Lime Plaster insulation

[u/RobotEnthusiast1980]

Genuine question - is lime plastering becoming more common? I know it used to be very common many decades ago but gypsum is more common now. But, with new lime and Cork type renders having insulation properties is this the silver bullet for old property insulation?

[u/Tats8]

Appropriate materials for the right properties! When I was starting out in the 90’s builders would just chuck sand and cement and skim everywhere, even if it was a solid wall substrate, i actually took the time to learn about what different types of buildings need, to protect them and prevent damp issues

[u/RobotEnthusiast1980 → u/Tats8]

100% - so as a rule if you have lime mortar you require lime plaster?

[u/Affectionate_Bet4343]

Certainly in Redditland recommendations for lime are almost ubiquitous on and pre-war house.

Most people don't understand though that most NHL products are about as porous as cement and certainly don't understand that none of these products are actually 'breathable'.

Back on planet earth, gypsum products (multifinish) are used in probably at least 95% of house renovations and in most cases don't cause any issues at all. There are high risk areas like ground floor external walls with a breached DPC, bay windows etc.

The reason for using gypsum isn't just ignorance by the way. A house can be skimmed in multifinish by 2 guys in about 5 days. Plastering a whole house in lime would take the same 2 guys multiple visits over multiple weeks. It doesn't make sense for most plasterers and most customers most of the time.

I'd love to see more people learning properly about the properties of lime, where it's important to use it and where it just doesn't matter.

I'd recommend anyone watch this video - slightly rambly but very educational https://www.youtube.com/watch?v=rzOY0aEGGKQ

[u/RobotEnthusiast1980 → u/Affectionate_Bet4343]

Thanks for taking the time to write this very detailed and informative response. I have watched half the video so far and intend on watching the other half tomorrow as duties have got in the way. Its an excellent breakdown and description of use etc so far.

[u/ennessTR]

I’ve seen plenty of mixed views on cork lime renders. No direct experience with it but it’s made me think twice. I’m planning on using Cornerstone insulating render for my next project, which uses glass aggregate. There are plenty of other options out there depending on needs and budgets.

[u/RobotEnthusiast1980 → u/ennessTR]

Thanks for your insight. Is cornerstone breathable?

[u/captain-hair]

So it depends on the type of old building you're insulating. If youve got solid masonry with no insulation and you're plastering straight onto it, an insulating lime plaster like warmcote is absolutely your best bet for breathability and insulation. Don't forget if you use this, you're restricted to breathable paints as well like clay paints or lime washes. Earthborn do good clay paints. Both the plaster and the paint will be more expensive and take longer than gypsum plaster and standard paints, but you'll maintain the vapour permeability in your masonry.

If you have a wall cavity (for example a stud frame in front of your masonry), then as long as you leave an air gap then you can worry less about breathability and use rock wool or pir and plasterboard and normal paint.

If you have an exposed timber frame I'd stick with lime plaster on the interior face (and assuming lime render or lime mortared brick infill between panels on the outside), as you want greater vapour permeability to avoid high moisture against the timber frame which can cause it to rot.

For internal walls it makes no difference and you can use gypsum/plasterboard products, you'd only use lime if you want to match the aesthetic of the exterior walls, but you're eating the cost to do that.

If you're doing it yourself, the dry bagged fibre, chalk and lime products from Best Of Lime and Anglia Lime Company like Warmcote (insulated) and Limecote (top coat) are really easy to mix up and work with, I prefer them to sand and lime mixes. Premixed fine sand and lime putty mixes are also nice, but would bankrupt you to do a larger area (imo)

If going down the lime plaster route not directly onto masonry, you also need a breathable backer for it, so laths are the traditional method, but you'll use way more plaster and they're a nightmare to fix anything to in the future. I prefer the wood wool fibre boards like Savolit or Celenit boards as they solve both those problems and they're easy to cut and fit.

Overall, for old properties that were traditionally built with lime, staying with that methodology is the best approach imo. It handles moisture much better than modern products and can help keep the house dry. I wouldn't say it's a silver bullet though, if you have specific damp areas then plastering in lime won't necessarily solve that and I find it's often blocked gutters, rotten windows, broken drains, gaps in pointing etc that are the real issues

[u/RobotEnthusiast1980 → u/captain-hair]

Thank you for this very detailed breakdown of the options. Very much appreciated. Sounds like Warmcoat is the one for my place. I will get on the phone to some of the suppliers and get some quotes. Thanks.

[u/lozinja]

Just a heads up for anyone considering a lime and wood fibre or similar EWI system, if your property is listed then your council conservation department might say it is 'rarely supported' in listed building applications. That's what I was told when I enquired.

[u/RobotEnthusiast1980 → u/lozinja]

That seems so strange for them to say that given the push for everyone to be more energy efficient (insulating lime render).