Materials advice - my shopping list (UK)

[lightsofroy]

Hello all,

First of all it would be remiss of me not to say thanks to for your many inspirational build diaries/ galleries that have already and will continue to be immensely useful as this project kicks off in earnest. There are some absolutely sensational builds out there, and if I can even manage to get something half as polished as many of you out there, I will consider myself a lucky guy!

Now, as I currently stand I have a hole in the ground, rebar tied, ready to mix and pour concrete next week (exciting step 1). Step 2 will be building the structure to hold my oven and adjacent workspace.

In anticipation for Step 3 (the oven itself) I’m just trying to get my materials in place and i'm looking for some advice and for some of the resident professionals on the forum to check my calculations before pressing the purchase button.

I’m building a Pompeii style oven with a 38” cooking floor.

My intention is to lay the first course onto the cooking floor, which as far as I can tell appears to be the favoured option of folks on the forum, even though it does look a little easier to me to lay a soldier course that buts up against the side of the cooking floor…..but I’m a newbie and so keen to go with the consensus.

That aside, I think my materials list needs to look a little like this:

225 x 42GD firebricks (230 x 114 x 64mm). This is approximate but I think should give me a bit of margin for error.

2 x LBP HT Blanket 1200GD 7.32M – 610 x 25mm (I think that this should be enough for me to give 3 inches of insulation for a dome of this size)

3 x Calcium Silicate 1000GD – 1000 x 500 x 75mm (which I think (?) should be enough to cut so that it goes under the entire 110cm wide dome plus the landing area, offering 3 inches of base beneath the brick floor)

1 x chicken wire 300mm x 13mm hexagonal x 6M

Now the bits that I’m not sure about are the various bits and pieces for holding all of the bricks together and covering the dome exterior, in sufficiently weatherproof fashion.

Vitcas sells a range of products in the UK, all helpfully labelled quite similarly, and to a complete novice seem to be doing very similar things! I can’t quite tell which product should be used for each part of the job.

I’ve also been looking more actively at Kilnlinings who are a little bit more local to me and likely to be the place I purchase the rest of my materials from. I dropped them an email to ask for advice and they helpfully responded as follows:

Cement
[Most customers purchase KL-WASC Its very heat resistant though should only be used in 3-5mm thickness max. 1 tub covers approx. 75 brick joints at this thickness of application It also needs to see approx. 300 degrees Celsius right through the joint to make it fully set. So if used on the outside of the brick work it may not fully set without seeing this heat].

This sounds straight forward enough to me – I would use this to bond all of the bricks to each other and will probably need about 3 tubs overall to finish the build (maybe a 4^th tub just to be safe). I had expected that the act of building the dome, getting the bonds just right would result in me making a bit of a mess and as such, a fair amount of this cement ending up on the outside of the dome – not for functional reasons but rather just because I’m likely to be a messy novice. And so, the comment about needing the 300 degrees Celsius to set causes me to question whether this is the best product for the job.

I’d appreciate views from all on that point.

Now, after I’ve (hopefully) constructed the dome, I’ll be putting my blankets on, followed by chicken wire. I’ve also been advised to put aluminium foil on (just before the wire) because the foil stops the blanket absorbing the moisture from the final render. This is crucial as if the blanket gets wet it won’t work as it should. In addition the castable render would then crack as it hasn’t the water content it needs.

Does this sound right?

Final render

The final advice I have been given is that…

[Then a final render is applied. Usually KL-LWIC insulation castable is the castable of choice 6-8 bags for your size oven is the norm. Finally people then brick around the dome or finish it as they wish to ensure its as weather resistant as possible. As the refractory castable is technically a heat resistant concrete it does require protection against the elements and is susceptible to freezing temperatures especially].

Again, this makes sense. The bit that has caused me to think a little is that final point about elemental protection. At this point, I hadn’t thought too far ahead when it comes to final finish. My assumption was that I might cover with those small hexagonal tiles that I’ve seen people use so well, or maybe a mosaic of some description. That said, I wasn’t necessarily thinking I would do this decorative bit straight away and that I’d have some time to think about it and could figure it out in due course. So, I’m slightly concerned about this comment that it needs protection against the elements.

I suppose what I’m asking is this – am I overthinking it? Do the two products I have included links for sound like the right ones and are they similar to what you yourself have used? Overall, just buying the suggested amounts of cement/ castable refractory will cost around £600 (about a third of the overall build cost), so I just want to make sure that I don’t make a rookie purchasing decision.


