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Examples of Brazilian Vernacular Architecture — 3 Comments

  1. Hello. I love the idea of building a home with cordwood in Brazil.
    What would be the proper local wood to use and proper cement mixture etc.. Considering bugs hot humid the weather,and it could also get very chilly in the winter. any feed back will be very much appreciated
    Thanks

    • Rob Roy, an expert in cordwood building writes:
      The characteristics that you should be looking for in a good log-end are

      1. Stability. Shrinkage and expansion are two sides of the same coin. Wood that shrinks a lot can expand a lot, and vice-versa. In general, dense, hard, heavy woods (usually characterized by small annual growth rings), will shrink more than light, softer, airy species. This may seem counter-intuitive, but, with few exceptions (such as hemlock), this is the case. Shrinkage is a cosmetic problem that can be addressed a year or two after construction, by a variety of methods described in the literature (and some of my other replies in this column.)

      2. Insulation (R-value). Once again, the lighter airier softwoods perform better as insulation. Dense heavy woods are more like stone: they are good heat storage capacitors (thermal mass), but also transfer heat rapidly (poor R-value.)

      3. Consistent dimension. By this, I refer to a log-end maintaining a consistency of size and shape from one end of it to the other. If there is a severe twist or taper to a majority of your log-ends, this will be a very difficult wall to build. Further, because there is no chemical bond (and very little “paste bond”) between wood and mortar, a wall built of irregular log-ends will be inherently unstable. Cordwood is strong on compression, but not on tension, even worse than other masonry units such as brick, block, or stone. So, log-ends cut from “bushy” or severely twisted or tapered species are a pain to work with and will not yield as stable a wall.

      4. Rot resistance . Oddly, wood rot is hardly ever a species-related problem, if you pay attention to basic building principles: (A) Do not use punky or insect-infested log-ends, (B) Get the bark off, (C) Don’t have log-ends resting against each other, which traps moisture, (D) Keep the first course of cordwood masonry well clear of the ground, and (E) Use a good overhang on the building, at least 16 inches. With regard to “D”, I like to keep the wood two to four inches off the ground in dry or “normal” areas like where I live in northern New York, 8″ to 12″ in wet areas. In Mountain View, Big Island Hawaii (with 190 inches of rain per year), we kept the wood a full eight-inches off the footings (on a course of blocks) and there has been no ill effects to the cordwood.

      5. Aroma. This one rarely comes into play, but some woods do stink, like the so-called “piss elm.” I’d avoid ’em. Some aromatic cedars may seem like a nice smell in small doses, but I know of one lady who had a sauna built for her of strong incense cedar and she could not go into the stove room at temperature. There is a reason that moths do not attack woolens in a cedar closet!

      So, readers with rare woods please cut a log-end sample of the wood you have in mind and evaluate it yourself, keeping the five criteria above in mind.

      Here are two different non-shrink mortars (not concrete, which contains stone aggregate):
      Mix A: 9 sand, 3 soaked softwood sawdust, 3 hydrated (Type s or “Builder’s”) lime, 2 Portland cement. The sawdust should be passed through a half-inch mesh screen and soaked at least overnight.
      Mix B: 9 sand, 3 masonry cement, 3 ounces of W.R. Grace Daratard 17 cement retarder.
      All mixes are equal parts by volume. Medium shovelsfulls will yield one wheelbarrow load in either case.

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