Straw and clay infill

[peter nap]

Is anyone familiar with this?

Light Straw-Clay (Leichtlehm)

Leichtlehm (literally "light-loam") is a German technique of ramming loose straw coated with a clay slip into forms as an infill for timber frame structures.

[moonhill]

I think this would be a great decision.  I am hoping to use a light clay wood chip wall system in the spring.  here is a link to Fox Maples site. 

http://www.foxmaple.com/FMNatBldWks.html#Alternative%20Infill

Tim

[peter nap]

Thanks Tim!

[sawdust]

there is a group in Minnesota that is working on clay slip. I will see if I can find the contact info.

sawduust

Found it!

http://www.designcoalition.org/features/lansing/concepts/makeslip/makeslip.htm

Call him, Doug loves what he does.

[moonhill]

That is a nice link.  I like the addition of lime and coloring.    Tim

[moonhill]

Bump....bump....thud... The thud is a lump of clay hitting the floor.

I mashed some clay and straw together and wove it into sticks wedged into the framing of my black smith shop and topped it with a lime was based form clam shells which I fired in a kiln.  Just a start to see how it all felt, it was a wonderful experience.  I am looking forward to this coming spring and doing more. This time with wood chip and a light clay slip with a clay plaster/render on the walls and white washed with my own clam shell white wash. 

Tim

[wkheathjr]

Moonhill,

Wouldn't this method also be known as "cob construction" using clay, straw, and some sawdust (to increase R value) as siding for the Timber Frame?  A woman was telling me how she would rather to use this method than using SIPS but she did mentioned that SIPS would have much higher value than this method?

I, myself, am curious about this method and when asked if I would like to take a workshop on it, I said sure!  Why not, just to see what it is all about!

[moonhill]

Cob is very different, well sort of different.  The method at the start of this thread by peter nap just about says it all.  Light clay/straw, light is the key word, the straw or wood chips are covered in a light coating of clay.  The clay slip is of a thick paint consistency, it is like coating shingles in a dip tank your just doing a lot at one time.  It seem like it would have very little structure but the wall is actually quite stiff and solid.  Cob on the other hand is heavy, soils lots of mud.  With a render and plaster on the inside and outside to seal the wall you create air pockets within the layers of straw, almost the same way wool insulates, but not totally. 

Toxicity came up in the sips thread.  It is known clay has the ability to absorb stuff, moisture is one great example at the same time it will get rid of it as well in effect keeping itself dry and the surrounding material, the straw and the timber, acting as a preservative.  I am not sure of the next comment but it has been pointed out by someone I know that has more experience than I in this area.  It was noticed that clay absorbs stuff, moisture, odors, toxins and the like, it attracts stuff and then releases it after it reaches a certain level.  With that in mind you build a clay house near a busy highway there are lots of autos going by exhausting stuff, this stuff is absorbed by the clay in your house and once it reaches a certain level it expels it all at once.  Supposedly exposing the sensitive home owner to a high level of toxin which she was trying to avoid in the first place.  This happened, I am not clear if it was exhaust or some other "stuff".  My personal opinion is that this person was just sensitive to stuff, like some are allergic to bee stings and other are not.  Just thought I would pass this on and maybe someone could add to it. 

Tim

[wkheathjr]

Interesting, thanks for explaining more clearly and the absorbing part could be trouble if you live closer to the city or to the highway.  Any chance that cob could have similar method of absorbing?

[moonhill]

It could if its base is clay.  But I am not completely sold on the issue as being a bad thing.  I keep bees and I am not allergic to them but some people are.  I think it is a beautiful system and has plenty of pros and few cons. 

I won't be responding to post for a week or two. 

Good night.

Tim

[bossltr]

Interesting information about the absorption and release of fumes in clay. Here in New Mexico the traditional building material is adobe. We've seen building inspectors  fuss over the interface between adobe and other building materials such as Romex wiring and electrical boxes. I'm not a profesional builder, so take this with a grain of salt, It seems the inspectors consider adobe, and cob to be the same as underground, and all wiring in adobe needs to be rated accordingly.

My question is what  about using straw - clay mixture next to timberframes? Are there ways to preserve the wood prior to filling with mud?

[moonhill]

It is my understanding that a straw and light clay mix would still assist in the preservation of the wooden framing members and the straw as well, the clay is still doing its job. 

