How do I make U-blocks from aerated concrete for pouring window and door lintels

When building a stone house, reinforced concrete lintels are required over windows and openings in load-bearing walls. In most cases, they are assembled and cast in place. I went the same way, although for aerated concrete there are factory-made lintels (type-setting, for standard wall thicknesses). But I alone cannot raise them and while their cost is high.

The most common way to fill lintels is to expose wooden formwork, reinforce and fill. Often this is done without external insulation and this layer of concrete is then a cold bridge:

Someone generally puts two corners under the jumper of the blocks. They do not reinforce or fill anything. Fast, but not reliable, especially if there is a slab or monolithic floor and the second floor on top.

The best option is when aerated concrete blocks are made in the form of a gutter. Inside they are insulated, reinforced and poured with concrete:

Fixed lintel formwork option. Someone makes them from blocks 100 mm wide, but for the walls the inner reinforced part becomes insufficient.

Some make cuts in blocks and chipping off the inner part, getting a chute. Can you imagine how much material will go to waste? No, this is not our method.

I saw the manufacturing method, or rather gluing U-blocks, in this video:

Here's my process in photos and videos:

As the video says, we need two blocks of 100 mm for one U-block 400 mm wide. We cut one lengthwise and these two halves will be the bottom and the inner part of the U-block:

I cut it lengthwise on a homemade machine for cutting aerated concrete. The article about its assembly was here

Sawed the required number of halves (on the third slide, only half of what I need).

Process video

Further, on pallets from aerated concrete, I glued these three elements with glue-foam. Do not spare glue-foam, then it is better to cut off the excess. And the surface of the blocks must be thoroughly dedusted.

Simple foam is not suitable because it expands too much. Make sure that the vertical parts are vertical, the block is horizontal and each previous block must be supported by the next one. Otherwise, the foam glue pushes the block away and it may tilt.

Made in two approaches, because I didn't want to occupy half of the house area with U-blocks.

To make a 300 mm wide U-block, I cut horizontally a 200 mm wide block into 5 pieces (this will be the bottom of the U-block). And in half lengthwise one block 100 mm wide (sidewalls).

Then I put the supports for the jumpers. Boards 120x25 mm put on an edge with support, too, on the scraps of the board, screwed with long 72 mm self-tapping screws to the walls. In wide openings, propped up for reliability with props. But as it turned out, with the width of the openings up to 2 m, they were unnecessary. No load was transferred to them.

Installation of jumpers. The seams between the bridges were made with glue-foam. In those places where the U-blocks rest on the walls, the horizontal seam was made with mineral glue. Under the U-blocks, where necessary, put wooden spacers and wedges. Everything is set according to the level.

Top and bottom view of mounted jumpers. Next, there will be Penoplex insulation, binding of reinforcing cages and concrete pouring.

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