Silocone injection damp proofing effective?

[Jake]

Woodchip - paper.

Yes, it does. I noticed too that the tarmac public pavement running along that wall is above the level of the bottom of an airbrick in that wall.

Jake

[Jake]

It's certainly tempting, except that I wouldn;t know if I could trust 'em to do it right... There's the old adage: "If you want to do it right do it yourself, yes"?

Cheers,

Jake

[raden]

In message , Jake writes

I did

[Jake]

The pavement is the council's. I'm really not sure if that's the cause of the problem though. The rain doesn't settle that badly. But I noticed that it's probably higher than it was when the house was built because it is above the level of the bottom of an airbrick (it doesn't look like a Victorian airbrick, but maybe a 1940's one. I suspect it was installed back in the 1940s to try and cure the problem which had already started way back then. I can't imagine what the council could do to improve the situation.

If the cavity was empty, and deep, I would have expected the damp to stay in the outer skin of the wall. But for all I know, the cavity could be filled up with old mortar that's dropped down from above, etc.

The one thing I am sure of is that the plaser used on the bottom four feet of the interior, is definitely the worst sort that could have been used. It sems to soak up damp like a sponge.

Just outside the affected room, the same wall extends about 9 inches before the front door jamb. That 9" was one of the worst-affected bits. I installed a 9" x 6" terra-cotta air brick just there, and covered it with a white plastic vent-cover, so that it wouldn't stick out like a sore thumb. It certainly did go a long way to curing the problem just there, because the air brick absorbs the damp and lets it evaporate into the air that passes through the air brick. Perhaps I should employ that method all the way around the affected room, installing them every five four feet or so. I think it might work, but it's not the most aesthetic solution. I think rendering the bottom 4 ft of the interior with sand+cement mortar would also be desirable.

Jake

[The Natural Philosopher]

BUT you will get guarantee from them which looks good when selling.

[Jake]

Good point. Thanks for that one.

Jake

[N. Thornton]

1. Understand how these buildings work. 2. Go look at some. 3. Talk to some experts too.

1900 houses are built of very soft very permeable bricks. They usually have no dpc. So water is drawn up the wall through the bricks and mortar. This evaporates from the brick surface, keeping levels of damp below problematic.

Now, if you add a chemical dpc, this water dissipation is considerably hampered, and the bricks below the dpc reach a much higher dampness level. When it freezes, the water expands slightly and the bricks steadily disintegrate. This can be seen on many Vic houses, bricks below injected dpcs disintegrating. Uninjected houses that have been maintained more appropriately do not suffer anything like as much from this problem.

Depends on brick type. Vic bricks were very soft and very porous, ie very easily damaged by too much water content freezing.

Obviuosly, one should consider them all and evaluate them. Some stand up better to scrutiny than others.

if you prise hard cement off brittle slate it tends to break.

I'm not familiar with that, why is it not to be injected?

NT

[N. Thornton]

if all you want to do is sell, a dehumidifier would be cheaper than buiding work.

NT

[N. Thornton]

2 causes of damp right there. You need bare brick at the wall bottom so that damp wicked up can get to evaporate away. Thats how Vic non-dpc walls control damp.

The airbrick issue is fairly obvious

NT

[N. Thornton]

theres another cause of damp walls. Victorian walls use the wall surface to evaporate the water they wick up: sealing the walls prevents this evaporation and so worsens damp. Classic mistake.

you can get good advice free if you follow the link.

NT

[Jake]

Thanks - yes, I guess a dehumidifier might be significantly better than no dehumidifier.... I can't imagine it drying the walls out very much, especially in the wet season, but I might be wrong..

Jake

[Jake]

That's unfortunate.... the rendering at ground level is particularly hard. Looks like a 4+1 mix. I wonder if it could be removed...

Jake

[Owain]

"Jake" wrote | .... the rendering at ground level is particularly | hard. Looks like a 4+1 mix. I wonder if it could be | removed...

That sounds like an excuse for a thread about SDS drills and chisels

Owain

[N. Thornton]

Well, bear in mind youve got soft brick underneath... chisel it off and the bricks will be trashed. If you ask people on

of them have successfully done it - I wouldnt dare myself though. But it is whats needed to sort the damp out. What I would dare do is locate the joints and angle grind the render off over the joins, and repoint those with lime. Lime is porous and lets moisture out, cement doesnt so well.

