We are renovating a double brick house c. 1900. The house had severe water ingress when we bought it - we thought mainly rising damp and ingress round windows. We've dug out floors and poured concrete and tanked external walls up to 1m. Have stripped off all plaster and were about to instal Gyproc Thermaline insulated plasterboard internally. However, during the heavy rain of the last week, rain has penetrated the front wall. This is not just through mortar joints but also through decayed bricks. We have thought of rendering the internal face of the external walls but are now wondering if we should bite the bullet and render externally. Should we do this and if so what mix should we use? We are doing our best to be green (solar panels, GSHP, renewable insulation where we can) but are struggling with some aspects.

I have grappled with these problems for 40 years. Many bricks are like a sponge, eventually they become saturated in wet windy weather. Without a cavity, a cure is difficult. Render can help, but it needs to have a very rough surface and be unpainted - certainly not a hard smooth waterproof cement beloved by builders. The theory is that a rough render / pebbledash acts like a towel - soaks uo the rain and then dries out quickly due to its rough surface (ie = enlarged surface area).

An ideal solution is traditional slate hanging with Welsh slate - can look attractive in certain situations. There may be problems of details to consider around doors and windows.

If you are using a dot and dab drylining system, there might be a long term problem if the adhesive is affected by damp (check on that point) Otherwise it may be a good solution.

Cost-wise the dryling system will be attrative, but you need to construct on the assumption that the inside of the brick walls will be fairly damp, particularly as it will no longer benefit from the drying warmth of your heating system.