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Vermiculite based insulation

Vermiculite in bags used for insulation I pay 24 bucks per 1x 100L bag (3.53 cu-ft), you will need more of them for insulating of the whole oven as per below described quantities.

What is Vermiculite? Insulation applications

Where to buy vermiculite insulation? Best places to find vermiculite containing products, or most importantly dry loose-fill vermiculite insulation in bags, are large landscaping yards (because in horticulture the vermiculite, as well as Perlite, are used to prevent soil compaction or as soil conditioner/amendment after adding a composting matter.) Pool shops and businesses that build and install swimming pools also work with large quantities of vermiculite.

Then obviously those who work with different kinds of insulation materials. Such as; refractory firms (handling mostly refractory and high-temperature insulation) or factories producing various vermiculite based thermal insulating floor boards for use either with floor heating and without, walls, 3rd grade vermiculite size granule detailed image or floor levels construction to lower down a total weight of a building (vermiculite lightweight insulating concrete is highly suitable for building. A 5:1 – vermiculite to cement mixing ratio, it is light, insulating and, fire resistant with a great degree of sound absorption – more below). Then there are thermal roof panels and ceiling insulating layers, these are durable plus moisture resistant goods. Not to mention a packing material or even incubation of eggs for they remain in the warmth and protected, etc., vermiculite has many practical uses.

My advise is; negotiate with different suppliers what you’ll be charged for ~10 bags of vermiculite versus any price for one bag to source a much better deal. However, these jobs can be very easily done using a lot more cost effective and suitable insulating materials that will save you; and with the same or even better insulative properties than Vermiculite or Perlite have (with no material efficiency compromises, they do what they’re intended to do in kilns, furnaces or ovens with no quality reduction.)

Comparing the insulating lightweight concrete produced by mixing vermiculite and cement, depending on how it is mixed, this concrete is around 80% to 90% less heavy in weight sense, per same volume, than a conventional heavy/hard concrete. One inch or 25.4mm of vermiculite insulation layer thickness will have the equal insulating property values as 508 millimeters – 20″ thick regular concrete layer has. How is that for an interesting differences in material?

More on Vermiculite heat insulation and the quantity required

I am using both US and Metric measures for the quantity explanation.

From the industry/manufacturers, dry loose vermiculite comes in sizes from 1 to 4 grade. Each number is intended for different purposes. One 100 liters bag of granulated No. 3 grade vermiculite (not dust) weighs close to 9 kilograms – which is 90kg/cu meter. Although much lighter in larger granules form exists, example is the No. 4 Grade, it has bulk density from 65kg/m3 up. The dust or tiny vermiculite packed, the first grade 1, is heavier around 160kg/m3 and it is not suitable for our reasons.

To be precise, I don’t often refer to loose vermiculite in bags as pellets. I think, typically pellets are created by compressing of small material particles, or mixture of materials, into denser pellets. This insulation material produced is expanded exfoliated vermiculite, very light, low heat absorbent, not compressed nor heavy.

Insulation with vermiculite vermiculite insulation

Lighter in weight is better” is the rule for insulating. Plus any extra thickness applied on top, is only for an extra degree of benefit. It depends on the size and how they pop it; crushed volcanic mineral rock goes into kilns and in the heat they pop it just like a pop corn in the heat. The result is the mineral puff enlarges, expands into vermiculite in the heat and becomes that light.

1 cubic meter = 35.3 cu feet (0.1 cu m = 3.53 cu ft)
1m3 = 1000 Liters (0.1 cu m = 100L)
1 cubic meter = 264.17 US Gallons

For the whole job, when using vermiculite for the insulation that is, I buy 7x 100 Liters bags (larger bulky but lightweight paper or plastic bags.) 700L makes it 25 cubic feet (or exact measure convert is 24.717 cu ft equals 700 Liters). The amount is same for both Swishy and Masterly Tail oven designs.

Insulating with vermiculite work with vermiculite insulation

This is amount for extra insulation layer added especially on the oven top. The job can be done with only 6 bags too but of course it is always better if more insulation thickness is applied. If you purchase say 28 cu ft (790 L), or more (1 cubic meter = 35.3 cu feet), if the structure design proportionally allows, add the left over extra on the top of the cooking part for even better efficiency results. (I turned more towards using ash instead of vermiculite for cost reasons (as mentioned before it has the same insulation properties like vermiculite and Perlite.) If you DIY for single project maybe the money won’t always matter.

