The company, which includes the Cradley Special Brick factory on Corngreaves Trading Estate in Cradley Heath, has posted a pre-tax profit of £27.1 million, up from a loss of £2.3 million in the same period of 2020.
Meanwhile, revenue increased to £180.3 million from £122.4 million over the same period.
Forterra said there was a strong recovery in first half trading, underpinned by robust demand from both the new build and the repair maintenance and improvement (RM&I) markets.
Looking ahead, it said the current favourable market outlook and trading conditions are expected to continue, and its order book remains strong.
CEO Stephen Harrison said: "We saw a strong recovery over 2020 in the first half, which exceeded our expectations. This performance, primarily in Bricks and Blocks, was underpinned by robust demand across both the new build and RM&I markets.
"Overall, group revenue increased 47 per cent over 2020 and, notably, revenue in Bricks and Blocks was slightly ahead of 2019 levels.
"The current strong trading conditions appear set to continue in the second half of the year, with our customer base signalling that they expect current levels of demand to continue.
"However, we remain watchful that ongoing economic uncertainty surrounding the longer-term impacts of the pandemic, coupled with the shorter-term effects of the present shortages of labour, materials and transport across the wider sector could potentially impact demand for our products.
"Whilst we anticipate that the result for the full year will be weighted towards the first half reflecting the timing of maintenance shutdowns, the impact of cost inflation and near-term labour and material shortages in the second half, we now anticipate a 2021 full-year result modestly ahead of our previous expectations."