Grout in floor tiles?

I am in the process of scraping out grotty top surface of grout in the floor tiles of our conservatory to reveal a clean surface.
To protect the exposed grout so that it doesn't go 'manky' (dirty to those not in UK ) my thoughts are to paint the grout with clear marine varnish to stop dirt ingress what's the views of those in tiling profession who either sell or lay tiles. Thoughts are sealing surface with non porous sealant easy clean when floor mopped.
Many thanks