For the heat insulation layer under the heated floor slab and, if done that way, also for the final contours over the top; when you’re mixing your vermiculite with bonding agents, like building GP or Portland cement (same thing), add water gradually in little quantity as vermiculite doesn’t absorb water, it could become too runny otherwise. Mix by hand and shovel on a concrete ground or in a wheelbarrow, it’s very easy/straight-forward (mix not in a mixer because vermiculite granules are on a soft side and the mixer’s metal parts would surely damage its small particles.) Most ideal is to pour it simply out of the bags in its simplest loose-fill form covering all around and above if the oven was boxed in among e.g. house brick walls or in some metal casing. For vermiculite mixes here is the page dealing with heat resistant insulation applications including how to make own vermiculite based light weight concrete.

Typical physical properties of exfoliated (expanded) vermiculite

Bulk density: 4-10 lb/cu ft or 64-160 kg/m3
Temperature use: 2100-2280°F or 1150-1250°C
Non combustible material

However, if needed, you can use ash from burning coal (fossil fuel). It is sold mainly in large gardening yards (or directly from the production where it’s being burned, in hot water heating boilers, power stations; currently 80% of Au. electric power production is run on burning coal, for instance.) For the comparison, this ash costs only 35 bucks to fill my UTE and the amount will suffice for insulating 4 ovens. When I am able to source it closer to a job I always use it as it performs just the same in these temp. heat conditions like either Vermiculite or Perlite plus it saves me.

*** Let me know a price you got for vermiculite or the ash when you locate it. If you can also who sells it (address/phone web contacts) I will find the info useful when building/insulating around your location area.

Respond to the Vermiculite based insulation article:

50 Comments - post your thoughts

  1. […] under slab. Here’s the vermiculite insulation layer that goes under the hearth slab. This was before I found a good place to buy the […]

    Pingback Keith's wood fired oven. Concrete slab, walls, main oven, wall rendering technique.Permalink

  2. Rado- Building is going well, given the cold wet weather season it not any help. I am having a difficult time finding vermiculite for now. I have tried doing searches on the internet vermiculite versus perlite. What do you say on substitution of perlite for vermiculite and vise-verse in the insulation sense? William

    added by Rado: Hi William,
    Yes of course you can use Perlite instead. In insulating sense these two materials have very similar typical physical properties, thermal conductivity and density – important in insulating effects. Perlite is brittle, some people believe it is more effective as fill insulation than vermiculite. Where do you buy it, do you have the seller contacts, and how much for what quantity, size? In case I build around there one day, might be useful.

    Bulk density of Perlite loose weight 2-25 lb/cu ft or 35 – 400 kg/m3 range, depends on individual particles size average found within the bulk.
    Thermal conductivity of Perlite is also very similar to what Vermiculite insulation material provides.

    By Vermiculite versus Perlite as thermal insulation materials — Permalink

  3. Rado Howdy thanks for the rapid reply! The supply for the perlite is a Nursery they use it for potting soil additive. Endless supply, bigger nuggets in a 4 foot bale @ 32.00 dollars per bale. Nuggets are about a half inch in size and also a smaller bag with small pellets. What ratio for the insulation mixture? Same as with the vermiculite?

    added by Rado: Yes just like with vermiculite. Same way of work with these two materials/insulations.

    By Vermiculite versus Perlite as thermal insulation materials — Permalink

  4. Was looking for info on which type of vermiculite insulation grade to get … i was very sure the right one is the #3 because grade #4 looks quite big in size. I’m buying only the 2 bags of vermiculite amount for casting the insulating layer for under the floor slab as it gets heated and the 5:1 mix will also support its weight well. For the rest I’ll spread around some of the cheaper (not worst) substitutions for it described in your cd’s … thanks.

    By Best size of vermiculite for insulation. Nick — Permalink

  5. I am getting this same vermiculite insulation for my building job. Thanks for the close up images on the bags I’ve noticed the address and contacts information. I am buying my from the same business although here in Victoria.

    By Vermiculite for my pizza oven job.Permalink

  6. All I was looking for to calculate the amount of material needed for making a lightweight concrete form vermiculite. 1 cubic meter for an area in 100mm or 4 inches thick layer or possibly with an increased thickness for extra structural strength. Also page for how to add back up insulation to refractory hot-face.

