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Damp Proofing

Penetrating damp on rendered gable end wall in Victorian end of terrace

Anonymous user 21 February 2014 - 9.54 AM

Hi, We are having an issue with damp patches appearing on internal walls of our Victorian end of terrace house. The exterior wall is rendered in what appears to be concrete (browney-sand coloured) which when tapped doesn’t appear to be blown. The patches started in an upstairs bedroom about mid-height on the wall and with the recent rainy weather have spread to cover most areas of this wall. The patches are a tan/brown colour and in some places there is black mould or white fluffy areas (plaster salts?). The damp is now starting to show at ceiling level at the room directly below on the ground floor with the same brown-ey patches. We’ve had several “damp specialists” round who don’t seem to want to deal with the work upstairs and will only do a damp proof course. Only one person who has been out to survey the area has made a suggestion which was to use thermal boarding on the interior wall and re-plaster it then paint the outside render. If we went ahead with this would this actually solve the problem? Surely the damp would still come through but we would no longer see it? As there are floor joists in this wall, is there any chance that these may become damaged from the dampness in the wall? Could anyone give us some pointers on what the issue may be? Thanks in advance for your help.

5 answers from MyBuilder tradespeople

Best answer
ADR Property Maintenance
Rating: 5 out of 55586 reviews

the problem is you live in a solid wall building constructed with lime mortar, lime mortar allows your walls to breathe, it has been rendered with a cement render this stops your walls breathing, the only way to alleviate the problem is to remove the render, re-point the brickwork with lime mortar and if necessary re-render with lime render this will allow any moisture in the structure of the building to escape, anything else is only covering the problem up which will come back twice as bad as before. as you are suffering from penetrating damp, a damp proof course is a total waste of money, that is why it never works in this type of property. most modern damp proofing is designed to cover up the issues rather than solve them. you want a specialist who deals in older properties and how the materials used work. there is no cement or additives in lime mortar or render anybody who tells you different don't touch with a barge pole. it is natural hydraulic lime, sand and aggregates, it is not hydrated lime and builders sand which can be purchased from most builders merchants but requires cement added to go of. lime mortar/render can not be used at this time of the year as the outside temperature does not remain stable enough. it is a spring summer job. all the materials required to carry out your repairs are still available although they are a lot more expensive than modern materials, finding someone who is able to use them correctly maybe a tad harder to find. should you require any further information just ask. good luck alex


21 February 2014



Anonymous user

I agree with ADR , this problem needs addressing from the outside . The sand cement render has bin put on in an attempt to cure this problem in the past . The render becomes porous in time and hairline cracks appear . Old bricks become like sponges and hold the moisture and the render keeps the moisture in . Modern external insulation and polymer renders can be used but are far more expensive and not always suitable for the building ! It's taken a long time for the trade to come full circle and realise that these old buildings stayed warm and dry due to methods of construction and materials used at the time of construction ! Removal of the sand cement render , repairing of cracks and obvious problems and then a traditional lime render , applied by someone who knows how to use it , is by far the best and cheapest option ! Let your house breath and it will love you for it !


31 January 2015


Rating: 4.7 out of 54.7514 reviews

Scaffold up,Cover windows,protect boiler flue,Make a pencil line (if semi detached)Diamond disc grinder cut 10-15mm deep to devide neighbour property and so make straight line will be easier to chip off render.Remove render with sds power breaker tool back to bricks.Tidy up,brush down all dust,Spray or Paint undercoat primer PVA or SBR diluted with water.Allow dry.Repair cracks on brick if any with stichings insertion or galvanized mesh.Spray or Paint twice with KA Dampproofing sllury.Fit 50mm Insulated render composite system on top of the pre-treated wall,Upvc corners,reinforced mesh between two base coats, and primer again under top coat essential. Final top coat should be finished with Silicone thin render typical structure 1.5mm thin .Premixed in colour of your choice in 25kg buckets.If installed corectly Guaranteed 25years no paint needed Breathable,no mould,no cracks,no algue, .Jet wash clean from 1m distance.Always like new..Do not spent for rising damp injections until not rising 1meter up from ground should be visible or check with damp meter for moisture levels.From inside do the same.could use 30mm Insulation boards.EPS 70F graphite thermal conductivity of 0.032 K/w. Inside can be finished to smooth multi finishand paint or silicone render suitable for interior too grainy structure.To hang pictures,mirror etc special plugs must be used.If you want to solve your damp problems once forewer this is the solution.Do not leave "just paint outside render" this would be investment to nothing.Enjoy rather summer holiday.Insulated plasterboard is also solution but brick wall must be treated first with KA Dampproofing sllury and skirting must be removed.Good luck.


25 January 2015


Hyndburn Roofing and Gutter Repairs
Rating: 5 out of 555157 reviews

The answer from ADR is spot on regarding treatment and is the way to go. In addition to removing the rendering and re-pointing with lime mortar, I would stress that the initial source of your water ingress is identified and explained logically to you so that you can understand the fuller picture and are confident with the proposed treatment. We specialise in problems associated with penetrating damp and I would like to make the following observations: Although the rendering is holding the moisture within the property and will allow condensation - since a damp wall is a cold wall - given your information that the problem started high up and has spread downwards, I would be looking for a cause at a high level. You also mention that there are floor joists in this wall – so it is imperative that the problem is correctly identified and rectified . It may be that the rendering is cracked or ineffective further up which could be the explanation. In which case, all well and good. However, as a safeguard, since it is a gable, I would prefer to carry out further checks. In particular, that there is sufficient overhang of the slates so that rainwater is not seeping behind the rendering. This is a common mistake that we come across as the roofs were not designed to accommodate the extra layers of render. If this is the case then the problem could be alleviated when the rendering is removed but it is worth checking that the slates have sufficient overhang and are all in order. Similarly for the end ridge tile. Otherwise water could still penetrate behind the rendering / pointing Other considerations (part of my checklist) could be: Is there a chimney on the gable and is it in order? Are there any vents and are they fitted correctly? (We have come across some that have been fitted upside down!) Being a gable - are the rainwater goods in order - gutter, downspout? Are there any windows? And if so, are they free from defects? It is also important to check the condition of the floor joists within the building to assess whether there has been any deterioration and whether treatment is needed Rendering became a fashion just like painting stonework / brickwork on houses. Combine this with modern ‘improvements’ such as upvc windows/ doors, cavity insulation and other draught proofing methods and the houses are likely to suffer from excessive moisture with the byproducts of condensation, mould, timber rots and infestation, and a consequent deterioration in the fabric of the building. Regards, Chris


8 December 2019


Dovedale Dampcure Services Ltd
Dovedale Dampcure Services Ltd
Rating: 4.9 out of 54.9546 reviews

Absolutely agree with ADR sand and cement render will not allow a building to breathe especially on a gable end as described as this will have a lower dew point than the other walls and will this be more prone to dampness (condensative). Best practice is to repoint using hydrated lime after removal of existing render.


8 September 2018