Andy,Would you care to write an article on your "french dip" method for the The last straw. Based on your mail you are probably besides Tom Rijven the most experienced user of this system. I have taken careful notice of your cob like approach making really solid walls.
I only used French dip on a few small projects until so far one of which was load bearing. The main gain for load bearing is the vastly increased stability of the wall whilst working on it. I am a keen convert to this method. Another bonus is that it allows you to use sub standard, not so dense/tight bales and still have quite a stable wall while building.
Rene On May 24, 2007, at 19:35, Andy Horn wrote:
Hi all Just to add my support of the dipping method.Pre-dipping is for me by far my favourite way of pre-plastering Straw bale, and have found it helps shave hours and hours off the plastering process, resulting in a really sturdy solid impregnation of the plaster as well as helping with the pre-compression/settlement. Furthermore any risk of fire and weather is hugely reduced as the time that the walls (un-plastered) are at risk is a matter of an hour or 2 vs. days or weeks! I like it so muchthat I have been doing it will all my projects for the last 3 years.I first raise the wall for a good fit (allowing for shrinkage in the top course) and then sequentially take down the walls course by course. I then dip the bales in a bath of an adobe type clay/sand mix thinned down to a yogurt like consistency, taking care to only dip the surfaces that are to be exposed...helping with the weight and in maintaining the insulation. We use a non load-bearing on-edge system dipping panel by panel. We place the balesin a bath of "slip" and then turning the bale over, use our hands and acobbing stick to really work the slip into the straw, usually achieving at least 50mm of penetration. We then allow the bales to partially dry out,until they become more firm and tacky (but not hard)....more like theconsistency of cob. I sometimes call it "cob-bale" building because it is more like building with giant cob bricks. One sometimes needs to retard thedrying out of the first course/s of bales if there is a lot of wind orstrong sun so as to give oneself enough time to get all the bales dipped. As the walls go up, we immediately start to work the bales with a cob-stick to knit the bales together and help compact the coating. As straw falls off in the bath and makes the bottom too straw rich to dip with, we scoop out this mix and spread it out to partially dry to a cob like consistency and thenuse this as our cob to help fill in any gaps around the base, eaves, openings etc. I also use a small plank to whack the sides of the bales,which also helps straighten and compact the coating. Plastering trowels are also useful for this task. The result is a wall that is really solid, that when tapped is closer to the feeling of a cob wall, avoiding having that partly disturbing hollow sound. From there on the subsequent plaster layersare really easy to do. If any of you want to see pictures of the process there are some on our web-site.Besides the above advantages mentioned my conviction in the dipping method has recently hugely re-enforced having this year helped a friend with the building of 2 load-bearing structures. The builder on site had neglected tocover up and a huge storm blew in soaking one of the only half roofed structures. We then had to prop up the roof structure and insert a polesupport system to convert the structure to a non load-bearing building. It was no fun having to rip out all the mouldy walls that had quickly startedcomposting.In such regard, I would be interested to know if any of you have tried thepre-dipping method with load bearing systems??? Cheers Andy Horn ECO DESIGN Architects & Consultants A. R. HORN - B.A.S. (UCT), B.Arch (UCT), Pr.Arch (SACAP), MIA, CIA Telephone: 021 462 1614, Fax: 021 461 3198 Cel: 082 67 62110 4th Flr, The Armoury 160 Sir Lowry Rd CAPE TOWN 7925 www.ecodesignarchitects.co.za -----Original Message-----From: GSBN [<a target="_blank" href="mailto:GSBN@...">mailto:GSBN@...] On Behalf Of Rene DalmeijerSent: 24 May 2007 08:04 AM To: GSBNSubject: Re: GSBN:Re Thermal Properties of (french dipped) Straw Bale WallsChris, I fully support you in this it is essential that the dipped bales are used quite rapidly after dipping. This is a messy business but working with two people to lift and place the bales makes a big difference. The bales tend to fit in much better the need for stuffing joints is almost diminished to zero. Another tip once the bales are in place a tamping of the still tacky bale surfaces with a plank and a hammer will align and flatten the bale surface to a great extent. The best technique is to lay the plank across the bale joints and then tamp. To work effectively the clay rich slip should still be quite moist. Rene On May 24, 2007, at 03:50, cmagwood@...:I'd like to kick in on the "French dipped" method, as I believe they do a great job of helping to provide a really good "seal" across the entire face of the wall. It would make sense that if dipped bales are left to dry before being stacked that they wouldn't work as well, but they shouldn't go in when dried, but when slightly tacky. Then the straw/clay that goes in the gaps bonds very well to the bales and makes, for me, the best wall surface going. ChrisMarty suggested that the 'French dipped' bales might give a good tight fit between the bales. My experience is the opposite. If the bales are dried after being dipped the diped sides get rock hard and do not compress. If the bales