New damp proofing failed - re-plastering help needed

[WELLY417]

Hi
Long story but i'll try to not to go on for ever!. We had a 'pro' in who injected DPC and re - plastered bottom metre or so of our ground floor to solve rising damp. 6 months on we still have some damp and have now given up on trying to get hold of the guy that did the work. This is our first house and we simply cannot afford to pay anyone else so need a DIY fix.
To be fair the job is not an entire disaster as it has worked in areas where cement / sand undercoat was used. We opened up a chimney breast before dampwork was done (to about 6 feet for a cooker) and for some reason the guy has used plasterboard in this area plus in one other small area of wall. We now appear to have penetrating damp in these plasterboarded areas. you can clearly see damp circles where the dabs are holding the plasterboard to the wall which get noticably worse on wet days and salt crystals have formed on the surface of these patches.
My guess is that the DPC is fine and the plasterboard is 100% the problem (i know chimney breasts are problem areas but the other area of plasterborded normal wall has the same problem and either side of it is fine)
I'm guessing i need to rip out the plasterboard and re plaster as per the rest of the house. Looking for a blow by blow run down of how to do this, in particular how to treat / prime the brickwork, ratio of mix for the undercoat and which damp proofing additives to use in the mix (also not sure if i need to use additives in the skim coat?
Thanks to anyone who got through that lot and any advice will be much appreciated.

 

[Softus]

If you temporarily allow yourself to believe that the DPC was never a problem, but the source of damp was elsewhere, then can you see any of the following conditions that might account for the original problem?

1. Leaking guttering.
2. Render too low.
3. Ground level too high.
4. Cavity breached.

Notwithstanding the above, if the wall was wet and not allowed to dry out before replastering, then you will have a continuing problem.

 

[markwm]

We have a similar issue, putting plaster board directly on to damp/contaminated walls is not a good idea because the damp will still be there even after a DPC.

What I would do is put some membrane on where the walls are damp like so: http://www.safeguardeurope.com/products/oldroyd_p.php

Then you can either plaster over or use plasterboard.

We too recently knocked out our chimney which appeared to be damp at the bottom. Actually the problem was salts, not damp, therefore a membrane will prevent the salts from coming to the surface.

 

[jaggyboy]

I am in the middle if a similar renovation project on a 100yr old house, whre there was damp on the plaster on an external wall. This was where the plaster/render was applied directly to the external wall with no cavity or DPM between the wall and the plaster.

Because the plaster was directly bonded to the wall any damp in the wall transferred into the plaster. Where one of my other walls was plastered using lath and plaster there was no damp problem, just old plaster which I had to remove.


I am finishing the room with with plasterboard and providing a gap between the plasterboard and the wall to avoid damp coming through.

All advice I have had (and this is for Scotland so weather conditions may allow other options in other areas) is to never apply plaster/render directly to the inside of an exterior wall as any damp can travel straight through from the outside.

My local building control said that battening and applying pasterboard was ideal for the property and should be significantly better than was there. Other than this I would be looking at replacing about 30m2 of lath which would be prohibitively expensive

I do not know too much about plastering but I would assume that if you dot'n'dab to an external wall there will always be a risk of damp pentetrating due to the direct bond, and the only way to stop this is to use either some sort of physical protection between the boards and the external wall or create an air gap.

dont know if this helps but this is how I am carrying out a similar refurb.

 

[MKD75]

I HAD THE SAME PROBLEM, THERE IS A WEBSITE WITH A FREE HELPLINE WHO GAVE ME SOME GREAT FREE ADVICE, THE WEB ADDRESS IS--********** .- IF YOU HAVE A LOOK ON IT THEY SELL LOADS OFF DAMP PROOFING PRODUCTS, THEY WERE A GREAT HELP TO ME AND SAVED ME LOADS OF MONEY AS I WAS QUOTED OVER £2,000 FOR IT TO BE FIXED BY A PRO. HOPE THIS HELPS.

 

[Softus]

How nice to see such a genuine post - all too often these days we get companies create a new user name and masquerade as a newbie, just to peddle their pointless and overpriced wares. Thank goodness MKD75 isn't one of those.

 

[Micilin]

You could consider tanking it if some of the wall is below below ground level , or damp proofing it .

That way you do not have the problem of the salts or damp getting through.

One such tanking system would be to brush on a 1:1:1 (Sand: Cement :SBR) slurry, covering the whole wall. LEave 24 hrs.