    By Adding insulative vermiculite lightweight concrete thickness in an area space. — Permalink

  7. Excellent information. Couldn’t source where to buy these vermiculite insulation in bags for pouring-in. Plus what is mix ratio for vermiculite portland cement to cover the oven top. Had a thought it would be a weaker mix no strength is needed up there. For instance 3:1 vermiculite cement portions. It’s different compared with the 5:1 insulation part that goes under the floor slab, so to avoid underfloor heating there, which is heavy considering also the extra weight the whole dense part on top would have. They couldn’t give me a price for any vermiculite in my local building materials shop but in gardeners yard they have it available in ample supply. Ordered your cd’s Rado minutes ago ….. spring will be here soon so my building time’s finally coming. Kenneth

    By Who sells pour-in insulation in bags? — Permalink

  8. Can I use moisture absorbtion vermiculite in heat applications? Also, I was wondering where to buy vermiculite insulation?

    added by Rado: If you use a vermiculite type which absorbs water you can still use it for heat insulating applications. You don’t want to be keeping any water in any structure in which a heating above water boiling point takes place. You simply keep your vermiculite layer ect. dry from the water, as you would do with any other insulation. Otherwise steam will build up and rip a portion off due to the steam expansion. Also, water in any insulation conducts the heat, the heat would run away through it fast. Same would ash, or ceramic fiber products or porous insulating bricks and blocks. See the points?

    * Where to buy vermiculite insulation? I will post in here few contacts I cane across with, when I get back home.

    By Can moisture absorption vermiculite be useded in a heat application? — Permalink

  9. In the past, I cured another vermiculite concrete floor slab created inside of our entrance room, as one would with any other cement in a concrete, and ever since there were no problems at all with keeping the whole room warm. Thanks for all the information on the vermiculite insulation, where do you buy it, the suitable vermiculite grade and how to work with vermiculite as to insulate under, sides and over the top cladding of an oven. Much appreciated. Will post my pictures soon.

    By David — Permalink

  10. I arrived in this page when finding where to buy vermiculite and price of vermiculite. How much do these ovens cost if I was to purchase? They truly are fantastic.

    By where to buy vermiculite? — Permalink

  11. Hi Rado,

    Just wanted to ask a quick few questions.

    Could you describe what i need to do for the part where i need to fill the gap between the external brick wall and the sides of the oven, the upper slab and the oven itself. You stuff chicken wire between the gap then fill will the vermicrete mix. But you had mentioned that the oven expands and contracts. If i do this won’t the ove expand and then push the vermicrete aginst the brick wall?

    My plans for insulation are to use a fire blanket and the loose vericulite. Is vermicrete better or loose vermiculite?



    Added by Rado:
    Hi Gi,
    Thank you for asking, and also for sending your photos.

    First push the chicken wire into the gaps (see in the sequence imagess zb5 to zc3). Then mix a little amount of 5:1 mix (vermiculite : Portland or GP cement) to drop a little amounts of it onto the wire only – notice this is half inch or 12mm only thick cover. In the front you can smooth it for esteathic reason where it would be visible. That fills or seals all gaps in the wire-net so no loose fill vermiculite drops under below the hip level. The seal is soft and it doesn’t have large surface at all to be a part of the dense inside so no worries at all. Otherwise as you asked it could push if it was done somehow diferently, like, if it became a part of the solid dense inside.

    Then, say after 1 hour, I pour loose vermiculite around the walls of the boxed in oven (also in MTo if you see the images 847a to 847j in sequence). Then I use a weaker mix, e.g. 6:1 or 7:1 (again vermiculite cement) to finally cover the oven top – the thicker the layer the better it insulates. It goes very fast. You can use the vermicrete on the top or on the chook wire but it will cost more. Ceramic blanket can also only help, you may get the lightest in weight sense they have, which is also cheapest type, but better and more appropriate for this purpose! In a case when the walls for example were higher than the oven inside, you can just use only the loose vermiculite fill poured inside, plus a thin 1″ – 25mm layer of the mixture with cement vermiculite to finalize it. When you mix it; mix by hand with shovel, manually, not in an electric mixer because its metal parts would be destroying the vermiculite particles because they are soft. r

    By Gi on vermiculite on chicken wire in the gaps. — Permalink

  12. Thanks for the advice. I am at making insulation stage on my oven and then fully finishing it. Will send photos. Josh

    By Insulation for oven. — Permalink

  13. Please let me know the details of the different sizes of vermiculite.

    By r.p.latha — Permalink

  14. I looked for how to mix vermiculite and cement together to create insulation for onder my floor slab. This one and your other page for vermiculite based insulations mixing directions explains the matter in the lot.

