insulating under wooden floors

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Peter Taylor snipped-for-privacy@DELETETOMAILMEclara.co.uk typed: <SNIP> I would suggest you take a look at

Peter Thanks for a reasoned and informative reply, I initially doubted your motives and understanding (the air brick bit) but yes rising damp has effected the party walls on this house to a height of 1m. You did not make any comment re my other post, regarding my proposed remedial work. If you do have any comments I would be very pleased to hear them.
-- Mark
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Mark wrote

Thanks. And I thought you were one of that vociferous and misguided "there's no such thing as rising damp" brigade! :o)

I can't really make any worthwhile comments in your case without more specific information. If you want to email me this and hopefully send me some pics I will be pleased to help if I can - and (despite what John Rouse said) without charge! In particular I would like to see the quotes you've received so far - 3,000 sounds extremely high.
As I understand it, you are intending to use a membrane system - presumably Newlath 2000 or similar. I have experience of using this in many pub cellars and also the basement of a Vet's surgery in 2001. I'd like to be sure you've made a properly informed decision about it. You hear a lot about injected dpc failures, but in fact the vast majority of installations are very successful. There are many damp-proofing firms I would class as cowboys, but there are also some very reputable, knowledgable and extremely helpful companies too (these would all be members of BWPDA). Also there are various different materials and techniques and choosing the right one is very important - most damp-proofing companies seem to promote only one particular system, which makes you doubt where their interest really lies.
Have you thought about doing the damp-proofing work yourself, or getting your own builder to do it? You won't get a guarantee of course, but is that really a major problem? Getting many firms to admit fault and redo the work is virtually impossible, and if your own job is successful then the lack of a guarantee when you come to sell is not an issue.
If you can get back to me with more information I can help a lot more.
Peter
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IIRC The Building Research Establishment were the ones who said they couldn't get damp to rise in brickwork, so the brigade may have some justification :-)
My own experience of all this suggests that discussion about the porosity of bricks is almost irrelevant given the condition of the mortar between them. In most Victorian houses, replacing it with breadcrumbs would be an improvement. Personally, I replace it with cement mortar, heavily laced with pva and, 20 years on, none of the houses I have worked on has fallen down or shown any signs of degradation in the bricks.
As we've got an expert round the place (for a change) I'd be interested to know to what extent you think modern additives (e.g. SBR) can modify cement mortars for use in old buildings.
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I believe capillary action gets water to rise in bricks. A brick garden wall, generally doesn't have rising damp. Put render and plaster on the side and the moisture may rise. Putting a brick half in water only soaks it to the water level, not above.
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writes

Yes, and in most cases the surface available for evaporation is twice that in contact with the ground.
J.
--
John Rouse

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stuart noble wrote

I'm surprised by that. As far back as 1981 they published BRE Digest 245 "Rising damp in walls: diagnosis and treatment" and it's still current AFAIK. They also publsh Good Repair Guide 6 "Treating rising damp in houses".

I agree totally about the porosity thing. I'm not so sure about using PVA for damp treatment though - that's not something I would have immediately thought of as damp-resistant. Why don't you use a waterproofer additive?

Firstly, please don't hold me out as an any more of an expert than a good number of other folk on this newsgroup. I think we are extremely fortunate to have a wealth of knowledge and experience in many fields. Sadly, we also have a few people who feel they need to pontificate on things they know little about.
I do have personal experience of many aspects of designing and constructing buildings as well as their defects, maintenance and restoration. But, like everybody else, I don't know everything and have to research things when necessary. As far as additives are concerned my knowledge is limited - I have experience of epoxy resin additives for repairing damaged concrete and also fast-curing screeds like Isocrete K with fibre reinforcement. As far as mortars go, I have never used additives other than anti-freeze, plasticisers and waterproofers, and the only use of SBR I know anything about at present is thin latex screeds.
Generally speaking I have a deep distrust of "modern" materials in repair and restoration work on old buildings. Half the time they seem to be by-products of some other manufacturing process, (eg Synthaprufe) or else they are cheap alternatives (bitumen felt v lead sheet roofing), and they never seem to have the same durability as original natural materials. For instance, I cringe when I see adverts for Thompson's Silicon Waterproofer for external walls, as I've seen several houses where the face of the stone or brick has been severely damaged by frost action on moisture retained by this type of coating. I'm not totally against all modern materials though - I used epoxy resin and stainless steel rods to repair some large oak beams at Hampton Court Palace that had been severely damaged by Death Watch Beetle.
Does that answer your question OK?
Peter
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Peter Taylor wrote in message ...

