. I ended up doing about 3 layers and grinding it back once dried using a flap disc/angle grinder.
Please do the above ^^^
I didn't and it caused the urethane to bubble a bit.
I just got carried away and made the urethane one thick layer straight away. Which caused it to bubble when I sanded it back it looked crap due to the smooth urethane surface having bubbles in it, I went to dig the urethane out with sharp flat tip and thought it would come out easy. As it come off very easy from the base and the top, but its tough as between the base and the top, so I just left it and ran a thin layer of urethane to seal the small bubbles on the surface.