from a web site....
We don’t recommend the use of steam cleaners on hardwood. The number one rule of hardwood maintenance is never to use water. The use of a steam cleaner would clearly violate that rule. Here’s why: over time, the moisture generated from the steam would be absorbed by the floor boards. Eventually, it would cause these boards to swell in place which results in buckling. Once the board swells, it has nowhere to go and will begin to “pop up” over time. Excessive moisture could also have a detrimental impact on the finish of your hardwood floor. Keep in mind that it makes no difference whether your hardwood is of a solid or engineered construction in relation to steam cleaner use. Each structure would still be negatively impacted when excessive moisture is generated on its surface, especially after several uses. Steam cleaners are very bad for wood block flooring especially that fitted with bitumen (black) adhesive– avoid at all costs.