The previous owner of my house laid slate tile over hardwood in the entryway. A 9 square foot area has become loose and I need to re-set the tiles. Pulling everything out is not an option; I'm wondering how to make best of a bad situation.
Several products I've seen say specifically "don't apply directly to hardwood" (eg http://www.custombuildingproducts.com/TDS/TDS-133.pdf). I'm wondering if using an appropriate primer first will make success more likely, such as CBP's Multi-Surface Bonding Primer (http://www.custombuildingproducts.com/TDS/TDS-115.pdf). They describe it as "polymer-modified mortar ... for tiling difficult surfaces, such as plywood, vinyl and laminates, and for hard-to-bond, nonporous tile, such as porcelain and glass."
More generally, when a tile adhesive says "don't use directly on" hardwood or another surface is this because the product will perform poorly or because there could be unintended consequences (eg chemical reaction).