Realise the net moisture flow is from inside the wall out, not from rain in, so porous is whats wanted on these non-dpc walls.

NT

[N. Thornton]

Water evaporation from the wall is slowed down by dampness in the air. Dry the air and evaporation will happen faster. Consider that clothes will dry overnight in a dry house, but take days in a damp house.

Whether its enough on its own, who knows, only one way to see, but certainly it'll help. IIRC your walls are covered on the interior with some kind of waterproof paint or something, this wants removing really. Gypsum plaster and emulsion all considerably reduce evaporation, thus increasing damp in the wall. The standard proper fix is to remove plaster and replaster in lime. Lime is porous, and greatly improves the drying.

When built, these walls would always be plastered in lime, they are not designed for gypsum plaster, and some cant work with it.

Realise though that building material is very slow to dry, weeks per inch of brick. A dehumidifier would speed this up.

NT

[Jake]

But it's very absorbent too - so that is sort of contrary to the usual advice about plastering with sand & cement mortar to block the flow of moisture to the interior wall surface, yes?

Thanks for the suggestions. And after lime mortar is applied and dry, what sort of finishing coat would you use? And what paint would you use, if not emulsion?

Cheers,

Jake

[N. Thornton]

Its contradictory to that popular poor advice, obviously. The idea is to dry the wall out, not trap the water in it. If you seal the 2 sides of the wall, the wall will simply head for the level of damp of the ground it sits on, which will be more wet than damp.

distemper would be the best choice. However with Vic houses you can usually still get away with emulsiion once you fix the other issues.

NT

[Jake]

The plaster that's already on the walls inside, seems about as absorbent as lime plaster. There's a party wall, perpendicular to the damp side of the house which divides the lounge from the hall. In the hall, the plaster is lime plaster, but in the lounge, the plaster is some modern but similarly absorbent plaster. Both felt equally damp to the touch.

I appreciate your comment about the rendering going down to the ground outside preventing evaporation. It may be difficult to emove that, but it would be easy to install absorbent air bricks, say every six feet, close to ground level. But drying out the exterior skin of the cavity wall isn't really going to cure the rising damp in the inside skin, is it?

I could install some absorbent airbricks in the inside skin, below the level of the suspended floor. I'm not sue how many to install.... one every four feet or so perhaps. When the holes for the air bricks are cut, I can also clear out any debris in the cavity hopefully. A lot of air bricks will obviously detract from the thermal insulation of the cavities, but if it cures the damp, I'd be likely to go for it...

Jake

[N. Thornton]

How did you judge absorbency? I'm not sure how you can. Either it'll lime or gypsum, clay plaster is most unlikely.

modern plaster is not similarly absorbent.

You cant judge moisture content by feel as far as I know, hence the widespread use (and misuse) of damp meters.

Air bricks arent absorbant. Removing that render is the one big effective thing to do, but really only if you can do it without damaging the very soft bricks underneath. If not, you could at least cut through it gently over the mortar joints and expose those. The remaining render will fall off one day, but will take years to loosen its hold, sometimes a lot of years.

It would, if you had rising damp. Swapping the saturated cavity air for fresh would reduce the RH in the cavity air, thuse permitting evaporation from both skins. But what looks like rising damp is normally not rising damp. Rising damp is far from common, it is now realised that it has been very overdiagnosed, and often still is.

Hang on, are you saying you have a cavity wall, timber suspended floor, and no airbricks? If so, something is wrong there. And will need putting right before the floor structure rots. People have been known to render over airbricks before!

Jake, I'm going to be absolutely straight with you, you dont understand what youre doing, and need to learn. Otherwise youre thrashing about in the dark, doing work that doesnt need doing and wont wotk anyway. Its not difficult to learn, really its not. Try these guys:

'll take you through it bit by bit, then you can apply true expertise to your house.

Best of luck,

NT

[Jake]

Actually, come to think of it, I did see airbricks below floor level, but didn't notice how many.

That's why I'm seeking advice here. :-)

Thank you for the suggestion. I'll see what they say. Thanks for the other suggestions too.

Jake