Lime rendering and plastering is one the key ingredients of a sustainable older home. Lime putty render with a stone dust aggregate has a very low embodied energy, it is very breathable and it is the correct render of choice for solid walled houses. So the choice of using lime render is a really obvious one.
So are there any issues to worry about?
The short answer is yes.
The main issue is that lime is not cement (hurray for that!) and builders are not trained in using lime. Some builders even get cement wrong, so what are the chances with lime? Well, to be honest, not good. Lime is a more natural product and it cures using natural processes (carbonation) and so it is subject to the fluctuations of the weather. Getting the mix right and applying it correctly takes experience and a real sense of how the lime is curing. Getting it wrong is therefore quite easy. Temperature, humidity, type of substrate, method of application etc all effect when the layers of render are applied. It might be that the second coat is applied the following day, or it might be the following week. An experienced lime renderer will be able to have a look, a touch and then gauge what to do and when. An inexperienced renderer will not be able to do this. They might be able to follow instructions from a book, but it really does take a lot of hands-on knowledge and experience of a product in order to get it right.
Different substrates might require different types / mixes of lime. So a renderer needs to be really au fait with the range of mixes etc in order for the render to be successful.
It is therefore possible for an application to go wrong. If it does fail it can be down to two possible factors. The specification of the mix OR the application of the render. This is where you can become Mr Piggy stuck in the middle, because, no doubt the lime supplier will be tempted to blame the trades person and vice versa. You, on the other hand just want your render done correctly. What do you do?
Answer – get stressed.
Is there a solution? Thankfully, yes (well in fact two).
1. Read up on lime and the need for it and also all the different types and choices
2. Source some good experienced lime professionals (seek some references)
3. Ensure that the supplier and professionals engage with each other to come up with an agreed mix
4. Have an agreement in place to cover eventualities
5. Investigate having an insurance policy in place (similar to the FMB Build Assure Warranty)
1. Use a reputable company that actually makes and installs the lime render and that offers a guarantee.
I know which alternative I would choose, but either should work and give you the peace of mind you require.
If you choose Solution Two and live in or around South Wales I would recommend contacting either:
Welsh Lime Works (Mark – 07800 892521) http://www.welshlimeworks.com/
Vale Lime (Martyn – 07702 150138)