freshly painted DPM and plastered wall gone 'fluffy'.

[brianos]

Yes.. I know everyone kept saying don't DPM and old house. Well.. we ended up DPMing just one room which was 'a little bit subterranean', so hopefully you'll all let me off.

So, we used a DPM slurry against a wall that is subterranean. I did also have fench drain outside AND fix the drainpipe sloshing water into the area. Then plastered the wall. Then painted it with contract matt. A white emulsion. A week later and a few areas of the paint have a layer of 'fluffy white on it. Like super light white crystals.

What might cause this? Of course it's going to be wet but.. what's happened here?.perhaps those walls just haven't tried out?

 

[a twig]

Difficult to see from the photo but probably just efflorescence as the wall drys out, brush and vacuum should do the trick

 

[aockenden]

Wait so you tanked and plastic-painted a wall that is underground and therefore perpetually damp, and now your finished surface is all manky and salty? Hopefully it’s just a short term issue associated with the newly completed work and will subside soon. If not, then I guess a couple “told you so”s are probably in order…

 

[Stevers]

Unfortunately that is eerily reminiscent of when my tanking failed. I was also told to brush the salts off, before I eventually managed to get the wallies back to do it again well enough to prevent salting in all the bits that weren't to be hidden by built in furniture. I was still left to rebuild the chimney breast in one room using NHL mortar repairs and renders, and the effect of those was, I have to say, a revelation.

Pink gypsum plasters really do seem to be wildly intolerant of salts, and are a poor choice for our purpose when groundwater and old buildings are often full of salts.

 

[brianos]

Difficult to see from the photo but probably just efflorescence as the wall drys out, brush and vacuum should do the trick

Wait so you tanked and plastic-painted a wall that is underground and therefore perpetually damp, and now your finished surface is all manky and salty? Hopefully it’s just a short term issue associated with the newly completed work and will subside soon. If not, then I guess a couple “told you so”s are probably in order…

Yeah, the whole tanking thing was a tough journey. I really didn't want to do it but felt pushed into a bit of a corner. When the slurry went on, this one corner (where the fluffy patch appears) took an age to dry, and I'm not convinced it had finally dried when it was finally rendered. The slurry also doesn't reach the ground fully so any moisture will just seep out the bottom anyway so I really didn't know what to do.

Incidentally, by'plastic-painted', do you mean contract matt emulsion is non-breathable paint? (the wife painted it whilst I was away because we needed to get boiler installed).

 

[Stevers]

Contract matt emulsions are on a par with F&B Estate emulsions on the breathability spectrum, and are what I use. Flat Matt emulsions also in that area. 'Plastic' paints would be Vinyl Matt emulsion through to Vinyl Slyk and 'bathroom' paints. The sceptical might say the more washable the greater the problem, which would put contract matt emulsions ahead of F&B estate emulsion (and other flat matts) - if it comes off on the cloth - it's good!

I also noticed that it was the parts of my tanking that remained wet that seemed to be problematic later.

 

[brianos]

Unfortunately that is eerily reminiscent of when my tanking failed. I was also told to brush the salts off, before I eventually managed to get the wallies back to do it again well enough to prevent salting in all the bits that weren't to be hidden by built in furniture. I was still left to rebuild the chimney breast in one room using NHL mortar repairs and renders, and the effect of those was, I have to say, a revelation.

Pink gypsum plasters really do seem to be wildly intolerant of salts, and are a poor choice for our purpose when groundwater and old buildings are often full of salts.

This group has drummed into my brain that I need to use breatheable materials. I assume this means proper breathable paints too? Is there a recommended paint range I need to guide the wife on? same question for wall paper!

Wrt the breathable materials for wall repairs & finish, I understand I need to be using a lime based plaster. Are there any product recommendations? Someone I met mentioned Limerite (see product table below). Is that ok to fill holes too? i.e. fist size? and for making good the wall where the sparky has laid new cables etc.

Part 1 - Limelite Easy Bond – breathable primer
Part 2 - Limelite Renovating Plaster

Part 3 - Limelite High Impact Finishing Plaster

 

[Stevers]

Those Limelite products I would regard as damp proof wally territory rather than what we're looking for.

I use NHL 3.5 available from my local builders' merchants for everything. I vary the mix to be coarser for filling, pointing and base coats, very fine and rich for the top coat. We have limestone dust up on the Mendips which I mix 50/50 with building sand and sharp sand according to how coarse I want the mix to be. NHL is used 1:3 for everything apart from finishing coat where it needs to be 1:1.5 or even 1:1 with very fine sand. I didn't know this when I did my chimney breast so ended up filling that twice with a pure NHL mix as if it was Polyfilla.

Contract emulsion works for me, is cheap as chips, and can be dyed to soft colours. For stronger colours F&B Estate emulsion also works for me, and I suspect that this is the 'flat matt' emulsion available from other companies. Not washable is good in this context!

