In the past, people would kosher their tables by pouring boiling water over them, and some took the stringent approach of pouring boiling water onto a white-hot stone on the table, so that the koshering would be at the level of kli rishon. However, today’s tables are more delicate and fragile, and would be damaged, warped, or defaced by boiling hot water.
Therefore, the mainstream approach is to clean the table well and affix nylon or paper to it, creating a set barrier between the table and Pesaĥ utensils and foods. In addition, a tablecloth should be spread over the nylon or paper, and it is a good idea to avoid placing boiling hot pots directly on the table.
One may kosher a tablecloth used for ĥametz by laundering it in a washing machine.
Those who wish to knead dough for Pesaĥ must prepare a different surface, because it is difficult to kosher tables for kneading dough.
A table on which no hot ĥametz foods were placed throughout the year must be cleaned well, but there is no need to cover it.
. SA 451:20 states that the custom is to pour boiling water on the tables, since ĥametz soup would sometimes spill onto the table. MB 114 adds in the name of Responsa Mahari Weil §193 that since sometimes hot quiches are placed on the table, it absorbs taste on the level of kli rishon, so one would need to kosher it with a white-hot stone. Additionally, it states in par. 17 that one must perform hagala on kneading tablets since dough is routinely left on the tables until it turns into ĥametz, making them comparable to a container for storing sourdough (“beit se’or”). Rema states that the custom is to avoid Pesaĥ use of tables that were used for kneading ĥametz, since they would need to be koshered via light libun. Rema also states in par. 16 that the custom is to kosher a beit se’or via light libun.
It is clear that there is a difference between their tables, made of thick, strong wood that could withstand a koshering process involving boiling water and white-hot stones, and our tables, made of fiber board or plywood covered in Formica, wood veneer, or an alternative. Technically, when necessary one may follow the main use of the table, which is with cold items; therefore, SA states, “the general practice is to pour boiling water on the tables,” implying that this is not an absolute requirement. Even according to Rema, who says that the koshering method follows the most severe usage, if the table is separated from the Pesaĥ food by a nylon or paper covering, there is no concern that the food absorbed in the table will pass through the barrier, especially if one is careful not to place boiling hot pots directly on the table, only atop a plate or trivet. Moreover, since our tables are more fragile, people rarely place boiling hot pots directly on the table, so the concern that the table will absorb ĥametz on the level of a kli rishon is more implausible.