Hi all, I hope this is the right section to post. Apologies if not. I have been in discussion with a structural engineer to determine total load rating of my apartment floor joists. I'm trying to rebuild the floor with a thin layer of cement substrate as one component, so we are looking at total load limits. What are suggestions on how to deal with lumber that is not stamped or graded? My floor is taken apart, so I can visually inspect the joists. My joists are nominal 3x10 (true 2.5 x 9.25), span 19' at 16 o.c.. The S.E. suggested total load rating from 80 to 95 pounds per square foot. After doing research, based on the AWC's 1986 Edition for Wood Structural Design Data, the 80 to 95 pounds per square foot corresponds to a wood's Fb value of 1200 to 1400 (see pdf page 130). I suppose the question then becomes, how would I know if the joist doesn't have a higher or lower rating, so to better support a cement substrate? Also, I found the architectural firm that designed the building, but don't think they are around anymore. Any clues on how I can find such information on my floor joists? Or are 1962 and Fb values from two different eras? Did anyone invent a time machine yet? Thank you!