This is what we had before.
You might remenber we painted the pergola on the other side of the terrace a while ago, but the conservatory side of the terrace was still unfinished. The grid on the right side of the last picture can be removed and I took it out to sand and paint it.
I used the belt grinder for the grid, but sanded the rest of the terrace beams by hand because the grinder is heavy as hell. After the sanding I washed all surfaces and then had a good nights sleep. Next day everything was dry and ready for the first coat of paint. And then second coat of paint. It looks so good now, I'm so happy!