Then coat with 1:1 (Cement :SBR) slurry, then onto this a 3:1 (sand: cement) render scratch coat (or better still the second coat keyed with a scud coat rather than scratched) mixed using 3 :1 (water:SBR).

Leave at least 24 hrs, then apply a floating coat of render, 4:1 with the same water:sbr ratio. You can either rub this up with a float and sponge it or skim it. I'd rather not skim it myself, if I could help it. The SBR can be Ronafix , Cementone, Isocrete whatever. Dont' use any beads . The wall can be lapped onto a floor and screeded over too if belwo ground level.

You could also use Sika products which are excellent. They have similar systems

For damp proofing, (ie rising damp, above ground level no water ingress from outside) as long as the wall is brushed down and dust free, a propriety dampproof additive in a 4:1 or 3:1 sand and cement render (see spec on additive) will be fine, and keep salts and damp at bay. You can skim it up, no worries and again dont'use beads in the float coat, but you can stick them on for skimming.


Or, if you don't fancy the full rendering and want the insulation /ease of finishing of plastering of plasterboard, you can seal up the wall with dampproofing or tanking as above and stick the boards onto this and skim as normal.

I can be a bit more specific if you want to go into any method in more detail.

 

[jj plastering]

Spot on post above , follow it letter by letter and you will be ok .

 

[captain_scarlet]

hi micilin. interesting reading there about tanking. i've got a party wall that is partly below the neibours ground floor level and its suffered some serious damp. 2 of 3 causes of this is now sorted( missing guttering and broken soil pipe) and i now need to plaster the wall now thats its almost dry. could this wall be plastered as you described even though it isnt quite dry yet? 2 bricks seem to want to stay wet forever.
i've been told that carlite should be used to cover this wall but reading other posts here it seems that carlite is just browning and i'm not confident about browning stopping any dampness coming through again.
also could you be a bit more specific about each stage of the process. i dont understand what you mean by scud coat and floating coat?
any help would be appreciated.

 

[Micilin]

hi micilin. interesting reading there about tanking. i've got a party wall that is partly below the neibours ground floor level and its suffered some serious damp. 2 of 3 causes of this is now sorted( missing guttering and broken soil pipe) and i now need to plaster the wall now thats its almost dry. could this wall be plastered as you described even though it isnt quite dry yet? 2 bricks seem to want to stay wet forever.
i've been told that carlite should be used to cover this wall but reading other posts here it seems that carlite is just browning and i'm not confident about browning stopping any dampness coming through again.
also could you be a bit more specific about each stage of the process. i dont understand what you mean by scud coat and floating coat?
any help would be appreciated.

Will do -

 

[Micilin]

hi micilin. interesting reading there about tanking. i've got a party wall that is partly below the neibours ground floor level and its suffered some serious damp. 2 of 3 causes of this is now sorted( missing guttering and broken soil pipe) and i now need to plaster the wall now thats its almost dry. could this wall be plastered as you described even though it isnt quite dry yet? 2 bricks seem to want to stay wet forever.
i've been told that carlite should be used to cover this wall but reading other posts here it seems that carlite is just browning and i'm not confident about browning stopping any dampness coming through again.
also could you be a bit more specific about each stage of the process. i dont understand what you mean by scud coat and floating coat?
any help would be appreciated.

What floor do you have - and if it is screeded or concrete , could you take off a 300mm strip along the wall?

Ho w high up the wall is the dampness and how high up is the soil on teh other side?


Can we hack off the adjacent walls , back about 300-400mm?

Is any plasterboard or timber in contact with the damp areas?

The floating coat is the final coat of sand and cement, and the scud coat is thrown onto the wall as in pebble dashing - others call is spatterdash, harling or spritz coat. I will give more info when you reply to the above.

 

[captain_scarlet]

hiya micilin
floor is timber and removing it isnt a problem. the height of the damp in this wall at its highest is about 5 foot ( where the leaking soil pipe and missing gutter was) more or less tapering down towards the centre of the house to about 1 foot high. pictures would have been handy here. this is where a stud framed wall is with bricks laid on thier side instead of lathe and plaster, though with no studding in contact with the damp wall. the plaster can be removed since its blown anyway.
the other adjacent wall is also damp but drying out quicker with its plaster removed about 3 foot up the wall but not along its full length.(got some strange damp patches here internally and externally under a window that wont dry out).
at the moment there is no plasterboard in contact with the wall because its timber frame was rotten so had to be taken out ( boxing in around soil pipe). the neibour's floor is roughly 2 to 3 feet higher than my floorboards. hope thats enough info for you and i could get pictures if you think you need them.
i've just had a go at sand/cement plastering on my fireplace opening and did find it a bit tricky. i've plastered many times before with bonding, browning and finishing plasters with good and often brilliant results. whats the best way to get it on the wall?
i found myself squeezing the stuff on and shaking the float and seem to get lots of little stones that stop me from getting a smooth finish.
i ended up 'pointing' it up with a pointing trowel, embarrasing.

