Waterproof pizza oven

[Man Food]

hi there

i am am a total novice but am building a brick oven in my garden....slowly!

I have got to the part where I need to render over the chicken wire/ cf insulation. What I am stuck on is whether I can simply render the oven down to the concrete lintel plinth or do I need to have some form of damp proof surface to render down to in order to prevent water wicking up the sides of the dome via the dome render and making my oven damp.

i am not building an enclosure over the oven as I like the look of the dome, but making sure it is watertight is proving to be a headache!

some further info:
110cm internal diameter dome constructed from half fir bricks
dome sitting on concrete base / concrete lintels, over which is a damp proof membrane ( under floor and walls only), on which are a layer of Thermalite insulation blocks covered with tin foil (100mm), 2 inches of c/f board and then a fire brick floor which I have cut to sit inside the dome.

i have attached a couple of photos so that you can see what I mean.

any help or advice would be hugely appreciated.

thanks

[SableSprings]

Congratulations on getting your oven to this point...however, it looks like you can no longer claim to be a total novice...

As you know, the base insulation board will readily absorb water. The perimeter of the board is where water may/will collect (the flat top of the support slab) and will probably be your primary problem area. I've seen folks use either silicon seal and/or paint with waterproofing membrane liquids to basically make a little dam around the perimeter. Since this interface is fairly stable, the flexibility of these two materials is good enough to keep water from seeping in underneath. The addition of a waterproofing agent to the base render coat is also pretty effective and something to consider. If you don't somehow seal up that seam along the perimeter you will always end up with some water being absorbed into the insulation board whenever it rains and water collects on the top slab.

The good news is that even though you may get wet insulation through excess humidity or rain incursion...the oven will just need some slow, curing fires to return it to "working condition". As to the waterproofing aspect...if it's outside and you live in a "moist" climate ...you can make the oven extremely water resistant but not waterproof forever. You will need to be proactive and watch for cracks in the dome. You might also consider putting in a vent towards the top (back side) of the dome to help in moisture release from the covering insulation.

[Man Food]

Hi Mike
thanks so much for your response and advice - really useful and much appreciated

When I made the plinth, I put a ceramic tile layer on top of the concrete lintels in the area where the oven would sit and then on top of that I placed a pvc damp proof membrane - to stop water coming up through the floor. I really like your idea of creating a "dam" with silicone sealant or some form of waterproof paint that I could paint on to the Thermalite blocks and also on the side of the c/f board.

Since posting this this afternoon I have done the following work

1. Laid a layer of stick-on bitumen flashing on the lintel plinth around the base of the oven so that when I render the oven down to the plinth it will form a waterproof barrier

1. Completed my first insulation render layer over the c/f and chicken wire layer.

this initial render does not reach down to the plinth, but I plan to use a tough silicone synthetic render system over this first layer which will finish at the plinth level. So before doing this I am going to take your advice and apply a silicone bead around the base and also paint on some waterproof paint.

kind regards

simon