WFO in Utrecht, the Netherlands

[Mr. Slowhand]

Hello everybody,

This is Marko, from the Netherlands, province of Utrecht.
Hope you are all doing well, I wanted to share with you my progress on a project started, long, long ago, in a galaxy far away.....

Anyhow, sometime in 2016, we moved to a new place, which had, for Dutch standards, a pretty nice garden. I wanted to build an fire place to be used for general BBQ, cooking pots, Sač pots (more on that later), etc.
Next to it, was a good place for a WFO.

[Mr. Slowhand]

The fireplace for BBQ was done, and we are using it, come sun or snow eversince

[Mr. Slowhand]

(apologies for my uploading, still have to get around how to upload and post more content in one post)

The Pizza oven was on a standby..... Until last week, when I started building it.
4 years to cure the foundation, I presume it is pretty settled by now....

After great amount of hours spent on this site, I settled for a 42'' oven.
This is the basics on it:


Two layers of CalSil board, each 5cm, total 10cm under the floor of the WFO




Expert assistance on mixing fireclay and sand (1:1) for a layer below the WFO floor






Floor will not be connected to the walls around, to facilitate possible replacements of the WFO floor.

After that, I made the opening template/support, and the floor was done in herringbone pattern.




I am currently at third row, it is going OK. This is a perfect project for procrastinators, as you can do only one row a day (at least that is how I do it, hehehe)

[Mr. Slowhand]

A couple of questions:

1. The oven opening is 31.4 cm, I was following some guidelines on the FB site, I presume this is OK?
2. Due to the lack of my masonry skills, I did not want to start with a sailor row, but just one row of evenly placed bricks. The second row is placed already using the IT, is this OK?

3. The oven will have a lip, I presume 1.5cm lip is enough?

4. I have not yet started developing the landing (is that the name from the dome opening to the oven opening / below the chimney), but I have maybe seen that some WFO designs have an angled landing. The landing extends, and is wider at the oven opening, than at the dome opening. As I remember, this is to facilitate cleaning, etc. Is this something you would recommend?

5. The oven will have a heat stop, that is why you see the end of the oven floor at the dome opening. Is 1cm enough for the heat stop?

6. I went through pages and pages of suggestions what to put in the heat gap/stop. Is there some consensus, something that is food safe, but still has isolation properties / kaowool / ceramic rope, etc?

6. As you see, I am not much involved in tapering the bricks. I am using a high temperature pre-made Mortar by Thermall BV. I know this one is to be used for only very thin applications to connect the bricks. I was wondering what to use for filling the big gaps. I presume this is refractory cement. Due to some language differences, I wanted to check before commiting. This is the product that is available through a local fireplace/WFO company




The website states to mix it in the following ratio:

1 part cement
1 part sand
20% water

Does this sound ok?




I still have not decided what to for covering the WFO, but most probably will be some sort of enclosure. Still deciding, will I make the walls with bricklaying facade bricks, like the fireplace I made next to it, or something else. The idea is to have a big roof over both fireplace and WFO, and to extend a bit to the left, in order to complete an entire outdoor kitchen


Anyhow, all suggestions / critiques are welcome. I understand that this oven is as far away from perfect, as my lovely Utrecht is far away from the foothills of mount Vesuvius, but enjoying every moment in building it. I forgot to mention, we enjoy a lot coooking outside, and even in winter, at least one meal per week is made outside. I plan to use a lot the oven, not just for pizzas, but for many other meals.
I also made a test version of a tandoor oven, using terracota pots and vermicrete isolation / maybe will build one in the extension from the fireplace.
But, for now, focus is to finish the WFO



Hope to post updated pictures soon.


Cheers!!

[david s]

I wouldn’t want to contradict the manufacturers recommendations, but a 1:1 calcium aluminate cement: sand sounds way too rich in my book. Is the calcium aluminate cement pure or does it already contain some sand? Sieving a small quantity with a fine drive would answer this question. Be careful to only mix small quantities at a time as calcium aluminate cement goes off really fast and is particularly temperature dependant.
CAC combined with high temperature aggregates are more suitable for high temperature (1000C+) applications and for our purposes where the temperatures are generally below 500C area waste of money in my view. The popularity of the homebrew that relies on OPC and hydrated lime mixed with some clay and ordinary sand has proved time and again cheaper and more user friendly than CAC based mortars. However, as you have the CAC you may as well use it. I use it for a few different applications. For an oven mortar I use 4:1 sieved silica sand: Pure CAC. My product is a different brand to yours, so may behave differently.
’

[Mr. Slowhand]

I wouldn’t want to contradict the manufacturers recommendations, but a 1:1 calcium aluminate cement: sand sounds way too rich in my book. Is the calcium aluminate cement pure or does it already contain some sand? Sieving a small quantity with a fine drive would answer this question. Be careful to only mix small quantities at a time as calcium aluminate cement goes off really fast and is particularly temperature dependant.
CAC combined with high temperature aggregates are more suitable for high temperature (1000C+) applications and for our purposes where the temperatures are generally below 500C area waste of money in my view. The popularity of the homebrew that relies on OPC and hydrated lime mixed with some clay and ordinary sand has proved time and again cheaper and more user friendly than CAC based mortars. However, as you have the CAC you may as well use it. I use it for a few different applications. For an oven mortar I use 4:1 sieved silica sand: Pure CAC. My product is a different brand to yours, so may behave differently.
’

Dear David,

Many thanks for the answer. I just researched a bit, the recipe above is actually given by the store selling the cement, not by the manufacturer, so you might be fully right.
I think I will be using the homebrew, as it is used by many builders here, without major complaints.

