448 PHILOSOPHICAL TRANSACTIONS. [aNN0 1778. 



use any nails to fasten down either these short pieces of laths, or those short 

 pieces hereafter mentioned (§ 7)- 



§ 5. These short pieces of laths ought then to be covered with one thick coat 

 of the rough plaster spoken of hereafter (§ g), which should be spread all over 

 them, and which should be brought, with a trowel, to be about level with the 

 tops of the joists, but not above them. This rough plaster in a day or two 

 should be trowelled all over, close home to the sides of the joists; but the tops 

 of the joists ought not to be anywise covered with it. 



§ t). The method of double under-flooring is, in the first part of it, exactly 

 the same as the method just described. The fillets and the short pieces of laths 

 are applied in the same manner; but the coat of rough plaster ought to be little 

 more than half as thick as the coat of rough plaster applied in the method of 

 single under-flooring. 



§ 7. In the method of double under-flooring, as fast as this coat of rough 

 plaster is laid on, some more of the short pieces of laths, cut as above directed 

 (^ 4), must be laid in the intervals between the joists on the first coat of rough 

 plaster; and each of these short laths must be, one after the other, bedded deep 

 and quite sound into this rough plaster while it is soft. These short pieces of 

 laths should be laid also as close as possible to each other, and in the same direc- 

 tion as the first layer of short laths. 



§ 8. A coat of the same kind of rough plaster should then be spread over this 

 2d layer of short laths, as there was on the first layer above described. This 

 coat of rough plaster should (as above directed § 5 for the method of single 

 under-flooring) be trowelled level with the tops of the joists, but it ought not 

 to rise above them. The sooner this 2d coat of rough plaster is spread on the 

 2d layer of short laths just mentioned (^ 7) the better. What follows, as far 

 as § 13, is common to the method of single as well as to that of double under- 

 flooring. 



^ 9. Common coarse lime and hair, such as generally serves for the pricking- 

 up-coat in plastering, may be used for all the purposes before or hereafter men- 

 tioned; but it is considerably cheaper, and even much better, in all these cases, 

 to make use of hay instead of hair, to prevent the plaster-work from cracking. 

 The hay ought to be chopped to about 3 inches in length, but no shorter. One 

 measure of common rough sand, 2 measures of slacked lime, and 3 measures, 

 but not less, of chopped hay, will prove, in general, a very good proportion, 

 when sufficiently beaten up together in the manner of common mortar. The 

 hay must be well dragged in this kind of rough plaster, and well intermixed with 

 it; but the hay ought never to be put in, till the 2 other ingredients are well 

 beaten up together with water. This rough plaster ought never tc) be made thin 

 for any of the work mentioned in this p.i[)er. The stifier it is the belter, pro- 



