When should you start looking at buying beaten down engineering contractors

When should you start looking at buying beaten down engineering contractors? Investors trying to pick the bottom for the sector are in for some heart-stopping times and they should remember there's no first mover advantage to be had in terms of risk/reward. The profit downgrade from Cardno (CDD) is particularly worrying given that it was one of the few with significant exposure to what should be the recovering US market. Softness in Australia was expected but the slower than expected ramp up in the US along with higher costs are particularly worrying. Monadelphous Group (MND) isn't helping sentiment either with management tipping 15%-20% fall in 1H revenue. I'll be waiting for turn in sentiment towards resource stocks before bargain hunting in the sector.