are placed before they are dried there is more chance for settling but this is a messier way of going about. As for the test Nehemiah mentioned where the top was stuffed. A suggestions (if such a test is ever to be repeated) is to compress and stuff the wall from below with car jacks between the 'foundation' and botom plate'. Bye, André "drop that bale" de Bouter John Swearingen a ?crit :Straw-clay seems the best material for this purpose, although too much claymight increase conductive heat loss in the stuffed area. < ...for several other reasons, too. When straw is stuffed in joints it's relatively loose and so provides a ready channel for moisture into the depths of the wall. Straw-clay will form a seal against moisture entering the joints between the bales. In addition, it stops air infiltration and can be screeded off to make a flat plain for plaster, thereby reducing the occurance of cracks that result from abrupt changes in the thickess of the plaster. Also, it's fun to get dirty.... "Hurlen" John Swearingen On 5/19/07, Martin Hammer mfhammer@... wrote:Nehemiah - Good explanations. You talked about the straw-stuffed gaps at the top and sides of a wall as being places where convective losses could occur. So I'll add the thermal importance of stuffing vertical joints/gaps between bales for the same reason of limiting convective losses. (This would also be important between bales and "posts" that go mostly or all the way through the thickness of the wall. I've seen I-joists or steel trusses used this way.) Straw-clay seems the best material for this purpose, although too much clay might increase conductive heat loss in the stuffed area. Horizontal joints between bales don't seem to be an issue because the weight of the bales appear to cause the surfaces to lock in well enough to limit air movement between them (although the French dipped bales might seal that joint even better, and bales on-edge probably nestle together better than laid-flat). Then there's always the question of what material is between the bottom of the plates, and what the insulative qualities of the roof bearing assembly are. And then there's the ceiling/roof, and the windows/doors, and the amount of infiltration throughout, and . . . . . Martin HammerJohn, I did not see a response from Andrew. Was that offlist? I am alwaysinterested in what new or other information peoplehave on the thermalproperties of straw bale construction. Care to sharehis input?Also, your Q about how compaction affects R-value isa potent question. Ifhot box testing wasn't so expensive and timeconsuming, or if there werefunders lined up to pay for it, I'd already have ananswer for you. Thereare a number of confounding factors, so until someonehas done the actualresearch, we can throw around lots of theories. For example, it is air that creates the insulationvalue of almosteverything used for wall insulation. ,,,not the spunglass, not the solidportions of the foam, not the cellulose, not thestraw. Therefore, ifbales are compacted too much, one would expect theinsulation value to godown. But, what is "too much?" If bales are tooloose, then the air cancirculate in the air pockets and research HAS shownthat this can lead toconvective currents that lead in turn, to a dramaticdrop in R-value. Thatwas one of the causes (we think) for the relativelylow R-values in the ATIlab tests in Fresno, CA. Once we stacked the balesin the hot box wallopening, and compressed them as they'd be in abuilding wall, we had a sixinch gap at the top. We filled it with straw astightly as we could, butwe are not match for either a baler or truckers'strap tightening levers,so we KNOW that the top (where the greatest amount ofheat exchange wouldnaturally occur anyway) was much looser than the restof the wall. Dittothe sides, though those gaps were significantlysmaller (so perhaps, harderto compact straw into). Further, though in theory greater compaction - afterthe optimal point -will lead to a decreasing R-value, no tests have yetshown that to be thecase. Perhaps we just haven't found the optimalcompression force yet.Perhaps the theory is wrong. Lastly, I would question your assertion that jumbobales are "naturallycompacted a lot more than the smaller bales." It ismechanically moredifficult to compact a larger bale to the samedensity as a smaller one. Iam not saying that the machinery isn't designed to doso - perhaps it is.But, from a pure physics point of view, it is not"natural" as you said.One way to verify whether the compaction is greateror not is to measurethe water content and density. Rice straw bales inCalifornia (the ones wetested) are typically at least 8 pounds per cubicfoot at a moisturecontent of about 6%. Do you have similar data on theAussie jumbo bales?If you want to get an accurate reading of themoisture content (moreaccurate than a moisture meter stuck a random depthinto the bales), let meknow and I will send you (offline) a description ofhow we did it. Thedensity (#/cf or kG/cM) is pretty easy, assuming youcan weigh arepresentative sample of the bales. Hope this helps. Thanks, Nehemiah Stone stoneandstraw@...---- For instructions on joining, leaving, or otherwise using the GSBN list, send email to GSBN@...HELP in the SUBJECT line. ------ John Swearingen Skillful Means, Inc. Design and Construction www.skillful-means.com --- StripMime Report -- processed MIME parts --- multipart/alternative text/plain (text body -- kept) text/html --- ---- For instructions on joining, leaving, or otherwise using the GSBN list, send email to GSBN@... 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