Breathable 'sealant' for exposed brickwork (interior)

When I finally strip the 70s wallpaper out of my house, and all the hollow sounding lime plaster behind falls off, I'm considering leaving a few brick walls exposed.

Reading up on it, most people doing this then 'seal' the brick walls to make them wipeable and to stop excess dust.

I'm wondering if anyone on here's done this, and what they used. Is there a breathable solution?

The expert in this article advocates 'Watco’s Wallseal'...
http://www.telegraph.co.uk/finance/property/advice/8773885/How-to-treat-crumbling-brickwork.html
...but it looks a bit harsh to my eyes and nowhere in the spec does it mention it's breathable!:
http://www.watco.co.uk/watco-wallseal.html

Any other ideas?

smartseal or stormdry seem to fit the bill

I have read that isinglass, otherwise known as water glass or sodium silicate, makes a breathable surface sealant. It's the stuff your granny used to use to preserve eggs.

http://www.amazon.co.uk/500ml-Water-Sodium-silicate-liquid/dp/B00BVZ66JC

I can't confirm this from personal experience.

Sodium silicate does things to lime, too - changes it from calcium carbonate to calcium silicate. That's the basis of Beeck, as used on Fachwerkhäuser in Germany (and on the lime plinth on my house).

Beeck reckon 25 years life for their treatment (how long for a coat of limewash?), but I know houses in Germany that haven't been painted in living memory and are still in good condition.

Sadly, it's not as simple as "just paint it on", and don't get it on the windows.

BTW I'm not sure if isinglass is the same as waterglass, which is the traditional name for sodium silicate.

Having looked more carefully into the definition of isinglass, I think Keith is probably right - it's not exactly the same as water glass. My mum used to use the two terms interchangeably, when she was preserving eggs, so I always thought they were the same stuff. However, while water glass is specifically sodium silicate, it seems that isinglass is a more general term for hydrous silicates of various minerals.

My comments above referred specifically to water glass.

Keithj said:

Sadly, it's not as simple as "just paint it on" . . .

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Can you elaborate on that Keith? I was thinking about Beeck for painting our plinth.

The details come with the Beeck'sche Farbe instructions (which I've filed in a too-safe place), but it goes something like this:

- The carbonated lime has a "skin" on it (which the Germans call "sinter"). That has to be removed before you can add silicate. That's done by a brief dose of acid, which eats off the skin, and is then neutralised after a few seconds and rinsed off.
- There is then an "undercoat" of fluid A, which I think is neat potassium silicate solution, but the tin doesn't say.
- ... and some more coats of fluid A, with a time interval between to allow the reaction to happen.
- Finally, a coat of the coloured stuff (fluid B) on top, to set the chosen hue.
- Further coats of fluid B should you feel the need.

The catch is that you mustn't stop part-way through any of the coats. Once you've started, you have to finish - and you can't do "patch repairs". That wasn't a problem with my plinth, because I could do a complete run in half an hour or so. Likewise not a problem with lime that's in smallish panels. I wouldn't want to try to do a large wall in one go.

I'll see if I can find anything online. The German may be easier to find, wenn Du die Sprache verstehst

Here, if the link works is a PDF with an explanation.

... and here's a description of the process.

While it's a bit of a faff, it took me an hour or so on two successive evenings to "do" our plinth, and I'm very happy with the results.

waterglass or sodium silicate is not permeable. I would suggest that it is not used for work in historic buildings. however, it is fine to use fro concrete consolidation etc................ just stick to the use of traditional materials that are tried and tested.

Beeck is potassium silicate, not sodium silicate, and their literature stresses that it has "low resistance to water vapour diffusion".

Read, for example what Cornish Lime say about Beeck.

It would be advisable to ask the relevant Conservation Officer's opinion, but I've not heard anything adverse about it.

I have looked into this, believe me. I would only use limewash.

FKA will know 100% more about this than I do!

I've looked into it too! So have thousands of folks in Germany living in Fachwerkhäuser, almost all of whom use Beeck. I trust Cornish Lime's opinion (and, indeed, that of others I consulted).

For the walls of our house, I've chosen to use limewash. For the plinth, that wasn't going to work with all the rain and such splashing over it, and Beeck has been excellent.

10 years or so ago, numerous suppliers were advising that hydraulic lime was the best thing to use .................... and now its almost a 360o spin on that - my point being, one shouldn't always believe what is being stated by the supplier. Thats all I have to say.

Indeed, and I'm as wary as the next man, having had to deal with some seriously damp churches (now mostly fixed) and a seriously damaged house (now fixed).

But Beeck have been around since 1890, and I hear only good things from those who use their product. For the OP's requirement, it may be just the job. For those who don't want to use it, there's no compulsion.

Thanks for digging out that info Keith - and the interesting discussion!

I wouldn't be thinking about Beeck (or similar) if I could obtain black limewash - I just want to match the pre-existing black painted 'plinth' around our house (it's not actually all plinth as some of the walls are solid brick or chalk - only part of the house is timber frame).