My interest is precisely that, the use of modern materials in restoration. PVA and SBR added to cement mortar gives it extra flexibility which *I* think can make it a good substitute for lime mortar in old buildings. Some water resistance at least.

siloxanes, a kind of rubberised grease. Basically the same stuff used in dpc injection but doesn't work as a surface treatment because it is eventually dislodged by the elements.

sliding sash window that would have ended up in the skip otherwise. Restoration shouldn't just be about stubbornly sticking to traditional materials. And as for that bloody IMM, I applaud his right to comment but I do wish he'd SNIP. Like most idealists he has no real regard for anyone else.
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stuart noble wrote
in message

You may well be right. I have clients to worry about, and I would need to see it in action successfully for a good length of time before I'd be convinced enough to recommend it to them. I'd be interested to hear about any research results you get theough!

I just wish he'd check his facts before he starts an argument, or at least question things in a more polite way.
Peter
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I am not an idealist. I am down to earth pragmatic.

I am the epitome of politeness.
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But a waterproof mortar is doing exactly the opposite of a (fat) lime mortar. If you want the underwater set, then use a hydraulic mortar - they've held many a lighthouse together for several hundred years.
I can't imagine PVA and SBR performing autogenous healing either.
J.
--
John Rouse

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John Rouse wrote in message ...

I can't see that there's too much difference between hydraulic lime mortar and cement mortar. If it sets underwater, it can't then be said to have healing properties. It sets and has total water resistance, end of story.
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I was thinking of a partially hydraulic lime, not an eminently hydraulic one - I don't think too many of us will be building lighthouses!
J.
--
John Rouse

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Indeed current thinking in all bit the least informed circles is that it is a myth. We seem to be the only country in the world to experience the phenomenon - no doubt because we are the only country with a rising damp industry.

Clearly you have not studied Roman buildings, nor mediaeval ones.

Come back in 2000 years time and tell us if they are still standing, the Roman ones are!

Expert!
J.
--
John Rouse

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stuart

I don't think he intends the wall to last 200 years.

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John Rouse wrote in message

Oh, clearly not!! No, I specifically referred to Victorian buildings. I've no doubt that lime mortar works well in certain types of thick walled buildings where it never fully dries. But I know from experience that it is next to useless in the repair/ re-pointing of 9" brickwork, where it is vulnerable to the next downpour. IME most Victorian mortar is a crude form of hydraulic lime where they chucked in handfulls of brick dust, and any other rubbish they had lying around, to achieve a quick set. So, although technically they used lime mortar, I doubt if the real benefits of lime ever existed. Volcanic ash pozzolans were probably far more sophisticated but those classical geysers weren't exactly in a hurry by our standards.
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I really don't know where you get your strange ideas from - not been talking to the RICS have you? A well pointed wall is going to have dry mortar in it - the whole idea is that the moisture can evaporate from both the brick and the mortar.

Then you are mixing it incorrectly. You have to keep it damp whilst curing but once set it will withstand the heaviest of downpours.

They weren't interested in speed. It is unusual to find hydraulic limes in building mortars.

SO that must be why all the pre-war houses have fallen down then.

