A decade of damp

The garden flat 2003

Our paths first crossed with damp during the purchase of a lovely garden flat in Cotham in 2003. It didn’t feel damp to us but the survey assured us it was, ‘rising damp’ probably, and our mortgage was allowed on the condition that we treated it. Quotes were duly sought and a firm was appointed to hack the plaster off to a certain height, inject it with some chemical, and then replaster. That was pretty much the end of the affair.

The small terrace 2008

Damp turned up again some years later in our next home, a turn of the century half-end terrace on St Andrews road. I say half-end terrace as it stuck a bit where the terrace ended but had later been extended in a different style, along in a different set back line. This time it was that other kind of damp I sort of knew about, ‘penetrating damp’. The part of the side wall that stuck out was the problem. There were cracks in the cement render and these were letting damp in it seemed. The wall inside felt damp and the plaster felt loose behind the wallpaper. We were looking to sell so it became an important thing to sort out. Quotes were duly sought and a lovely builder appointed to re-render and paint the area, about 12 m2. It looked great. The house sold fine and the fact we had done the wall helped the buyers feel better about the damp they found on the inside wall. Recently, however, about five years after the job, we have noticed that cracks appeared again and the current owners are doing what seems to be the same work again.

The old Georgian end terrace 2010

We moved and again bought another odd half-end of terrace (!) that stuck out from the street line. And again it has been this area of the house that has been problematic for us in terms of damp. There were cracks in the external cement render again and to start with we suspected this was the sole reason that some of the walls on that side of the house were damp, salt crystals were coming through the plaster, and paint we put on was coming off.

But different things were happening on different levels. On the top floor, there were layers and layers of moisture block paint and the walls were dry to touch. On the middle floor, it was damp to touch with lots of salt crystals and peeling paint. On the ground floor, it was a bit damp to the touch and more peeling paint but less severe than the middle floor.

We suspected that the moisture blocks out measures on the top floor were pushing the damp down into the middle floor, given the worst bits were at the ceiling and top half and it got less bad as it reached the floor. So the layers of paint, plaster and cement render were removed on the top floor, revealing extremely damp walls. The stones left to dry for a bit before attaching some new plasterboard to plywood that was in turn attached to wooden baton strips fixed to the wall, thereby leaving a cavity for the wall to continue to dry and for moist air to evaporate into the roof space. We figured that if the moisture was getting in through the external render and we couldn’t afford that massive job, then let it in but just make sure it can get out again. It was a pragmatic solution arrived at by our builder and Simon discussing options and it has seemed to work well

Next came the middle floor and again we removed layers of vinyl paint, wallpaper, plaster and lots of lovely lime render mixed with horse hair. It was like an archaeological dig and you didn’t know what was coming next. Revealing the stonework, again the wall was very damp, dark and wetter higher up, and lighter as it came down. The muddy mortar between the stones was absolutely sodden and months later, drilling holes deep into the wall for the wooden dochans we used as part of the hemp and lime render technique, it was still soaking wet. It seemed that as well as the damp coming from above where the walls couldn’t breathe, and no doubt some damp coming in from the cracks in the external render, internal condensation had been a major factor. This was a cold, north facing corner that juts out in the street and catches the wind, so any moist air in the house is going to rise and condense in cold corners like this. The fact that we were also using the room to dry laundry no doubt had not helped.


The hemp and lime technique has been well documented elsewhere but essentially it has made the room ‘feels cosier’, in my wife’s words. It is hard to pin down but there is a sense of warmth and a sort of yielding strength about that wall now. In any case, being both insulated and breathable, it should act to eliminate any condensation problems and counter any penetrating damp problems, and we look forward to re-decorating soon and hopefully for the last time in a while!

– Ben Bywater


This Georgian end terrace changed hands in 2016 and the new owners took things further. More information below.


Case Studies

Baumit RK38 base coat Lime plaster on Hemp and Lime internal wall insulation

This cold damp corner is under repeated attack from both external and internal weather. What looked like moisture getting in, turned out to be moisture trying to get out. Remediation reinstates the moisture buffering capacity using Hemp Lime.



The external typography, local weather and cutting corners during the original construction has made this a cold corner. This end of terrace doesn’t follow the building line of the street, the prevailing wind is funnelled onto the north-west corner.



Repeated attempts have been made with external render coats to stop moisture getting in. It seems plausible that water must be getting in through the cracks in the render and a costly proposal to remove and re-render has been prescribed. Water penetration has been misdiagnosed

Without quoin stones running up the corner it is colder and less able to evaporate the moisture condensing on the inside. Meanwhile internally the limestone walls have been plastered with hydraulic mortar, breathable but very little capacity. Moisture vapour is passing through and then dropping out behind the vinyl paint, the low capacity lime plaster soon becomes saturated.



Removing the exterior cement render will be costly and complex, a pragmatic approach is to mitigate the problem internally with a Hygroscopic capacity. Inside, cement render, vinyl paint, PVA and ‘damp stopper’ is removed to rectify the damaged decoration. Internal doors will be operated to prevent moisture migrating from the kitchen and drying laundry internal will be reduced.



No specialist tools or equipment is required, just no-cost and low-cost knowledge-led renovation.



Pegged out with ‘Dochans’ a true, flat level surface is reinstated more affordable casting with Hemp and lime.



Different thicknesses don’t cause moisture drop-out problems unlike Gypsum plaster or Lime render.



The shuttering is quickly filled with the correct density of Hemp and Lime, the shuttering can be stuck off and moved up straight away.



Now we’re off the ground the boxes of Hemp and Lime are hung from the shuttering using ‘S’ shaped kitchen hooks, speeding installation and catching any overspill.



Satisfyingly simple.



Tea break and time to step up a level.



Shuttering moves up quickly.



Approaching the top and problems are solved instinctively as a team.



Live risk assessment mitigates an improvised scaffold in preference to working on a ladder.



Working as a team momentum builds, problems are solved, knowledge is exchanged and with understanding comes cooperation.



The wall is completed in one sociable Saturday afternoon with friends and neighbours dropping in to have a go.


Baumit RK38 base coat Lime plaster on Hemp and Lime internal wall insulation

Lime plastered and then wallpaper.


This Georgian end terrace changed hands in 2016 and the new owners took things further.

A warm and cosy family home

Early adopters looking for a more sympathetic approach to insulating our heritage housing stock with support from Joseph Little Dublin Institute Technology and Bristol City Council Principle Historic Environment Officer.

A warm and cosy family home

Jess Walker

Two areas of damp in the kitchen were both sitting on either side of the kitchen door.

One of the main reasons for this were some cold air draughts coming in through holes in the kitchen wall. How can there be holes in the kitchen wall? They were hidden behind the fridge and washing machine. The first was a large one, left in place from a previous tumble drier and half-heartedly filled with rags by a previous owner. The others were left over from the current and previous waste pipes of the kitchen sink.

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