We often talk about how well cordwood works and how it looks good and how it performs even better. Posting pictures of well built cordwood homes is a real joy and explaining how to build cordwood correctly is the nature of this blog. However, people have been asking for a post about mistakes made on cordwood buildings and what they look like. This is a brief attempt to show potential pitfalls. Most cordwood is built by amateurs and most study the literature and make the necessary decisions, that each cordwood builder must make (the type of wood, mortar mix, foundation, framework, etc.). Here is a set of pictures and commentary of Common Cordwood Problems.
When the mortar is too strong and not covered and cured properly, it develops cracks that extend from log to log.
These are not structural problems but are unsightly, and if the log shrinks (like in the picture below) there is a fair amount of air that flows to the inside.
Every year I get a dozen calls from real estate agents, construction companies, and new owners (who bought older cordwood homes). They ask if I have any idea of how to fix the problems.
Above is a cordwood home that has had the mortar crumble (mortar mixing mistake) the logs loosened (not dried properly) and the structure has become unstable (because of poor building decisions).
What are the other problems?
1. Rotting bottom logs (caused by building cordwood “on grade”–aka near the ground).
2. Air-infiltration gaps where logs have loosened and the result is a drafty, cold cordwood home (this is caused by using wood that is not dried to 12% moisture content and used with a mortar that is too strong). This log has a huge primary check that will allow cold air inside and the log could actually be “punched” all the way through.
3. Windows that have become stuck because of the weight of the cordwood wall. These workers are tearing down all the cordwood because it shrunk away from the mortar and made the house difficult to heat.
4. (Below) Mortar cracking caused by a mortar that was too strong (too much Portland).
5. (Below) Severe mortar separation caused by an improper foundation (unable to handle the weight of a cordwood wall).
Common Cordwood Building Mistakes
- Choosing the wrong wood and not drying it to 12% moisture content. Cedar is the absolute best wood to use for cordwood (low shrinkage rate, insect/rot resistant, light, high R-value per inch, pleasant aroma) but other disease-free, insect-free, rot free softwoods can be used, but they should be dunked in a borax solution to prevent problems with bugs.
- Poor mortar mix: within a framework, the mortar can be enriched with organic matter and become as “slow-setting” as possible. Using sawdust, papercrete, hempcrete, clay, lime all help to add natural components and in the correct, tested proportions, will create a stable wall. There are 5 different mortar mixes and variations on each one, investigate thoroughly.
- Allowing the cordwood mortar matrix to be exposed to sun, wind and cold while building and not covering the wall for 7 full days, to allow it to SET and CURE will lead to mortar cracking and shrinking.
- Not slowing the set and cure of the mortar (using soaked sawdust, paper-fibers, industrial hemp-fibers, vermiculite, clay, etc.) WHILE BUILDING the wall and not creating a TARP TENT to stop the sun and wind from sucking moisture out of your freshly mixed mud.
- Not splitting most of the wood, which then leads to LARGE PRIMARY CHECKS and consequently air infiltration. This is usually not noticeable until after a heating season and results in a cold, drafty building.
RESULT: Log Loosening, mortar cracking, primary checks developing all the way through the log to the inside (mostly on larger logs +8“ diameter).
HOW TO FIX:
- Choose the best wood. https://cordwoodconstruction.org/best-wood-for-cordwood
- Split 70% of your wood.
- Dry your wood to 12% moisture content
- Use a slow setting mortar
- Our favorite mortar by volume: 3 masons sand, 2 soaked softwood sawdust, 1 Portland, 1.5 Type S Hydrated Lime
- Set up a Shade Tarp so the sun and wind don’t suck the moisture out of your mortar.
- Use Permachink, Log Jam caulk/chink paint or Vasari Lime Wash, if you have any mortar cracking or log loosening.
- Stuff the primary checks in your round logs on each side.
Use a Best Practices approach to building. Watch current, up to date videos, read the latest literature, ask questions on cordwood social media sites. Get the right wood (cedar is best), dry it to its lowest moisture content, mix a workable enriched mortar, cover it at the end of each day and let it set and cure properly.
The following books and videos are the best on the market and will give you the opportunity to build a sturdy, tight, well-insulated cordwood home. If you follow the recommended guidelines, for much less than a conventional home.
Should you wish to learn how to build a cordwood cottage, cabin or home, please visit www.cordwoodconstruction.org While you are there, click on the pictures, read the brief articles, check out the latest workshops and newsletter and if you are interested click on the Online Bookstore to see all the cordwood literature available in print and ebook format. If you have questions that aren’t answered on the website you can email me at email@example.com
Readers have requested a brief bio, so here goes:
Richard & Becky Flatau built their mortgage-free cordwood home in 1979 in Merrill, Wisconsin. Since then, they have written books, conducted workshops, facilitated the 2005, 2011 and 2015 Cordwood Conferences and provided consultation for cordwood builders. Cordwood Workshop DVD (2018), Cordwood Construction Best Practices (print 2017) and Cordwood Conference Papers 2015 are the newest publications available from their Online Cordwood Bookstore. The books & DVD are also available as ebooks for a quick and easy shipping free download. www.cordwoodconstruction.org
This is our current Cordwood Workshop DVD. It will show you how to build a “best practices” cordwood home. It’s like taking a workshop from your easy chair.
The 30 detailed menu items from the Cordwood Workshop DVD.