Advice for fixing a failed paint job

[longrob604]

I have been trying to paint some of the woodwork in my house black (window sills, stair treads, newel post and hand rail).

I first tried using Ronseal products - a primer/undercoat (2 coats) and then their "diamond hard" floor paint (2 coats). It started flaking off immediately back to the bare wood. A friend (former painter and decorator) thinks that I didn't stir the primer/undercoat and therefore didn't grip the wood properly ? I remember shaking the tin fairly vigorously but apparently that's not sufficient ?

On one of the sills, I have now sanded back to bare wood, but doing that but that took ages. Do I need to do that on all the sills and the stair treads too ? Sanding one sill took 4 hours. I hate to imagine doing that on the stair treads.

I have now invested in Zinsser Bin Aqua and put one coat down on the sill. Please advise if I should do another coat, and if I should also use an undercoat before the black top coat).

And please advise me on the stair treads. Do I really need to sand them all back down to bare wood ? I

Thanks
R

[dewaltdisney]

Pictures would help, it is hard to imagine and comment constructively without sight of the work

DWD