Not really rocket science I accept, but it is the part I have been looking forward to. The dwarf walls, at damp course height first need a mortar bed - level all round - to lay the damp proof course on. This is simply a thick plastic roll that stops moisture wicking up the wall by capillary action from the ground, so it is important that it is not breached at any point and that it is at least as wide as the bricks. I chose 125mm wide dpc so it would overhang the bricks by 12mm each side. The overhang will be masked on the outside by the drip bead at the bottom of the render.
Before the mortar hardened I bolted the wall starters to the existing walls so I could tie the new blockwork in with the old. The bricks drilled well, but after just three holes my Bosch cordless drill was running out of juice - I think it may need a new battery - so it was back to my old B&D which managed the job well. I was pleased that the wall starters came with 10mm hex-headed screws so I put them in with a socket on the drill and tightened them up by hand.
Once the mortar bed had gone off and the dpc was set, I started to lay the blocks. I use a Bricky tool to ensure a constant thickness of mortar and to cut down on wasted mortar. It is a great piece of kit but it relies on the fact that you can get to both sides of the wall - something I patently cannot do with the wall up against Jean's conservatory. The Bricky sets a 12mm bed of mortar so I cut a piece of 12mm OSB and fastened a batten to it that would give a 10mm overhang onto the blocks so I could match the bed the Bricky would set.
I discovered one thing straight away; if the bed runs right up against the adjoining all it gives no space for the excess mortar to be pushed out to - so the best bet is to leave a small gap alongside the existing wall for the excess to spread into when tapping down the block.
I am using a 5:1 sand-cement mortar mix and my mixer - the rusty legs of the stand having now been repaired with my rather dubious welding - holds 2.5 bags of sand and half a bag of cement at each mix. I have been adding a small amount of mortar plasticiser to each mix to try to keep it useable for longer as I am a slow bricklayer.
I had two 3m lengths and 2 2.4 metre lengths of 4"x2" which I cut and nailed together to form a frame to build the door aperture around. I cut a couple of spare pieces of timber to 45 degrees to brace the corners and keep it square. the gap itself is 3m wide and will run for the full height of the wall up to the steel lintel which will extend pretty much for the full width of the building.
The insulation, 75mm thick Celotex board, is very easy to cut and slot into the wall cavity. A basic hand saw does the job with no trouble at all. It is the same product that I will use for the floor insulation under the screed. It's not cheap but it seems the best product for the job.
The two different types of block I am using; 7Nm Medium Density Concrete block and 3.6Nm Aerated blocks cut rather differently. The Aerated blocks cut with a saw to give a neat edge, the medium density blocks, on the other hand, need an angle grinder to give them a neat finish, but will cut with a hammer and chisel, if you don't mind a more jagged edge.
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