started by barnjules, Jan 30, 2017 . DPM (1200 gauge visqueen) Old Concrete Slab. 3k. A water based is more likely the screed itself will blow as it cant take moisture at all, so it would be the 1st thing to blow. Still struggling with how to retrofit the DPM (on rough old solid concrete floor) and insulation etc Am not going to manage brilliant insulation as I failed to realise we couldn't take the DPM above the DPC ( at 150mm), even tho there is the head height. The previous concrete floor failed due to a lack of DPM and has now been removed. "Your insurance company should be able to instruct property drying. Doggit. com. Small hole dug through 2" soft sandy concrete to reveal hardcore and soil. The correct installation of polythene DPM, rigid insulation and separating layers are highly important to the. The asphalt screed provides a membrane to the surface of the concrete floor preventing moisture within the constructional slab causing decay to the floor coverings. Visqueen EcoMembrane DPM. 2m3). To avoid damage to the insulation layer and the dpm it is necessary to take care in tipping, spreading and compacting wet concrete or screed. 14) Screed. The DPM should extend up the external foundation walls to meet. At its deepest it’s 150mm, what I’m stuck with is the builders trying to push on with the job. Like x 2; Agree x 2; List (You. The screed has water anyway, so a bit of ingress isnt an issue. The floor make up is compaced hard core, 125mm concrete, dpm, 100mm insulation, 75mm concrete screed ( polished and heated). doors. . When sand-blinded, BAL DPM allows tiling onto difficult substrates such as steel. How to install vacuum insulation panels below a floor screed. The Epoxy DPM 5kg is supplied in two 2. As a rough guide, laying conventional screed costs around £15/m2, increasing by around £5/m2 when delivered ready-mixed. Effectively a thick plastic sheet, a damp proof membrane (DPM) is used to create a barrier between a concrete (or screed) subfloor and a wood floor. 100mm c35 concrete with mesh. New-build install: £120 to £135 per square metre. DPM sheets should be overlapped by at least 300mm. If there is an operational DPM beneath the concrete you don't need one on top. A section of the old screed layer has broken up around the edge of the patio door threshold. To add to this, when we bought the house about 6 months ago the existing felt roof (on the extension) had a gaping hole that was letting rain water. ) chrysotile (white) asbestos fibres. Top. The damp proof membrane (DPM), normally 1200g polythene or radon barrier, should be laid over the blinding,So not convinced glue down is right. 8). This barrier is intended to stop moisture passing from one to the other. Kingspan GreenGuard is available in a range of compressive strengths starting at 300 kPa 10% compression. The blockwork above the DPC will become saturated and cause damp problems within the extension, the skirting boards will rot and the mould will occur on the plaster. It's a complete lack of knowledge on your floorlayers part or possibly just a carpet fitter trying his luck. I've dug down and exposed part of the DPM sheet under the slab so I'm happy using trade plan, turbo then renovation screed. As a waterproofer, BAL DPM is an easy two-coat system when used with BAL Self-Adhesives Butyl Tape in corners and junctions. O and the Answer to Mapei and Uzin is no. ), then 500 gauge plastic (or just use the leftover 1200 gauge DPM) then 100mm concrete slab. The DPM (Damp Proof Membrane) is laid under the insulation on top of a soft blinding to ensure it is not punctured. If under the screed this is normally a polythene dpm so the screed is then an unbonded screed, whereas if the dpm is on top of the screed an epoxy-type dpm is used. The surface should be of sufficient quality and. I could put the dpm under the concrete which would be as effective. Also, even with 80mm screed directly over Celotex the sab can feel a bit "hollow". Insulation sheets should be laid tightly together with the joints staggered to avoid movement. Since that period I've take out the bitumen screed/dpm and been on the concrete slab since about mid February/March. A latex based screed isnt as affected by moisture/damp as a water based is. hallbeck New Member. Damp proof membranes (DPM) A DPM should be a minimum thickness of 1200g polythene and linked to the DPC with a minimum 100mm overlap. But on the basis of more insulation is better, consider fitting more and laying cupboard flooring on top, or on joists. Hi All, I'm purchasing a new build and want to put Amtico Spacia down throughout the downstairs. If there was no dpm I would suggest a uniformal distribution across the whole floor. Can be used as a Damp Proof Membrane on sub-floors not under hydrostatic pressure. Aug 18, 2010. 