Using "young" lime putty for lime plaster

[GillesF]

Hi all

I've made my own lime putty from good quality hydrated lime today since it's difficult (and too expensive) to get commercial lime putty in my country. I'll be using this lime putty to repair some of my lime plastered walls where the lime plaster failed due to water ingress (fixed now).

However, I've read that the lime putty should be at least 3 months old before using it but I'm planning on starting my repair work in 2 weeks. I understand older lime putty is better regarding workability, adhesion etc but has anyone tried plastering with "young" lime putty? Will this have any negative effects on my lime plaster?

Thanks!

Best regards,
Gilles

 

[aockenden]

Yes, the whole “aging” thing is largely bollocks when dealing with modern powdered hydrated and quick limes which fully slake with water in a matter of days. Back in the day when the lime came out of the kiln still in lumps / rocks then the “aging” dogma was more relevant, as it took the water longer to penetrate deeper into the big chunks of lime to achieve a full slake.

The only nuance is that after slaking your powdered hydrated lime, if you add too much water and stir it all up to get all the lime slaked, it can become very sloppy wet and low-density if you scoop it back out to make a mix too soon. Under those circumstances It just needs a week or two to settle back out from the water and become more dense / compacted at the bottom of the slaking barrel. Then it’s ready to use.

 

[aockenden]

At the end of the day, it’s always good advice to just judge the putty coming out of the bucket on a case by case basis. If it seems to be a bit less dense / sloppier, don’t add as much water to your plaster mix. If it seems denser and less wet, plan to add a touch of extra water when you mix your plaster.

This is prudent because even my barrels of slaked quicklime AND my barrels of slaked hydrated lime, both of which have been aging for almost a year now, have variations in putty density as you get deeper into the barrel, with the deepest layers in the barrel being the most dense and the topmost shallow layers being the most watery / least dense.

 

[GillesF]

Thanks all for the replies!

I used scales and added 10L of water + 11kg of slaked hydrated lime to a 20L bucket. This gave me a creamy, yoghurt like consistency but would still stick to the trowel. Can't wait to see how it evolves and use it for the first time in a few weeks.

Regarding the lime plaster: if my research is correct, I should use 1 part lime putty and 3 parts sharp sand for the base coats and no extra water (unless too dry)?

 

[housegolem]

from the book for three coat work

1st coat lime 1 - sand 2.5/3 depth 6-16mm (sharp)
2nd coat lime 1 - sand 3 depth 13- 16mm (Plastering)
3rd coat lime from 1to3 - from 3to1 depth 3-5mm (silver) Trowel finish go Rich 1:1 1:2 Textured wood float 1:2 or 1:3 The book said the lime ratio on the setting coat is dependent on the sands sharpness, more sharp more lime but unless you have a lot of experience this is pretty useless info really.

I go 1:2.5 scratch then 1:3 float then one coat of 1:2 setting followed by a richer 1:1 final setting coat - In my experience, getting a good smooth finish on the final coat is helped by richer lime mixes

As for wetness/dryness, drier is better to stop shrinkage and cracking, but it also makes it harder to work and more tiring to apply. Fine if it's a small area, but difficult on say a 10sqm wall.

Use dry sand when mixing, then you can always add water to get to a workable mix. I would bet you will be limited by your physicality, unless you are a plasterer/builder by trade.

I mix as stiffer mix as i can apply over a large section. Any shrinkage cracks that might appear over several days of slow drying can be pressed back in. An overly thick coat will crack more.