Tim

[Thehardway]

Here in southside Virginia there are hundreds of tobacco barns that were chinked with red clay and wood or straw.  Although they have stayed together for about 100yrs. they are in pretty bad shape.  The clay has not helped to preserve the logs in any way. similar barns without clay chinking are in better condition.  It also did nothing to discourage pests and termites.  I would be concerned with termite and rot issues if it is used in any humid or southern environs.  Probably not so much of an issue in NM.

[moonhill]

In what condition are or were the roofs on these failed buildings using clay infills?  If the roofing was in bad shape this could contribute to the demise of the structures.  There are buildings around the world using clay infill system which have seen hundreds of years of life.  It is my suspicion something else is going on with these barns, the climate could have a factor, something to consider.  I would like to know more on these barns, can you share photos or other related information?  You say they were tobacco barns, were they used in other ways recently?  Is the infill for sure clay?  Modern materials like cement can have detrimental effect just as you are pointing out.  This is a true oddity for I have seen absolutely no information which would lead to rot in timber, in fact just the contrary. 

Not sure what to say about the bug issue.  I have heard that ants don't like clay systems. 

I have little experience in the everyday use of clay, I am just starting to use it.  I have no personal testimonial just literature I am reading.  So, please share more info if you have it.

Tim

[Thehardway]

I will take some pictures and post them here.  The structures were used for storing, drying, and curing tobacco. Some of them were built using pine, some chestnut, and some of oak.  Most of them had standing seam metal roofs and the roofs could not be blamed.  They were in use and fairly well maintained up through the late 1980's. Since the tobacco lawsuits/settlement put most of the local tobacco farming out of business they have mainly been used to store equipment or have been left empty.  Don't misunderstand me, 100 yrs. is a long life for a untreated log, but the clay/rock/straw chinking is far from a low maintenance system in south-side Virginia climate..  I have also been told they would not have lasted as long as they have had it not been for the nicotine residue from the tobacco acting as a pesticide.  I cannot verify this, it may be a wives tale.

[Thehardway]

moonhill,

here is a picture of one of the tobacco barns that has been well maintianed and is still in good condition. It is being used for machinery storage. I will take a picture of a similar one in poor condition saturday if I can remember.  This gives you an idea of the age and construction though.  These things are everywhere here today but in another 15 years will most likely be extinct.  The Virginia Historic Preservation folks are trying to get them on the endangered list before that.  They are definitely a piece of cultural heritage that is going away.  Many of them have four stovepipe chimneys that were used for drying tobacco with heat.







The below cabin is of approximately the same vintage and uses a lime based chinking that has been painted.  It is also well maintained

[LeeB]

Could the clay mix be lime stabilized?

[moonhill]

Was the lime chinking painted with a lime wash or modern paint?

The issue with logs is they contain a lot of sap wood which is susceptible when exposed to the weather.  Could it be that the ones with more rot are of southern pine, if I am not mistaken it has a high sap wood content.  Are the hardwoods holding up better than the pine structures?

Do you know what the small rectangular holes are for?

Tim

[Thehardway]

Tim,

The rectangular holes are where horizontal cross members (probably drying poles or racks) were once located.  I don't know what type of paint the lime based chinking was covered with.  I imagine it has been a variety of products over its lifetime.

When I was younger we used to paint the inside of the dairy barn beams, floor and walls, with a lime based whitewash.  When it dried it was very hard and durable.  It did however disguise a lot of structural deficiencies in the timbers.  Timbers would dry rot inside and you would never know just to look at them. We ususally discovered it when we saw them starting to sag or you tried to drive a nail in to hang something on and it was like powder inside.

The structures made of red oak have failed the worst, pine slightly better and white oak slightly better yet. 

Here is a barn that prabably dates to late 1800's.  It was used for hay storage in the loft area up until about 10 years ago.  the logs are still sound but the sills are failing.  this barn was not chinkined and logs could breathe and aclimate.







Here is a nearby log cabin which probably dates to early 1800's with lime based chinking.  It is in need of modest repair near the sills but otherwise appears sound.  It is in a flood plain and has been at least partially under water on a couple occasions.

[moonhill]

Thanks for taking the time to post these photos and opening the possibility of the clay infill as a "problem", I would say it still needs further investigation.  It seems species has a big effect on timber durability.  I can't help wondering if the open log structure at one time could have been chinked with clay.  Was it always a hay barn? Could it have been a drying shed as well in its earlier years?   Just a rhetorical question.

Tim

[PlicketyCat]

Slip-form infill is essentially the same as wattle & daub infill. Wattle & daub has been used for hundreds of years in Europe as infill in timber framed buildings and a lot of those places are still up and running in good condition. Well, at least they WERE until someone decided to replace the lovely lime plaster with cementatious stucco and they all started to rot.

