The construction group fell £6.2m into the red last year after lifting sales 9% to £270m.
It has blamed one long-term loss-making contract for underperformance.
Chairman Robert Carter said: “For the construction division, 2018 was a challenging year and a year in which disappointingly the financial reward we have received on the successful delivery of a long term project has not matched the effort and skill expended or the quality of the delivery we have achieved for our client.
“Discussions continue with the client and we are hopeful that the position will be rebalanced to some extent.”
He added: “This is not a reflection of our business as a whole; the underlying business remains strong.”
The firm said that last year’s experience reinforced the need to adopt capability-led tendering and a delivery strategy that put continuity and long term sustainability ahead of the short-term pursuit of turnover and margin.
Cash at year-end edged up £1m to £57m.
The group said it still enjoyed a strong order book and directors had put in place measures to help return to profitability this year.