waterproof brick coating

Good morning all, We have just bought an old cottage with a cement render that is shot,it is cracked and very porous and is causing damp patches in the living areas as it is trapping water between it and the very soft bricks,as it is single course the water is just soaking through the bricks.We have decided to have all this render removes and we can then examine the brickwork to decide if we can have it all pointed up ,or as we suspect previous alterations have left a legacy of ismatched bricks and blocks,in which case we will have it all re rendered,when the existing render is removed and the brickwork dries out what is the best liquid waterproofer we can apply before it is re rendered?many thanks for your help,Bob
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On Thu, 16 Aug 2012 02:17:33 -0700, bob wrote:

I would think you would be very well advised to look at external insulation before rendering. And then a proper damp proof membrane can be install between the insulation and the brick. You can probably get a grant for much of the extra cost.
TOF.
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TheOldFellow wrote:

Yes, that might well work.
thinking about what was done here to a timber frame, something like nailing vertical battens over a breathable DPM to the walls, infilling with celotex, and then horizontals with more infilling then vertical battens and a metal lathe rendered over..
Of course that might make the roof not fit :-)

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It would be mad to not insulate it. VB goes on the warm side of the insulation, no liquid waterproofer then needed.
NT
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bob wrote:

Don't apply anything to the brickwork, the waterproofing goes in the render, if you waterproof the brickwork first, it won't stick
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On Thursday, August 16, 2012 10:17:33 AM UTC+1, bob wrote:

The wall was probably saturated because it was rendered. Water vapour from inside migrates through the wall. When it hits the cold outer surface, in winter, the vapour condenses into water. It usually evaporates, . If the wall is rendered, it can't pass through the cement render and can't evaporate. It accumulates in the brickwork. Look up 'interstitial condensation'.
You paint on waterproof crap, the same thing will happen. It's like putting on a waterproof coat when it's raining; you end up saturated in your own sweat because it can't evaporate. I don't think they do Goretx for houses.
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Onetap wrote:

cracked and very porous and is causing damp patches in the living areas as it is trapping water between it and the very soft bricks,as it is single course the water is just soaking through the bricks.We have decided to have all this render removes and we can then examine the brickwork to decide if we can have it all pointed up ,or as we suspect previous alterations have left a legacy of ismatched bricks and blocks,in which case we will have it all re rendered,when the existing render is removed and the brickwork dries out what is the best liquid waterproofer we can apply before it is re rendered?many thanks for your help,Bob

water. It usually evaporates, . If the wall is rendered, it can't pass through the cement render and can't evaporate.

on a waterproof coat when it's raining; you end up saturated in your own sweat because it can't evaporate.

so lacking in actual understanding as to be almost complete twaddle
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wrote:

for once onetap is right However with 4" masonry you do also get rain penetration, it complicates the picture.
NT
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NT wrote:

cracked and very porous and is causing damp patches in the living areas as it is trapping water between it and the very soft bricks,as it is single course the water is just soaking through the bricks.We have decided to have all this render removes and we can then examine the brickwork to decide if we can have it all pointed up ,or as we suspect previous alterations have left a legacy of ismatched bricks and blocks,in which case we will have it all re rendered,when the existing render is removed and the brickwork dries out what is the best liquid waterproofer we can apply before it is re rendered?many thanks for your help,Bob

water. It usually evaporates, . If the wall is rendered, it can't pass through the cement render and can't evaporate.

putting on a waterproof coat when it's raining; you end up saturated in your own sweat because it can't evaporate.

damp is simply a matter of more moisture getting in than getting out.
It is not as simple as saying 'let it get out through porous walls' it is equally as specious to say 'stop it getting in by making walls impermeable'.
You get rid of damp by not letting it in, and breathing or ventilating what is generated inside.
The modern approach is to create an utterly impervious insulated shell and VENTILATE the interior adequately. Th reason is this works BETTER than breathable walls.
All this twaddle about breathable walls arises from not understanding that some older houses stayed dry because they were built like sponges.,. That doesn't make it a good thing to do. It merely highlights the fact that if you coat a sponge house with a plastic mac it will be damp until you arrange proper ventilation.
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wrote:

I do agree with some of what you say, but I think there's more to the subject than you give it credit
NT
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Also, what was relatively waterproof 100 years ago may not be now. The lime mortar in most old houses has degraded to a point where it is little better than sand. I don't know what the chemistry of the degradation is, but the idea that it somehow heals itself doesn't apply to any lime mortar that I'm familiar with
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On Friday, August 17, 2012 2:54:53 PM UTC+1, stuart noble wrote:

I believe the long term change in lime mortar is the lime (calcium hydroxide) turning to calcium carbonate; i.e. the principal constituent of limestone. This squares with some of the old lime mortar I've met with being considerably harder than relatively new mortar. The suggestion I've seen is that weak mortar in old houses is due to the original builders scrimping on materials and not putting enough lime in in the first place - possibly, in damp conditions, aggravated by a certain amount of leaching of the lime before it's converted to carbonate. They may also have used other materials than sand and lime to bulk out the mortar, and what those may do long term is pretty much impossible to predict.
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On 17/08/2012 15:11, snipped-for-privacy@gmail.com wrote:

AIUI the idea with lime mortar is that only the surface is converted to carbonate, and this forms a surface skin to prevent the rest of the mortar being converted. This explains why the mortar survives in Roman buildings with walls 2 feet thick but fails in 9" Victorian walls
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So you dont know therefore you know. Interesting.
NT
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