So I'm almost finished the stand for my oven - inner solid blockwork tied to outer brick skin. I need to decide on what i do for the top - do I use lintels and aircrete blocks or top with flags and a layer of concrete. I don't fancy shuttering and mixing an entire hearth load of concrete by hand due to time and mess and the lintel solution seems pretty quick and easy though I know its a bit more expensive. Also I have very limited lengths of time that I can spend doing this and parenting 2yr old twins seriously cuts into my "spare" time - glad the evening are getting lighter.
Its going to be a fairly big base at 1350 x 1600mm. If I were to span the 1350 would I need to use 100 x 65 or 100x100 lintels - the width is a bit tricky at 1350 as lintels usually come in 1200 or 1500mm lengths - my understanding is tough that you can cut prestressed lintels without degradation in performance - I could always build a central block wall to support the middle of the lintel if that was needed.
I posted my design on here some 18 months ago - I used lintels with a middle supporting wall topped with the thickest and largest paving slabs my local builders merchant had - they were something like you'd get on a council pavement rather than a home patio. The back wall was solid (breeze blocks) with a lintel at the front and one mid-way back. I haven't (and don't know how to) do the structural calculations to decide if I could have got away without the central wall, but I had two reasons: 1. It looked nice (two smaller arched holes in which to store wood) 2. Given the width of my oven, it was just a bit over half the width of the top, plus the insulating render took up a bit more, leaving around 1/4 to 1/3 of the width to the side for pizza/food preparation. That meant that the bulk of the weight was over one half, so one side wall and the middle wall, rather than trying to bend the lintels in the middle. That seemed more logical to me without doing proper structural calculations. Having said that, a house wall on top of a lintel is heavier, but then the weight may be better distributed down the rest of the wall rather than concentrated over a door or window where the lintel is located. It's been there for 18 months - no cracks so far :-)