Lime Plaster with Chalk (No sand)

[MD]

I am a bit of a notice when it comes to lime plaster, but as I have a few infil panels to do I thought I'd have a go. I bought some lime putty from Anglia Lime in Sudbury. I explained to the chap there that the panels I need to repair seemed very chalky. He said that it was quite common to use plaster using just lime/chalk/hair with no sand. He recommended a ration of 1:3 lime/chalk, with plenty of hair. I have given tihs a try, and to my dismay the results were none too good. The resuling finish was cracked and glazed like the bottom of a dried-up muddy riverbed!

I thought that perhaps I had put in too much chalk, or the base was not dampened down enough, so I cut the ration down to 1:2 and wetted the area well. Still got the same result. I'm sure that I've put in loads and loads of hair, but maybe I'm still a bit light on this? Would the hair make that much difference to the cracking? The resulting misture seems almost too heavy and sticky, but not sure if a little water would help? Maybe a little sand in the mix would help?

I've been told that this type of mixture is dead easy to mix and use and should also be very resistant to cracking so any ideas on where I'm going wrong would be most appreciated!

 

[CHRIS]

I had the same experience with the chalk but by adding a bit of water it will help, but the main thing is to get the wall very wet by getting it soaking about 24 hrs before then about an hour before you start and then right before. Also get it very hairy as this will help (1/2 inch long). Beware of the little bits of flint in the bagged chalk as you thing you are a pro with the trowel and then a bit drags across your work and buggers it!!!!

 

[Mark]

are you keeping it damp after you plaster?

how thick a layer or plaster?

 

[MdB]

How does using chalk rather than sand work?

With a 3 parts sand to 1 part lime mix, the sand gives the strength and the lime holds the sand in place.

With a 3 parts chalk to 1 part lime mix, the chalk doesn't have much strength and is just carbonated lime anyway so where does the strength come from?

 

[MD]

In reply to Mark - its not a very thick layer - maybe an eight of an inch, not much more. After I plastered it, I gave it a light spray, but my two attemts have been done late at night, so I haven't returned to it until the following evening. Do you need to keep wetting it at regular intervals? There is no hrating in the house so its fairly cool.

In reply to MdB - I presume the strength comes from the hair. The old plaster I'm repairing is very supple - more like a carpet really with the hair very much like the fibres in a carpet.

the more I think about it, I think that perhaps I just haven't put enough hair it it - my plaster is nothing like the 'carpet' i described above. Also, the old plaster is very pliable and chalky - mine has set solid!

 

[ian]

It sounds like you need to be damping down much more often, - but only lightly. What is the underneath layer you are plastering on to.? is it daub or a lime substrate? Old lime indoors, especially earth mixes tend to be very thirsty. You need to water for a couple of days before hand to get the moisture right in to the old wall in my experience, and water morning (noon if possible) evening and before bed. A pump up 5 litre garden sprayer makes a good fine spray that is controlable indoors for the task I have found. Just mist the surface after plastering, you don't need to see running water on the surface. That will enable you to tighten up what are hopefully fine cracks.You should see a different colour change on wetting as the surface starts to carbonate, Don't forget that the subsequent limewash coats will help to smooth it out - at least 6 is my preference. Also sounds like you need more hair!

 

[charlie-ia]

we sprayed twice a day (indoors and cool) untill it got firm enough not to leave thumb marks - is that right? we're not sure how long we should spray for

 

[MD]

Ian, some panels are wattle and daub, others are red brick with lime pointing. Sounds like I didn't water for anything like enough - just gave it a spray down prior to applying plaster. Also I think you are right about the hair - much more needed.

Do you think there is any way of rescuing the plaster I've already done, or do you think its a hack off and start again job?

