This section is from the book "Commercial Gardening Vol1", by John Weathers (the Editor). Also available from Amazon: Commercial Gardening, A Practical & Scientific Treatise For Market Gardeners.
These houses are each 200 ft. long x 30 ft. wide and were erected at Waltham Cross and Cheshunt by W. Duncan Tucker & Sons.
If the box is treated as one part, no mistake can be made. The materials are shot in a heap on the platform and turned over twice dry to mix them. They are then spread out over the platform and water added through a fine rose, while Canterbury hoes are raked backwards and forwards through the mixture till it seems fairly wet. The mass is then turned up into a lump again, water being added whenever a dry portion shows, the lump being worked all the time with a Canterbury hoe as before. If not wet enough then, it must be turned once more. The finished product should be neither too wet, so as to be sloppy, nor too dry, so as to be solid. The concrete is wheeled to the mould and shovelled in. The first layer may be shot off the shovel with some force, so as to make it spread out beyond the boards, any space that is not so filled being filled up from outside up to the lower edge of the first board. As the work proceeds the louvre boxes are put in, well bedded in, and fixed by a couple of nails lightly driven through the boards. These louvre boxes are made with the sides projecting beyond the ends, for building into brickwork, etc, and for concrete work these projections had better have a V cut in them and have the concrete worked into the V when they are set in the wall. As the concrete rises to the top of the planks the plate ties must be put in. These are simply pieces of flat iron 1 ft. long by 1 in. by \ in. thick, bent at right angles, with one arm 4 in. and the other 8 in., and a |-in. hole punched near the end of the longer arm. These are put in at every 10 ft., and always one at each corner or where a door post will come. They are set touching the inside boards of the mould, and the hole should be about \\ in. above the top of the wall when the concrete is filled right up. The top of the wall is best finished off with a builder's trowel, being nicely smoothed down. The concrete should be left alone for twenty-four hours, and then the little crosspieces are unscrewed, the posts taken out till the last few feet of finished wall are reached, and the planks lifted out, scraped clean, especially along the edges, and placed in position farther along and filled with concrete as before. When putting the planks in place it is best to arrange them so that the ends all come in different places, then where two planks meet their ends are made secure by screwing a piece of wood over the join on to the planks above and below. The joints in the top and bottom planks have to be made with a short piece of board put lengthways. When the walls are finished they should be left to harden while the woodwork is painted and prepared. All the wood can be bought ready formed, and it only requires the joints to be made, and the sash bars cut to the right length and angle, to be ready for use. When ordering, make allowance for the joints and order a few sash bars extra, for some are sure to be a little short or twisted; these are reserved for filling in the ends. The bars where the ventilators come can be shorter than the others, and are supported by the ventilator seat instead of the ridge. This plan makes a better job of the ventilators and saves a little wood into the bargain.
All houses are the better for a purlin, even if the bars are short ones and no purlin supports are used. Many houses 16 ft. wide have no purlin supports, but the facilities these offer for the supporting of shelves soon make up for the extra cost. Besides this, a house built with purlins properly supported and tied to one another across the house will be much stronger than the other form and will not require the iron ties running from the plate to concrete blocks in the border. These ties are nothing but a nuisance, and a poor substitute for the purlin ties at the best.
Fig. 169 - Scarf Joint.
Fig. 170. - Half-lap Joint.
The best joint for the plate, purlin, and ridge is the scarf joint (fig. 169). It takes a little more wood than the half-lap joint (fig. 170), but is stronger and easier to make. The latter, however, is used at the corners. To get the correct angle for the ends of the bars an experiment must be made. A piece of plate is laid in position on either wall, and a small section of drip nailed in position on either side; a little piece is also cut off a length of ridge - about 2 in. will do. Two bars are then taken and carefully fitted until they will occupy their final position with the little piece of ridge between the upper ends, and fit nicely down on the plate as well. Care must be taken to keep the bars exactly the same length while fitting. The cuts can be made almost exactly right the first time if a good large-scale drawing is prepared first and the bevel gauge set to the angles so obtained.
When once the correct angles are obtained the rest is easy. A trough is made to take the finished bar and a saw-cut made through the sides of the trough at each end of the bar as in a mitre block. The uncut bars are now laid in the trough, one after the other, and the saw, guided by the cuts in the sides of the trough, will cut every bar exactly alike. The short bars where the ventilators come have only the lower end cut like this; the upper end is cut to fit the seating.
After all the wood is cut it should be gone over and all the knots and resinous places be painted with patent knotting, then a good coat of priming should be given. As soon as dry, the second coat is given, special attention being given to the joints. The lower side of the plate should be tarred, but even if the remainder of the plate is ultimately to be tarred it should be left for a year till thoroughly seasoned: for unseasoned wood, tarred, will develop dry rot very quickly.