Plastering advice please

tdiman

Hello, 
12 months ago I discovered a seriously leaking gutter that had resulted in a big leak of rain water into the wall cavity of our house. I sorted the leak but it damaged the newly decorated wall in the middle room. The leak had penetrated the plaster and was showing on the wallpaper. To cut a potentially 
long story short, I have now removed the bottom metre of affected plaster back to the brick. In effect treating it as a rising damp problem, which it isn't. I am not looking for a plasterer, but just advice please. I am well able to replaster this, but I wonder the best route to take to avoid problems from this area again whilst he bricks continue to dry. Sharp sand and cement or a product  new to me - Dryzone damp resistant plaster - has anyone used this? I am unable to go the plasterboard vapour barrier route, as the previous plaster depth is all over the place and would result in an unsightly step. I also have most of an Ardex WPC tanking kit left over from when I installed a shower. Would this work here?
Thank you for reading.

FreeBear

Just give the wall a month or three to dry out, and don't waste your time or money on expensive plasters (that Dryzone stuff is cement based, so more of a render than plaster).

Put a base coat of bonding plaster on first to build up the depth (perhaps two coats if you need a real thick layer), and then finish with a skim of multifinish. Even if the wall is still slightly damp when you apply the plaster, moisture will still get out. Just don't be in a rush to paint & decorate.

Tip - If you don't need full bags and/or want to reduce costs, go to somewhere like B&Q and look for damaged bags. The price is often reduced (I've never paid more than £5 for a damaged bag).

stuart45

What's the original plaster? Lime, or sand/cement and plaster skim, or bonding and skim?

tdiman

Sorry for the delay - I had a right nightmare signing in to MSE.
Thanks for the replies - appreciated.
Freebear - I stripped the wallpaper off over 12 months ago - and had my Ebac going on and off for that time. Took out loads of water. I came to the conclusion that the  plaster was shot and was just absorbing anything going so I decided to take it off. An unusual birthday that was. Stuart - the plaster was of the sand and and cement with a skim. Not sure if it was lime. The house was built in the 1950's and the pointing to the rest of the house has a very  gritty texture, so I would guess a lime mix - but really don't know and that's for another day.

I rely very much on various people I follow on youtube, but with plastering it gets a bit confused. I was very close to using and so purchased the plasterboard with a vapour barrier to be simply gunned to the wall, but too late I found that the 12.5mm was too big for one part of the wall and I didn't fancy skimming a whole wall. I was mainly concerned about using a bonding plaster in case I still had an issue with the wall, hence the Dryzone idea. However I now find that there is a problem with this solution - it is a lime filled plaster and not recommended for use where you intend to wallpaper. I think maybe the bonding and multi finish, which I have used before, might be the way to go but with the Ardex WBS tanking that I have left over applied to the wall first. The internal wall is of those plastering bricks - big ceramic things like used in Spain etc. Caused me a major problem when I came to rewire and flush fit the sockets. Like the idea about open bags I think I will need a few bags of bonding and 1/2 bag of finish as I have about 4m square to do. I have never plastered with sand/cement before. Lee

FreeBear

1950s house - They were still using a lot of lime in them days, but as you have cavity walls, I wouldn't be overly concerned about using traditional materials. With hollow ceramic blocks on the inner leaf, the wall should dry out pretty quick. And I certainly wouldn't be using any tanking or waterproofing treatments on it. But I'll defer to stuart45's greater experience.

35har1old

FreeBear said:

1950s house - They were still using a lot of lime in them days, but as you have cavity walls, I wouldn't be overly concerned about using traditional materials. With hollow ceramic blocks on the inner leaf, the wall should dry out pretty quick. And I certainly wouldn't be using any tanking or waterproofing treatments on it. But I'll defer to stuart45's greater experience.

If it's a cavity wall why did it penetrate the inside wall?
If the water pentration continues the bonding won't last.
Sand and cement with additives like triple strength Medusa water repellent 

stuart45

35har1old said:

FreeBear said:

1950s house - They were still using a lot of lime in them days, but as you have cavity walls, I wouldn't be overly concerned about using traditional materials. With hollow ceramic blocks on the inner leaf, the wall should dry out pretty quick. And I certainly wouldn't be using any tanking or waterproofing treatments on it. But I'll defer to stuart45's greater experience.

If it's a cavity wall why did it penetrate the inside wall?
If the water pentration continues the bonding won't last.
Sand and cement with additives like triple strength Medusa water repellent 

Water can make it through to the inner skin sometimes. A well built cavity wall will keep moisture out, but not all are that good. There's a number of ways it can happen. 
When driving rain gets through the outer skin, it runs down the inside face of the outer skin. It pools at the bottom of the wall, but the concrete infill should be 6 inches below DPC, so it shouldn't be an issue. However mortar droppings and other debris can mean the infill is much higher. Excessive water running down from driving rain, or from constant soaking from the gutter can mean moisture soaking into the inner skin above DPC.

tdiman

Hi, 
This wasn't just a simple leak from a broken guttering. To make it clearer, we purchased the dormer bungalow which had issues, but I missed this one. It wasn't simply a failed/leaking bit of guttering but a displaced downpipe which was connected to a water butt by means of a connection in the downpipe. The diameter of the downpipe was effectively reduced to about 25mm, but this was further complicated by having an unseen weed growing in it into the roof, completely blocking it off. I would guess that the blockage had been like that for a long time and was overflowing the wall plate directly into the cavity wall. You couldn't make this up. It answered my question why I had to replace 4 small joists in a seperate adjacent room that had rotted and swollen. From the outside none of this could be seen as the corner where the downpipe was located was hidden a large climbing rose - now removed. The damp proof course is in perfect condition. Add to all this, that I did remove 3 bricks from the outer wall to have a look inside the cavity. The previous owner, an 84 year old had had blown cavity insulation fitted and this had absorbed the water. I removed as much as I could at the time filling 5 - 6 large waste bags. So Stuart you were on the right lines. My major concern and reason for the original post was would I be wise to use a different method for plastering or would the wall dry out sufficiently in a reasonable time before J decorate the wall again?

stuart45

Textbook answer would be to use the same materials. 50's-70's was usually 2 coats of sand/lime/cement and a gypsum skim. Scratch coat 5/1/1, float coat 6/1/1. Or 4/1/1  then 5/1/1. 
However most plasterers would use bonding, then multi finish as FreeBear suggested. I don't see any problems with that provided the leak is fixed and the wall reasonably dry. Those terracotta blocks don't hold a lot of moisture, so most of it will be in the mortar joints. 
If the wall's too damp you might find salts being drawn through onto the surface of the finished plaster.

tdiman

Thank you
is that plastering sand, any particular type of lime, ordinary portland cement?
I would prefer what I am used to though - bonding and multi finish, but if it's about the same using the cement/lime I will give it a go
Respect
Lee

stuart45

Plastering sand has less shrinkage, but is slightly less workable than building sand. A lot of plasterers preferred building sand for inside work, or a 50/50 mix.
Hydrated lime and OPC. If you want to use sand/cement you'll usually need 2 coats. The first one use deeper horizontal scratches. The second one lighter scratches done with the devil float.
You can use bonding if you feel more comfortable with it.