The attached video by USLawEssentials provides an excellent explanation of what an Expert Witness is and how it differs from fact witness or percipient witnesses.
BFI is a provider of expert witnesses for concrete, cement and other related materials such as reinforcing steel, plaster, aggregates and sand. BFI also provides experts for water proofing, petrorgraphy, stucco, shotcrete to mention a few.
Enjoy this informative video.