 

[brianos]

Those Limelite products I would regard as damp proof wally territory rather than what we're looking for.

I use NHL 3.5 available from my local builders' merchants for everything. I vary the mix to be coarser for filling, pointing and base coats, very fine and rich for the top coat. We have limestone dust up on the Mendips which I mix 50/50 with building sand and sharp sand according to how coarse I want the mix to be. NHL is used 1:3 for everything apart from finishing coat where it needs to be 1:1.5 or even 1:1 with very fine sand. I didn't know this when I did my chimney breast so ended up filling that twice with a pure NHL mix as if it was Polyfilla.

Contract emulsion works for me, is cheap as chips, and can be dyed to soft colours. For stronger colours F&B Estate emulsion also works for me, and I suspect that this is the 'flat matt' emulsion available from other companies. Not washable is good in this context!

Stevers, thanks.. you'll have to spoonfeed me a bit here. Does "Limelite products I would regard as damp proof wally territory..." mean "its ok for those who dont know what they're doing.. but expensive" or, "a total ripoff" or, "not required - go and learn how to mix NHL as required with sand".

 

[Stevers]

Travis Perkins refers to it as a 'lightweight cementitious plaster' which is how it was described when I first looked into it. The Limelite website doesn't currently use the word cementitious, or even cement. I briefly considered using it until I read the 'c' word, so don't have any experience of using it good or bad. Definitely something that would be specified for and used by damp proof wallies though.

 

[Lacan07]

This group has drummed into my brain that I need to use breatheable materials. I assume this means proper breathable paints too? Is there a recommended paint range I need to guide the wife on? same question for wall paper!

Wrt the breathable materials for wall repairs & finish, I understand I need to be using a lime based plaster. Are there any product recommendations? Someone I met mentioned Limerite (see product table below). Is that ok to fill holes too? i.e. fist size? and for making good the wall where the sparky has laid new cables etc.

Part 1 - Limelite Easy Bond – breathable primer
Part 2 - Limelite Renovating Plaster

Part 3 - Limelite High Impact Finishing Plaster

I think Limelite is most likely an NHL lime (Natural Hydraulic Lime) which just means it sets under water. NHL is a more modern form of lime which usually comes in powder form and you knock it up with water, some people are suspicious of what actually goes into the stuff, which is probably a bit unfair as the specs are readily available to read. Another manufacturer called Lime Green have suffered the worst rumours, in fact they threatened to sue a well known plastering forum because their products were constantly getting defamed as cementitious.

NHL is fine if nothing else is available. The mortar (NHL 2 and 3.5) is particularly good for various situations when you need a bit of structure and strength. I use it quite a bit for filling service holes in walls, repointing vulnerable areas of external walls, and refacing blown bricks. The plaster is probably best avoided though if you can, especially if you plan to get your hands dirty. It usually goes off like a bitch, probably due to accelerators, so its wise to employ a professional.

Ideally however you should use as much non hydrated lime as you can on your house, this simply means a plaster or mortar that's made with matured lime putty. This will replicate what was originally used. Its softer, which allows for structural movement, and more breathable than NHL lime. You can either purchase it ready mixed or you can slake your own lime putty and produce your own mixes, which many traditionalist still do and indeed some people on here do.

 

[brianos]

I think Limelite is most likely an NHL lime (Natural Hydraulic Lime) which just means it sets under water. NHL is a more modern form of lime which usually comes in powder form and you knock it up with water, some people are suspicious of what actually goes into the stuff, which is probably a bit unfair as the specs are readily available to read. Another manufacturer called Lime Green have suffered the worst rumours, in fact they threatened to sue a well known plastering forum because their products were constantly getting defamed as cementitious.

NHL is fine if nothing else is available. The mortar (NHL 2 and 3.5) is particularly good for various situations when you need a bit of structure and strength. I use it quite a bit for filling service holes in walls, repointing vulnerable areas of external walls, and refacing blown bricks. The plaster is probably best avoided though if you can, especially if you plan to get your hands dirty. It usually goes off like a bitch, probably due to accelerators, so its wise to employ a professional.

Ideally however you should use as much non hydrated lime as you can on your house, this simply means a plaster or mortar that's made with matured lime putty. This will replicate what was originally used. Its softer, which allows for structural movement, and more breathable than NHL lime. You can either purchase it ready mixed or you can slake your own lime putty and produce your own mixes, which many traditionalist still do and indeed some people on here do.

Thanks Lacan07, I've just spent the last hour or so reading up on NHL! Appreciate the help

 

[Stevers]

The widely available NHL 3.5 is referred to as 'moderately hydraulic', the less generally available NHL 2 as 'feebly hydraulic'.

At least in theory you can mix NHL 3.5 plus Hydrated Lime to produce a 'feebly hydraulic' mix roughly equivalent to NHL 2. I did this for the lime slurry that I used like Polyfilla to get a better finish on my chimney breast to extend working time. This approach can be useful to fine tune the hoped for characteristics of a mix.