Hi lefthanded. The tables are about 30" diameter. They are a resin type.
Sealing the grout helps to avoid staining and perhaps a little weather proofing, but not much. There may be heavier duty sealers available though.
These tables have been outside in the weather and have suffered. Grout has cracked and bits broken off.
This may be because the table top expands and contracts at a different rate to the tiles and grout.
So they are not weatherproof.