The floor at Poplar forest being intended for an under floor must be laid with oak. poplar would not hold the nails, and pine is too distant & dear. all the floors in Europe are of oak. so are the decks of ships. good nailing will secure it against warping. perhaps it may be easier done in herring bone, as the hall floor at Monticello was. in that case your sleepers should be but 14. I. from center to center, in order that the plank may be cut into two feet lengths.   I pray you to have the floor of the North pavilion laid if not already done. I tender you my best wishes.