Posted By Steve Armstrong Malcom, It sounds to me like what you have been using are not bon-fide scaffold boards. At 3" these sound far too thick. There is a BS (2482) covering specifications for scaffold boards. This includes maximum permissible knot dimensions and extents of knot travel through the thickness and width of the board. However, standard boards tend to be either 1 1/2" - 2" thicknesses. I've had similar incidents occur due to poor quality timber and excessive (out of spec) knotting. Ensure all your boards comply with BS 2482 and that you purchase them from reputable suppliers. Carry out regular inspections (use a competent person) to identify suspect boards. Scrap any that you're not sure about. Someones life may depend on it! Also, ensure that boards are supported at the distances specified in BS 5973: 1993: Code of practice for access and working scaffolds and special scaffold structures in steel. Failing that, get support information from your scaffold supplier if it is of the pre-fabricated type, e.g., Kwik-Stage, CupLok, etc. I hope this is of help. Please feel free to get in touch on sarmstro2@LineOne.net Regards, Steve Armstrong HS&E Advisor/Registered CITB Advanced Scaffolder.