This article appeared in TLS issue #42. This issue includes articles about experimentation and development of bales made from various types of materials. Articles about methods and equipment for spraying bales with plasters appear in #43 Spraying Earthen Plasters in Colorado), #33 (Stucco Pumping Iron).
by Peter Mack – Ontario, Canada
Very early on in our careers as straw-bale builders, we realized that being able to pump plaster was going to be important if we were going to attempt multiple projects. Bodies and spirits just wouldn’t be able to keep up with endless hand-plastering. So, we bought an ancient pump and started spraying.
Oh, how I remember the days of the sprayer nozzle! The comforting “farting” sound, the reassuring overspray sticking everywhere, plaster in our eyes, noses, lungs, hair, shirts and sometimes ending up on the new roof of the house we were plastering (do not trip while spraying!). The nozzle end was a tiny opening 1/2 to 5/8inch(12-16mm), so if a tiny pebble made its way through the screening and into the nozzle, it could (and did sometimes, much to our chagrin) jam up and create back pressure, even to the point of exploding the hose. Luckily no one has ever been in the way of the hose at the time, but what a sorry mess it makes!
Devising a Solution. We talked often about improving the system. I had read about trowel ends for plaster pumps before, and this kind of fitting seemed like it would be cleaner and easier to use, but it seemed impossible to find one for a large stucco pump. As often happens in life, I set about to make my own. The first step was to buy some new supplies:
- 8-foot(2.4m) length of 1-inch(25mm) rubber air hose
- 6-inches(152mm) of 1-inch steel pipe threaded on the outside.
- 1-inch inline swivel (grease twice daily!)
- 1.5-inch(38mm) cam lock coupler, NPT threads
- 2-feet(0.6m) of 3/8-inch(9.5mm) round and square bar
- various 1-inch hose barbs and bushing reducers
- aluminum hawk or similar sheet metal
Then I followed these steps:
- Make a 30-degree (approximate) bend in the 1-inch pipe, leaving an 11inch(280mm) section of the pipe straight at one end. Use an acetylene or propane/ oxygen torch and wind a coupler onto the threads or they will get bent!
- Grind a flat face roughly 3/4inch(19mm) across along the straight, 11-inch section. This is where the trowel will attach.
- Grind a slot through the pipe in the flattened section, 3/8-inch(9.5mm) wide by 5-inches(127mm) long, centred five inches from the bend. The plaster will exit through this slot.
- Place the flat face on the workbench with bend up and weld on four reinforcement bars flush with the face. Use the 3/8-inch square bar. These are necessary to support the trowel attachment, as the trowel material is not strong enough by itself.
- Weld on the handle. Shape to taste from 3/8-inch round bar, remembering that heavily gloved hands will be trying to hold the handle.
- Lay out the trowel face. An aluminum hawk makes decent material. Our trowel has very rounded corners and is 12-inches long by 6-inches wide(305x152mm), with a 3/8-inch by 4-1/2-inch(9.5x115mm) slot. Bias the slot towards the end of the trowel by 1/2 to 1-inch to allow closer application to ceilings.
- Use a drill and saber (jig) saw to cut the trowel out. File off sharp edges.
- The aluminum is fastened to the steel pipe with polyurethane caulking and annealed steel wires twisted tight with pliers. Our earlier experiments using Lexan for the trowel, attached by 20 machine screws failed, lasting only one or two jobs.
- The rest is basic plumbing: use Teflon tape on all threads and heavy-duty hose clamps. As we’re reducing the hose down to 1-inch, a full size quick-connect is necessary at the upstream end of the eight-foot hose to allow for proper clean outs.
- After trying several types of plugs in the open end of the pipe and wasting too much time searching for them at clean out time, we’ve settled into a groove using hand cut plugs made out of styrofoam. They hold just enough that, if the slot plugs up, the pressure pops out the plug. Foam rubber would probably work just as well.
