DAS Stone 1kg Air Hardening Modelling Clay, Non Bake, Ready To Use, Suitable for All Ages, Ideal for Professionals & Hobbyists

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These are a relatively new foundation solution consisting of slender, hollow steel shafts with a small number of steel helices (or screw threads) welded to them. The piles are screwed into the ground until they achieve sufficient friction to support the required load.

The rest of England and Wales generally have low plasticity clays but even these still carry some risk. The first 900-1,200mm layer of clay is subject to movement due to expansion and shrinkage from seasonal variation in moisture content, so it is generally necessary to excavate foundations to a depth where the amount of moisture present remains stable. In this practical, I’ll be focusing on a few methods you can use to construct some of these prototypes. For best results, I’ll be using materials suitable for scribing; a harbour wall made from rigid insulation and plaster (with another using DAS air-drying clay), an ashlar arch and various rubble walls made from styrofoam, and finally, a dry stone wall made out of more air-drying clay. Please note; as the painting technique I’ll be using will be similar for every practical, I shall share this at the very end. WHAT YOU NEED

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Medium plasticity clays are found in the rest of the South East, across the Midlands and up beyond the Humber Estuary towards the North East. They also turn up in some isolated areas in the North West of England near the coast Clays with the highest plasticity (and so the highest risk) are generally found in the South East of England, stretching up through the East Midlands to the Humber in the North and down to Bath in the West There are three types of clay in the UK, classified by their plasticity, which is how much their volume can change due to their water content.

In cases where clay becomes softer as you dig down, a traditional strip foundation is sometimes acceptable, but it is important not to over dig as this may increase the stress on the softer clay beneath. A common solution is to dig wide strip foundations with embedded steel reinforcement, however an engineered foundation such as a reinforced raft or piled foundation may be necessary in some cases.

Using rigid insulation and plaster

Providing the chalk is not too soft, foundation widths of 450mm for low-rise buildings are generally acceptable. The depth of the foundation must be below any frost action, a minimum of 700mm. Electricity and gas don’t usually need to be ducted or installed at this point as they are normally surface mounted. Finally, the building and warranty inspectors will have to approve the excavated foundations prior to any concrete being poured.

The process of making stone walls using styrofoam is very similar, but there is no need for plaster, nor to scribe any joints; the pressure from the mechanical pencil on the soft foam while marking the courses will achieve the same result. As such, the Styrofoam rubble walls on the diorama (the ruined barn shown here, and the retaining walls) don't require further explanation, but the construction of the ashlar arch certainly does… A reinforced suspended concrete floor slab, or a reinforced concrete ring beam, is then cast over the top of the piles, linking them all together so that the load of the Strip, trench fill or pad foundations must be cast at a minimum depth of 750mm in low plasticity clays, 900mm depth in medium, and British Standard 8004 recommends a minimum depth of 1m for foundations in the highest risk areas. If there are, or were, trees nearby, depths of up to 3m may be necessary. The depth necessary will depend on the type of tree, as species have different water demands, with tall broad-leafed species such as poplars having the greatest impact. Diagrams of strip foundations (left) and trenchfill foundations (Image credit: Homebuilding & Renovating) the prototype arch is a listed structure at Pennsylvania Castle on the Isle of Portland, and will be closely matched stone-by-stone! A printout of a photograph taken square-on helps gauge the size of the stonework, as well as general dimensions and information obtained from the Historic England listing. Note how I’ve emphasised the mortar joints on the printout to aid visibility, and written notes to help speed up the process.

Using DAS air-drying clay

The standard foundation solution in most parts of the UK is the strip foundation, also known as strip footings. Where the soil is soft or of a low loadbearing capacity, wide strip foundations can be used to spread the load over a larger area, reinforced with steel so that the loading per square metre is reduced. The rear of the arch differs in three ways. Firstly, the crenellations are only half-depth except at the outer ends; which wrap around the sides. Secondly, a slope joins the bottom of the crenellations to roughly the same level as the top of the cornice on the front. Thirdly, the entire archway has a rebate where the gates once sat. These all require careful trimming with a sharp blade. Michael is Homebuilding & Renovating's Director of Content, Vice Chair of the self build industry body, the National Custom and Self Build Association ( NaCSBA), presenter of multiple property TV shows and author of Renovating for Profit(Ebury).He also runs an architectural and interior design practice, offering design and project management services. He is one of the country's leading property experts and has undertaken over 30 building projects including two self-builds and the renovation of a Grade-II listed farmhouse.

Now use a flat needle file to create chamfered edges along the archway. With the styrofoam walls complete, apply a layer of gesso to everything. Gesso is an acrylic paste made from chalk, binder, and white pigment. It’s used as a primer to prepare surfaces for painting, but it also provides a little more strength and texture. Simply apply it with a brush, and leave it overnight to dry. Where the foundations are affected by tree roots (or their previous removal), you may be required to employ a fairly deep trench filled with concrete but with a compressible material to one or both sides of the external trenches to counteract any heave or expansion in the ground. To cover the entire quay, I use household filler/plaster as it’s cheap, available in large quantities, and you can make it to the viscosity desired by varying the amount of water in the mix. Apply a thin layer of PVA to the quay walls, followed by a generous coating of plaster. Once left to harden (which can be up to 48 hours), sand the plaster until the required smoothness is achieved. If the water table is high (for instance if the gravel is submerged), the bearing capacity will be halved, so it’s important to keep the foundations as high as possible. A shallow, reinforced, wide strip foundation may be suitable.

Using styrofoam and gesso

If sewage pipes leaving the building have to be deeper than the top of the foundation concrete then they should also be ducted; they cannot be trapped within the concrete and must be able to move freely. building is spread evenly. For a post and beam structure, the piles or groups of piles are capped with a concrete pad. Screw Pile Foundations The painting technique for the dry stone wall is slightly different from the rest. To ensure the paint reaches the crevices, spray a fine mist of water, then apply a very weak dark grey wash. Next, apply a slightly watery colour that matches the prototype stone in its un-weathered freshly-cut state. Finally, add additional dark grey washes as necessary, along with dry-brushed yellowy-green ‘lichen’ spots. This can be a cost-effective way of building on sloping ground too, as the steel piles can be left above ground and linked together with tension wires or rods, and topped with a steel ringbeam or grillage to build from. Factors to Consider What Might Affect my Choice of Foundation System?