Carillion has sold Mowlem's environmental sciences business to Inspicio for £16m.
Carillion acquired Mowlem for £313m in February.
Carillion is also expected to sell Mowlem's Australian business, Barclay Mowlem, as well as its specialist cleaning company, Mowlem Pall Mall.
Last week, Carillon said it had been forced to write down a further £90m on Mowlem contracts, on top of the £45m it had already written off. The biggest problems were on the Dublin Port tunnel and an Exeter PFI schools deal.
It was also forced to pay £30m of costs associated with businesses that Mowlem had closed before Carillion bought it.