No, if you use teflon tape there is more chance the union wont seat properly, it should work just fine on its own without anything, technically, if there is ever water in the threads of the union it has already failed.
Similarly, it is asked, should I use Teflon tape on copper fittings?
If this is copper pipe, give the area a sand and inspect the pipe. A photo would help assist further. As for the use of teflon tape on joints in concealed in walls: this is totally acceptable and is the standard practice. Most plumbers tend to us both teflon tape and pipe dope for threaded connections.
Also Know, which is better plumbers putty or Teflon tape? Teflon tape gives a reliable seal on threaded pipe joints for liquids and gases that may be under considerable pressure. Plumber’s putty acts as a flexible caulk in situations where you need water resistance—but it cannot withstand any significant pressure.
Similarly, you may ask, should I use Teflon tape on brass fittings?
teflon tape and firm is sufficent because if you’re just jaming the brass together you can break the seal provided by the teflon or similar, if using unions they seal brass to brass and use the above mention nudge and grunt rule, just be carful not to mishape the fitting as brass can crack or bend with undue force.
What can I use instead of Teflon tape?
However, there are alternatives for each. Some plumbers prefer to use a liquid compound for pipes (also called “pipe lacquer”) instead of tape. And in some cases, such as in granite, where plumber’s putty is undesirable because it can cause stains, and silicone putty is a better choice.