We are due to move into a cottage ( Somerset) in the next few months. Originally it was built in the 1600’s with additions as you would expect.
I have no idea what it was originally plastered/rendered with, there is a possibility due to a major renovation in the70’s, modern plasters are present. However, it is Grade 2 listed so, great care ( I assume) would have been taken.
I am considering making a 3D design in one of the rooms and I believe lime plaster ( is it the same as your lime putty?) is required due to the open time.
Obviously, I haven’t made anything in a malleable plaster before and am quite excited in using a new medium.
Or do you have the raw products necessary? I have looked at various sites (building conservation.com) but I am happy to experiment, but hopefully you can give me some pointers.
I’ve had very pleasing results using a 2:1 lime putty and sand mix with enough water to make it into a runny slip (maybe like thick pancake batter?). Then i get straw and toss it in the lime (rubber gloves and wheelbarrow or big bucket etc.) adding as much straw as possible whilst coating it all over. I’ve built this up to 5-10 cm deep. You could probably let set some then use more layers to go deeper. It is strawy and rough so this make the core of your sculpting. I’d finish with 5-15mm of 3:1 lime putty and sand without straw.
All sorts of variations work including doing it all with clay instead of lime. This is nicer in that you don’t need gloves etc to handle it. Lime sets stronger quicker and clay will go soft /wash away if it gets wet. Straw/clay can be covered with lime finish – thats prob my favourite combination.