floor preparation

The subject of floor preparation is an important one. In fact, the final installation of your floor really depends on the condition of the existing floor.
There are many kinds of floors and all are not treated equally. For instance, a clean new cement floor requires little or no floor prep. If there should be expansion joints, of course you would need to fill them level with a portland based patching compound. Please allow this to dry completely before any installation. It is also important to note whether there is a moisture issue.
Moisture is not our friend in the flooring industry. Will write more on that issue at a later date.
Existing flooring can be troublesome depending on what the material is and when it was installed. Most times we recommend not pulling up the existing flooring. There are many sub-floor applications which can be utilized under these circumstances. Most popular is putting down a 1/4 inch underalyment board. This will not only stabilize the floor, but will also correct any uneven or damaged areas.
Another option is called a skim coat. This is a portland based patching compound which is spread over the existing flooring. This will fill any existing pattern in the original flooring so that it will not telegraph through the new flooring. This is only recommended if the existing flooring is secure and not loose.
For ceramic installs, of course the floor prep will differ. Also, with hardwoods or laminates the original floor shouldn't be an issue unless it is extremely uneven or mushy. Each flooring product will differ in the prep department.
Feel free to forward any questions you may have regarding your project.