# Education is the Best Solution to a Healthier Home > A damp patch appears on a wall and you take a moisture reading. What else do you need to know before you can tell the homeowner what's causing it? *Source: https://www.thehealthyhousepodcast.co.uk/episodes/education-is-the-best-solution-to-a-healthier-home* [![](https://www.thehealthyhousepodcast.co.uk/images/episodes/education-is-the-best-solution-to-a-healthier-home.jpg?v=f3b31e715c) Play the video: Education is the Best Solution to a Healthier Home](https://www.youtube.com/watch?v=XaSsC4DS_XM) [Open in Spotify](https://open.spotify.com/episode/7vPah0S8mox6B41Hk1oLyV)[Watch on YouTube](https://www.youtube.com/watch?v=XaSsC4DS_XM)[Listen in any app](https://pod.link/6800464905) ## The short version - A moisture meter reading is not a diagnosis. The episode describes surveyors who walk straight in, press a meter to the wall and call it rising damp, and says a correct diagnosis starts with a proper survey of the whole building. - Look at the outside of the house first. Kevin Topping of Mapei says the exterior gives a lot of the answers: gutters and downpipes, moss on the brickwork, the condition of the bricks and mortar, and whether the damp-proof course has been bridged. - Mould at the bottom of a wall is not proof of rising damp. Aaron describes a survey where a homeowner had been quoted for a new damp-proof course, and the cause turned out to be a downpipe that stopped short of the drain. - Take the humidity and the air temperature outside as well as inside. Kevin says to note both, and that his team works out the difference in vapour pressure between the two, while remembering it is only a snapshot of one visit. - Sort out ventilation before you insulate. Kevin says people ask to insulate without having thought about ventilation, and the pair agree that insulating one wall does not deal with the reason moisture levels in the home are high. - Isotherm is a thin membrane for cold walls, and Kevin's employer makes it. He describes it as a multi-fibre material with a waterproof layer in the middle, stuck to the wall on a waterproof adhesive and then skimmed with plaster. - Isotherm is a damp-proofing product with clear limits. Kevin says it is not for heavily salted walls, plaster that is coming away or wet walls, and that it is not a waterproofing product. - Most fitting problems come from too much adhesive and untidy joints. Kevin says the adhesive should be notched so the wall shows between the ridges, and the pieces butted tightly together, because adhesive squeezed into a joint creates a cold bridge. ## What this episode covers Aaron Worrall of WeatherWise sits down with Kevin Topping of Mapei to talk about damp surveys, condensation and basement waterproofing. The first half is about diagnosis: why a moisture meter reading is not an answer, what a surveyor should look at before naming a cause, and why ventilation comes before insulation. The second half is a detailed, practical conversation about Isotherm, a thin thermal membrane for cold walls: what it is, where it should not be used, and how to fit and skim it well. Mapei makes Isotherm and Kevin works for Mapei, so his enthusiasm for it should be read with that in mind. Aaron says his own firm fits it too. Both are clear that a product comes after the cause has been found, never before. ## From a lorry cab to waterproofing Kevin left school, spent a spell in the armed forces and then drove a lorry for a builders’ merchant, a job he says he hated. He told his branch manager he wanted to be a sales rep. One day she asked if he had a suit, told him to come in wearing it, and let him go out in her car to see if he could find some business. It went well, but she still needed him as a driver, so he left to do sales elsewhere. He moved to an independent builders’ merchant and then into distribution, where he specialised in fire protection, acoustics and insulation. After many years he found he was no longer enjoying the work. A phone call to a damp-proofing and waterproofing supplier on behalf of a customer led, half as a joke, to a question about whether there was a job going. There was. That business later became part of Mapei, and Kevin now looks after a regional team doing the job he used to do. He says he arrived knowing insulation and very little about damp, and learned by shadowing a more experienced colleague on surveys until he was told he was ready. He still rings people who know more than he does, and Aaron says he does the same. Kevin also describes a visit to Mapei’s head office in Milan and its testing facilities. He says the amount of testing each product goes through was what struck him most. ## Why a meter reading is not a diagnosis The pair agree that damp work is about finding the root cause before recommending anything. Kevin describes a pattern he sees often: someone is handed a damp meter, goes straight indoors without looking at the outside of the property, presses the meter against the wall and announces rising damp. Aaron’s view is that these instruments are conductivity meters. In his words they are good at telling you what is dry and poor at telling you what is wet. Kevin adds that condensation on a wall will produce a very high reading, and that many people only test the bottom of the wall. They mention surface and deeper-reading meters, salts tests and long-reach meters for tall rooms, and Kevin’s advice is to use everything available. Two examples make the point. Aaron describes a survey where mould at the base of a front wall had been called rising damp and the homeowner had been quoted for a damp-proof course. Outside, the downpipe ended above the drain. The pair also talk about a first-floor bedroom that had been diagnosed with rising damp. ## What a good survey looks at Kevin starts outside, because he says the exterior of a property gives a lot of the answers. He looks for moss on the brick work and trees growing out of the guttering. He checks that the brick work is in