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1、Garden walls can be constructed of plastered straw, but since they are not covered with a roof, particular attention should be paid to protecting the top of the wall from water entry into the straw. A simple and secure method is to cap the wall with a waterproof covera mini-roofwhich may be metal or
2、 other roofing material, including an impervious masonry top. A less secure alternative is to install plastic underlay sheet on the top of the wall before render is applied. The purpose of the plastic underlay is to direct away from the straw any water that enters the top of the wall through cracks
3、that might occur over time. Although some garden walls built by this method appear to be quite sound after several years, that is a short test period. It remains desirable to use a suitable mini-roof for straw bale garden walls to ensure that they will survive for many decades. Of course the horizon
4、tal pre-construction method can be applied readily to the construction of garden walls, though a suitable flat surface on which to construct the wall might not be so readily available. The footings of garden walls should reach sufficiently above the surrounding ground level on both sides of the wall
5、 to prevent later problems with water. Sloping sites need to be considered carefully with respect to where water will flow and lie. Substantial weep or flow holes through the footings will be desirable in some situations. Although it is, no doubt, possible to design moisture barriers and structural
6、features that would enable straw bale walls to be used as earth-retaining walls, the extra effort required usually would not make straw bale construction cost- and labour-effective compared with use of other materials. The raised footings required for straw bale garden walls lend themselves to easy
7、utilisation of the new tensioning system (see page 60), because there will be free area above ground where the tensioning tubes can be inserted in the 12 Garden walls and creative shapes footings at the time of laying the concrete. These tubes should extend sufficiently from the face of the footing
8、to enable one to attach the twisted wire loop wire-lock holders. The ends of these tubes must be kept free of concrete during pouring of the footings, and there should be means to find them easily when the footings are finished. To satisfy both of these requirements, a suitable method is to insert i
9、nto each end of each pipe a plastic tube that fits the pipe fairly neatly and extends well beyond the edge of the footing. The plastic tube is withdrawn after the footings have been poured and cured, and only just before tie-down wires are installed. Curves, slopes and holes and other things Straw b
10、ales lend themselves to the construction of relatively free form structures. For example the garden wall illustrated is curved and tapered on a varying slope base. The footing was laid using flexible flat galvanised iron sheet for the formwork and holes were included in the footing for tie-down wire
11、s. The first layer of bales was laid as full-thickness bales on top of the footings (with a damp course between). The other layers of bales were then laid in the fashion detailed in the diagram, so the topmost layer was composed also of full-thickness bales rather than including any biscuits of stra
12、w in that top layer. To achieve the curve of the wall, each bale was simply deformed into a curve before placing it. Garden walls and creative shapes89 Fig. 27Method of laying bales in a strongly tapered wall. Note the top layer is composed of full bales laid parallel to the top of the wall. The hat
13、ched areas are filled with straw biscuits. layer of full-bales to achieve good top of wall shaded spaces are filled with biscuits of straw this bale tapered on end The top plate was not pre-made, because it was not feasible to calculate the required shape of the top plate before the bales were in pl
14、ace. With the bales all in place two pieces of 16mm NB steel pipe were bent to fit the curvature of the top of the wall. Then pieces of 12mm reinforcing rod were welded between the pipes, so the curved ladder-type top plate conformed to the contour of the top of the wall. There seems to be no easy w
15、ay that a suitable wooden top plate could be constructed for this application. The wires could then be installed and the wall tied down. In this case fence strainers were used, but the new tensioning system would be a better option. There is another twist to tying down strongly tapered walls: vertic
16、ally orientated wires sometimes will tend to distort the wall from the desirable shape. To overcome this, one can slope some wires or install additional wires to pull the wall into the desired shape. Practical straw bale building90 Fig. 28A curved and tapered wall. Bales can be shaped in any way tha
17、t is consistent with structural requirements. Simple bending of bales is straightforward, and can be done to a curvature radius at least as small as 1.5m mean radius. However one should note that the lengths of the inner and outer faces of the curved bale remain equal. Therefore when placed together
18、 in curved wall or an arch, gaps will occur and should be filled with straw. For walls with only small curvature (large radius), the gaps might be small enough that no filling is necessary. Straw filling the gaps should be orientated in the same manner as the straw in the bales, and is best inserted
19、 as the bales are placed, rather than after all bales are placed. If excess straw is allowed to protrude from the wall, that can trimmed after all bales are placed and the wall has been tied down. Garden walls and creative shapes91 normal vertical tie-down wires additional tie-down wires Fig. 29The
20、technique of using additional slanted tie-down wires to prevent distortion of strongly tapered walls. For large curvatures, such as might occur in arches, filling the gaps with straw biscuits is not very satisfactory. To eliminate the gaps the ends of the bales should be tapered before the bales are
21、 bent. Bale ends can be tapered by inserting a shortened tie and then trimming the bale end to a taper with a brush cutter. This is fairly labour intensive, and therefore should be done only if the gaps become a significant problem. The bale can also be tapered along its length. This will require th
22、e installation of new ties if the taper is substantial. If the taper brings the face close to the tie, but does not interfere with it, it might be sufficient to pull the existing ties towards each other using the clips described for use with the new smaller straw bales (see page 64). Even the height
23、 of a bale can be tapered, rather than using biscuits in a tapered wall, as described above. That will require the installation of new ties using a needle that is longer than the bale length. Removing the unwanted straw in this case is quite messy, because of the random straw arrangement within bisc
24、uits, so it is not very satisfactory. Small niches in bales can be made for decorative purposes. Holes can be cut, though not very easily if it is done after the wall is built. A variety of tools may be used for shaping bales and making holes in bales. These include: brush cutters, nylon cord trimme
25、rs, hedge trimmers, simple handsaws and custom tools such as the push-pull device previously described (see pages 1617). Drills are not very useful, because the straw tends to wrap around the drill and can bring it to a rapid halt. Practical straw bale building92 A A B 900 mm (typical) 900 mm Fig. 30Plan of a curved wall showing how gaps will form due to the inner and outer faces of the bales being of equal length. The gaps may be eliminated by tapering the bales as indicated by the dotted lines. A and B are alternatives.