I appreciate any and all guidance that you may have to offer on the matter

Oh – and the keen eyed amongst you may have noticed that I haven’t included the chimney on the shopping list……this is a conscious delayed decision, I’ll get this at a slightly later stage once I’m settled on my roofing design. All I can say for now is that I do currently expect to construct a roof, and so will have a fairly tall stainless steel chimney that goes through it.

Thanks

Alex

[Wickolad]

Hi Alex,
welcome to the forum.
Where in England are you? May be able to give you heads up re suppliers of some of the materials. I'm based Wickersley, South Yorkshire.

You've made a great choice joining the Forno Bravo Community, it was certainly the best move I made, gleaning a wealth of information and advice from previous build logs and the many fantastic contributors.
I'm no expert and have only completed the one oven, however, if I could give you one piece of advice it would be to do away with the premixed fire mortar idea and make the homebrew fire cement.
Far cheaper and very effective.

Standard 3-1-1-1 recipe of Sand, hydrated Lime, portland cement and fire clay powder. All readily available in the UK.

Best price I found hydrated lime was B&Q @ £10 for 25kg bag. I used 1.5 bags as I used it throughout 40" floor diameter build, including the cement render. Builder Sand @ £2 for 20Kg bag available B&Q, Wickes etc as is the Portland Cement @ approx £6 per 20Kg bag, I used approximately 2 bags but did other brickwork too. The Fire Clay powder I got from a pottery and foundry supplier just outside Newark just off the A1, Nottinghamshire @ £10 20Kg bag. I used almost 2 bags.
it is available on eBay from same company at around £14 but delivery wasn't cheap. I understand it can be purchased from most potteries if you have one local or near enough to make it financially viable to collect.

Your other question about the render. A standard cement render mix is quite sufficient, include a frostguard waterproof admix and a final sealer and you can take whatever time you need to decide the decorative finish. I actually applied a vermicrete render over the insulation blanket before completing an outer dome using insulating firebricks with vermicrete pointing to maintain the insulation, before a final 30mm render built up over 3 coats before a final mosaic finish using Mapei flexible waterproof tile adhesive and Mapei Ultracolor Plus waterproof flexible grout. Both of which are suitable for underfloor heating applications, wet rooms and exterior use, thereby, suitable for the dome.

By using the homebrew fire cement and standard cement render including admix, at no detriment to your build, you could save yourself in excess of £450 on your £600 quote.

The floor and dome arrangement in my own view is best with the floor inside of the dome wall. That was almost always recommended previously and is the way I went.
Of late it seems more builders are building on top of the floor, apparently 'for speed' & 'It not being necessary to be accurate with cuts'. Those are its advantages. Disadvantages are that ive seen input from some builders of problems with floor bricks being unstable on extreme edges when setting up 1st course of dome. Also, when built and in use, first course is not bonded to the floor to allow expansion, therefore its somewhere for the peel to stick/dig into when moving things around or clearing ash.
My way of thinking was, why skip accurate cuts of the floor bricks just to save a couple of hours in the grand scheme of things its nothing. Advantages of floor inside dome wall - soldier course layer around floor with ⅛" cardboard strip layer between edges of floor brick and soldier course to provide an expansion gap. This will burn out and fill with ash eventually with oven use.
Thus, the cuts can be straightforward and do not have to be to the mm. But the soldier course will have something to butt up to and be perfectly round, also no seam for peel to wedge into.
Further advantage that any of the floor bricks are easily replaceable should they sustain damage or fail.
Overall, the build is a tremendous task and I don't think a shortcut to save a couple of hours work outway the benefits of doing it the recommended way. But that's my opinion.

One other thing I should mention is to consider fitting a vapour vent in the top of your dome which allows any moisture/steam to escape when fired up. The vent is placed from your insulating blanket and breaches the render and finish to allow the release of any moisture that may have found its way in. I used some brass tube fittings and screwcap from Toolstation. I remove the screwcap when firing up the oven and replace it once I know all moisture has gone.

Also, if you've not already done so, download the Oven Dome Calculator Spreadsheet. A fantastic tool, masterminded by one of the many brilliant forum members.

Finally, as said before, I'm no expert by any means but if there is anything I can help with regarding information and experience I've gained and gleaned from this forum and my own build, I would be only too pleased to help where I can.

Good luck with your build and I surely hope you get as much pleasure and satisfaction from it as I did my own.

