In part 2 of the oven build I utilised my bricklaying skills and built the base structure and now it’s time to actually get onto building the oven floor!
This is where the costs start to mount up and it’s worth being realistic about how much things cost:
- 600mm Slabs x 4 (around £5 each from B&Q)
- Pre-mixed Mortar (£6 for a 25kg bag… but I had some left over)
- 100 litre bag of Perlite (less than £20 from Amazon)
- 25kg bag of cement (£6)
- Block Paving bricks x 20 (42p each)
- Fire Bricks x 45 (£67.50 + £45 delivery from eBay)
- 25kg Fire Clay (£9.45 + £10 postage from eBay)
You’ll also need general things like mixing buckets, trowels, etc which we’ll already used earlier, plus an angle-grinder for cutting bricks.
Slabs rather than concrete
Most guides will tell you to build a wooden form (a support structure) and then pour a solid concrete top but knowing how much it cost for the foundations and how tricky it could be I decided to try something else and used concrete slabs instead. These only cost around £5 each from B&Q and as you can see I had already factored this in with the lintel support.
I’ve opted for a less traditional diagonal facing oven and so I cut the final slab with an angle grinder to get a neater finish. Going for this design is a little trickier than just a square structure but it works better with the space I have and should be a great focal point in the garden.
Concrete doesn’t perform well under high temperatures so I’d be asking for trouble if I just put my fire bricks directly onto this base and so we need an insulation layer. This is the first part of the build things didn’t go 100% according to plan but that’s part of the fun eh?
Perlite is a low density volcanic rock which is used for it’s insulating properties in building and also gardening. It’s really light but a great insulator and so our insulation layer is made by mixing 5 parts perlite to 1 part cement. You can get a 100 litre bag for less than £20 on Amazon which is great value.
Manually mix the perlite together with the cement so there is no white left and then add a little water to bind it all together. Don’t be tempted to use a cement mixer or any too rough and it will break the perlite down.
Most pizza oven build guides talk of making a wooden frame, pouring in the mix, and letting it set hard. This is where is didn’t work for me.
I poured in the mix, levelled it, and then left it to set for a few days. When I removed the wooden form I expected the insulation layer to be rock hard but whilst most of it was, some, especially around the edges, was quite crumbly and reminded me of Coco Pops! Not what I expected and it could be down to not enough water, not enough cement, or something completely random.
The Oven Base
This is one of the most important parts of the build and not an area to scrimp on. As mentioned in the ‘materials’ section at the start of this post I purchased 45 fire bricks from eBay at a cost of £1.50 each totalling £67.50 but these arrived on a pallet and there was an extra cost of £45 for that. These bricks measured 230mm x 114mm x 64mm and it’s important to note the 64mm thickness. There are some bricks out there at the same cost and with free postage but these are half as thick so are a false value and will retain less heat.
Your bricks will need to be arranged in a herringbone pattern when viewed from the oven mouth entry and this is so that your pizza peel doesn’t catch on the edges of bricks…. plus it looks very nice too!
Once you’ve worked out where your bricks will go then you will want to put a dry levelling mix down of 50% fire clay and 50% sand and then you can start your oven base! This mix is basically a heat resistant mortar. You can use a wet mix too but dry allows for you to move bricks around without whilst you’re working on your pattern.
Make sure the bricks butt up well against each other and use a wooden or rubber mallet to knock them into place. You’ll also want an angle grinder to cut the bricks for edging.
As you can see I was a couple of bricks short and so used the offcuts for a few of the edge sections.. These won’t actually be in the oven so I’m not as worried about these but make sure the bricks in the cooking area are nice. Those few brick bits on my bench are actually all I had left so I was pretty happy at my guess work!
The finished oven base
So here it is and the next stage will be building the actual done! Building a pizza oven certainly isn’t a quick or easy job but it’s pretty fun!