![]() ![]() Powdered Gypsum plaster is mixed with water, and reacts to re-crystallise and form a set as it dries. When mixed with water, pure Gypsum can set in as little as 10 minutes, and so modern bagged gypsum plasters, such as the type you might buy in a hardware store, also contain fillers and retardants to slow down the setting process. In the UK, the most commonly quarried form of Gypsum is Alabaster, which is heated and ground into a powder. Gypsum, also known as Plaster of Paris, is a naturally occurring soft sulphate mineral, a crystal of Calcium Sulphate. Lime plaster is a breathable material, meaning it encourages moisture to ingress and egress through solid walls, helping to alleviate and prevent damp problems. Lime mortars set slowly through a process called Carbonisation, in which the lime in a plaster or mortar absorbs Carbon Dioxide from the air to form CaCO3 crystals, akin to limestone. Slaked Lime can be combined with sand and water in varying ratios to create lime mortars. The Slaked Lime (aka Hydrated Lime) is matured in pits for a minimum of 3 months, which gives the lime better adhesive qualities, helping it to bond to the wall more better. Lime (a form of Calcium Carbonate) is made from a process of burning limestone to form quick lime (Calcium Oxide), and then slaking the quick lime with water in a dramatic chemical reaction (watch the video from about 1:20 to see this) to form Slaked Lime (Calcium Hydroxide). However, whilst they are both historically used, naturally occurring materials, they have extremely different chemical compositions and properties which make them suitable to very different applications. Lime plaster, mortar and paints have been used for thousands of years, and ancient lime plasters have been found in the preserved ruins of Pompeii, Italy, whilst Gypsum was used in Ancient Egypt in Pyramids. ![]() Both lime and gypsum are naturally occurring materials which have been used in the UK, and throughout the world, for hundreds of years. There are two main materials that are used for plastering, lime and gypsum. ![]() Before we start digging into the nuances of lime, it’s important to define what we’re talking about. If you’re new to Lime altogether, I’d recommend having a read of my earlier blog post, Dealing with Damp, which explains breathable materials in a little more detail before reading on. The below is just a summary of what we have found works for us, and whilst I hope it will help you too, it is important to note that as with all things construction and renovation based, one size definitely does not fit all, and it may take some trial and error (and even some expert help) to find a solution that is right for your home. Overall, I’m probably just about the least qualified person to be even broaching this topic, and so please be sure to do your own research alongside using the following post as a guide, and remember there are people far better equipped than me to teach you about Lime. We don’t have any training, other than what we have learnt through our own research, the brilliant free online sessions run by Cornish Lime (sign up for those here), and a decent chunk of trial and error. Neither Will or I had ever touched a plasterers hawk before starting to renovate properties, and neither of us had even considered plastering a full wall, let alone an entire house, before we started work on the Cottage 9 months ago. The truth of the matter is that whilst lime is not a new material, and in fact has been used for thousands of years, it can be tricky to find easy to understand, jargon-free information on how to use it that is accessible and easy to understand for the likes of you and me. Since sharing our journey with lime on our Instagram page, I have had no end of questions ranging from why we are using lime, to what it is, where to buy it, and how to use it. ![]() As many of you already know, we had originally thought we could get away with just cosmetic work on the Farm, but soon found ourselves stripping the Cottage, the first of the buildings we’re renovating here, of its cement and gypsum plasters, going right back to the stone and effectively starting again. Lime, and lime plastering in particular, is a material that we have had to wrap our heads around quite quickly since moving into the Farm last April, in order to ensure we have been making the best decisions for our property. However, I think the likelihood is that whilst many of you will have experienced gypsum plaster, only a few will have had much to do with the mysterious lime plaster. Most of you reading this will have knowledge of plaster to some degree - you will either have some form of plaster in your homes, you will have seen a plasterer at work, or perhaps you’ve even tried some patch plastering or skimming yourselves. For the past few months, I think about 70% of the renovation work Will and I have been doing on the Cottage have been related to Lime Plastering. ![]()
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