A Maine-based concrete block manufacturer, Genest Concrete, has developed an insulated block combining concrete and expanded polystyrene. The blocks are designed to be assembled with a thin layer of adhesive rather than conventional mortar.

The product, called Comfort Block, was developed at the manufacturer’s Sanford, Maine, plant after co-general manager Chris Genest returned from a trip to Germany in 2006. It’s an inside-out version of an insulated concrete form (ICF), a building component that also combines rigid insulation and concrete but in a way that leaves the insulation exposed on both outside faces of the wall.

Comfort Block uses three 2 1/2-inch-thick pieces of EPS insulation, protected inside concrete cavities. Like ICFs, Comfort Block is reinforced with steel and grout. It forms a wall 16 inches thick.

Blocks sell for about $7 each, or $10.50 per square foot of wall, not including labor to set the block or the application of plaster and stucco finishes.

German construction methods are far ahead of ours

Genest said he went to a Munich trade show a decade ago to see the high-quality block-making machinery that German manufacturers are known for. But while he was there, Genest couldn’t help but notice that many of the buildings in the area were made from extruded clay blocks forming insulated walls up to 20 inches thick.

“At first I thought these guys were crazy,” he said. “But the more I looked into it, the more I saw an incredible amount of research and development was going into these products.”

When he got back to Maine, Genest started sketching a version of the block that would meet U.S. building codes and would be accepted by builders here. Limitations with the block-making equipment he had, plus a desire to replicate the German model, led to the design. Genest also is working on an 8-inch-thick version of the block.

The block includes an internal chase for wiring, so there’s no need for gypsum drywall on the inside or conventional siding on the outside. The elimination of a thick mortar layer between courses is another time-saver. Genest says that mortar is used between courses of conventional CMUs because of their slightly irregular dimensions. Comfort Blocks are sent through a grinding machine after they are cast to bring them to a precise, uniform height.

So blocks need only a very thin layer of mortar or adhesive between courses, Genest says. The mortar can be applied with a hand-held tool (see Image #2, below) that dispenses a layer 1 mm thick (0.04 inches). An alternative is spray adhesive in a can. Both products are imported from Germany, as is the dispenser. The tools are so common there they can be purchased in any hardware store, but are unknown in the U.S.

“It’s really quite embarrassing how far behind the United States is with the advancement of modern masonry construction,” he said.

Blocks come in a variety of sizes — wall block, end units, and corner block, for example. Wall blocks, what Genest calls the CB Stretcher, are 8 inches high, 12 inches long and 16 inches wide and weigh 45 pounds each.

The company’s website says that the blocks have a “thermal mass performance” of R-30 or more. Genest says that’s based on the R-value of the EPS, about R-4 per inch, plus estimates and modeling on both a similar German-made block and an earlier version of the Comfort Block. There has been no third-party testing of whole-wall R-values, so it’s not clear how thermal bridging through the concrete webs of the block would affect performance. Genest acknowledges that coming up with a precise R-value for an assembled Comfort Block wall has been a challenge.

Making the product worker-friendly

Genest says that the simplicity of the system will make construction approachable for owner-builders. Working with a single trained mason, homeowners should be able to pick up what they need to know in an hour or less.

Genest said that could be a plus in an era when younger workers are failing to take the place of older masons who are hitting retirement age and getting out of the trade. If the product is going to be successful, he said, it can’t be complicated and fussy to use.

“You have to get this product to market, and it has to be friendly to the trades,” he said. “All the trades around here know lumber, and if you don’t have a solution for them and you don’t make it relatively easy and not scary they’re going to throw it under the bus so quick you won’t have a chance. They’re not going to want to do it. We need to work with them.”

Genest’s market area is New England. Because block is heavy and expensive to ship, Comfort Block will remain a regional offering unless the company can find block producers elsewhere who are willing to become licensed partners.

Genest Concrete was founded in 1927 by Chris Genest’s great-grandfather, who emigrated to Maine from Canada and opened a sand and gravel pit in Sanford. His grandfather, then his father and uncle, took over and expanded the business. The company, which employs 80 people, produces architectural masonry, landscape paving stones, stones for retaining walls, and pavers and slabs for roof decks and plazas.

Note: An earlier version of this post incorrectly gave the price as $10.50 per block, not $10.50 per square foot of block.