In strict historical terms, what was the traditional treatment for the lower part of walls or a true plinth anyway? I can't imagine it was bitumous paint in 1550, so perhaps limewash down to the ground is the truly traditional treatment?

Alternatively, I've read that limewash can be coloured to a quite deep grey - has anyone any experience of such a drastic coloration? Presumably it requires a great deal of pigment - would this affect breathability.

And just one more thought . . . In a true plinth situation, I.e. a few courses a brick standing clear of the ground on which a sole plate is located, how important is breathability anyway? Especially if the inner face of the plinth is completely untreated and exposed to the air underneath a suspended floor with good ventilation, allowing any moisture in the plinth to disperse on the inner side if prevented by an impermeable coating outside?

Way back I don't think it would have been painted, just left with the bricks or stones showing so I suspect the victorians invented black plinths. My medieval plinth is rudimentary flints and shows no sign of paint

Black limewash is not feasible. You would need so much pigment that the lime becomes irrelevant

I discussed the plinth with the chap who did the lime work on the house - a respected local lime expert. The plinth was done in NHL. He said it was essential to treat it with something, and warned that limewash would need re-doing quite often in that location. He'd heard of Beeck and of Keim but had not used them (he didn't do limewashing either - he recommended others for that). The bottoms of the brick and concrete 1940s parts of the house are jet black, probably some modern masonry paint. They wash down well, so we've not done any more to those, but we wanted black if possible to match them.

I did some phoning around, and found one local firm that could produce dark grey limewash, but not black. They didn't mention any breathability concerns. The same firm suggested Beeck, which was when I did the research. I spoke to Beeck in Germany, and their friendly staff told me the history of the company and explained what the product is and how it works (it reminded me of O-Level chemistry). I then spoke to Cornish Lime, who were equally helpful and confirmed they can do "black black". That, in Beeck, is what we have. We've subsequently looked at similar houses in Germany: most were treated with Beeck or Keim. Beeck is the older and better known firm (at least where we were). Although Beeck recommend 25 years between applications, I gained the impression that it will last a lot longer.

Our plinth is at the bottom of a low brick wall, which sits on the earth where the sole plate used to be. The new sole plate is higher, reflecting the fact that the bottoms of the studs had also rotted and had to be cut back. The outside shows as brick, the inside is lime rendered under the sole plate to match the finish above. The interior lime has had many coats of limewash, and looks absolutely fine. The plinth helps keep the water out; there is slate in there as part of the water exclusion effort. There is a French drain alongside that (where there used to be a concrete path all the way round) It works well. Where damp meter readings showed red on the sole plates inside when we moved in, they now show nil.

In terms of what's normal for a plinth: our local church is 12th century Grade I, and a good mixture of all sorts. Some of the walls are stone, some are flint and lime, some are brick, some are lime over who knows what, and so on. Some parts of that suffered the inevitable modern "waterproof paint" which has now been removed. Where the walls needed repair, we used stone or lime as appropriate and treated the lime with limewash (plenty of coats), but in many places the original lime remains untreated. It's discoloured in some areas to a selection of hues, probably vegetable in origin. I don't think it was black (or even dark grey) until the modern waterproof nonsense was added. I suspect there was limewash there, but the DAC and the architect don't think any treatment is needed so we aren't doing any.

Our house doesn't have any suspended floors downstairs - it's all oak or tiles on earth. It's a pair of 15th/16th century farm workers cottages with no frills, with some Victorian and 1940s additions (and our 2011 garden room). The outside and inside are breathable (now). There is no DPM and no sign of damp in the floors.

Black plinths arrived with coal tar as a by product of gas during the mid C19th; prior to this plinths were limewashed with the rest of the walling. Coal tar is - surprisingly - vapour permeable once it has dried and turned matt. Mistakenly, people redo the plinth in bitumen/synthaproof/blackjack thinking that all 'tar' is the same thing. It is crucial that this lower section of walling is as vapour permeable as possible, more specially when it is flint - which is 98% silica and therefore not permeable - so a non hydraulic mortar here is the best option for above ground work. Shaded north walls could well require the use of non hydraulic mortar with the addition of brick dust/small pieces of brick as a pozzolanic addition - this makes the mortar slightly hydraulic, although this is not the same as using a hydraulic quicklime. Several years ago, research stated that all mortars were hydraulic, although the testing did not factor in the fact that aggregates were not cleaned like they are now and that lime was usually contaminated with material from the lime kiln. I have found also that a fair number of buildings up until the mid C18th used earth mortars for core work with lime reserved for outer facework. I know that I am going slightly off topic, but it needs to be appreciated that historic mortars were far weaker than those 'conservation' mortars that are used today.

formerly known as said:

a fair number of buildings up until the mid C18th used earth mortars for core work

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FKA - would it be fair to suggest that an "earth mortar" is in fact mud?