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http://www.surfbaud.co.uk/html/concrete_base.htmlYou may hear a lot of people talk about using “a yard of concrete” by which they mean a cubic yard, a cube three feet per side.
This is only half the story, the biggest mistake people make is in the proportions of the block they pour, they end up pouring a “slab” and not a “block”, presumably because nobody likes digging holes.
Lister specified a block 2’ 6” deep, with 3” above the surface of the surrounding floor, in metric this is 76 centimetres deep, 8 centimetres above the surface of the surrounding floor.
Lister specified width of the block to leave a 3” ( 8 cm) gap all around the standard Start-o-matic base, so for the 6/1 2.5 kW set this meant a concrete base 54” x 26” (137 cm x 66 cm) You were supposed to leave 4 off pits 15” deep (38 cm) from the top of the block for the 4 anchor bolts for the cast iron Start-o-matic base. These bolts were supposed to be 0.75” (19 mm) shaft diameter.
Once the concrete base was poured and set, you placed the cast iron Start-o-matic base on the concrete, lined it up, set the hold down bolts in place, and filled the hold down bolt cavities and any uneven spaces between the top of the concrete base and the bottom of the cast iron base with a slightly different mixture of cement referred to as “grout”
The base concrete should be at least 6:1 with a good proportion of 3/4 gravel, and don’t forget to put it some reinforcing steel before you pour. When you do pour take great care to “float” it off, filling ALL voids and the entire volume with concrete. Give it a few days to set, before you think about the next stage.
The “grout” mix should be just sand and cement, no aggregate, in a much lower ratio, 2:1 or even 1:1
I’m not going to tell you how to mix or use concrete, presumably you already know or can find out for yourself or have a builder friend.
If you’re feeling lazy you can buy premix, just add water and mix, or for quantities of a cubic yard and up you can often get the ReadyMix truck to deliver, seeing as your base will be about a yard and a half no worries there, keep an eye out for local building projects, they often have some “spare” in the wagon...
Every time I read about someone having a problem with a Lister “walking” it is someone who has a “slab” and not a “block”, someone who has insufficient mass, eg less than a yard and a half of concrete, or someone using too small diameter hold down bolts. When you personally have build and sold and installed more stationary diesel engines than Lister, feel free to argue with their specifications as set out here...
A cubic yard of 6:1 Portland cement when set weighs about 1.6 Tons.
