K11 tanking slurry, Renderlite & 'normal plaster'?

8 Sep 2015
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United Kingdom
How would you finish the 'top coat' if you will in this setup?

Our walls are largely to be taken back to brick, have the affected areas coated in the K11 tanking slurry with Renderlite plaster on top of that.

I have no experience of Renderlite plaster so don't know what its finish is like.

I am pretty sure the top section of the wall will remain with the old plater (which is just Multifinish i think).

Obviously the Renderlite is to be used as it is breathable.

Would you paint on top of this? Could you use 'normal' plaster on top of this (like Multifinish) & then you would paint on that?

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My opinion only:

K11 in my opinion is a solid water proofer similar say to gluing a sheet of plastic to the wall - it does not breathe and allow moisture vapour to pass thro. Renderlite might be breathable but K11 isn't.

Any damp entering the wall, penetrating or rising, will have no place to go but up - above the K11 barrier height.

Moisture vapour in the warm room hitting the impermeable, slightly colder K11 barrier will condense on the finished surface - maybe not immediately but eventually it will show.

Sand and lime render in a 3:1 or 4:1 mix with a multifinish skim will work far better.

Your fire and fire surround should be removed before any remedial work is done to the chimney breast.

FWIW: what has the Damp Company had to say about any causes of dampness in the wall(s) - or the possible condition of the joists in any damp walls?
Hi ree. Thanks for your reply.

I'm not challenging you here (you'll have knowledge far greater than mine) - but from personal experience of this system - this approach appears to work. Keyword: appears.

I say that because our immediate neighbour has (had) the exact same problem as us. If anything, theirs was actually worse as far as the visible side of things went - they would have water dripping down the walls.

Someone came in & did the damp proofing. We discussed in detail what they did..... Injections into the wall, plaster off to 1mtr, K11 tanking slurry applied (walls washed down with anti sulphate wash), Renderlite plaster over this. A pump & sump was installed in the subfloor. Not a cheap one either.

That was 2 years ago. The house was bought by someone adding to his portfolio & we checked throughout with him & he was willing to let us keep looking at the wall. In fact he was grateful of it because he hadn't been made aware of the work & knew nothing of the pump. The walls looked perfect throughout.
Then the house was recently bought & we introduced ourselves & told them about the situation in case they hadn't been made aware (they had). Still - the walls are perfect. No more condensation on top. It's as you would want a wall to be.

As for the cause - it is manageable, but can't be solved. There is a stream running through the area & just so happens to pass under a few houses (ours being one).

The water isn't gushing/flowing. It comes 'up' slowly, but it comes up all the same. The suggestion most have given is to put a good quality sump pump in & simply manage it.

We do need the joists & boards replacing. They are 80 years old & they would probably last another good number of years, but for peace of mind....

As a side note - we did have a guy out who said he would eradicate the entire problem by putting in a solid floor. We were open to this until the figures came in .... £13,000. We simply cannot stretch that far, nowhere near. Not even if it was the last job to do on the house (which it's not).

My way of thinking is - everything has lasted 80 years so far. In 80 years I will be dead. So if the option to 'manage it' (which is replace flooring like-for like but this time with the ends wrapped in DPM, and include the tanking slurry & sump pump) lasts our lifetime, or even most of it, then we are happy, as it will allow us money to spend on other areas that need addressing.

Sorry for the long post.
If your neighbour had the party wall injected I hope you gave them permission to do so any injections into party wall requires consent party walls are just normally tanked both of these actions can have an adverse effect on the neighbours side
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No, we weren't asked.

Next door was rental, the owner was (godknowswhere) & had to sell up. It was this guy who got someone out to deal with the damp issue (those renting had moved out).

At no point were we told what was going on. We only found out because we went round & asked.

After this was all done we heard about a party wall act & what it was.

Obviously we will need our new neighbours permission. We have spoken to them & they have said no problem (let's hope it remains that way).
if i was your neighbour i wouldent let you inject it if i was having no damp problems, there are houses in pompey like yours built on marshlands and gets effected with tides you know if you buy a house in that area there either is damp or was damp , i have just been on sovereigns website to have a look because ive never used it i cant see any reason why you cant skim it with normal plaster but if you want to carry the breathability scheme further they do there own skim coat for it, "NOW" if you go to there site they say its useful where condensation may be a problem such as cold walls which i think ree may be trying to explain to you looks like its better to have this stuff but not sure why they want this to breath when the brickwork is getting tanked behind it so its not breathing anyway i could understand if you wanted a fully breathable wall, if you have bricks thats been tanked and a breathable plaster where do the moisture go? if it can not escape through the bricks? just as a thought are you also going to have breathable paint? roy c used to work with sov chemicals maybe he can chip in here http://www.sovchem.co.uk/renderlite-25k.html
I will have a look through my old Sovereign folder and get back to you later I am on my half hour lunch break at the mo...
Regards the breathing side of things - I can't answer you i'm afraid.

I just go off what the 'professionals' say. I trust that they're (supposed) to know their stuff.
Regards the breathing side of things - I can't answer you i'm afraid.

I just go off what the 'professionals' say. I trust that they're (supposed) to know their stuff.
Well my friend I think you will find a breathable base coat is useless if the bricks are tanked and have non breathable paint as for you getting a quote saying a solid floor will fix it for ever that's nonsence
Again, this is what we was told - solid floor would resolve the problem

As there would be no moisture under the floor joists & boards as well as there being no joists & boards full stop. The walls (on that method) would been given an anti sulphate wash with K11 applied so then no damp coming through from the walls.

We asked what would happen to the water as it would surely have to go somewhere. It doesn't just disappear (& our concern was it going up the walls).

Chap said it wouldn't happen & the water would just find its way around the house.

We weren't sold & when the price came in we most certainly wasn't sold.

But since the method we have accepted has been used next door which has been fine, we're happy to go with that since we've seen it work, at least for the past 2 years anyhow.
I've seen lots of damp walls with solid floors my daughter even has one the damp will travel up the foundations and up the wall he's talking nonsence
Out of curiosity, what would your suggestion be?

I appreciate you haven't seen the whole thing for yourself, but still...
If it was my house I would buy dryzone and inject it into outer walls tank that for good measure and just tank the party walls then I would use render or maybe give that limelite a blast because I've never used that before and always wanted too, I would then give the whole lot a nice skim, bare in mind I'm not a damp proof contractor just a normal plasterer , just as a note a few years ago my son in law was sorting his damp out I asked what you going to do? He said I'm going to put tanking over that wall "internal" and skim it he put tanking slurry over the skim that was already there then skimmed over that , I told him how its supposed to be done but he didn't listen but do you know what? Its held the damp back for about 4 years now. Every time I visit I check the wall still dry it is "well there's a story for you to ponder

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