What have hot-water springs got to do with the topic?
J.
--
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Peter Taylor snipped-for-privacy@DELETETOMAILMEclara.co.uk typed:

Hmm Understandable given my flippant comment ;-(

Briefly;-( I recently bought a property for letting, there is evidence of rising damp along both party walls (on both sides) to a height of 1m, and considerable wet rot to the wall plates and joists were they meet.(But Thank God no dry rot) There is no evidence of an original DPC, the walls themselves are made of a gritty Victorian engineering type brick. I was initiatory going to install a solvent DPC myself but after doing an experiment on one brick injecting 200cc of a silicone water-seal at 40psi 185cc immediately leaked out through the pores of said brick. So I thought I would get some expert advice (sic). Two firms quoted one a small outfit from the local paper, one a large supposedly reputable firm that clam BWPDA and GTP. Both were proposing to inject solvent dpc at skirting level. Nether proposed to make any alteration to underfloor ventilation and when asked about airbricks one said they were too low the other said they were too High. Its also worth noting that both adjoining properties are also suffering dampness their side of the party walls.
Later after removing the floorbouards I realised that the void was completely filled with rubble/bricks and old decaying wood from previous Fixes, this filled a 4m skip. On the first wall that I removed the plaster from the bricks were visibly wet to a height of 1m, now after two weeks drying (and almost 1m between top of skirting level and the very wet sub floor) the wet line is down to .5m. So baring in mind that this property is for letting and a chemical dpc with re-plastering will take months to dry out, im proposing to use either a Newton or Trident membrane.
If you or others don't object ill keep the discussion on here as others may in future benefit from any advice you can offer. Thanks
-- Mark
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Mark wrote

OK but I can't make any sense of it without seeing some photos. A sketch plan would be helpful too. If you can't mail me, can you put anything on a website?
Please answer the following to enable me to picture the house properly:
1 Whereabouts in the country is this? (the county will do). Local construction methods and materials are important.
2 I take it this is a terraced house with external and party walls of solid brickwork about 240mm thick overall, with bare facing bricks (no rendering) outside and plastered inside, and internal walls on ground floor about 140mm thick overall, solid construction with plaster both sides. If not please correct me.
3 Is there a typical Victorian rear addition?
4 Exactly which walls are affected by dampness and which appear to be dry? Can you give any possible explanation why there is dampness in only some of the walls?
5 Is there a physical DPC anywhere at all? Has any chemical dpc or other form of damp-proofing been attempted in any of the walls in the past?
6 What is the external ground level in relation to floor level at front and rear?
7 How deep is the floor void now you've cleared it out? Is the oversite bare earth or is there a surface or any kind?
8 Are there any areas of solid ground floor in the house and where is this in relation to the damp walls?
9 Are you dooing all the work yourslef or do you have a builder?
10 How would you describe the overall condition of the house?
That'll do for starters. I'll have more questions later about the quotations you've received.

That's about normal.

I don't see a problem there. The real problem occurs when the fluid disappears down a void inside the wall which you don't know about.

I still feel a chemical dpc is the best method for you, short of cutting out and installing a physical dpc. It's certainly much cheaper. The membrane system will need to go up to at least ceiling height at ground floor level. It will only hide the dampness and I'm worried there's a risk it might cause it to spread. Also, it is impossible (and nullifies the guarantee) to fix anything to the wall mechanically if you haven't put the fixings in to start with. So you won't be able to put up any shelves or even hang pictures unless you glue them.
There are various other ways to provide a chemical dpc other than fluid injection. There's the gravity system where the fluid infuses into the wall slowly from individual pots, which I've generally found very reliable, and various pastes and gels etc. Also it needn't take months to dry out, and you can plaster straight away if you use Limelight or other renovating plaster.
Come back to me with answers and hopefully a sketch plan.
Peter
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Peter Taylor snipped-for-privacy@DELETETOMAILMEclara.co.uk typed:

Ok Thanks. I'll do a floor plan and take some pictures, and post again with all the info you asked.
-- mark
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typed:

Put a snake down there, Andy will advise.
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