rendering/plastering after damp treatment

[sambotc]

Hi,

My brother has a 1920's house which has suffered from damp for a few years. The kitchen is being replaced and on removal of the units the damp became apparent and needed sorting before the new units went back.

he had a damp proofer out and we were informed that an injection damp proof course needed to be done and that the internal bonding coat and plaster needed hacking off, the damp course needed to be carried out then a cement render applied, followed by a finishing skim to make it look nice. The wall in question is a solid (no cavity) red bricks wall approx 8" thick.

I have done a fair bit of plastering in my house and a bit of rendering externally, so offered to help him out to save him a few quid.

The existing plaster has been knocked off and the pointing seems poor and some bricks are loose and various 'objects' found in the wall have been removed which has left a few voids which will need sorting out. Also the brickwork is quite uneven with some bricks sticking out about 10mm in places.


The question i have is, how would you best approach the job? Would you repoint the brickwork and fill the voids etc before hand, then attempt the rendering another day, or work the render into the gaps etc as you go along? Also, seeing as the wall is so uneven, would you apply 1 thick coat of render, or a scratch followed by a float coat, finishing with a skim?

Finally, I realise a water retarder, plasticiser is needed to protect the skim from damp/salts coming through and add some protection, i have also seem lime being recommended. Would anyone be kind enough to give me there opinion on the best mix to use in this situation.

Finally, when you suggest wetting the wall down, would you hose it down with a fine mist type spray, even internally? I can imagine the bricks being quite porous.

Thanks for your time, sorry for the long post!

Sam

 

[jrplastering]

the damp company i work for usually hack off inject then fill any voids giveing the render used a scratch, then do one or two scratch coats with water proofer in and then a final top coat with water proofer added again rule it flat float it up then devil scratch it so the plaster has a key.
i spose if you wanted you could use thistle limelite or dricoat these are just a premixed (you just add water) damp proofing renovation plasters these might be easier for you to use if the wall is so out of bonk as it mixes up thicker than render so you can lay it on a bit thicker.
if you render it, provideing you have the depth then fill the voids do one scratch brining it up to the level of the most pokey outy bricks then a second heavy coat again scratching it but covering everything almost up to level makeing sure you leave 10mm for ya final top coat to go on

 

[sambotc]

Hi,

Thanks for that advise. How long would you leave between coats? 24hrs? I have been advised against drycoat by the damp proofers, so for them to honour the guarantee, have decided against it.

In the paperwork they supplied, they have said to use '3 parts washed, salt, loam and soil free sand to 1 part cement'?? Firstly, I presume that means plastering sand, and secondly from what I have read up on here the 3-1 ratio seems a bit OTT?

Would you hose the wall down with a hose gun until it is not taking any water? This sees a bit backwards considering we are treating the wall for damp !! but I presume the water is still fairly surface?

Thanks for the help so far

Sam

 

[thatbloke]

Perhaps you should find the source of the damp rather than try to hide it behind cement?
In my experience of working on older properties with no dpc , dpm's etc adding modern materials such as cement etc where breathable materials such as lime have been used originally simply hides the damp problem which soon manifests itself elsewhere.
The moisture has to be coming from somewhere.
Look for higher groundlevels outside, cement render can trap moisture, leaking guttering , cracked render outside or cement where lime should be, cement paths trapping moisture etc etc.
If your house has no DPC it was designed to breath, adding modern materials will prevent this process from taking place.
If the property has had a concrete floor and dpm recently put in this can push moisture out towards the walls.

 

[jrplastering]

hence i suggested limelite as i dnt know what sort of stuff this house is, id have a guess it lime but i cnt be sure so i gave options

 

[thatbloke]

Most times it's hard to know without actually looking at it in person , could be blatantly obvious if you know what you are looking for , is limelite breathable then?

 

[sambotc]

Hi,

Appreciate the replies. as far as we were concerned, the injection DPC was 'curing' the damp caused by rising damp, and the plastering job was the suggested course of action to prevent any future problems with the plaster failing due to it absorbing salts etc? Is this not correct?

I am not experienced in damp treatments so we are really going with the advise given by the damp proof company, which in all fairness have been very reasonable during the process with lots of free advise even to the point of losing out on work.

The ground level outside is at a suitable level it would seem, approx 6" below the finished floor level of the concrete kitchen floor.

I would welcome any advise on the situation which may lead to a better result in the long run.

