If you have old tile that you love you should use a professional sealer. Try these links for more information: http://www.miraclesealants.com/products/penetratingsealants/porousplus.html http://www.miraclesealants.com/products/penetratingsealants/impregnator.html http://www.aldonchem.com/index.html
Call or e-mail the companies on these websites and they will give you good advice. Also, try calling or visiting your local tile store. They will tell you the advantages and disadvantages of different sealers.