Tag: lime putty mortar

So last year we were pretty conservative and stopped cordwooding the third week of September. Remember, the mortar we are using sets very slowly since it contains no cement – it’s just lime, water and sand (Lime Putty Mortar, or LPM). Conventional wisdom says it shouldn’t be allowed to freeze for thirty days. This year we decided to push it.

We figured that in the five years we’ve been here, we haven’t really had a hard frost until the tail end of October. We also figured thirty days seemed a bit much, that after a week or two the mortar was set to the point where a hard freeze wouldn’t harm it. We were half right.

We had taken the first week of October to work on the house; we laid up logs Saturday and Sunday, then the following Thursday and Friday, 8- and 9-October. On Saturday, it rained so we didn’t go out to Nerdwood. Then it got colder and the rain turned to snow. It wasn’t bitter cold by any means, but it did snow. Sunday the snow/rain mix continued and we couldn’t get out to the house until Monday.

When we checked under the tarped-over wall panels, we saw the areas we had laid up Friday hadn’t enjoyed the cold one bit:

The outer layer of mortar had frozen and flaked right off! Using a wooden shim, I was able to scrape off spongy mortar to a depth of about half an inch on both the front and back of the wall. Ugh! Not very attractive:

By now, the cold snap was over, so we decided to wait until the weekend to try and fix the damaged sections. The sections we had cordwooded six and seven days before the freeze had no trouble at all, so at least we were right about the mortar not needing a full thirty days before being exposed to any freezing.

The weekend weather was sunny and fairly warm, and looked like it would continue warm for at least a week to come, so we decided to repair the outside of the damaged sections and finish cordwooding the bays we were currently working on. After scraping away the crumbly mortar, we mixed up a new batch and slathered it over the damaged sections. It was a bit tricky, but adhered well enough once we got the hang of it.

Here’s how the repairs looked:

And here’s how they look a month later:

So, looks like we’re done laying up walls for the year. All fifteen panels on the first floor are done and four panels on the second. A bit of a disappointment, but now we know how long it takes us to build a cordwood wall. One of the second-floor panels had the largest area of cordwood of any of them – this one became known as the “Devil Wall.” It’s the solid second-floor panel:

And here are the other two panels:

No, not that kind of mud! Although we have been getting a normal amount of rain this year, unlike the previous two years of drought.

By mud, I mean mortar. The plan this year is to lay up the outer cordwood wall and if we’re really on the ball, install the windows and the in-floor heat, and have spray foam insulation, er, sprayed, on the inside of the walls. This way, we can continue working on the interior this winter.

Since we’ve only done one wall of the shed and three wall panels (out of 30 outside panels) of the house, we’re still not sure how quickly we can work. It seems as though different people have a very wide range of cordwooding speeds. Of course, things would go faster if we didn’t both work full time!

So, we’re cranking up the mixer, making lime putty and hauling buckets o’ sand around. The first new panel is in the back of the house – it features the French door that leads to the the porch:

Ha! That didn’t take very long! Of course, that panel is mostly air…

Next in line is the panel next to the proch and the panel that the upper deck stairs are next to. It would have been much easier to cordwood these two walls before the stairs went up – there’s only about a half-inch gap between the stair treads and the wall, making it a challenge to lay up logs and mortar, as well as to point the mortar (smooth the surface) after the logs are in place. No gap at all between the deck of the porch and the wall either. Couldn’t be helped, though; we really wanted the deck finished this spring. Here’s the stairs panel:

Those two took quite awhile – hard to lay up, plus no windows in either of them. It’s looking pretty cool from the inside though:

Here’s the most recent one to date. It has a small window in it for the downstairs bathroom:

So, as of July 7, 2009, that’s seven panels of thirty done, three finished last year and four so far this year. Ulp…

Some nice bottles ought to cheer us up:

And, how about some poppies?

Finally, we get to the meat (and by meat, I mean wood) of the matter – laying up the logs. We’re building a double-wall cordwood house – what this means is we build an eight-inch thick cordwood wall, have the inside of the wall sprayed with five inches of spray-foam insulation, then build another eight-inch thick cordwood wall on the inside, up against the foam. This gives us a twenty-one-inch thick wall with a very high R-value (R-40+) and a tight building envelope. We’ve been told we’ll be able to heat it with “a hair dryer” and/or “a candle.” It also gives us a whole lot of cordwooding to do.

Because we have so much to do, we have to make it as efficient as possible. One suggestion lots of cordwood builders make is to get a mortar mixer – faster and more thorough than a cement mixer, and much faster (and easier on the back) than mixing by hand. We went with an electric mortar mixer since it’s quieter and doesn’t stink up the whole process. They delivered it to the loading dock where I work, and the receiving manager told me I’d better pick it up quickly, since everyone was eyeballing it. Clare and I managed to roll it off the back of the pickup truck and park it next to the house. It’s the most orange thing we’ve ever owned:

You can bet it won’t look this clean much longer! So we dump in two and a half five-gallon buckets of sand and one bucket of lime putty (half a bag of hydrated lime that’s been soaking in water at least three days) and fire it up. Five minutes later, it’s ready for the “Sploosh test.”

This bit o’ cordwood wisdom says you should toss a softball-sized ball of mortar three feet in the air. When you catch it, it should hold together without cracking (too dry!) or splooshing out like a cow pie (too wet!). Having never handled a cow pie personally, I had to wing it a bit. After you lay up a few batches, you get a pretty good idea of how wet the mortar should be. Finally, on August 21, 2008, the momentous occasion:

Woohoo! One log down, a million billion to go! Because the lime putty mortar sets up so slowly, we build up a couple of feet of one panel, then move on to the next panel. After a few days, here’s how it looks:

Some of the wall panels have windows, so we build window boxes out of rough-sawn cedar and fasten them in place before laying the cordwood:

We couldn’t resist the temptation to buildall the way to the top as quickly as possible:

Finally, done with the first panel: