2. The Plinth Foundation, Plinth and Brick Oven Floor

The Completed Plinth

The Completed Plinth

Your plinth has two main functions.  Firstly, it raises your oven to a height that makes it practical to use.  Imagine trying to slide pizzas in and out of the oven on a baker’s peel if the entrance is at ankle level. You would end up with a bad back and a charred mess in the oven!  Secondly the top of the plinth forms the all important brick base to your oven.

Materials for plinth construction

Your choice of materials is dependant on personal taste, availability and budget.  If you scour around the Internet you will find plinths made from natural stone, bricks, cob, wood and earth and wood alone (like mine).  No one solution is better than the other so take your pick.  I am going to show you how to build a simple but beautiful plinth made from wood.  I was lucky enough to get hold of some oak beam off-cuts from a local timber merchant.  They are very attractive and very heavy!

Plinth Foundation Construction

If you are going to use a construction material with substantial weight from which to build your plinth and are building on soft ground you will need to establish a foundation first.  This is pretty easy.  In my case I dug a 40-50 cm deep hole slightly wider and longer than my intended plinth dimensions (120 Cm x 120 Cm) and filled it with hardcore (rubble) to a level just below the top of the hole.  I then topped this off with a layer of builders sand and finally laid a paving top onto the sand.  Continuing with the spirit of recycling, I managed to get hold of some broken slabs which I laid as crazy paving to form the flat level of my plinth foundation.  You can of course use other foundation methods such as concrete.  If you are lucky enough to have a chosen a location with a solid floor on which to build your oven then you can skip this step.

Plinth Construction

So you have a nice flat and solid base it is time to start building the plinth.  This is where building with timber comes into its own because it is just so simple!  Before you start building though you need to think about dimensions and this will involve a little forward planning. 

Plinth Dimensions

Plinth Dimensions

The plinth needs to be wide enough (and as your oven is going to be circular I suggest you make the plinth square) to accommodate all three layers of your oven.  The most important measurement is the diameter of the first layer – the inside of your oven.  You need to decide what is practical for your needs.  If you only ever intend to bake pizzas in it then it could be quite small but if you want to use it to roast legs of lamb or pork joints you need to make the oven layer wide enough in diameter to accommodate a roasting tin.  The internal diameter of my oven layer is 80cm which therefore means the brick floor on the top of my plinth is also 80cm x 80cm (you wouldn’t want any part of the wooden walls to be inside the oven when you fire it!).  Working out from here, each of the 3 layers should be approximately 7cm thick, so the total thickness of the oven walls Will be around 21cm.  Add this dimension to each side of your brick floor width and you will end up with the correct dimensions for your plinth.  Phew!  So my plinth top dimensions are 120cm x 120cm

Once you have your dimensions sorted, construction of the plinth is very easy.  Simply cut the timbers to the correct length, not forgetting to leave enough space for the overlapping end of each side.  Then build the sides up as if building a wall – overlapping the lengths of wood to add strength to the structure.  You shouldn’t need to use any “cement” between layers if you are using heavy timbers like mine.  Try to make the top layer as level as possible as this will help when trying to level the brick oven floor.  I used four internal corner angle brackets on each layer in order to prevent the structure from moving out of shape.

Plinth part-filled with rubble showing internal structure and angle brackets.

Plinth part-filled with rubble showing internal structure and angle brackets.

Your next task is to fill the plinth “box” with rubble (hardcore) to a level of about 30-40 Cm’s below the top. 

After this stage I decided to add a layer of builders sand followed by a layer of glass bottles (whole with tops removed).  My reason for doing this is that the glass bottles should provide an extra layer of insulation and retain heat below the brick floor of the oven.  I have no idea if this actually works but I had loads of bottles lying around so thought I’d give it a whirl!

Finally add another layer of sand up to a depth below the surface of exactly one brick deep.

Brick Oven Floor Construction

This is the last stage in construction of your plinth.  The brick floor is obviously a critical component of your oven so I suggest you take your time with this and do it right. 

You’ll need some bricks, something to cut them with and some more builders sand.  I used bog-standard London bricks and a hammer and bolster to cut the bricks (although I’m not very good at this and broke quite a few!).  Use any bricks you can get your hands on but try and look for ones with a nice flat surface, without cracks and any that look too porous.  Bricks with hairline cracks will break when you come to cut them or later when they are fired in the oven.

Laying the brick oven floor.

Laying the brick oven floor.

All you need to do then is fill the top layer of your plinth with bricks.  I chose to use a herringbone pattern which holds together nicely without cement.  Remember to try and make the oven floor as level as possible. 

Once you have laid all of the bricks in place brush handfuls of building sand into any gaps to prevent any further movement of the bricks.

That’s it!  Your plinth is complete and ready for the next stage – building the oven!

Advertisements

91 thoughts on “2. The Plinth Foundation, Plinth and Brick Oven Floor

  1. Hi

    I was just wondering if clay would work for the base also, or if you use bricks for a reason? Getter hold of the bricks here is challenging, so I’m keen to avoid it if possible.

    Thanks

  2. Hi Simon,

    I’m planning to start building my clay oven based on your fine guidings. I still have a couple questions though:
    1. how do you avoid sand seeping through the cracks of your plinth beams
    2. how to avoid pinth sand to set later through rubble and bottles and your oven floor to sag
    3. I live in Holland and I have no idea how much 40 rods to the hogshead is or 0.1 fothers of clay, Can you fill metrically fill me in on the approximate total amount of clay (pref in kilo’s)
    4. did you really not use fire-resistant bricks and no cracks yet?

    • Hi Paul I have answered your questions below:

      1. the plinth beams are very heavy, fit together snugly and quite wide. Nothing seeps through.
      2. just make sure everything is well compacted down. I have had no compaction effects at all.
      3. to be honest, weight is not a fantastically useful measure for clay because this will vary dependent on the water content. It’s a bit trial and error. Remember the ratio is 2:1 (sand:clay). I used a builders bucket (plastic) which holds approximately one bag of builders sand (approx 25kg I think but don’t quote me on that!). I used approx. 15 buckets of sand for the inner and outer layer construction. You’ll need more clay for the insulation layer. Sorry I can’t be more precise!
      4. Yes really 🙂

      Best of luck with it.

      Simon

  3. I am currently building my oven but I am worrying about getting it right 1st time.Things are going well so far but its the dimensions and heights of internal roof and door that I just want to check.

    I am building a 90cm diameter internal floor. ( River cottage say “The internal height of your oven should be 60 – 75% of its diameter”)
    I am going with a 57cm high internal roof (63% of diameter of floor)

    Door height (River cottage say The door should be cut to 63% of the internal height) I have 63% of 57cm high internal roof is a door height of 36cm and I am having a door width of 42cm wide. (do you thinks this is too wide?)

    Do these seem correct to you. I have checked and double checked but don’t want to build it and it not be very efficient. Sorry to be a pain in the Cobs

    Love the site. love the pictures. A real benefit web site on the internet.
    Thanks Dave

    • Hi Dave

      I normally go oven height 50% of width but I’m sure your dimensions will be spot on. I wrote a post some time ago about oven entrance dimensions, based upon a specification from a Roman architect. You can read it here:

      https://clayoven.wordpress.com/2012/07/08/what-have-the-romans-ever-done-for-us/

      Having said that, the most important controlling factor as far as entrance width goes, for me, is the width of my pizza peel and/or a normal sized roasting tin. It has to be wide enough to accomodate those.

      You’ll see that I recently repaired my oven. The width and height of the entrance are larger than they were originally but it still fires beautifully.

      I think the dimensions you have described are fine – don’t worry too much about it though.

      Have fun

      Simon

  4. Hey there! I’ve been reading your website for a long time now and finally got the bravery to go ahead and give you a shout out from New Caney Texas! Just wanted to tell you keep up the great job!

  5. I bought firebricks and refractory cement to stick the firebricks to the flat floor and create the cooking surface. do i need mortar joints to allow for expansion and contraction of the firebricks? it seems in the foto above you use clay bricks without joints, which i think would be preferred and would last longer, but i don’t know what happens to bricks when they get hot and are all up against each other :-/

    • I have never used mortar so I can’t really advise you on this one I’m afraid. My bricks are bedded up against each other and none have cracked yet (and these are not fire bricks). You certainly don’t want any gaps so if you do leave gaps you certainly need to mortar in between them.

  6. Hi Simon,

    Any confirmation on just how many kilos of clay were required for that oven you helped out with? I’ve managed to source most of the materials except for the clay. Local supplier in Dublin are selling 12.5 Kg bags for €9. If I’ll need about 125Kg as someone has said to build an oven the same dimensions as yours then it will start to stretch the budget quite a lot.

    I was mainly following the guide in the River Cottage bread book. I’m a huge fan of RC but I don’t understand why people can’t use accurate measurements? A “bucket” is not a unit of measurement Hugh, neither is a “metal pail”. Can’t we all just stick to SI units? I’d even settle for the crazy Imperial System! 🙂

    Reminds me of a line from the Simpsons:
    “The metric system is the tool of the devil! My car gets 40 rods to the hogshead and that’s the way I likes it.”

    Sorry…rant over!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google+ photo

You are commenting using your Google+ account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s