    By Mixing cement with vermiculite. — Permalink

  15. Ireland Supplier

    Hi Rado
    Reading your site with interest and I am planning to build an oven. This supplier of firebricks in Co Kildare ( Ireland ) also supplies pizza oven kits. I have seen this oven type ( in Spain ) but I didn’t like the design since the chimney is in the middle of the dome which to my mind would be inefficient?
    pizza ovens for you 1

    Ireland Supplier

    Hi Rado
    Reading your site with interest and I am planning to build an oven. This supplier of firebricks in Co Kildare in Ireland, also supplies pizza oven kits. I have seen this oven type ( in Spain ) but I didn’t like the design since the chimney is in the middle of the dome which to my mind would be inefficient?
    pizza ovens for you 2
    What is your opinion? Also do you think the bricks are suitable for a self build?
    Firebricks.pdf from Dineen sales website.

    added by Rado: Yes, if for instance you only plan to cook pizzas then with the current heat directly from the red hot coals you may cook pizzas I guess on that floor. The oven is though described as a ‘pizza oven’ which is then correct ( you will need to rotate pizzas or some grilling perhaps in the direct heat source from smaller active flames or again the cinders. Still a good fun. ) But cannot say how this system would bake or roast (especially achieving stable baking temperature or atmosphere for the most common long term roasting ~ 1 to 5 hours plus. ) Don’t know why the chimney is located in there, perhaps to make it compact/easier to ship and cheaper to produce. Those bricks are all right and you can cook bake the lot in brick oven from these firebricks. How much do they cost, price for each or per full pallet? Ask if they have also firebricks with a lower alumina content like between 20% and 25% would be good as you can get these cheaper as well.

    By Amac — Permalink

  16. Thanks Rado
    Sorry for intruding on the wrong thread btw.
    My plan was to not use the kit but to buy the bricks and vermiculite etc and take my time to build a domed hemispheric – about 36″ diameter.
    The bricks are expensive €2.70 each, and €20 for 100L bag of vermiculite.
    full price list:
    pizza ovens for you

    Pizza Ovens 4 U
    Dineen Sales Ltd.
    Co. Kildare

    Phone: 00353 (0)59 8635557
    Fax: 00353 (0)59 8635655

    added by Rado
    Amac, thank you for sharing the information. Yes in some locations firebricks cost easily 30% more than elsewhere, or even more than that in fact. How about finding two more friends who would also want to build ovens, buy all material in bulk at once for 20% special. Price is always negotiable. Normal businesses have quantities discount structures, it’s good and healthy to be flexible. I reckon they will take the offer happily and it’s a very good saving including on the vermiculite. Just an idea. Currently here in Brisbane basic retail price for firebrick is $3 and the same size bag of vermiculite insulation grade-3 is $30/bag ( I buy it at 23$ no more per bag when I get 8 of them ). r

    By Amac — Permalink

  17. Hi Rado
    Again thanks for the cd, my question is, after i set the floor which is about 4 inches thick i used concrete mix with perlite than above that i mixed sand and fireclay 50/50 ratio my problem is that its taking forever to dry its been two days and still not dry i think i made it to thick dont laugh its about 2-1/2″ thick, do i need to removet it?

    added by Rado: Hi Frank, ah too thick. Yes scrape it off the concrete surface and reapply but thinly, it’s easy and quick to do. In MTo design see images 120 to 135 for the details (in the first Swishy disk see images ‘p4’ to ‘r2’) only little amount is needed, half a bucket at most. This mud can be normally remixed with water again (and again even from a completely dry state – if already dry, brake the green clay to bits with a hammer, add water, wait 2 hours, mix with using any stick and it will be ready for use). Apply back onto the concrete with the “notched trowel”, this tool looks like a normal trowel with with zig-zag edge-s (as seen on the photographs, it is common tiling/plastering hand tool for spreading and combing. This trowel causes only thin lines of the fireclay to remain on the surface, the rest in between these lines is scraped off by this tool. You could possibly scrape out the empty lines in the soft clay also by using a screwdriver or a knife, etc. anything like that; gradually for each row/line of bricks at the time as you progress, however it would be just a bit time consuming (although can be done just fine if a half an hour extra doesn’t matter.) When you place firebricks on such thin fireclay layer (even if the bricks were uneven), the firebricks will form a nice smooth surface, flat cooking floor.

