Damp stone walls: tanking plus lime plaster?

19 Feb 2015
Reaction score
United Kingdom

First time poster on this great forum so be gentle with me and please excuse my ignorance.

Common problem: rising damp through gypsum plaster on 19th century rubble stonework here in beautiful Cornwall. Damp consultant report (who has also quoted for the work) has suggested both vertical DPC plus tanking render AND hydraulic lime plaster (and a roof fitted ventilation system to gently force old air out). At a substantial cost. Bells are ringing...

I thought it was an either/or between tanking and lime plaster, the former effectively waterproofing by diverting water away from the plaster, the latter allowing the water in but to then evaporate gently into the room where appropriate heating and ventilation takes care of it.

If a vertical DPC is installed, then the tanking (2x10mm sand/cement with waterproof additive; 2x1.5mm cementitious tanking compound) then I don't understand what function the 12mm of sand/cement/lime plaster and 3mm limelite would have as a breathable coating.

I've read a LOT of posts here and elsewhere but haven't quite found the answer (although I have seen a lot of Celebrity Grudge Matches between PCA and RICS affiliates ;) ).

I'd appreciate any help. Have I got this wrong? Am I doing the consultant a disservice?

The Grockle
Sponsored Links
The "Damp Consultant" is nothing but a salesman - this week damp & timber, next week double glazing etc.

Independent Damp Consultants such as Graham Coleman (01747 840 715) of Sherborne, Dorset could advise you.

If you post pics of inside and out side the suspect areas then perhaps we can advise you.Why have you had damp issues/inspections? What specific signs or damage?

Presumably the "vertical DPC" referred to is two applications of, say Vandex, and then to remedial render over the second tacky coat.

Keep reading but dont prescribe for yourself.
Many thanks for posting, Ree.

Have since had authoritative advice from the excellent RICS surveyor who did the full survey (Tony Morehen at RTP if anyone needs a firm recomendation).

Apparently it is accepted practice to both tank and use lime plaster, and to the specs I posted. However, an injected DPC (if that's what he meant by vertical DPC) was not considered helpful on rubble walls.
Sponsored Links
I've followed this lime vs tanking debate carefully, I hope and it seems there are proponents of both systems. My personal experiece is a 1800 house (Somerset) made from a very porous stone and lime mortar with various 'repairs' with cement on various parts of the house. One room was bad and it was the interior walls that were worse despite the exterior being cement pointed ontop of lime. Floor had been DPC membraned beneath a shellac wood floor since sanded back and recoated. The solution I chose was 1m from floor tank and replaster and I can say 6years hence I'm very happy with the result. Perhaps it will take long to 'fail' but ther room has been bone dry compared with the 'breathable' corridor outside. Not that it's that bad, just that it gets rising damp in heavy rain (house built on clay). Another area was a gutter problem which kept a wall wet and leaked inside at celing level. Fix gutter, big improvement, and then used a brushed on silcone which I did as an immediate quick repair. This has stop the spalling and the wall gettting wet and as a result I've not bothered following up with further repairs. Several other issues which were dealt with by fixing the roof and soffit/fascias/felt. These were largely cause by that part of ther roof being to shallow for loose roman tiles but hey ho I can't easily make the pitch steeper without huge expense. Current issue is an outbuilding that has damp lime mortar walls which do dry quickly but, if as I do, I want a modern plastered interior then the same issues present. I think I'm going to repoint the exterior wall with lime and then tank the inside. Imho best of both worlds, exterior can breathe, interior can stay dry. Don't worry roof and guttering are sound.

DIYnot Local

Staff member

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local