Tanking is where you apply an impermeable substance to the wall - either internally or externally - to stop penetrating damp. It's most commonly used with structures that are below ground level - in cellars or on walls that are built into the side of a hill, for example.
Ideally you want to do the tanking externally, but that isn't always possible.
Steer clear of any DIY stuff - you can get all sorts of bitumen-based paints and the like from stores, but they're all pretty useless. Ideally you need a sealed membrane or a proper waterproof render, and the usual materials used are Vandex and Newton 500, both of which will effectively seal the walls against water penetration.
Thanks all for your appreciation, and appologies to Armchair for temporarily hijacking his thread
Armchair
Joined: 14 Jan 2007 Posts: 205 Location: Winchester
Posted: Thu Jun 07, 07 8:54 pm Post subject:
Barnie wrote:
Thanks all for your appreciation, and appologies to Armchair for temporarily hijacking his thread
Not at all Time to ressurect this thread...
I had a couple of damp proofing contractors in and they recommended (surprise surprise) an injected DPC. Now what they weren't aware of, and what I only discovered when chatting to my new neighbour this evening, is that the party walls (where the damp is predominantly found) is made of chalk rubble with brick piers. Probably a rather unusual form of construction but the row of houses is about 100 yards from a railway cutting so my neighbour thinks they used the free building material that was dug up there.
This begs the question, would an injected DPC be of any use and if not, what are the alternatives? Am I better off just leaving things as they are (on the basis that the walls have probably been damp for decades and aside from damaged plaster there don't appear to be any problems)?
Last edited by Armchair on Fri Jun 08, 07 6:37 am; edited 1 time in total
Chemical DPCs only work in bonded brickwork (sometimes!) - they most certainly do not work in rubble stone walls (it's down to something called 'viscous fingering' which means that the chemical takes the line of least resistance). If the contractors still recommend such a course once you've told them what the wall is made from, I would suggest politely showing them the door.
My advice would be to ensure a good air flow and to leave things as they are. Changes in drainage and ventilation are generally far more effective than mechanical treatments.
Armchair
Joined: 14 Jan 2007 Posts: 205 Location: Winchester
Posted: Mon Jun 11, 07 5:14 pm Post subject:
I spoke to both companies this morning and both said that injected DPCs on a rubble/cob wall wasn't going to work.
Company A suggested a quarter inch thick dimpled membrane to full ceiling height with plasterboard internally.
Company B suggested tanking with a cementious plaster!
Neither of these sound appropriate. I think I'll stick with improving underfloor ventilation and plastering with a lime-based plaster.
I think I'll stick with improving underfloor ventilation and plastering with a lime-based plaster.
By far the best option - and the cheapest. It's best to avoid using any cementitious mortar or plaster on rubble or cob - it's not good for it.
Do check all soil levels outside to make sure they're a good six inches below internal floor levels, as well.
Milo
Joined: 16 May 2005 Posts: 342 Location: Oop North-ish.
Joined: 14 Jan 2007 Posts: 205 Location: Winchester
Posted: Thu Jun 14, 07 7:43 am Post subject:
Any ideas on what ratio the plaster needs to be? I've been hunting around on Google for some advice but can't seem to find anything concrete (please excuse the terrible pun).
One part hydrated lime (or lime putty) to three parts sharp sand. If you want a particularly smooth and hard top surface, use 1:1 silver sand and lime as a skim coat.
For more advice on cob, try to find a copy of Jane Schofield's Cob Buildings - A Practical Guide. You should be able to get it from Black Dog Press. Jane herself is hugely knowledgable and helpful, and is also the author of the indispensible Lime in Building - A Practical Guide.
If you're not far from Winchester, make contact with Bob Bennett at The Lime Centre at Morestead.
He runs courses in plastering and rendering and can also supply all the materials you might need. The site also has some useful fact sheets you can download.
Time to ressurect this thread...
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