Many old houses have tiled or flagged floors. Most of these were glazed when they are installed to give a hard wearing surface. However some quarry tiles were not and of course flagged floors are natural and hence not glazed. So how to stop them from getting dirt ingrained or from slowly being worn away by abrasion.
There are a number of product types that are available. Any quick internet search will show them up. However there are a few things to bear in mind when choosing:
Look for low / zero VOC products
You need a breathable / micro-porous seal as there is a constant flow of moisture vapour up through the floor
You need a finish that is not slippery / glossy
Most of the products will not give you a fantastic lifespan unless the tiles are not being stepped on. So be prepared to have to recoat the tiles every year or so in the high traffic areas. This can cause problems with some sealants, so again look for ones that can be re-applied over the top of existing.