What adhesive should be used to attach metal to porcelain tile?
If you are trying to adhere metal to a tile with no screws or anchors of any sort, I would try using pl400 construction adhesive. It comes in regular caulking tubes and sticks to anything just about. You should however, buy some drill bits suitable for porcelain tiles and drill some holes to anchor whatever metal you want to attach. You will also need some drill bits for drilling through the metal. I hope this helped. Make sure you read the limitations of the adhesive on the back of the tube itself to ensure it is adequate for what you want to do. Be safe.