Thanks, Sam

 

[jrplastering]

yeah limelite is breathable its a specialist renovation plaster specially designed for these old houses with damp, im not 100% on how it would perform when compared to san and cement i spose as you said thatbloke its hard to tell without looking at it, usually if im unsure about it i think of a couple of questions and just ring the damp company i work for and they tell me which one of the options ive chosen would be better to use.
i dnt very often ring them but on that odd occasion thier a very handy contact to ring, at the end of the day we all need help sometimes no one will know every last thing about said trade, thiers always summit to learn

 

[thatbloke]

What are your views on rising damp JR, some say its a myth.

http://www.askjeff.co.uk/rising_damp.html

Lots of old building built say on canal banks such as mills etc have no dpc's and no signs of damp. It would be interesting to hear your views.

 

[thatbloke]

the concrete kitchen floor.

I would welcome any advise on the situation which may lead to a better result in the long run.

Thanks, Sam

I think that could be part of your problem right there.
Have a read here, its the very last subject.

http://www.periodproperty.co.uk/ppuk_discovering_agony_uncle_200911.shtml

Also there is a forum on that site full off info on damp in period houses.

My advice would be to cut a section 600mm out of the floor around the walls , remove the dpm from this section and replace with limecrete, you wont need to get BC involved to do this.
This is only if you are sure the damp is being caused by the insertion of a dpm in the floor.
Has it rained much where you are lately? You really need to locate the source of the moisture, you have to cure the cause and not the effect.

My house had a concrete floor with DPM put in where a breathable floor once was, it had concrete render and plaster on the walls.
The sole plates and bottom half of the studs rotted out as a result.

Each situation could be different though so do your homework first.
Perhaps your local conservation officer may be able to advise you better?

 

[Alastairreid]

This subject was a bit of a debate a while back.

//www.diynot.com/forums/viewtopic.php?t=34549&start=0

Another.

http://www.konrad-fischer-info.de/2auffen.htm

 

[thatbloke]

This subject was a bit of a debate a while back.

//www.diynot.com/forums/viewtopic.php?t=34549&start=0[/QUOTE]

Thank you for the link , I shall give it a read.

 

[WalksWithTurkeys]

What are your views on rising damp JR, some say its a myth.

http://www.askjeff.co.uk/rising_damp.html

Lots of old building built say on canal banks such as mills etc have no
dpc's and no signs of damp. It would be interesting to hear your views.

I've been reading around a bit having found what I thought was penetrating damp, but it turned out to be condensation due to vinyl floor tiles on a screed floor. That bloke you link to is rather contentious and my impression is that he is rather ill informed, though many do agree with some of his statements. Here is a review of his book:

http://www.buildingpreservation.com...cle&id=80:the-truth-about-rising-damp&catid=3

The author of the review seems to have a lot of qualifications and memberships of respected societies, giving me some confidence in his knowledge.

One key point made by many including Howlett is that damp proofing companies cannot be trusted because they have a vested interest in diagnosing rising damp, whereas most damp is apparently penetrating or condensation. Treatment for rising damp does not correct for penetrating damp or condensation.

My house was treated for rising damp, and yet I have found plastic membranes under the screed as well as the damp proof course. When I removed the carpets I found vinyl tiles which were trapping condensation, and it was worst where the damp treatment was done. My suspicion is that there was no rising damp, though that is conjecture.

I should stress that I am a typical internet expert i.e. I know nowt apart from what I have read online, including at the site linked to above.

 

[MarkWG]

In my sisters house, we simply hacked the old lime plaster off up to a meter, with it's GLOSS paint coat and replaced with new lime plaster and breathable paint.

Victorian terrace, solid masonry walls, lime plaster.

No reoccurance of damp thus far.

The 3-1 is a cement render, as said this will just trap moisture in the wall, if indeed it is rising, but you can slap it on quite thick so it has the benefit of being able to build up cheaply and quickly - perhaps why they use this technique?

 

[sambotc]

Thanks for all the replies, sorry I have been a little tied up with other things so couldn't reply earlier.

Well my brother had the damp proof injection carried out anyway. The next task is for me to have a go at rendering the wall. The damp course has been installed fairly low and the wall that is effected will have kitchen units infront of it, so I was going to render down to the damp course. This will leave the damp course clear of any render so hopefully there is no chance of it bridging via the render?

So really all I am asking is what mix you would recommend and which waterproofer so I can buy the gear and have a pop at sorting his kitchen out!

I've seen sika do a waterproofer concentrate in travis, or would you go for SBR or another?

Thanks in advance

Sam