A New and Valuable Tool. Thus was the birth of the power trowel. It worked! No more overspray! We won’t kid you…we still make a mess when we plaster, but at least it’s more controlled now. The power trowel needs two operators (or one if that person is truly a power-power troweler, such as Andrew McKay!). One person handles the hose, the other holds the trowel end up against the wall. The trowel end emits a continuous “ooze” of plaster (hence the nickname “Barfing Snake”), and the speed is controlled by the throttle on the pump.
The trowel can be either moved sideways across the wall, or more popularly, up the wall. If you are using an up-and-down motion, the trowel must be held perpendicular to the ground, catching the material being squirted until you can begin applying at the wall’s base again.
There is quite a knack to this grueling job, and the pairs who are quite talented at it actually seem to dance together as they pass the power trowel back and forth, weaving gracefully around scaffolding, rocks, bales and other typical plastering obstacles.
- fills hollows, good penetration into bales, flattens mud as it applies
- less clogging because of wider opening, can pass fibre mixes
- blow off valve works
- less back pressure, easier on pump engine and workings
- less loss of paste and water to atomization, resulting in longer working times
- no more overspray on windows, ceilings and people (although we do still drop a bunch on the ground/floor)
- overhead areas difficult
- does not quite reach ceiling, trowelers often have to push the mud up the last three or four inches(75100mm)
- occasional air pockets between coats
- somewhat more physical effort for the nozzle person.
We still sometimes reminisce about the old days of the “farting” spray, and will occasionally bring it out of the closet and take it for a test drive; once a friend wanted to record it for a CD, but do we really miss it? Not a chance! The power trowel has made life as plasterers easier, cleaner and quieter.
Peter Mack is a full-time bale builder and a partner in Camel’s Back Construction. He is co-author of the book Straw Bale Building (New Society Publishers). Contact: Peter Mack <[email protected]> www.strawhomes.ca
This article appears in issue #57 of TLS. There have been other articles about moisture sensors in recent years.
by Habib John Gonzalez – British Columbia, Canada
This article appeared in a slightly longer version in TLS#22/Spring 1998.
Here are the simple steps and materials needed to build your own bale wall moisture sensor:
1. Determine what depth of the bale you want to monitor and cut the 3/4-inch PVC pipe to that length.
2. Make the white pine sensor disk 1/8-in. thick to fit snugly into one end of the pipe.
3. Solder two lengths of telephone wire to two pairs of small bolts. One end of the pair of wires is bolted to a PVC pipe cap so the tips will protrude from the finished interior wall. The other end of the wires will be bolted to the sensor disk.
4. Use epoxy to glue the disk to one end of the pipe; run the wires through the pipe and fasten the other pair of bolts to the interior wall end cap. Glue the cap to the pipe.
5. Glue a perforated pipe cap over the sensor end of the pipe.
6. The sensor is ready for installation in the bale wall.
7.The TimberCheck moisture meter is available from www.leevalley.com
8. A number of bale wall moisture studies were sponsored by the Canadian Mortgage and Housing Corporation (CMHC). You can get a summary of all of the CMHC moisture work on their web site www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/dblist.cfm?mode=year. Scroll down to the bottom of the list for 00-103 (year 2000, document 103) on straw-bale moisture monitoring.
1. Outer end-cap
2. Perforated PVC pipe
3. Wood disk with screws
5. PVC pipe
6. Inner end-cap
7. Screw contacts
This article is original content and has not yet appeared in the printed version of The Last Straw.
St. Astier Natural Limes, a producer of hydraulic lime products from France, is offering a set of DVD videos called The Master Stroke DVD Tutorial Series. The Master Stroke is a 4-disc series beginning with lime mortars. Other discs cover plastering and rendering with lime, and building and pointing with lime. In this article we will review the first in the series, Making Lime Mortars.
The content of the DVD is laid out very clearly and is easy to follow. The quality of the video is very polished. The main purpose of the DVD is to show the construction worker how to create a consistent, high-quality mortar or render. Tips include how to properly keep your sand dry, how to measure each bucket of sand, etc. But there was one piece of information that really make this video important. Nearly half of the video is dedicated to the concept of the sand void ratio and how it affects your mix.
