My 2c worth. 19mm is not very thick at all. If you build a 16" f/4, the sagitta (mirror depth) is nearly 7mm. Little room for error in grinding. You will probably need to build an 18 point flotation cell for the mirror or better. I'm not saying it can't be done but it would need to be done well.
https://stellafane.org/tm/atm/grind/measure.html
http://www.newportglass.com/grind1.htm