There appears to be zero negative affect on the timber from having a lime and clay plaster in contact with your timbers (or straw bales for that matter). Clay wicks water, and lime breaths vapor... but stucco and sealants (like paint!) trap moisture. Hence, stay away from cement and paint, and stick with plaster and lime wash. 

If you're really concerned, you can always seal your timber first and/or put a membrane between it and your infill.

In your plaster mix: clay and lime give it compressive strength, your fiber (straw or saw dust) give it tensile strength, and sand keeps the mixture flexible so it resists cracking.  Lime has the added benefit of becoming stronger with age because it will actually return to stone through the process of carbonifaction over time. You can completely mend any cracks in lime plaster with a skim coat or lime wash because it will actually heal the crack, not just fill/patch it.

[moonhill]

Nice summary, where have you gained your information?  Have you worked with these materials much?  Do you have a source of clay on your property in Alaska? 

Tim

[PlicketyCat]

Lots of good info on earthen and lime plasters in "Serious Straw Bale" and "The Natural Plaster Book".

I've done some smaller projects with cob, adobe and straw bale. Nothing extensive, so I'm no expert   Two projects in TX, one in CO and one in WA.  I grew up in Germany, and have always loved the Tudor Style (real Tudor is W&D in TF). I got obsessive about researching natural plasters and building material when I found out my hubby was allergic to latex and I was sensitive to formaldehyde.

I got a lot of info from my cousin in Norway. His farm has been in the family for 5 generations, and the farmhouse and barn are estimated to be 200-300 years old. Both are made with wattle & daub infill on timber frame. There are no records of any major repairs or reconstruction, not even after the fire in the main house in 1864. Once a year whitewash is the only maintenance on the interior and exterior plaster, and they apply boiled linseed to the exposed framing once a decade or so (although, after a few centuries of that, I think the wood is good and well preserved by now!). The roof is thatch, which gets patched if needed, the ridge rethatched every decade, and everything replaced every 30-40 years.

I haven't played around with our soils up here in AK yet. I might have to source my clay further sourth since we have a lot of glacial silt in our subsoils up here in the Tanana Valley. Wont' know until I dig up a clump and do the jar and ribbon tests. Of course, I could take it to the Co-op extension AT uaf for a proper soil test, but where's the fun in that?  Silt is bad for earthern plaster, makes it all crumbly... you want a good ratio of sand and clay for optimum "stickability".

[moonhill]

I like the taste/texture test.   

That is a good testimonial on the Norway farm house. 

What do you think of the clay chinking in the log barns in this topic?  Some good, some bad.

Tim 

[PlicketyCat]

My suspiscion on those mud-chinked tobacco barns is that 1) there wasn't appropriate roof overhang, 2) there wasn't enough fiber to stabilize the chinking, and 3) not enough or no lime in the mixture to add water resistance. Not controlling bulk water (rain) looks to be the big problem here.

Of course chinking is completely different to plaster and infills. Chinking is horizontal, and if you don't point it well and maintain it as it shrinks, you get water trapped in the joint which speeds up rot. With a plaster or infill that is the right balance of sand/lime/clay/fiber you get minimal shrinkage and the plane is vertical. It's also a continuous skin, when pointed well, that does repel water, insects and vermin. It might not extend those qualities to the timber itself, but it does significantly minimize bulk water in contact with your wood.

Lime definitely seems to be the key as it has many beneficial chemical properties in these applications, the least of which being it returns to stone. As long as you have proper ventilation and an adequate drying cycle seasonally, lime plaster can resist mold & mildew indefinitely. If you live anywhere with high rainfall or humidity, simple clay/mud plasters probably won't be enough to resist erosion and absorption of bulk water. Even a lime plaster would need some help in those conditions, probably limewash a couple times a year with good inspection.

Plasters are not "low maintenace" in the respect that they can't be ignored for 10 years until they ultimately fail; but they are low maintenance in the respect that an hour of periodic inspection and some cheap/quick maintenance can extend their life indefinitely.

Personally, I'd like to spend an hour every 6 months looking at my building to make sure everything is tip-top and a weekend doing spot maintenace and white washing than to ignore my siding for years until a whole chunk rots out and I have to spends weeks and thousands replacing the whole system. Why own a house if you don't want to love it and take care of it? If you're inspecting your home regularly, you'll be able to spot any system that needs maintenance well in advance of it becoming a big problem.