Light Clay Infill a.k.a Leichtlehm
Leichtlehm, said from the throat easily by any native German speaker, translates directly as “light loam”. Loam is a composition of earth including relatively equal parts of sand, silt, and clay – which makes Leichtlehm easily translated to “light clay”. Light Clay Infill is a fairly old building technique, and quite a basic one at that. Many of you are probably familiar with the Tudor style buildings that make English and German architecture famous. Well, guess what, many of these, from old to new, are built using the technique of Light Clay Infill! This building technique has migrated to many countries, and is quite popular in not only North America, but also British colonies such as New Zealand. The New Zealand Earth Builders share a little on its history and their experience with Light Clay Infill.
Light Clay Infill is one of the easiest (if not the easiest) natural building techniques to learn, though you will probably still want to find skilled framers or timber framers for the carpentry. There are a few extra considerations when framing for infill compared to framing a conventional home. Firstly, it is important to ensure that the framing is set up to take the desired thickness of infill. One can get away with framing for infill in a number of ways. I have most often seen and used the typical 2×4″ stud-framed method of construction. In order to get a thickness any more than the available 4″ of the stud member we have to double-frame our walls. This uses quite a bit of lumber, as you can imagine. A good alternative is having a Timber Frame erected and using simple 2×2″ fake “studs” instead. These fake studs do not need to bear any load, hence being able to be such small members. This not only saves quite a bit of lumber when it comes to framing, it also gives you a beautiful Timber Frame for your home. You can even finish it in the ancient Tudor style!
Robert Laport of Eco Nest has yet a different method for framing infill homes. He runs a smooth site and teaches great workshops on this building method. Whichever your framing method, it is also a good idea to stagger the studs in order to optimize for insulation, and have members spaced at about 2′ intervals onto which you can attach the form-work.
Though similar, the form-work for infill is much more simple and user-friendly than the form-work used when pouring a concrete foundation. Infill forms do not need to be braced since the material isn’t heavy enough to push them out of shape. They don’t need to be coated in a petroleum product to ensure they come off, as the clay mix will not stick to the form. One simply has to screw the forms into the “studs”. Access is usually from one side of the wall, enabling the other side to be covered completely with form-work while the forms on the filling side are usually around 2′ tall. Leap-frogging the forms as soon as the top one is filled is my favourite system. You don’t need to wait for anything to dry or set before you take down or move up your form-work either! In fact, the sooner you take the forms off, the sooner your infill can start drying. And drying is one of the most crucial aspects when timing your infill building project.
Due to the thickness of Light Clay Infill walls, it is best to start your project early, and plan for the walls to be being filled during the height of summer so they can dry all the way through. If you’re lucky enough to live in a place where it is always summery, then this isn’t so much a concern. But up here, in the Pacific North West, this can mean build or no build. Like many natural building materials, we really don’t want our infill walls to freeze. Though not a devastating event, this can cause some of the infill at the surface to flake off, especially if wood shavings have been used. So plan wisely and build in the right season! Besides, it’s just more enjoyable to be working outside when it’s sunny and beautiful.
Light Clay Infill is an amazing building material which can be adapted for a number of different climates. Offering both the capacity for thermal mass and insulation, it is a good choice just about anywhere you live. By adjusting the proportions of clay in your mix, you can achieve a wall that can hold heat, or a wall that keeps the outside temperatures at bay. If you haven’t guessed it, the more clay you add to your mix, the more mass it has, leading to better storage of a given temperature. You can also add some sand to this mix if you are really after this thermal storage effect. There have even been studies done to test the performance of various mixes. Builders in the Pacific North West, and elsewhere, usually tend to mix in just enough clay to make the straw or wood chip sticky enough to hold together. This gives us the confidence that we will have enough insulation in the cold northern winters without the added thickness found with super-insulative straw bale walls. Another way to influence the performance of your Light Clay Infill walls is to change their depth. Around here we typically build our infill walls between 6″ and 12″ thick, though I have seen 4″ and 16″ thick walls.
Some of my favourite features of Light Clay Infill walls are that you end up with nice smooth walls ready for a base coat plaster, you have studs available for hanging shelves, cupboards, or other furnishings, and they are easy to run radiant heat through with pex tubing. Here is a good article about radiant heating in floors. Don’t forget to mark where your studs are, as sometimes a standard schedule isn’t always followed. Oh, and I don’t want to forget to mention that infill walls don’t have to be straight!! Yes, you read that right. It is very easy to achieve that curved wall even when using form-work. So, you can have your smooth walls, and your curves too!
