Do you always need to replace render and plaster?

[theswellguys]

Hi there,

Great forum you have here. I am new so please be kind :)

After reading this forum for a while and checking websites there are still some aspects of the cream based DPC treatment that don't seem to have a consistent answer that I am hoping to get some clarification on.

I have a damp problem the front bedroom of the house which is at the high part of the block. 100 year old house in Sydney, Australia (solid double brick on sandstone foundations).

The walls are damp to the touch up to a certain point, especially after rainy spells. Had the odd contractor around to assess and they all say the original DPC (slate?) has obviously been compomised and so need a new one.

Thing is I have no visible signs of the damp on the internal wall e.g. efflourescence etc (although there is on the external walls)

I really would rather not rip the floorboards off, or replace render/plaster if I really don't need to.

So to my joy when I read the following at http://www.ultimatehandyman.co.uk/damp/ ... oofing.htm)

Best practice, though perhaps not always the most practical, is to leave the plaster above the new damp proof course on the wall for several months following the DPC treatment. This allows the salts to surface during the drying out process and the extent of plaster replacement to be properly ascertained.

So questions are:
* Can I inject a cream based DPC and leave the render and plaster on for a few months to see how it works, or if the plaster becomes obviously damaged.

* Can I repair and repaint external wall straight away or does that need to be left as is to allow drying out to outside to occur (I saw one post saying to apply silicone paint straight away, but then suggesting that the moisture would be carried away by wind from the drying out wall)
* Do I really need to inject DOC all around the whole room or just on the walls that seem bad. (one contractor said I needed to do the whole house, internal and external to avoid moving problem from one place to the next)

Thanks in advance
Michael

[ultimatehandyman]

Hi Michael,

I have not used the dpc cream yet, but I have used the electro osmosis DPC.

Someone told me that if you used an electro osmosis DPC you did not need to remove the plaster, unless it was blown ( had come detached from the wall ), so I checked this with the DPC manufacturers. They said that although the damp problem would be fixed the plaster would still need replacing because of the salts that come to the surface of the plaster.

I can't understand a slate DPC failing to be honest, so perhaps the cavity is full of crap, which has bridged the dpc.

Have you checked the internal walls with a damp meter?

A damp external wall could be caused by penetrating damp rather than rising damp

What is the condition of the render like on the external walls?

As for the question about Do I really need to inject DOC all around the whole room or just on the walls that seem bad. (one contractor said I needed to do the whole house, internal and external to avoid moving problem from one place to the next) The answer is no, normally you can get away with just treating the walls that are affected, if it is crap in the cavity, then treating any solid internal walls is pointless as the slate dpc will still be doing it's job.

[python]

I don't think there is a cavity.

I have a damp problem the front bedroom of the house which is at the high part of the block. 100 year old house in Sydney, Australia (solid double brick on sandstone foundations).

[ultimatehandyman]

I don't think there is a cavity.

I have a damp problem the front bedroom of the house which is at the high part of the block. 100 year old house in Sydney, Australia (solid double brick on sandstone foundations).

Yes, you are right, I missed that bit

The problem could still be penetrating damp rather than rising damp though.

[theswellguys]

I don't think there is a cavity.

Ahhh, in fact you are both right. There isn't a cavity in the wall I was thinking of, on the north side of the house, but I've just realised that there is a cavity wall on the front wall which has a window and is under the eaves at the front. Bullnose verandah, as they call them out here I think.

Jumped in the attic and had a quick look at it. Hadn't really taken too much notice of it before. So interesting to see that it does have the odd loose brick half falling into the cavity and a lot of dust/material around the top. Will try check it out tomorrow with a mirror as the gap between roof and top of wall is too small to get the angle.. and its getting late..

Be interested to know how I might clean down in there. Do they have vacuum cleaner for this type of job?

Oh, and funny you mention the electro Osmosis. I thought it was a great idea, the ultimate solution. The wife said "I'm not having a piece of electronics holding the water at bay". She's actually an electrical engineer so it was back to the drawing board :)

I don't have a damp meter but a dump busting tradesman came around took some measurements with one. He seemed trustworthy and looked to be doing the type of measuring I have heard about on this forum. He was showing me the levels but it didn't mean that much to me at the time (I hadn't been reading this forum at that stage).

He said we did have a damp issue at the front and prescribed the pressure style chemical treatment DPC allong with bigger airblocks for ventilation.

We are now just getting round to extra quotes and got the idea of treating as much as we can ourselves.

And yes, I was also thinking pentrating damp, which is kinda why I was asking if there was anything to lose from painting the outside of the house (its been begging for it) with a good waterproof barrier type paint thing and seeing what effect that had before moving on to DPC. Or would that be a dumb idea if at some stage we might be drilling holes in the mortar and patching I presume once the DPC cream has dried out?

Also having trouble understanding why there is no sign off salts on the inside walls at the moment? Maybe because its not coming from the ground? Or maybe sometimes they only come out and mess up your plaster as the wall dries out. So many questions seemling unanswered, or at least contradicted :)

Nice to know that slate isn't looked back on as such a bad choice DPC material. I like the idea of it being rock solid, but when I look from below it does look fragile. Perhaps I might even get under there in the morning and check its general integrity in a bit more detail.