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Cutting out the Chimney Breast

The original back room of the house will be opened up to the new extension so that it forms one large room. To take full advantage of all the potential space, the chimney breast is being taken out. The rest of the chimney above will be staying so a large steel spanning between the front and back walls of the room needs to be installed to take the weight of all the brickwork above.

Pocket in wall for steel Pocket in wall for steel work

Before starting the work, the pockets for the new supporting steel are cut in the front and back wall of the room. This is a fairly large section and will require a lifting hoist – way easier than struggling to lift the steel by hand. The pockets are cut out with a bolster and hammer. The holes are cut slightly oversize allowing room to manoeuvre the steel into position. Obviously the steel is longer than the internal dimension of the room as it needs to bear fully on each wall. So, to get it into position, the end will need to be fed through one pocket at a slight angle before straightening it and feeding it back into the other pocket.

Pockets cut for acro props Close up of pocket for acro prop

Before any of the main work starts, the contractors cut out three pockets at the top of the chimney breast. These will be used to prop up rest of the chimney above while the steel is being fitted . Personally, I’d be a little nervous with all that weight of brickwork sitting above but these guys don’t seem phased. All in a days work for them ! One of them explains that there’s not as much load above as there might be though – the chimney breast is a lot narrower in the room above so the brick work that will need supporting is actually only the right hand side.

Stongboy and acro prop Close up of strongboy

With the pockets cut out, acro props are set up. These have neat attachments fitted at the top called strongboys. Basically these are heavy gauge steel plates that sit over the top of the prop and are braced off the acro with an inbuilt bracket. The end of the plate is set into the pocket cut out at ceiling level and the acro prop is tightened so that the load is now taken by the floor below. With these in place, work can start on cutting out the chimney breast in this room.

Top section of chimney cut out Old flue and metal flue liner

As work gets underway, the metal flue liner is revealed. In the pictures, you can see the sooty outline of the original brick flue. The metal flue liner will have been added at a later date. As Dale from G L Smith explained, the old flue lining had probably deteriorated years ago and a simple solution was fitting one of these metal liners. Because the gauge is considerably smaller than the original brick flue, they can simply be fed in to the old flue and sealed top and bottom.

The brick work is cut out with a bolster and hammer. As you can see in the pictures, either side of the flue is solid brickwork so there’s a fair bit of rubble to cart out to the skip. Once this has all been cleared, it’s time to get the new steel in.

Steel in place in wall pocket Steel bedded and packed with slate

This is hoisted up to ceiling height and the left hand end fed into the pocket in the outside wall. As mentioned earlier, it is fed through the wall a little way so that the other end can be swung round, aligned with the other pocket, and fed back into position. The base of the sockets has already been tidied up with engineering bricks and the steel is carefully aligned. Using acro props to support the steel in it’s correct position, the load on the strongboys can be released and those props can be taken out. The ends of the steel can now be packed. As you can see in the pictures, small pieces of slate are wedged in tightly between the steel and the brick work below so that it is now fully supported.

Steel in position

Once this is complete, the props can be removed. The remaining chimney stack above is now fully supported.

If you live in the Hertfordshire area and are looking for a professional building contractor, you can get in touch with G L Smith and Sons via their website:

G L Smith and Sons