Tile installation is commonly done directly onto a subfloor, usually made of plywood. Then a tick-bed method of 1-1/4” mortar is applied to the subfloor ready for the tiles. This is a fairly expensive way of setting tiles because it generally requires a very skilled installer taking careful time to do it right.

Less expensive is using a cement board (also called backerboard) installed over the subfloor. Cement board is made of Portland cement, commonly a 1/2” thick. The seams are usually taped with fiberglass mesh tape. This method presents a smooth and level surface ready for mortar and tiles.
Modified latex-Portland cement mortar or thinset mortar can then be used to adhere the tile to the cement board or the subfloor. Relatively odorless thinset mortars are available. Like their conventional counterparts, they are primarily made of Portland cement but usually without odorous additives. They’re generally considered inert once cured.
More sustainable grout for filling the spaces between tiles can replace the more chemically laden conventional grouts which contain many chemical additives, often including epoxies and silicones. VOCs can be emitted during curing. Grouts requiring damp-curing are generally considered the most inert. If toxicity of grout or mortar is a concern, remember that larger tiles require less grouting joints to fill. Cured grout joints can be sealed with a clear, odorless sodium-silicate solution called water glass. Tiled surfaces can be easily cleaned and maintained with mild soap. When stains appear, vinegar or hydrogen peroxide is often effective.