Best Wishes,
Lance. (Wickolad)

[Wickolad]

Hi Alex, I just checked the supplier I used for the fire clay powder, Pottery Pro UK, Tuxford, Notts. On ebay its coming up £32 for 25kg bag but free 2 day delivery, massive increase from last March. However, may be far cheaper buying direct and collecting as I did. I got it for about £9.99 25kg bag but collected so did away with the expensive delivery charge as was then.
Even so, you would still make a huge saving on the overall cost owing to low price of the other materials required for the home brew fire cement.
When I mixed the 3-1-1-1, I would dry mix a large bucket full at a time, then mix small amounts, probably enough for around 7 bricks, and mix to consistency required. It goes off quite fast so mix in small batches. Any small remaining amounts that were becoming too firm to butter the bricks for building, I would spread on the back of the already fitted courses/strings. Therefore adding thermal mass to the dome and no waste.

Best wishes,
Lance.

[lightsofroy]

Hi Lance

Thanks for your reply – super helpful and well timed, as I was looking to get my orders placed within the next fortnight and so you might have just stopped me from overstretching the budget!

I’m in Cookridge (North Leeds) so probably about an hour away from you – interestingly, Kilnlinings (Sheffield) is where I was thinking about getting my refractory materials (bricks, CFB, blankets) from – so that must be quite close to you?

Just to check that I’ve interpreted everything correctly, you used this 3-1-1-1 recipe for all of your dome brickwork – so no concern about the outward facing brick joints being a bit thicker?

And therefore, extrapolating a bit from what you’ve said, for your dome you used somewhere in the order of about:

Sand: 120kg
Hydrated Lime: 40kg
Portland: 40kg
Fireclay Powder: 40kg

And with sand, is this just straight up builders sand?

Then for the pointer on render – you’ve put my mind at ease on the weatherproofing! I’ve read conflicting views on ratios, ranging from 4-1-1 (sand, cement, lime) to 6-1-1. Where did you land with yours – and how many layers of render did you apply?

I forget where I’d pulled this advice from – possibly the original forno plans - but I was intending to have about an inch of render over the top of my blankets – I think my dome will have a surface area of around 2.25sqm and so that feels like it’s probably around a single 20kg bag of cement should be about right for that amount of coverage?

Just trying to gauge whether the quantities quoted above covered the rendering as well or whether I need to factor that in when I place my order. I think it's additional to those listed above?

Your build looks great by the way – very clean and neat – I’d clocked it a few months ago and it was in fact the inspiration for my thinking about a mosaic finish, so congratulations on a job well done!

The moisture vent sounds like a great idea so I shall add it to the list of gems that I’ve seen so far on the forum. I’m also trying to get my head around exactly how I would go about including a heat break (I note that you appear to have include 2!) so when the time comes, I’d be keen for advice on that stage of the process…..which still feels a way off!

So far, my build has been slowed down by the offer of a free cement mixer – clearly I was happy to not have to fork out for one – but it slowed me down by about 3 weeks, along with the weather! Anyway, my slab is now poured and curing nicely. I think my first step is going to be to construct the frame that will hold up the roof so that I can cover it with tarp in a bid to weatherproof my build - hopefully I’ll get this done in the next couple of weeks at which point I can dry stack my breezeblocks, fill the cores and then pour my hearth, meaning that in around 4 weeks I should be at the stage of scratching my head about how to start the oven build!

My ultimate plan is to try and complete the build this summer – or at least before the winter frost sets in – but then, I’ve never tackled anything like this so I’m expecting a whole bunch of unforeseen issues despite best laid plans!

Thanks for your help – and very keen to stay in touch!

Cheers

Alex

[lightsofroy]

thanks Lance - just seen your second post there which hadn't refreshed whilst I was typing my response. There is a pottery not too far from me as it happens and so I've dropped them an email this morning already to see if they can help me out. Collection would be easy there so it would be ideal if it comes through. If not, like you say - significantly reduced cost overall so not a great problem if I have to pay somebody a delivery fee - cheers

[Wickolad]

Hi Alex, thank you so much for your kind comments.
What a stroke of luck dropping on a free cement mixer, great result.
In answer to the homebrew quantities and suitability for the larger gaps at the rear of the dome bricks due to natural wedge gap created, the homebrew works fine in that application as per the numerous builds listed on the forum. However, I didnt have that to do owing to cutting my bricks into trapezoid blocks as per the angles listed on the dome calculator spreadsheet I mentioned. A lot of cutting done, but this resulted in relatively tight fitting blocks with approximately ⅛" mortar joints. All cuts done with a Hitachi Compound Mitre saw i picked up on Shpock or Gumtree for £20. I purchased a diamond saw blade on Amazon for about £45 ( Highly recommended, worked a treat). I set up a cutting bench and attached my Henry hoover to the saws dust extraction exhaust adapter to suck up dust as I cut the presoaked bricks. This helped tremendously. The dust collected in the hoover bag could have then been incorporated into a mix to point up the wedge gaps in the dome bricks had I needed to as this dust would contain the same alumina content as the bricks themselves. However, the 25 to 30kg of dust I had collected was given to a guy that purchased the excess bricks I had left from the build.
Maybe I went over the top with the cutting, wanting a close fitting dome construction but thats just me. A bit OCD about stuff like that.
An excellent tip i have seen since my build which cuts down the cutting effort drastically is to cut the brick angles just on the front ⅓Rd of the brick, less cutting, longer diamond blade life, and still closes the inverted V on the oven dome face, thus tighter joints as you get higher up on the chains.
Using this method, you may need slightly more materials than I did, but could incorporate the brick dust in this.

