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                                                                                          Lime Plaster

             Lime plasters, mortars and  concretes have been use in construction for over a thousand years. They are in many ways superior today's products. The disadvantage of lime products is the time needed for them to reach substantial hardness. A period of approximately 28 days is required. During that time the lime plaster must be kept damp and protected from freezing.  The term lime plasters and mortars are interchangeable the difference being the sands or fines  added. Lime plaster has the advantage over modern gypsum plaster in that it can be use outside as well as in. Historic buildings in fact had the same lime materials use through out   their construction. A lime concrete was used for the foundation followed by the laying of brick or stone for walls using the same material with sand rather than gravel for an aggregate. The walls were then stuccoed on the outside ( referred to as renders in England) with the lime plaster and then the interior walls were plastered with the same materials. The great advantage of this system is that it allows moisture to move inside and outside with out trapping it in walls. Lime plaster is also more flexible letting a structure move without fracturing walls.  If a structure was built prior to 1900 it probably was constructed using lime plasters and mortars. Modern portland cements  and gypsum plaster should never be used to repair lime plaster walls especially exterior walls. The cement will trap moisture in the walls causing  more damage that if the repair were not undertaken.  This has been show by studies conducted  by  England's Ministry of Building Works (Ancient Monuments Division).  It was shown that repairs carried out in the 20's and 30's using portland cements resulted in more damage after 20 to 30 years than had occurred in the previous 100 yrs. of neglect. 

           There is another type of lime cement (hydraulic lime)  first used by the Romans which is unsurpassed in it's resistants to water. these are naturally occurring materials which are mined crushed and prepared for sale. Hydraulic limes come in several grades NHL 2, NHL3.5 and NHL 5. The higher number indicating greater hardness. These materials have been used in Europe on sea walls where they are outlasting modern portland cements.  

           These products are not available at the average building supply in fact they probably don't know they exist, but there are now a number of suppliers in the United States who handle these material. An internet search will yield  several of these suppliers as well as organizations devoted to the promotion of the use of lime plaster. 


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Last modified: March 13, 2006