good condition, and that the damp-proof course (DPC) has not been bridged. On a cold wall he also looks for the drill holes left by blown cavity insulation and for signs of recent wall tie work. Inside, Kevin says the best things a surveyor has are the eyes, ears, nose and touch they were born with. He takes a long breath through his nose as he walks in, because the people living there stop noticing the smell. He feels the wall: is it cold, does it feel damp? Then come the questions for the occupier. When did you first notice it? Does it appear anywhere else? Does it come and go? A patch that is there in the morning and gone a couple of hours later suggests the air warming up, which points to condensation and to the question of why that wall is cold. Only then do the instruments come out. Kevin takes the relative humidity and air temperature indoors and outdoors, and says his team calculates the vapour pressure difference between the two. The pair use thermal imaging to find cold spots that a meter could miss, and Aaron checks how close the wall surface is to the dew point. Both stress that a visit is a snapshot. Aaron says data loggers would show more, but that some customers do not want to pay for them and a few have refused because they believed the devices would record their conversations. Kevin compares the job to detective work: gather enough evidence before you name the suspect. ## Ventilation before insulation Asked whether ventilation is key before fitting anything to a wall, Kevin says it is, and that people miss it. They want to insulate and have not thought about ventilating first. Aaron’s way of putting it is that a wall treatment fixes the wall it is stuck to. It does not fix the reason moisture levels in the property are high, which comes from ventilation, heating patterns and how the home is lived in. The case they then discuss is the one where ventilation has been dealt with and one wall is still cold enough to reach the dew point. ## What Isotherm is, and where it should not go Kevin describes Isotherm as a multi-fibre material, bonded with polymer, that is permeable on both faces and has a waterproofing membrane in the middle. It goes onto a waterproof adhesive and is then skimmed. He admits he did not want to sell it when it was first shown to him, and changed his mind once he had skimmed onto it himself. He sees it as suited to repairs under Awaab’s Law, where the work has to be done within a short period. The pair note that in England the law currently applies to social landlords and not to private ones, which frustrates Aaron. The older method is to hack the plaster off, which means noise, dust and sometimes moving people out. Where the plaster is sound and not heavily salted, Kevin says the membrane can go over it. The damp itself still has to be stopped at source first. Asked where it cannot be used, Kevin says it is not for heavily salted walls, delaminating plaster or wet walls, and it is not a waterproofing product. It has been used on cold concrete ceilings and behind kitchen units, where the pair say condensation is common. Any mould has to be dealt with safely first, and the membrane always has to be skimmed. On two common questions Kevin gives short answers. It will not improve an EPC rating, because its insulation value is too low to count. And he puts the risk of interstitial condensation as very small, because the membrane is fully bedded with no gap behind it, unlike boards fixed on studs or dabs. ## Fitting it properly Most of the problems Kevin sees are about adhesive. It should be spread with a notched trowel so that the wall is visible between the ridges. Too much, and it squeezes out at the edges and into the joint with the next piece, where it becomes a cold bridge. Edges should be cleaned off and the pieces butted tightly together. He says used this way one tub of adhesive covers one roll, which is the complaint he hears most. Other practical points from the conversation: - Cut with a straight edge, and use the offcuts. Kevin says there is almost no waste as long as the joints are tight. - If a piece from the middle of the roll will not lie flat, a light spray of water on the back relaxes it. - It does not bend round an internal corner. Trim it tight into the corner, then return a narrow strip onto the adjoining wall and feather it in. Aaron says he has seen mould form down that edge where this was skipped. A thermal paint is the other option Kevin mentions. - At sockets, take the faceplate off with proper care for electrical safety, cut round the box, skim, then refit. - You can screw through it. If you are worried, a little sealant in the hole is enough. - In window reveals its thinness helps. Aaron says blinds often do not need changing and less light is lost than with insulated board. - Square skirting boards can be butted up to. With a lamb’s tongue or pencil round profile, Kevin says the skirting board has to come off and be set back on afterwards. - Matt paint can be gone over. Silk paint needs the shine sanded off and the dust wiped away. Wallpaper has to come off. Where the membrane stops part-way up a wall, Kevin says a decent plasterer can feather the skim in so the step cannot be seen. He also says a newer adhesive lets the skim go on the same day most of the time, though a cold, empty property will take longer. ## Basements and bad workmanship The conversation touches on basements more briefly. Kevin says Mapei can specify and supply all three types of below-ground waterproofing, and mentions resin injection for sealing a leaking construction joint in a concrete basement, and fast-setting screeds. He explains that the first question to ask is what the space is going to be used for, because in a habitable space no water ingress or dampness is acceptable. Both have stories of poor work. Kevin has seen cavity drain membrane fitted back to front, with the studs facing into the room when they should face the wall, and a damp-proofing injection drilled from the