    By Frank Altobello — Permalink

  18. Please send me plans for making these Pizza and Bread or Roast Ovens. In Puerto Rico NO FIRE BRICKS on sale, no Vermiculite based insulation. So I need your ideas on functional equivalent material I can gather. The price for the CD’s for making brick ovens complete.

    By Jaime Mercado — Permalink

  19. In your article you mention materials that are better insulating and more cost effective than vermiculite or perlite, what are some of these substances? I’m very interested to know what they are.

    “.. However, these jobs can be very easily done using a lot more cost effective and suitable insulating materials that will save you; and with the same or even better insulative properties than Vermiculite or Perlite have ..”

    By Better than Vermiculite? — Permalink

  20. I think this is very interesting info about insulation application, vermiculite material matter details, if you could reply with information or what ever you have would be neat / enjoyed the read / give me a holler if you would. Have a great day/thanks.

    By Randal Lawton — Permalink

  21. re: pizza oven. Live in Ottawa Canada. Completed base for oven using concrete and steel. I now want to complete a base with 2 inches of 5:1 perlite before adding fire brick for base. I then will complete my dome More brick and Perlite.
    Question is whether the 2 inches of perlite base is strong enough for the brick and the rest of the dome, or will frost and other issues cause me grief?

    By mike — Permalink

  22. […] Vermiculite insulation grades. What is vermiculite layer, how thick, how to apply vermiculite part? Where to buy vermiculite? Insulation by vermiculite in thermal heating and heat resistant applications like kilns, various furnaces or of course making ovens more efficient. […]

    Pingback Vermiculite furnace | See it do it — Permalink

  23. Just thought I’d let you know of some prices here in andalucia, Spain. Unbelieveably cheap in comparison.

    The firebricks are 10cm x 20 cm x 5 cm, and are €0.24 each
    50 litre bag of vermiculite is €4.10
    25kg cement is €3

    All in all it’s been a cheap project over here!! :)

    (ps, as an aside, granite for outdoor kitchen, premium quality, 9 linear metres of brazilian red granite, with double front edging came in at €1300 – bonanzaaaaaaaaa!)

    added by Rado :
    Hi Alex, nice to hear from you. Are wood fired ovens popular in Spain? With these conditions I might even relocate, around the sea somewhere nice, Majorca for headquarter ;) ! Good size firebricks (are they called a Shamot bricks, what color do they have, a bit yellow-ish?), the cement at 3 Euro per bag, is that refractory heat resistant cement or masonry cement like Portland? Would like TO SEE the red granite and what you create using it. All the best Mate.

    By Alex Gabb costs of materials in Spain — Permalink

  24. hey rado

    no worries, i can post up some shots (??) somewhere… or email them? We are still finishing this latest job, so will get it to you somehow in next week or so.

    3 euros was 25 kg portland (though not portland!!) cement. 25kg of refrac cement is more, at €8

    I dont know of oz, but in uk, that amount/quality of granite would be in the £6k region

    the fire bricks are a light red colour. But there are many different types/colours/shades. I live east of malaga, near to an area which make a lot of brick/earthenware products/tiles etc so we have much to choose from, and it doesnt come from far away, which i guess is the reason for price!

    Pizza ovens are a relatively timely process to build for what is an awesome outcome. Cost of fuel here is prohibitive, we use almond or olive branch, which is around 80 euros a cubic metre, unless (like me!!) you forage! But it makes them less common, though everyone wants one!! just cant all affford!

    Same problem with my other business.

    My main business is building, and recently the new business and my pizza oven I’m going to do at home is going to be in this style, on the outside, and Im going to try and build in a smoking department (??) and a funky chimney… i’ll def post pics when done (when i get time to do the thing!)

    The jacuzzi on the homepage is the one next door to my to be pizza oven – i have already done the base at “pizza scraping” height, and need to build dome. Its going to be weird as I have the dome going out into a triangular outer wall, but its hard to describe, easier to do it, and show ya!

