1 TITLE OF INVENTION Plastering Method and Extruder for Same TECHNICAL FIELD [0001] This invention concerns finishing procedures used by plasterers on internal walls and an extruder for performing the procedure. Such walls stand at approximately 900 to each other and to ceilings. The coating of the internal corners requires special care. BACKGROUND [0002] Stud walls of buildings are drylined with plasterboard. The boards intersect with floor and ceiling and exhibit internal and external corners. Internal corners are finished by initial application of adhesive tape followed by depositing a bead of hardenable plaster along the length of the corner and subsequently smoothing it with a plasterer's glazing tool. The procedures require care because once the plaster has hardened it must be sanded smooth and unskilled work can spoil the wall appearance. [0003] These procedures add considerably to the cost of construction. There may be intermittent shortages of skilled tradesmen to carry them out. [0004] Standard procedure is to use a premixed air drying top or final coat jointing compound, typically consisting of limestone, clay, mica, perlite, polyvinyl acetate, quartz, crystalline silica, talc, polyvinyl alcohol, cellulose derivative and water. It is preferable to use a mix which is sufficiently viscous to keep its shape as it dries. It must cover nail heads and smooth to a finish which accepts final sanding. Plasterers meet operational difficulties when working with premixed jointing compound. If water is added, the mix shrinks unduly upon drying and when the plaster shrinks nail heads are seen, the hollow recess in square set is visible, a line in the paper at its edge is seen and creases in the paper are evident. The work must be repeated. 20 .02-19,C:\Uses\Shrlen\D u ts\SPECIFICATIONS kakov .i td,1 2 [0005] Water content is crucial to the operators for another reason. Hand pumps are not efficient at drawing in and expelling in plaster of a viscosity which the plasterer prefers. Accordingly plasterers tend to add more water to produce a more mobile mix and draw this in through the pump inlet until the pump is full. As the mix enters through the pump nozzle, a viscous mix requires considerable strength to draw back the pump handle. This can lead to strain injury. Other automatic internal machines which are not hand pumps but operate using compressed air will not work if the mix is viscous. The mix must be sloppy for powered machines to cope. Operators try such machines but poor results compel them to work by hand. SUMMARY OF INVENTION [0006] The apparatus aspect of the invention provides a plasterer's extruder comprising a piston-type reciprocable hand pump having at the delivery end an outlet nozzle, multiple inlets and a flap valve which covers and uncovers the inlets. [0007] The nozzle may be central in the end wall of the pump with inlets arranged coaxially around the nozzle. [0008] The inlets may together exceed the area of the nozzle and be 4-8 times the nozzle area. The nozzle also acts as an inlet therefore the total inlet area may be /2-% the end cap area. [0009] The flap valve may be an annular flexible diaphragm mounted at the delivery end overlying the inlets. [0010] The delivery end may be made as a metal or plastic cap which closes the end of the pump, retains the nozzle, the flap valve and is perforated by the inlets. [0011] The nozzle may be simply a spigot to which is attachable a special purpose extrusion nozzle. 2013-02-19,C:\UserslShadceD cnts'SPECIFICATIONraskov.inpat.wpd,2 3 Advantageous Effects of Invention [0012] 1. Rapid filling and extrusion rates. [0013] 2. Labour cost saving. [0014] 3. Ability to draw in and expel viscous mix. BRIEF DESCRIPTION OF DRAWINGS [0015] One embodiment of the invention is now described with reference to the accompanying drawings, in which: [0016] Figure 1 is a side view of the pump. [0017] Figure 2 is a perspective of the delivery end cap. [0018] Figure 3 is an exploded view of the end cap. [0019] Figure 4 is an end view of the cap of Figure 3. [0020] Figure 5 is a side view of the cap of Figure 3. DESCRIPTION OF EMBODIMENTS [0021] Referring to the drawings, the pump has an aluminium cylindrical body 2 (600 x 60mm) with a conventional piston 4, piston rod 6 and handle 8. The operative end of the pump has an external threaded end 10 to receive an aluminium screw on cap 12. The skirt 14 has an internal thread 16 to engage the thread 10. The end wall 18 of the cap has a nozzle bore 20 which is threaded to admit the threaded end 22 of tubular nozzle 24. The leading end 26 delivers plaster to the corner to be filled. The trailing end has a circular flange 28 for a purpose to be described 2013-02-19,C:\Users\Shrlene\Documeits\SPECIFICATIONS'kraskovimnpat.wpd,3 4 later. [0022] The end wall 16 has a bevel 30 and eight bores 32, each almost as large in diameter as the nozzle aperture. [0023] The tubular nozzle 24 supports an annular rubber flap valve 34 and flange 28 clamps it to the inner face of end wall 18. Ring 36 is a seal which makes a fluid-tight joint between the skirt 14 and the cylindrical body 2. [0024] In use the valve 34 is clamped to the end wall by annular flange 28 but is free to flex away from the wall during the phase of pump charging. [0025] A batch of mix is prepared in a bucket with a water content of 25% which produces a gel resembling thick custard. When the end cap is immersed in the gel and the piston retracted steadily, the gel enters the extruder through the nozzle and the inlets and displaces the valve from the end wall, filling the pump interior. The mix may be made by adding a small quantity of water to a manufacturers mix sold in containers by Boral Limited or CSR Building Products Limited among others. Such mixes contain 21-22% water. The resultant mix is very viscous and is gathered by a smoothing tool without spillage once the bead is deposited in the corner. Minimal cracking through mix shrinkages is encountered in the dried joint. [0026] The rate of pump filling is high because the entry area is equivalent to more than half the area of the end wall. As soon as the piston is advanced the valve closes and the plaster emerges through the end of the nozzle and forms a cylindrical deposit in the corner to be filled. The nozzle acts as both an inlet and outlet but the bores 32 only act as inlets. The pump capacity may be 3-41. This is light enough for an operator to lift comfortably. [0027] It is to be understood that the word "comprising" as used throughout the specification is to be interpreted in its inclusive form, ie. use of the word "comprising" does not exclude the addition of other elements. 2013 -02-19,C:XUsers\Sluden\Dcuments\SPECIFICATIONSkraskovinnpatwpd,4 5 [0028] It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention. 20]3-02-19,C:\Uss\Sharlene\Documents\SPECIFICATIONS'Skaskov.impat.wpd,5