SC is actually not as good for construction as it appears. Using oak doors, a Sacred Clay Hammer lasts for less than 6 minutes and saves 25,375 exp worth of oak planks - 244k. It takes about 15 minutes to obtain each hammer using an SC world. You therefore spend 21 minutes total to get 12 minutes worth of experience, saving 244k in the process. Therefore, if you value your time over 1624k/hour, SC hammers are a waste of time. Just for comparison, the time value at which using SC hammers for smithing adamant plates is about 4m/hour. Of course, you could say that SC is more fun to do than train construction, but in a skill that you can train at 250k+ exp/hr the cheaper way and 600k exp/hr the slightly more expensive way, you should not be worried about boosting exp rates. Well either way then IMO its still not worth using the XP weekend bonus on. Plus you will either have to pay more for planks or planking them yourself.