Just to be sure, when mentioning the homebrew you agree on the following ratios:
3:1:1:1 sand, lime, portland, fireclay

And the lime is hydrated lime, I presume.

Can this homebrew be used for sticking bricks together and for filling the space between the bricks as well.

Regards,

[david s]

Yes, that’s correct. You can use some of the smaller wedge shaped brick offcuts to fill the triangular voids on the outer side of the dome.

[Mr. Slowhand]

It is going good, but slower than expected

Just now on row 5 of the build, it is looking quite good, at least for me.





So, I am using this high heat mortar, pre-mixed and delivered wet. Once it solidifies, it is really strong, but for it to solidify, it takes such long time. Sometime up to 2 days.
If I even cover the WFO, it takes much longer. So, I stopped covering it, and extended the roof, to protect from rain. Luckily we had some good weather, for this time of the year.

I am afraid to touch and wipe of the excess mortar. I tried it once, and the brick moved, I had to re-join an entire row. By the time it is hard enough, the mortar also sets in quite hard.

The idea is to do maybe 2 rows more, than focus on the entry arch and the flue/landing part. That will harden the rest of the dome, so that I can start cleaning it.

Did anyone try to clean the interior of the oven with a wire-brush affixed to a drill (or dremel tool), seems like the best option now.

So, if all is well, I should be finished with 2/3 more rows and the entry arch this week.

From the last row, I started also tapering the bricks. Otherwise the triangle type joints between two adjacent bricks in the same row is too large.

Happy building guys, thanks

Marko

[david s]

Your build is looking good. Your mortar sounds like it’s a sodium silicate based mortar. Check the specs as they usually recommend a max mortar joint of 4mm.

[Mr. Slowhand]

Thanks, just downloaded the sheet, looks you are correct, I see both SiO2 and Na2O in the datasheet




Does this imply I should change whatever I am doing now?
Can you combine this with the Portland based homebrew, that I wish to use for the filling in of holes, or do I have to use calcium aluminate cement.

Thanks for the info guys, this really helps.

[david s]

I’m not sure, but if it were mine I’d be taking a punt and filling the outer holes with homebrew.

[Mr. Slowhand]

Thanks, as soon as I find time, will do it.
Another question, I have a bag of fireclay, purchased at least 3.5 years ago,. It was in a sealed bag, on the floor of my garage (not vacuumed).
Does this thing go off? Can I use it, or buy a new one?

[UtahBeehiver]

Plus one on David's suggestion of filling the backside with home brew. Fire clay should be fine as long as it is still in powder form, it should not go off since it is only clay.

[Mr. Slowhand]

Excellent, I already did some backfilling, and finished the dome arch, ended up quite good, posting pictures shortly, just another quick question for you guys.

So, I have a heat stop (break). So the arch that houses the flue and supports the chimney is not connected to the dome.

I have seen some designs here that, in my case, start the flue opening starts immediatelly within the arch. So that the first one/two rows after the dome opening do not connect, but form the opening. The only part of the arch that connects is towards the actual entry/opening of the WFO.

I think I also saw a design, where the first portion of the arch, albeit width of 1/4 of the brick, completes the arch, than comes the flue opening, than again the arch is completed towards the WFO opening.
The latter seems like more stable solution for the carrying of the chimney stack, and whatever is mortared above the oven entry. The bad thing is that it is either decreasing the size of the flue, or moving the flue more away from the dome opening. Does this affect the airflow?


Second question on the flue and chimney. I am just preparing to get the chimney and the anchor plates. I have read through here that an 8" (200mm comparable) is good for the 42'' oven.
Would it be any benefit to do the 250mm internal diameter chimney (9.8'' inch). Would there be any drawbacks.

In any of the combination, as I understand, the flue opening surface should be double of the surface of the chimney cross section, right?

Thanks all!!!

Marko

[JRPizza]

Above you talk about two alternate designs but I can't picture exactly what you are asking - if you have links showing pics it might be easier to get opinions. Some have built entirely independent vent arches, meaning there are front and rear vent arches that hold the chimney structure that do not touch the dome arch. Others have had a heat break at the bottom but either supported the upper portion of the rear vent arch on top of the dome arch or used the dome arch as the rear arch of the vent structure. I think all the options should be similar for air flow if you provide similar opening sizes. They will change depth of the vent (from longest to shortest) and theoretically change the amount of heat transferred from the dome to vent although we really don't have data to quantify how much.