I have an outdoor tiled area underneath the back patio. I’d like to know what would be a suitable way to cover it in a different colour and have it non slip... preferably the cheapest possible way
Welcome to the Bunnings Workshop community @Wendi. It's fabulous to have you join us and many thanks for your question.
You might like to read through these existing topics on painting outdoor tiles: Bi-fold door - and painting tiled steps by @jaga and Outdoor tile paint by @amykat86. Within them, I address why there are no products available for painting outdoor tiles.
Tiles have a glazed or water-impervious coating which prevents the paint from adhering to them. You will find paints for pavers or concrete, as they do not have these coatings and paint can soak into the surface. There are paints for internal tiled floors as they do not suffer from such extreme wear. Outside, hard rocks and debris are constantly sitting on the surface and would scratch the paint off very quickly.
The only way I can think of for prepping this surface for paint would be by grinding off the glazed coating completely. As you can imagine, that would be a very laborious task indeed.
If you have room to accommodate it, have you considered building a low-level timber deck over this area? You would need at least a height of 70mm between your door sill and tiled surface.
You could consider tiling straight over the top.. You would need to be careful to use the correct adhesive, as only some adhesives are suitable for laying over existing tiles (and you will pay a bit more for this type of adhesive). Also be sure to give the existing surface a very good clean prior to tiling.
Depending on the size of the area, you may be able to find a non-slip tile at a clearance centre - many tile shops sell small quantities for cheap, as they are the end of a batch. I recently got some good quality non-slip tiles for about $20 per sq metres.. At the time, they had around 50 sq meters, but only one colour to choose from (grey). Just depends on luck of the draw really...