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LIME PLASTER
Down to Earth Design Sigi Koko. Principal admin @ buildnaturally.com
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WHAT IS LIME ? MIXING & APPLICATION RESOURCES Lime plaster can be mixed by hand, but this is labor- Lime has been used for thousands of years as a binder WEBSITES intensive, so I recommend using a mortar mixer (not a in mortars, plasters, and paints. During the post-World www.mikewye.co.uk cement mixer!) for at least 20 to 30 minutes. The War II housing boom, quick-setting cement products en.wikipedia.org/wiki/Lime_plaster longer you mix lime plaster, the more plastic and eclipsed lime in construction. Lime does cure more howardhallfarm.com/limeplaster.html workable it becomes. Allowing the mix to sit overnight slowly than cement, but it holds many advantages as a www.nps.gov/history/hps/tps/briefs/brief21.htm also improves workability, but remember to remix workable, self-healing, breathable, nearly carbon www.buildnaturally.com/EDucate/Articles/Lime.htm before using. The plaster consistency should be thick neutral material, making it nicely suited to natural but spreadable, like cream cheese. building. (Cement production creates 1.25 pounds of BOOKS CO2 for each pound of cement produced.) Additionally, To prepare your walls, first shape them exactly how you Building with Lime: A Practical Introduction by Stafford lime plaster is breathable - meaning it allows air-borne would like them to look once plastered. It is time- Holmes and Michael Wingate This is my lime bible! moisture to travel freely through - so does not trap consuming to build up the lime plaster to fill in large moisture inside a wall system. Without moisture voids (since it must be applied in thin coats). Next, Using Natural Finishes: Lime- & Earth-Based Plasters, buildup, biodegradable materials, such as wood or install expanded lath to cover any slick surfaces, such Renders & Paints by Adam Weismann and Katy Bryce straw, are protected from decomposition. as wood. Make sure your lath bridges across the wood and at least 6" into the straw so you don't get a crack right where the lath ends. I do NOT recommend using HOW IS LIME MADE ? lath over all of the strawbale, unless you live in a 1. kiln burn. First limestone, seashells, or other seismic region and your code requires this, as it will material containing calcium carbonate is heated in a impede your plaster from bonding fully to the straw. kiln, driving off carbon dioxide and leaving calcium oxide , also known as quicklime. I recommend 3 coats for lime stucco over strawbale walls. The first coat can be up to 5/8" thick if it is 2. hydration. Quicklime reacts with water in a volatile applied to strawbale, otherwise each coat should be a process called “slaking”, resulting in calcium hydroxide , maximum of 3/8" to 1/2" thick. Any thicker and the or hydrated lime. Calcium hydroxide can look like a lime cannot absorb carbon dioxide adequately for curing powder or a thick, sour cream consistency putty. If to fully take place. Score each coat except the finish purchased as a powder, it must be rehydrated in water coat to allow for maximum surface area to key two for many weeks to create high-quality putty for plaster. coats together. Allow at least 4 to 5 days between 3. carbonation. Calcium hydroxide reacts with carbon coats to give each ample time to cure. dioxide in the air to create calcium carbonate …exactly I do NOT recommend lime plaster over clay plasters for what it started as! exteriors in wet climates. The clay substrate shrinks and swells depending on moisture content, causing the THE INGREDIENTS IN LIME PLASTER lime, which cannot shrink and swell, to crack. Lime can be used over solid clay walls, such as cob or adobe, 1. lime putty : sticky binder that adheres to the because there so much more clay is present to absorb wall/substrate and holds the sand intact ambient air moisture without measurable swelling. 2. sand : aggregate, provides strength and cracking control; use fine, angular mason’s sand for fine Soak all surfaces with water before applying each coat plasters, and course or fine sand for base coats of lime plaster and keep the wall substrate damp as you
I use a mix of 3 parts sand to 1 part lime putty for all work. Do not rework plaster once it has stuck to the plasters, though you can increase the lime putty ratio to wall, as this pulls lime to the surface and leaves what is up to 1:1 where very fine finish surfaces are desired. underneath sandy with less binder. You can work the HANDS -ON WORKSHOPS surface to create a desired texture once the lime is green hard. And you can buff or polish the lime as it is SAFETY curing to create a very fine surface texture. Down to Earth Design teaches workshops on Note that lime is highly alkaline and can severely burn plastering with hydrated lime putty on strawbale walls. You want the lime to cure NOT dry out. If it dries out your skin. Unlike acid burns, you generally do not feel before it has cured by reacting with carbon dioxide in WORKSHOPS INCLUDE : an alkali burn as it occurs. So please use full protective the air, the resulting plaster will be weak and possibly • overview of hydrated lime, including safety, surface gear whenever working with lime, including elbow- crumbly. So protect the plaster from wind and sun until preparation, troweling skills, and why calcium length rubber gloves, long sleeves, eye protection, etc. it has cured, and it helps to dampen the wall daily as it hydroxide outperforms cement and hydraulic lime If your clothes get lime putty or lime water on them, is curing. Do not apply exterior lime stucco if there is change so the lime is not in contact with your skin • guided hands-on experience mixing and applying any risk of freezing, otherwise moisture in the plaster through your clothing. I always keep a bucket of hydrated lime plaster can freeze, expand, and cause critical failure of the vinegar water nearby to neutralize my tools, gloves, plaster. The temperature needs to be above 40 F for at Check our website www.buildnaturally.com for and hands throughout the day. least a week to keep the curing process going. additional information.