 

[Micilin]

floor is timber and removing it isnt a problem.

Good, we won't have to lap the tanking into a solid floor. If you need to have timber against it, just isolate with DPC or DPM.


the height of the damp in this wall at its highest is about 5 foot ( where the leaking soil pipe and missing gutter was) more or less tapering down towards the centre of the house to about 1 foot high.

We'll assume this is solved and won't hurt the wall anymore.



this is where a stud framed wall
is with bricks laid on thier side instead of lathe and plaster, though with no studding in contact with the damp wall. the plaster can be removed since its blown anyway.

If it was in contact, isolate this wall from the damp wall , and seperate it with a DPC, before replastering what is blown. IF it was a solid wall in contact, we would tank back along the wall at least 300, but preferably 1000mm.


the other adjacent wall is also damp but drying out quicker with its plaster removed about 3 foot up the wall but not along its full length.(got some strange damp patches here internally and externally under a window that wont dry out).

We will tank back along the wall a metre, and damp-proof the rest if it is above ground level outside. Presumable the dampness was tracking back from the wet wall. Is there any ingress of water around the window?

at the moment there is no plasterboard in contact with the wall because its timber frame was rotten so had to be taken out ( boxing in around soil pipe).

The pipe boxing, when reinstated should be glued to the tanked wall, or fixed into fixing pockets - pockets of sand and cement (more later).



the neibour's floor is roughly 2 to 3 feet higher than my floorboards.



Okay, so we should only have to tank a metre above this. Guessing that your wall is no more than 2.4 high, and we have to tank 2m high, then we may as well tank full height.



i've just had a go at sand/cement plastering on my fireplace opening and did find it a bit tricky. i've plastered many times before with bonding, browning and finishing plasters with good and often brilliant results. whats the best way to get it on the wall?




Well........ without being funny, trowel it on . There have been good tips here from roughcaster and others on this, the mix is as important as anthing else- more later [/b]


i found myself squeezing the stuff on and shaking the float and seem to get lots of little stones that stop me from getting a smooth finish.

JUst sounds a little too tight a coat ,or aggregate too large



embarrasing. Embarrassing if you have done it every day for five years and cack it up, otherwise, save your blushes!



Tanking -

Prep - remove all loose background, timbers, etc. Brush down with wet brush to remove dust etc.

USe washed fine sharp sand, salt free. Worth asking supplier. when I was dampproofing, I had top get certs from them to satisfy BS audits .

For SBR tanking - you can brush 1:1:1 (SBR, , SAND, OPC) slurry over 100% of the surface . Go back over any patches you miss. (Alternative, scud it , ie throw it on with harling trowel or dasher) Leave 24 hrs

Cover 100% of surface with 1:1 (SBR OPC) . This will bond the render coat to teh first coat, and also give additional seal.

Apply to this 3:1 (sand OPC) render coat mixed using 3 :1 (water:SBR).

Trowel on about 8-10mm , not too worried about ruling off straight away, as it will take ages to set due to lack of suction. When it is picked up enough, you can rule it off and fill to get it flatish , not needed perfect. But leave 'it on the trowel', ie surface smooth .

Now, rather than scratch it, you could give it a light scud coat (2-3 mm) of the same strenght, but wetter. LEave 24 hrs.

NOw coat of 4:1 render, same sbr water, rule off and float up.



[/b]

 

[captain_scarlet]

hiya micilin
thanks a lot for all that information and your time. heres hoping i can do a cracking job but looks like it could be a while now. its likely that the drains are leaking as the foundations at this damp wall of mine are filling with water again after some fairly heavy rain overnight/early morning.
so thats missing guttering, broken soil pipe giving water penetration.
with all air bricks blocked with dust and rubble, builders rubble piled up to the floor joists causiing more damp. local water company reckons there is a water supply leak some where in the back yard and possibly leaking drains as well. anyone got any wellies????
the outside damp patches under the window sill looks to be caused by rain running off the upstairs kitchen roof and landing straight onto the sandstone window sill and bricks underneath, drenching them. will have to get the guttering looked at again.
did i mention the fact that this flat of mine is damp!