IMntOYEMEST OF TltES. £] Jf 



!iad caused the tar to penetrate into their substance. Their 

 pores were completely stopped, a nd they were rendered im- 

 penetrable to water, as I found by experience. The five 

 persons I have mentioned tarred four thousand tiles in six 

 hours. Both these experiments did not consume a barrel 

 of tar. 



The roof for which these tiles were used is open to the The tiles not 



north, and exposed to all the violence of winds and storms. in J ure(i in2 * 



. . years. 



It was repaired in 1779> and not one of the tarred tiles is at 



all injured or decayed. They are covered with a very fine 



mass, and their surface is in as good condition, as if the tar 



had just been laid on. On the other hand, several of those 



which, as I said before, I had set apart, supposing they 



would resist the weather without any preparation, because 



they were thoroughly burned, are cTacked, broken at the 



corners, or splintered on the surface. 



Some persons say, that tarred tiles would be more dura- Additions f 



ble, if they were powdered with iron filings and charcoal the lar in ^ u " 

 . . . nou9. 



dust: but I conceive these substances would render the sur- 

 face rough; and thus detain the water, while those coated 

 with varnish would let it run off. 



I am of opinion however, that a mixture of lime and tar Other sub- 

 would be more beneficial. I think too, that fats in general, stances * 

 whale oil, or the dregs of our oils, would be equally adapted 

 to the purpose, and still cheaper. 



ANNOTATION. 



Few people in London or its vicinity, where tiles are the Calculation of 

 common covering of houses, but must have experienced th e expense in 

 great inconvenience from roofs leaking, and the consequent thlS countryf 

 trouble and expense of frequent repairs. Sometimes in- 

 deed this is owing to the badness of the mortar employed ; 

 but is most commonly the consequence of a few tiles bein^ 

 cracked to pieces by frost, after they had imbibed water. 

 The method above recommended would appear to be a 

 sufficient remedy for this; and the expense attending it is 

 not an object at all comparable with the comfort and advan- 

 tage of a secure roof. I am not certain, whether the count 



be 



