‘Standard’ lime plaster vs Hemp lime application and level of skill

[DaveG]

I recently started watching a series on iPlayer called “The great house restoration”. Ive watched almost all of the house doer upper type programs under the sun but found this one a few days ago and particularly like its focus on conservation and original materials.

I think it was maybe the 3rd or 4th episode in of the first series a lady was renovating a complete wreck of an old Irish Croft type cottage dating back to 1700s that had been in her family for something like 5 generations.

Anyway, what caught my eye was during the build they visit a couple other people with similar/finished build and one family did theirs on a shoe string budget.

One of the things they mentioned was their use of hemp lime for its better insulation properties (those cottages are cold!). They also said how easy it was to use as an inexperienced DIY’er and for the most part were just pushing it on with their hands.
Is it that simple to work with? I guess you’re never going to get a smooth flat finish like you would by using a float, trowel, top coat etc but if your project lends itself to that undulating finish is it that simple? It’s quite a typical finish of these older farm buildings and painted up white had a real charm to it.

They also praised how much warmer it was to the touch than a traditional plaster. Have others that have used hemp plaster found a noticeable difference in warmth?

 

[a twig]

I’ve used hemp plaster, it’s hard work to apply as it is very stiff and heavy. If you’re happy with a rough and lumpy finish then it would be fine, but it is hard work to shift it about on the wall to get it flat enough for a top coat.

The insulating performance isn’t amazing, wood fibre or wood wool boards with a lime skim are a much better bet on that score, but it is better and “warmer” to the touch than just lime plaster on its own.

 

[DaveG]

I’m still not completely sure on what to do about insulation if anything. My walls are just under 2ft thick at around 21 inches.
I keep reading you have to be conscious of not making the wall too cold from the exterior where you can attract more moisture into the fabric of the wall and cause further issues.
I’m trying to find the middle ground if there is one or if the wall is sufficiently thick to have a good u-value as is, perhaps just avoid altogether. Now I’m at the point something needs to go back on, it’s knowing what the most appropriate choice is

 

[a twig]

Depending on the stone your wall is constructed from and what condition the wall is in, that thickness would likely give a u-value of somewhere between 1.9 and 2.2 which is fine.

 

[a twig]

If you say the wall is pretty lumpy and bumpy and you’re happy for it to continue to be then probably just look to get some lime plaster on it and call it done, potentially with a bagged finish to make it clear the bumps and lumps are intentional rather than a result of bad plastering!

 

[paulc]

A lump & bumpy finish is (I believe) referred to as rustic.
Back in the day, really skilled tradesmen were in short supply, partly due to the smaller size of population. So many rural homes were built on a shoestring budget using local semi-skilled labour. Smooth flat plaster was for the landed gentry that could afford to bring in skilled tradesmen.

 

[DaveG]

Depending on the stone your wall is constructed from and what condition the wall is in, that thickness would likely give a u-value of somewhere between 1.9 and 2.2 which is fine.

I hadn’t really given much thought to the type of stone material making a difference. It’s a Welsh stone cottage built around 1890 which probably narrows it down but here’s a pic. If you could confirm that would be hugely helpful thank you

 

[a twig]

Scottish regs but provides probably the best easily available methodology.

Domestic and non-domestic energy performance certificates review: supplementary notes

Notes supplementing analysis of responses to our three public consultations about energy performance certificates (EPCs).

www.gov.scot

Your stone looks like limestone to me - maybe blue lias? Looking at the internal photos all those big gaps etc will need fill / dubbing out - hemp based plasters are really good for that task.

 

[DaveG]

That’s super useful thanks

 

[Stevers]

The smoother stones could be a sandstone, the gnarlier ones perhaps a limestone possibly carboniferous - both are possibilities for Pembrokeshire. Above basement level we have the original plaster and only in the breakfast room that is open to the kitchen do we eventually get a degree of black mould in the corners. Our walls are mostly 20" thick (being white lias on front and the rest a more rustic probably carboniferous 'mountain' limestone). With smart TRVs fitted to a conventional gas central heating system from 1997, the house (5 bedrooms) is comfortable with gas and electric coming in at £260 per month on average. It helps that no room has more than two external walls since we're double fronted and two rooms deep. Almost all my rads are on internal walls which also minimised pipe runs and reduces heat loss through walls. Our original single glazed sash windows are mostly draught proofed with the self-adhesive Stormguard V strip system. All our suspended floors have fitted carpets with a heavy duty underlay, or a thick vinyl on oiled hardboard and I'm sure all that helps too.

Replacing plaster to the original thickness would be less work and will make the retention and replacement of original features and proportions easier - no reason why you shouldn't put a bit of insulation in it though. Your window splays almost exactly match ours, and generally from what you've shared our homes have much in common.

 

[DaveG]

Sounds very similar @Stevers. Do you live in Pembrokeshire too?
Our bills appear quite similar though my floors have been filled in (concrete) and my sash windows are not yet draught proofed although I have someone coming out to look at doing that alongside getting them working as they should again shortly.

No active mould here from what I can see though signs there’s been rot in the past - https://www.periodproperty.co.uk/forum/threads/is-this-dry-rot.19933/#post-257686 - and I do run it on the cooler side, generally 18 to 18.5c. Would like to boost it a little warmer over winter once I can get the heating bills down a bit but it’s a work in progress.

Interesting you mention rads being on inside walls. Mine are too but was actually thinking of moving some to outside walls near windows to try and reduce risk of condensation on exterior walls but as you say there’s then the issue you’re maybe losing some efficiency