plaster mix.

[livias]

Workers of old certainly did lay down their putty. According to ?Vetruvius? Roman plasterers had a system where grandfather laid down the lime putty for grandson. Even allowing for hype on the part of the plasterers, they must have kept it a while. For my work I can see a noticeable difference in 6 month plaster compared to new

 

[formerly known as]

chopped straw - I can buy bales locally for £2 and then chop it myself. Small amounts can be bought from a pet shop.
Type/s of lime + substrate - aside from the strength of hydraulic in comparison to most historic mortars, I don't like using it as it isn't fatty enough and is therefore more difficult to use and can also slump.
'popping' - This happens primarily because unslaked quicklime has slaked in the wall
quicklime in hydrate - I would doubt that
mixing - in a cement mixer or with a paddle mixer in a tub ........... I mix it and use it straight away - I have made it and stored it up and this will improve its o/a consistency which makes it great for flintwork.

I think this answers all the Q's

 

[formerly known as]

yes - wet the wall down and then keep it sprayed for a week afterwards to prevent it drying out too quickly. An old boy once told me 'if it (any lime work) goes white in a day, then you have had it' .............. by white he meant dry.

 

[livias]

Its also important where you are in the country. In wet and wooly west Wales, they use hydraulic externally. In East Anglia hydraulic render is unheard of

 

[MatthewC]

As regards ageing of putty, I have read that for quality work it was usual to make it up months in advance.

When you buy neat lime putty from a supplier they usually say somewhere how long it has been aged - for instance Mike Wye say "matured for a minimum of 3 months" (http://www.mikewye.co.uk/product/lime-putty/) (other suppliers are available...).

Whe you mix lime mortar (or plaster), including knocking up some older previously mixed stuff, people say you should then leave it for a while (like 20 mins) in the mixer before using it, but I've never been clear what difference this makes. I think it improves the workability?

 

[Zebra]

How do you mix lime putty with sand? Do you just mix for a very long time?

I measure out the putty and the sand, using a cereal bowl, into a bucket, add a little water, and use a drill and a paddle mixer. I do a little at a time, and as soon as it seems reasonably well mixed, maybe a couple of minutes, I tip it into a bin, make another bucket full, tip that in, and give it all a good stir in the bin. I don't mix for anything like the half hour / hour which seems to be recommended. But then I'm not doing anything of particularly high quality.

Can you buy thing pre-mixed and just use them straight out of the bucket/tin?

You can buy plaster ready mixed, but it still needs "knocking up" i.e. remixing before use, in a mixer or with a paddle, to restore its workability after it's been sitting in the bucket.

 

[Gervase]

Mixing is a doddle.
Pour off excess water from the top of the tub of putty (keeping it handy in a bucket in case you need to soften the mix. Chuck one tub of sharp sand into the mixer, then starting trowelling out the putty and bunging it in with the sand. About half way through, chuck a second tub of sand in, and then add the rest of the putty - a bucket trowel is the ideal tool to get it out. Let the mixer run for a good 15 minutes, then add a third tub of sand. Let the mixer run of another 10 minutes or so and examine the consistency. If it's too thick, sparingly add some of the water you poured off the putty earlier. Go easy, though, as the longer you mix, the softer the resultant stuff.
That works well in a Belle or similar drum mixer; just factor in a good half an hour per mix.
If you've got a pan mixer, just chuck everything in and run for 10 minutes. Beware though - if the rollers in your pan mixer are heavy, don't overdo the mixing, as they'll break down the larger particles in the sharp sand and give you too soft a mix. I left mine running for half an hour once and had a mix I could have used for slip-casting!
If you're using a paddle mixer, start with a 1:1 putty and sand mix, plus a little extra water, and once you've got a smooth, sloppy consistency, add the rest of the sand. It's tough on the wrists, though. Paddle mixers come into their own for mixing finishing plaster; a 1:1 mix of putty and silver sand can be brought to a fabulously creamy finish.

 

[formerly known as]

hello,

by way of an update, I have used this same mix - in two coats - over my light clay straw external walling, together with three coats of limewash. All has gone well.