I purchased my refractory bricks from Intocast, Rotherham. I purchased new bricks for the floor, and second hand for the dome, using the newly cut surface for the dome interior, this saved massively on cost of firebricks. Worth a call.

Just got to go out for a while, wife chomping at my ankles, its her day off. Will get back to you later.
Best wishes, Lance.

[Wickolad]

One other tip which i followed was to use a vermicrete screed over the insulation blanket and chicken wire. This has two benefits -
1. It is far lighter than cement screed so does not compress your blanket and thus reduce insulation properties.

2. It adds to your insulation thickness and increases cooking time.

3. Once dried it offers a suitably firm base for your cement render.

I gave the vermicrete a coating of EBR bonding prior to the cement screed to reduce moisture suck and provide a bond. Did 3 layers of cement screed totalling around 30mm as i recall.
Not going too heavy on the screed assisted in maintaining the shape of the dome.

The mosaic was made using 600x300x10mm granite quartz tiles which I picked up on Shpock for about £25. What was left i gave a guy at the end of my Street who is in the process of building a precast oven.

Regarding the floor heat breaks, I used 40x40mm Stainless box section. Installed the first at the mouth of the dome and made up the floor with vermicrete so level with floor bricks.
I purchased 1M of this from ebay, being a Yorkshireman, I hate waste, so used the remainder as a second heat break between landing and the Granite counter top. I must admit, I'm glad i did as I've since learned granite isn't too fond of heat. The temperature differences each side of the two heat breaks is extremely notable.
I also went with a ¼" heatbreak between my dome arch and chimney stack and used ceramic tape between the two.
Again, may be over the top, some do, some don't, but it is recommended and obviously helps reduce heat loss from dome.
My thought process was that this was to be a onetime build. I didn't want to cut corners and have any regrets or "I wish I had done that" moments. Hence over 12 months researching and collecting materials.
However, the onetime build isn't going to happen as my daughter who lives in Vermont USA is moving to California July 1st. She's renting for a year whilst searching for a property to buy and has told me that she and her wife want me to build their own oven. Happy days!

Anything else I've missed or can help with, please feel free to ask.

Best wishes,
Lance.

[lightsofroy]

Thanks Lance

I’d read a little on vermicrete but wasn’t sure whether it fell into the overkill category? What sort of quantity did you need for your 40”?

A quick scan suggests that it’s probably around £30 for 100L of fine grade vermiculite, which I think I’d read previously was the one that should be used (though the standard garden centre stuff is a third of that). It then seems to be mixed on a 10:1 ratio. If it’s easy enough and cheap enough to incorporate then I might well do so. I’m keen to try and retain heat wherever I can (hence the 75mm rather than 50mm Ceramic fibre board base that I’m going with). Did you mean SBR bonding by the way?

You’ve really got me thinking now about whether or not I should build on the cooking floor or not. It’s something I’d been going back and forth over for the last few months and thought I’d settled on the right choice but you make solid points and the proof is certainly in the pudding with your build.

The 40mm SS is a great shout for the thermal break – £15 for a 1m and I think I’ve got a good sense from your gallery of how you’ve gone about that.

As for the free mixer – indeed, couldn’t have been happier with that one! I’m still trying to get my hands on a saw for all of the brick cutting. As a default, I can just buy a new one but I’m hoping that I can find something pre-loved that I can just bung a decent blade on! A fellow yorkshireman here!

Sounds like you’re going to get the joy of doing this all again but on a different continent – I’m sure there’s plenty of California based gurus on here who’ll be more than happy to help with the sourcing of materials! As a beer lover, Vermont is on my bucket list – the home of the world’s best hops and of Hill Farmstead brewery – it’s like Mecca for a guy like me!

Cheers

Alex

[Wickolad]

[QUOTE=lightsofroy;n438157

And with sand, is this just straight up builders sand?