inside right through a cavity. Aaron notes that a tanking product is only as good as what it is applied to, so painted brickwork has to be taken back before anything goes on. Kevin’s line is that education is the best policy, and that if you see work being done incorrectly you should say something and call it out. ## A job timed around a routine Kevin’s favourite job with the product was in a home where a teenager found change very hard. Once a week he went to a sensory class. The team arrived after he left, fitted the membrane, skimmed the room and were gone before he came home. No dust, no days of disruption. ## Who should listen Homeowners and tenants who have been told they have rising damp and want to know what a proper survey should involve. Landlords and housing teams who need damp repairs done with as little disruption as possible. Contractors and plasterers who fit, or are thinking of fitting, a thin thermal membrane and want the practical detail. ## Questions this episode answers ### Can a moisture meter tell you what is causing damp? No, not on its own. Aaron says the meters are really conductivity meters, better at telling you what is dry than what is wet, and Kevin adds that condensation on a wall can produce a very high reading. A reading tells you something is going on, and the rest of the survey has to say what. ### What should a damp survey look at? The outside of the building first, then the inside. Kevin Topping looks at gutters and downpipes, the brickwork and mortar, signs of cavity wall insulation or new wall ties, and whether the damp-proof course has been bridged. Indoors the pair use their senses, ask the occupier questions, measure humidity and temperature, and use a thermal imaging camera to find cold spots. ### What questions will a damp surveyor ask me? When you first noticed it, whether it appears anywhere else, and whether it comes and goes at certain times of day. Kevin says a patch that is there first thing in the morning and gone a couple of hours later points towards condensation. Aaron says he asks a great many questions on every survey, because a visit is only a snapshot of how the home is lived in. ### Is mould at the bottom of a wall always rising damp? No. Aaron describes a survey where a homeowner had been told they had rising damp and had been quoted for a damp-proof course. The cause was a downpipe that ended above the drain and soaked the wall. The pair also mention a first-floor bedroom that had been diagnosed with rising damp. ### Can you diagnose damp from a photo or a video? Not reliably. Aaron says nobody can look at a clip of a patch on a wall, with no view of the outside, and say what it is, because so many of the factors cannot be seen without being on site. ### Should I ventilate before I insulate? Yes, according to the episode. Kevin says people want to insulate and have not thought about ventilating first. The pair explain that insulating a cold wall treats that wall, and does not fix the reason there is too much moisture in the home, which comes down to ventilation, heating and how the home is used. ### What is Isotherm? Isotherm is a thin thermal membrane made by Mapei, the company Kevin Topping works for. He describes it as a multi-fibre material bonded with polymer, permeable on both faces, with a waterproofing membrane in the middle. It is bedded onto a waterproof adhesive and then skimmed, and its job is to lift the surface of a cold wall above the dew point. ### Where can Isotherm not be used? On heavily salted walls, on plaster that is delaminating and on wet walls. Kevin says it is a damp-proofing product and not a waterproofing one, so it is not the answer for a wall below ground. He also says it is only as strong as the surface it is stuck to, so wallpaper has to come off and silk paint needs sanding to a dull finish first. ### Does Isotherm have to be skimmed with plaster? Yes. Asked whether it could be left bare behind kitchen units, where nobody sees it, Kevin says no: it has to be skimmed, because the skim is part of how the finished wall gets its fire rating. ### Does Isotherm cause interstitial condensation? Kevin says the risk is very small, provided it is fitted properly. Because the membrane is fully bedded into the adhesive, there is no gap behind it. He contrasts that with insulated plasterboard on studs or dabs, where a gap is left between the board and the cold wall. ### Will Isotherm improve my EPC rating? No. Kevin answers this directly in the episode: its insulation value is too low to be counted in an EPC rating. He says it will not match rigid insulation boards, and that what it does is raise the wall surface enough to stop it reaching the dew point. ### Who is Kevin Topping? Kevin Topping works for Mapei. In the episode he explains how he went from driving a lorry for a builders' merchant, through sales and distribution, into damp-proofing and waterproofing. He now looks after a regional team, still goes out on site, and trains contractors and housing providers to fit Isotherm. ## Go deeper [Damp and Mould](https://www.thehealthyhousepodcast.co.uk/topics/damp-and-mould)[Condensation and Ventilation](https://www.thehealthyhousepodcast.co.uk/topics/condensation-and-ventilation) ## Share this episode [Share on LinkedIn](https://www.linkedin.com/sharing/share-offsite/?url=https%3A%2F%2Fwww.thehealthyhousepodcast.co.uk%2Fepisodes%2Feducation-is-the-best-solution-to-a-healthier-home)[Share on WhatsApp](https://wa.me/?text=Education%20is%20the%20Best%20Solution%20to%20a%20Healthier%20Home%20%E2%80%94%20The%20Healthy%20House%20Podcast%20https%3A%2F%2Fwww.thehealthyhousepodcast.co.uk%2Fepisodes%2Feducation-is-the-best-solution-to-a-healthier-home)[Email a link](mailto:?subject=Education%20is%20the%20Best%20Solution%20to%20a%20Healthier%20Home%20%E2%80%94%20The%20Healthy%20House%20Podcast&body=https%3A%2F%2Fwww.thehealthyhousepodcast.co.uk%2Fepisodes%2Feducation-is-the-best-solution-to-a-healthier-home) ### Follow the show - - - - - -