1 or just a bit less. Bostik Screedmaster Rapid DPM is a ready for use; one part, water-based damp proof membrane. Choosing the solid concrete ground floor insulation is important for any project. There will be a damp-proof membrane under the insulation and possibly a second membrane on top, depending on the type of screed. For bonded screeds, M-Bond Extra epoxy resin combined DPM and bonding agent may beToday, new solid floors are far more substantial, typically comprising 150mm of compacted hardcore, 50mm of sand, a polythene sheet DPM, 100mm of concrete, then around 100mm of insulation plus a 60mm screed — in total, more than 450mm thick. The liquid membrane forms a strong seal and makes a permeable layer to enable moisture to evaporate off. you then have a continuous damp couse not inportant if concrete above dpc level. Unless there is an easy way. Lay the dp membrane over the concrete slab and lapped over the brickwork. They can feel wobbly when you walk on them but you get to the point when you can't get them any better and each give you walk on them or lift them you end up going around in circles. The old adhesive should of been removed. £20 per m2. There are two main options: 1. Fast drying screed cost. Drybase Liquid-Applied DPM should be used in situations where the final surface is going to be covered. Alan Jackson - Commercial Manager UK and Ireland - Gypsol. first of all check your existing floor is perfectly level, if not then forget the freeflowing screed as it will not level up with the existing floor. They are happy for the 25mm board to be laid on the screed, pipes clipped in then 9mm ply on top finally topped off with ceramics. Laybond Screedmaster One Coat Liquid DPM 2 part solvent free epoxy surface damp proof membrane developed to. com Do I need a DPM under laminate flooring? Simply put yes. If in the screed then no problem with this. Maximum depths are around 10-15mm, however with the addition of bulking aggregates (normally kiln. 15 Feb 2015. "Remove water with pumps or buckets and contact your insurance company straight away. If in the screed then no problem with this. . Visqueen ECO Membrane Data Sheet. co. Ltd. Use 1000 gauge or thicker – ideal for this is the polyethylene use for the DPM under your concrete subfloor. The DPM can be used as either below the slab application, directly below the flooring surface or in a sandwich construction, between base concrete and the screed. As with the Kooltherm installation, start by ensuring a clean and level surface. 30811761. DPM's must be carefully protected where folded up the perimeter walls, and lapped under the DPC particularly at door openings. Lay the damp proof membrane (DPM) (normally 1200g polythene sheet/300g micron or a radon barrier if specified), over the sand-blind base. The liquid membrane forms a strong seal and makes a permeable layer to enable moisture to evaporate off. As an alternative to under concrete or surface damp-proof membranes a damp-proof membrane may be sandwiched between the site concrete and the floor screed, as illustrated in Fig. Flexible - easy to detail and install on site. 9% screeds been down since February. #1. I was planning on putting 1200g DPM down, then 80mm celotex insulation (taped at joints), then 65mm screed (approx 1. Also, even with 80mm screed directly over Celotex the sab can feel a bit "hollow". On a job that’s had anhydrite screed pumped in, using a Wolff gm200 moisture meter readings in parts are 99. The installation of the DPM is extremely important as this acts as a barrier to prevent damp rising up through the substrate, from the ground below. This DPM is a ‘thick’ plastic sheet mostly 1000 – 1200 gauge polythene material. Pumped anhydrite floor screeds are not much dearer than ready-mix sand/cement, costing around £25/m3 (laid to a 50mm depth). bandejapaisa; 30 Jun 2023; Building; Replies 5 Views 1K. I really need to get the living room useable for my family and am hoping that a dpm under the engineered wood is possible. The maximum depth you would use a smoothing compound would generally be around out 10mm, you can add aggregates, to bulk up the screed going up to 30, 40, 50+mm. As a rough guide, laying a conventional sand/cement screed costs around £15/m2, increasing by around £5/m2 when delivered ready-mixed. pipes or cables for under floor heating should always be installed on top of the tanking membrane, not beneath it. If the coating is not going to be the final decorative surface and. 4. Using this latex based damp proof paint as a damp p. Express Liquid Screeds Limited. Country. 30 Jun 2023. It’s only to stop the screed running under the insulation. I would think a strip out and start again would be your best option, you should consider where/why there is water evident before. If you're laying Karndean over existing flooring, be sure it is properly prepared. 1200 Gauge DPMs should be used when a floor is direct to the ground. do I still need a DPM under that insulation? it is internal and sitting on a structural slab that is wrapped in DPM externally. This can include timber floors, tiles, laminate flooring and carpet. The excellent adhesive qualities and quick drying time of Drybase Liquid-Applied DPM make it extremely versatile. Small domestic areas that are going to have carpet, wood or synthetic floors as the final surface are ideal to use in conjunction with. It’s primarily designed for brushing onto concrete floors and fine concrete screeds. Country. It is important to ensure that a proper seal is achieved around all services. I would lay the DPM straight onto the existing and screed over. 3 Oct 2004. Thanks, Gastines3, FreeBear, and gwynlas! Well, I called a damp proofing guy in, he had a look said if it was him he would put in a screed at least 2 inches high and concrete outside. 