MELBOURNE, April 12 (Reuters) - London zinc fell to a four-month low on Thursday, tracking the prices of other steel materials as demand from construction got off to a slow start in the usually strong second quarter. FUNDAMENTALS * London Metal Exchange zinc slid 2.7 percent to $3,150 a tonne by 0244 GMT, having earlier touched a low of $3,133.50, its weakest since Dec. 12. Prices crashed through support at the 200-day moving average of $3,172 a tonne, triggering a rush in sales