Wednesday, January 2nd, 2008
RALEIGH - MORTAR - PUTTING IT ALL TOGETHER
Raleigh, North Carolina. Mortar Holds The Bricks And Stone Together. When you want to put some bricks and/or stone together all you do is mix some sand with lime or cement, throw in a little water, mix it all up, slap it between two surfaces and that’s all there is to it. Right? Well, not quite. If you are building a home you had better have a brick or stone mason who knows his trade if you don’t want instant disaster. However, that’s a top for another post. What I want to concentrate on here is mortar.
Over the centuries masons have used materials and mortars that have provided a varying range of hardness. Soft mortar requires re-pointing from time to time as does hard mortar depending on use and weather. One of the problems you can have if you use a mortar that is too hard is that the stone or brick can be degraded. But, I am getting ahead of myself.
Masonry mortar can be Portland cement or limestone based. It can also be a combination of the two. THe mixture masons used for centuries was basically a mix of one part lime and three parts sand. Furthermore, down through the centuries mortars have been formulated from so-called natural cements. Natural cements are deposits that contain clays and impurities that cause them to get hard under water.
The first commercially made hydraulic lime was by Joseph Smeatong in 1756. During the lime-burning process he added clays and ash to create a natural cement. What we know as Portland cement was patented in 1824 by Joseph Aspdin. Portland is a hard hydraulic cement that meets the needs of the building trades. It sets up harder and more quickly than lime cement. Lime mortar sets up slowly, can take months to cure fully and doesn’t have nearly as much compression strength as Portland cement.
Masonry mortar must do several things: (1) It has to work rather like the oil in your car’s engine. Oil lubricates the metal and allows the moving parts to work together without creating so much friction that your motor burns up. Mortar, in effect, acts as a lubricant between the brick or stone it is bonding together. As it cures it spreads the the weight of the stone or brick over the total area of the stone or brick below. (2) The next thing it has to do keep moisture and wind away from the what is behind it. (3) Assuming what is behind it is the inside of a home, it has to allow water vapor from interior space to pass through to the outside. (4) Finally, it has to be softer than the stone or brick it holds together and needs to flex as the brick or stone it holds together expands and contracts.
The age of a building determines the mortar a mason uses. For example, brick used in buildings prior to 1890 tends to be soft. Brick produced after 1890 was harder. Use of of Portland cement commenced in the 1870’s and replaced lime mortars. From around 1880 unit the second world war mortars contained both lime and Portland cement. After WW II most masonry cements were Portland cement and sand with no lime. With stone it’s harder to figure out whether to use a hard or soft mortar. For the most part hard mortars are used with hard stones. A mason trying to match mortar used in an existing home must try to determine when the home was built and, if possible, test a sample of the existing mortar for hardness. He is left with only a guess he will usually tend toward a softer mix.
NOTE: A time when you are very likely to get involved with mortar is when you are asked to select the color of mortar you want to use with the brick and/or stone you have or are selecting for a home you are having built. If you have had more than one home built you know how important this is and how much thought goes into it. If it is your first time, the time and thought it takes will surprise you. Your builder will recommend to you a company he usually uses to supply his brick and a company he usually uses to supply his stone. The company that supplies the stone will usually have cribs of stone for you to look at, stacks of various kinds of stone to look at, wall samples for interior uses (such as fireplaces) and a zillion folders of stone (especially manufactured stone) for you to select from. His brick supplier will not only have many photos of homes that have used various kinds of stone but sample boards you can view and compare. Color samples of the mortars used will also be there for you to select from. They should also be able to not only show you photos of homes in the area that they have supplied the brick and mortar for but their addresses so that when you have picked out several brick and mortar combinations you can drive by and see how they actually look.
John Fish (919) 696-3474 Email: Marvmax@mindspring.com Website: www.JohnFish.com