Have you ever wondered where the ratios we use for our mixes come from? This video explains how they are derived. Without going into too much detail, the ratio of sand to lime is determined by finding the void ratio of your sand. Once you know how much air is between the grains of sand you can find the volume of binder. If you use too much binder, the sand particles will be far apart, separated by water and lime. If you use too little lime you are not filling all the voids with lime and you will have pockets of air and water. The perfect ratio is one that fills all the voids and leaves little room for air or water. Once you know this ratio, based on your sand, you can then adjust the ratio to achieve your desired results. Don’t think you can just figure this out on your own through this article. There is a proper way to do this, and each step is clearly defined in the video.
To know the proper ratio of sand to lime (or any other binder – clay, cement, gypsum, etc) is like an enlightenment for most of us. Have you ever wondered why the code says 4:1:3/4 (sand:cement:lime), or why your friends used 1:2:9 (cement:lime:sand)? Now you don’t have to guess. This video will teach you how to properly measure the void ratio of your sand and the ratio of sand to binder. It will become apparent that the mix your friends are using on their project has little bearing on your mix.
Learning how to derive the ratio of sand to binder is obviously very valuable. The rest of the video walks you through the measuring and mixing process, showing how a professional would prepare his or her mortar. After being a sub-contractor and mixing thousands of batches of plaster, this video would have been great as a tool for estimating. In my mind it creates a baseline for high-quality that a builder can use to determine costs.
In summary, I would say buy this video! It can be purchased at the link above for $39. From novice to professional, you will find value. Good luck.
This review is intended to be objective. No compensation of any form has been accepted in connection with this article.
This article originally appeared in TLS #49. Articles on straw-bale wall panel systems are included in issues #30, #42, #47, #48, #55.
Northen Arizona provides an ideal climate in which to build with straw bales and has been the site of many such structures since the 1990s. Ed Dunn has been the principal designer and builder of straw-bale homes here for over a decade. In May‘04, Western Strawbale Builders (WSB) was formed by Jason Radosevich and Matt Robinson, former crew members of Ed Dunn. The focus of WSB is to increase the scope of straw-bale building to include affordable housing as well as top-of-the-line custom housing.
With affordability in mind, systems using prefab panels seem to us the most promising avenue of approach to building with straw bales. In order to spare you the well covered details of this method of building, you can reference several articles published by TLS including: Chris Magwood in TLS#42, Canada Guy TLS#47, and Brett KenCairn in TLS#48.
Western Strawbale Builders was able to show off our skills in a project this past Fall here in Northern AZ. Designed and overseen by Ed Dunn, this project was an additional building done for The Star School, an off-grid solar-powered charter school on the borders of the Navajo Reservation in Coconino County. Star School teaches middle school students subjects, including permaculture, cultural awareness, and sustainability. Proprietors Mark and Kate Sorrenson therefore wanted to build a structure that reflected these values while fitting into their budget.
Ed Dunn designed this structure to utilize passive solar principles, trombe walls and a greywater planter. It is to be used as a combination classroom, performance hall, and wrestling gym, as well as any other creative uses Mark and Kate come up with.
We decided to hold the bid on this project to the regular bid price for stick-framed structures in our area to see how well we could compete. To our mild shock and great relief, we were able to build to these numbers and still afford our business a modest profit. With a four-man crew including ourselves and the exceptional abilities of carpenters Alden Catherman and Phil Mason, the class room was completed in eight workweeks, beginning to end.
We feel that this project, although relatively simple in scale and design, can serve as an example of an affordable option for people who love the idea and feel of straw-built houses. Hopefully this structure and others like it will help in bringing straw-bale houses into the mainstream.
Matt Robinson and Jason Radosevich own and operate Western Strawbale Builders in Flagstaff, AZ. Contact: or westernstrawbale.com