Alex,
I used regular building sand throughout (An oversight on my part). However, it is recommended to use fine sand for the homebrew.
I did manage, but found there were pebbles and gravel in the builders sand which I had to remove when using for homebrew due to the close nature of my joints. Kiln dried sand would probably have proven better.
builders sand or plasterers sand for the cement screed and builders sand for the general mortar of stand construction and general brick laying.

I'll stop bugging you now and let you get on haha.

Best wishes,
Lance.

[lightsofroy]

all bugging welcome Lance - and great shout on Intocast - i've dropped them an email and a quick provisional quote back already seems to be working out much better than I had seen elsewhere! Only downside is having to layer up 3x25mm CFBs to get to my 75mm desired amount, but in the grand scheme of things, i'm sure the extra work will be worth the overall saving.

So, over the course of the last 12hrs, even with the addition of the SS thermal break, the vermicrete and the vapour valve you've still probably saved me about £4-500....think I might owe you a pint!

Feel free to share as much wisdom as you can - it's helping my bank balance

Cheers

A

[Wickolad]

Thats so good to hear, I'm so glad they sorted things for you at Intocast. They were really helpful with me and seem a good set of lads.
Re the CFB, underfloor insulation, I actually used Insulating firebricks I'd picked up during my initial search for materials. At the time not knowing the difference. I got approx 750 bricks for £50 from an old boy who'd retired and had bought them for his furnace. He just wanted them off his garden and I was happy, believing I'd sorted my fire bricks. It was only when I started researching that I realised my mistake. However, they proved very useful for insulation throughout my build. Underfloor, between chimney stack and dome and the secondary insulation capping of the outer dome. I sold the leftovers on and made my money back and some.

I know the Calsil boards are a bit costly, it may be worth pricing up the insulating firebricks at Intocast, I'm sure my insulating bricks were 76mm (3") deep, and understand they are on a par with the Calsil board re insulation performance. If you are intending to triple up on the boards to achieve the 3" then it may be worth comparing costs either way.
Alternatively, If i were you, I'd consider 2 or 3" Vermicrete topped with 1" Calsil board. A 50/50 mix of Vermiculite and Perlite is apparently the best combination with a ratio of 6-1 with portland cement for the sub floor and up to 10-1 ( you may have to check up on the exact ratios as its been a while and I've slept since) for dome insulation over the blanket and chicken wire prior to cement screed. Both Vermiculite ( medium grade) and Perlite available in 100ltr bags on ebay, free delivery. Or it was when I ordered last year.
My My, time has flown.

Couple of alternatives to consider there but maybe someone alot more knowledgeable than I may offer some advice on the most effective solution. It may already be covered in the wealth of information within this forum so maybe worth a search.

I'm chuffed that the advice so far has resulted in a more cost effective build so far. Please feel free to ask for any advice. I'm only too glad to help if I can and sure others on the forum will assist where they can too.

Best wishes,
Lance.

[lightsofroy]

Evening Lance - just doing some calculations as I work on sourcing my materials and just need an experienced eye.

Vermicrete 10:1 (essentially 5:5:1, perlite:vermiculite:cement)

For the layer of vermicrete render that i'll layer on top of the blanket/ wire, how thick was your layer?

I can't quite visualise how much I'll need to cover the dome, especially given the bizarre ratio.

Any advice?

Cheers

Alex

[Wickolad]

Evening Lance - just doing some calculations as I work on sourcing my materials and just need an experienced eye.

Vermicrete 10:1 (essentially 5:5:1, perlite:vermiculite:cement)

For the layer of vermicrete render that i'll layer on top of the blanket/ wire, how thick was your layer?

I can't quite visualise how much I'll need to cover the dome, especially given the bizarre ratio.

Any advice?

Cheers

Alex

Hi Alex, I put around 1" on it, just enough to give me a firm bed once it had cured to go over the dome with my insulating firebricks which added a further 4½" of insulation, I also pointed up the wedge shaped gaps with vermiculite/perlite cement mix to maintain the insulation as opposed to box standard mortar.
Also, the vermiculite I used was the medium grade, 2 to 6mm. Mixed 50/50 with the perlite which is a bit finer. I picked up on the forum that this is the preferred mix. I used a wheelbarrow to mix, adding the perlite and vermiculite, then adding enough water to wet it sufficiently til there was a little water at the bottom then added the portland cement and mixed thoroughly to coat everything. You don't want it too sloppy, but you also don't want it too dry..
if you are using this mix at all under your cooking floor, then the ratio is around 5 or 6 to 1. You may need to clarify that one though.

Hope this helps

Best wishes,
Lance.