Hi all, just wondering, I am renovating my bathroom in the basement. My house is 25 years old and i am going to lay tile down, What my question about tiling is; is it ok to tile directly over the cement, I know it is not the best way but is it ok. Thanks everyone

As long as there is no vertical movement in any of the cracks you should be ok.
Make sure there are no sealers or paint coatings on the concrete. Check by placing water droplets on the concrete. If they soak into the concrete your good to go. If they bead up then the slab needs to be scarified.
You can use modified or unmodified thinset to bond your tile.
I would personally use modified.

This is not a reply as much as it is a related question! I am looking to tile my master bathroom, which is cement slab and have several concerns and questions.

Overspray!: The previous owners never changed out any of the flooring in the house. I have mopped up most of the overspray from the wall texture that was left during the initial build. The builders (30 years ago) also stained and shellacked the doors and cabinets on the slab where many of these items were installed. Is this a concern?

There are still future changes for this master bath. Due to funds we are updating what we can now and in the future (3 - 5 years) will make changes then. Which leads me to my next question, can I place an underlayment (a cardboard stock sold at RC Wiley's) to make it easy for removal in the future? It makes the tile floor float in essence and I have found nothing on the product as far as reviews by anyone on the net.

Finally, I have removed a large amount of linoleum throughout the house and found some items that may be of concern when one wants to install tile in these same areas. Under each linoleum flooring the installers used a leveling compound on the concrete, which did not all come up with the removal (majority of the compound is still in place). So there are dents and dings (for lack of better description) that litters these floors. There is an abundance of glue residue (real heavy against the walls) that I am finding very difficult to remove. What are my options with this situation? Can I use the above mentioned floating technique perhaps after leveling the floor again? Please do not say remove all of the leveling compound and glue! Oh, the leveling compound is white and chalky when broken up if this matters to anyone.

I appreciate any and all help. We are walking on concrete floors and hoping to start moving to some other material before long.