Internal/External FD30 Fire Door Blank Certified FD30, 30 Minutes Fire Rated. Lippings top and bottom edges are 17mm thick with sides 10mm in thickness. Suitable for Internal and External use providing correct finishing products are used to treat the door. If you need to cut this door down to a particular size then it is extremely important you go to the trouble of putting the timber edges back, on to it especially of you are fitting this door externally. If the edges are not fitted back on the veneered face will most certainly peel away from the timber core. It is also very important that the door is treated correctly, if being used in an external location.