 

[NT]

Lime shrinks on drying, so going from 3:1 to 2:1 will only make it worse


NT

 

[ian]

MD
The daub panels are going to absorb a lot of moisture if not damped well for a couple of days before. You say the house is cool, but the air may be dry. The layer you are adding is quite thin so this will dry rapidly and the chalk and hair are going to absorb moisture as well initially so a small. quantity of water won't harm. As for "rescue", if the new coat is stuck well - leave it and use lime wash to smooth the surface. 1 putty: 2 to 4 water by volume, mix well and sieve. Apply in alternate directions to a slightly dampened wall each day for a week or so. If the plaster has not adhered well or dried without carbonating, it will come off and crumble easily. No waste though, just mix it in with the next attempt as more aggregate. How long to water the walls after? As I said the new plaster will change colour differently at the start to later when misting, A day or so after you see that - then do it if you feel tempted, it won't harm. A week is not a long time to be misting.

 

[Gervase]

To judge exactly how much lime to add, you could adapt a standard technique used when testing a new aggregate.
Put say 200ml by volume of your chalk in a straight-sided vessel (a small glass will do) and, from a measuing jug, slowly add just enough water to show at the surface of the chalk. You may need to stir it, and it'll be a bit sticky, but the volume of water needed to fill in all the voids around the chalk will be equal to the volume of lime you need.
The technique works extremely well with sand and heavier aggregates, but you may find that the chalk has an annoying tendency to float and clump together if it's very fine and dusty, so a couple of drops of detergent in the water may help.
On the other hand, you may end up with a glass full of an unappetising sticky, chalky mess with a good head on top!

 

[Penners]

200ml by volume

That's as opposed to 200ml by weight, is it? :wink:

 

[Gervase]

Grrr! You're asking for 28g by volume of lead shot in the fundament!

 

[Penners]

Grrr! You're asking for 28g by volume of lead shot in the fundament!

You'll need to aim carefully to find a clear spot. It's pretty crowded down there already.

 

[BMcD]

I've never used a haired finish with chalk before, but have used haired fine putty (3:2 lime:silver sand) over single lath stud work, where only one side of the stud work is lathed. The haired finish was plastered directly onto the lath on both sides, enveloping the lath with plaster. Cracking was avoided by regular sponging of the surface as it was drying, using a water brush and sponge float to dampen and gently scour the surface, first thing in the morning and before going home and finally brushing over the surface with a slightly damp brush. You may find hanging damp hessian in front of it helpfull. I've also used it on floated work without any trouble.
But the key is having enough hair, think Aberdeen Angus fringe when you pick up the plaster on the end of a trowel, also wet the surface as per CHRIS but don't have water sitting on the surface before plastering, allow it to soak in a little

 

[MD]

Thanks for all the advice - I think I'm getting there now!

On my next attempt, I put in loads more hair, and went back to 1:3 putty to chalk. I also added a little water as it was just too stiff to work with. I dampened things down a lot more and kept wetting as often as I could. this seems to have done the trick. It looks a bit like a mountain range (I really do need to learn some plastering skills!) but it is a mountain range without cracks. Still, as it is nice and chalky I've found a little bit of fine sandpaper helps to get a nice smooth surface.

 

[ian]

One way I have found to get a bit smoother with a thin top coat is to apply it with a thin plastic spreader, rather like a grout or floor tile adhesive applicator - but without the notches. I haven't tried it with a haired coat but it may work. Also, if you get to limewashing, it will end up over the panel framing. A small brass wire brush is a good tool to just remove the overpaint on the beams without scratching the beams or the plastered surface. Harris make a green plastic toothbrush style one, not sure if it is meant for suede shoes or spark plugs.

 

[Anne]

Can I ask you please where you have bought the chalk from I'm having trouble sourcing chalk.

Thanks

 

[CHRIS]

I got my chalk from Anglia Lime in Sudbury but I dont know where in your area would stock it. Try Ty Mwar they may know of a place and is not to far from you

http://www.lime.org.uk/map/map.html

http://www.stripperspaintremovers.com/anglialime/
(new website)

 

[Lady_Mari]

We've just had the sitting room lime rendered & the chap that did it used a putty & ground chalk mix as a thin final top coat about 2 weeks after the haired mixture was done which also filled surface cracks.