5kN/m2. . Jabfloor 70 has a nominal 1% compression value of 21kPa (2. A standard sand/cement screed would need to be laid at a minimum depth of 65mm for a domestic property. Bring the membrane up the surrounding foundation walls until it is just high enough to connect with or form the wall damp proof course. This will give calculated u-value of 0. Effectively, a damp proof membrane (DPM) is used to create a barrier between a concrete (or screed) subfloor and a wood floor. Normally you would put a compacted bed of about 50mm sand under the DPM. Yes run the dpm up the wall to connect wall dpc with floor dpm. Under Floor Heating; Screed Care; Testing; Tips; Blog; Contact; A Practical Guide to Screed Testing: What Do the Experts Say? Download. Hull. 16 Nov 2016. Checkatrade offers the following guide: Electric underfloor heating cost. Pre screeding, you lay the DPM, install the insulation sheets and create vertical upstands of insulation block around the outside perimeter of the wall. Made from a combination of sand, cement and water, usually in a sand/cement mix ratio of anywhere between 3:1 and 5:1. Liquid DPMs gave the best protection but were more expensive. To remove the screed in order to relay a DPM is, in most cases, completely unrealistic and actually completely unnecessary. Easy Handling & Installation. I 've dug down and put 100mm of concrete down will liquid dpm to meet up with the existing dpm and 50mm screed ontop easy. No mention of reinforced concrete screed. Will prim t be okay as primer on top of turbo? Thanks Pete Unless designed otherwise, the minimum specification for all partitions should be: sill and head plates 63mm x 38mm. 14 assuming 0. A full sheet DPM is 250 microns (1000 gauge) thickness or above. This means of course I can't get a DPM under the slab; is it ok to put the DPM over the concrete slab, and then put down 50mm insulation and then 100mm screed? Ed209 , May 1, 2020 #1Assuming that the damp proof membrane (dpm) under the concrete has failed in areas then yes you possibly would get the odd patch of dampness showing in the floor. ; Stiffness: Concrete floors generally possesses adequate prudery & does not parry under the applied load which result in generating problems in non-structural elements, e. weberfloor DPM is a two-component epoxy based chemical damp proof membrane that is capable of being applied in one coat, dependent upon the condition of the substrate and quality of workmanship to ensure full coverage is achieved at the required thickness. You are therefore at the edge of the joists capability. Step 3: Lay the watertight membrane. #2. Also there MUSt be a DPM under the screed to stop any substrate moisture coming up from underneath as a result of heating. There’s also ridges from where the tiles used to be. Only one coat though. DPM, Celotex, 1000 gauge poly, 100-150mm concrete with or without reinforcement, 50-80mm screed. Hi I have fibreboard underlay in the instructions for the underlay it states if using this product on ground floor you should also use vapour barrier or damp proof membrane beneath the underlay. Unbonded screeds are used either to install a damp proof membrane (dpm) between the base slab and the screed or where the base slab surface is unsuitable for a bonded screed due to problems such. I've read that you shouldn't install DPM under SPC flooring as it can affect how it clicks together 3. "Turn off electricity and gas only if it’s safe to do so," he said. water will be likely to collect between the DPM and the old floor. Hi, I have an area of approx 6m by 3m on a ground floor extension which is block and beam construction, that I now need to insulate and screed to finished floor height. New-build install: £50 to £75 per square metre. Out of the 7sqm of floor i guess about 1. Use polyethylene sheeting to create a waterproof membrane to ensure that there is no leakage of the screed when it is pumped in wet. The basic screed construction for under floor heating systems generally follows the ‘floating’ screed construction, where a Damp Proof Membrane (DPM) and tacker insulation panels are laid over the. Hi All come across this forum and would really appreciate some assistance. Should I lap DPM under or over Dpc then celotex, then another DPM lapped up the wall with. The engineer (who is a bit belt and braces) recommended a block and beam floor supported by new foundations so as not to add extra load to the existing 1930s foundations. I think underfloor heating would work if you layed DPM, insulation (as much as poss) woodchip flooring and don't use a screed. As you are always relying on the subfloor surface strength you are always at risk if there is no sheet DPM under the floor as it will be under pressure. Do you need DPM under screed? What DPM is Required? If the hygrometer reading comes back above 75% relative. or as a sandwich membrane in base concrete or between the base concrete and screed. celotex goes UNDER concrete. Assuming that the damp proof membrane (dpm) under the concrete has failed in areas then yes you possibly would get the odd patch of dampness showing in the floor. Let’s hope you have a good water table as that’s the wrong dpm used. JB Flooring Well-Known Member. What is DPM under screed? Damp-proof membrane (often called DPM) is used in construction to prevent moisture from entering the building, usually through capillary action. Depends where the UFH pipes are. 34 dpm under insulation and screed.