(Refiles to correct spelling of 'hit' in first paragraph)
WARSAW, March 1 (Reuters) - Polish builder PBG reported a worse-than-expected 57 percent drop in quarterly net earnings because of tighter margins on infrastructure projects and a hit from recent acquisitions.
PBG said fourth-quarter net profit fell to 31 million zlotys ($10.1 million), compared with a forecast for 36 million. Its 2011 net profit was 206.5 million zlotys.
While the purchase of boiler maker boosted its top line, PBG also cut its fair value in its books.
A higher share of road contracts with razor thin margins weighed on profitability.
Last month, PBG's deputy head told Reuters that 2012 earnings would be flat due to low margins, even as revenue rises.
PBG shares lost two thirds of their value last year, worse than the 55 percent drop by Warsaw-listed builders. ($1 = 3.0745 zlotys) (Reporting by Chris Borowski)