    Take it easy


    added by Rado :
    Alex, impressive work! Ahhh, wow the night-time photo down to the middle of your page, with the fire red hot embers alike red light in the water, it’s absolutely wonderful. We would like to have that. We actually want to try life in Spain in some point in a future. Hope not too distant future. We travel to Europe in June now, but I doubt I’ll get to create a space to be able to taste some of your culture this time. Dada spent some time around there before.

    Back to the main topic; I’ll be happy to see the granite in place when you are done (I am always thirsty for seeing some masonry art from around the planet.) It works out roughly 4.5 times better price compared to England’s market. Where I’m located we have several Granite quarries, one of them produces this nice dark blue hard granite stone, however not slabs which is rather somewhat pity. If you would like to advertise your ovens jobs on our website; create some interesting, practical for people in a way, text with photos for your page here with link – currently we get 15K unique visitors daily and people will definitively see you well, if you like. It deserves it!

    By Alex Gabb costs of materials spain — Permalink

  25. Hi Rado

    sorry to trouble you I would like to check with you that the hearth slab insulation for MTO is 50mm deep and mixed out of 13/2/1 vermiculite / Portland cement / lime i see that there is also mentioned 5/1 vermiculite /Portland cement insulation type described on the insulation page – which of these insulations is better to go with?

    Also could I check the concrete hearth slab is 4/1/1 (20mm blend /Portland cement/ lime) overall height 160mm minus the insulation layer level thickness.

    Many thanks again.


    added by Rado :
    Hi Ian,
    Thank you for the note.

    Yes you can make the insulation under the top slab 50 mm ( 2 inches ) thick out of 5:1 ( vermiculite/cement ), with metal mesh placed under for the whole surface. In the insulation page there is also exact hint for water / cement / vermiculite quantity-directions and help for manual mixing by hand, you may want to use or look at it; as Vermiculite does not absorb water, all of a sudden the mixture can go very wet and runny.

    Above the dome the insulation cover on top can be done using much weaker mix ratio, vermiculite 7 or even 8 parts to 1 part cement.

    Yes, the top slab is made out of 4/1/1 ( 20 mm concrete blend / Portland cement/ lime ) as you say and of course, as is, well reinforced.

    By IanPermalink

  26. Hi Rado,
    Compliments on your web site. I’m interested in building such a beautiful and useful oven. ONe question. Does it have to be freestanding or can it back against an existing brick wall? I look forward to your reply as well as sending you an envelope with the support/necessary funding :)

    added by Rado:
    Thank you for the note. Often these ovens are fitted or built into an unique already existing surroundings, against walls, on various slabs or in split level grounds etc. The inner dense cooking part, the actual oven, doesn’t lean against any wall as it expand by the heat. There is the gap for insulation between the inner oven and the outside encasing, or a wall. That insulation is soft which means it absorbs the expansion movement and basically nothing will push or lean onto the outer wall. They are heavy which is what should be considered as well prior building. For instance if it was a elevated deck and so on the floor under needs to be supported.

    Please drop me a line to my email with a couple of photos of that area, of the spot where you plan to build it, I will have a look and then can comment with ideas or advice better. That is if it’s still needed after seeing all building details in the sequences on either of the oven building disks with plans and visuals.

    By JohnPermalink

  27. I recently had some contractors build me a brick oven. These guys had never built one before nor did they use a pre-purchased kit. Needless to say they did not do their research and neglected to use any insulation. The inside of the oven (floor, walls,inside of dome) are all covered with firebrick and refractory mortar. The outside walls made of cider blocks are covered in veneer stone. The result is an oven that does not retain heat even with a blazing fire inside. I obviously would like to remedy this without tearing the structure apart. Would I be able to insulate with vermiculite -cement mixture covering the interior fire bricks? If so, would this vermiculite -cement mixture be able to be exposed to the flames or would we then need to re-brick over this insulating layer? Suggestions???

    added by Rado:
    Any layer or thin lining inside on the hot face could crumble or peal off. Other approach is needed. Please email me the oven photos for more details for me so I can comment on what to do, what will be better to do. Everything can be improved or fixed always. I would need to see the whole structure from the outside, and also inside floor and walls with ceiling. If there is ash from a previous firing leave it intact as I can read from that a lot too. Send original large photos for better details to see. How heavy were the firebricks your oven is built from? Are they the heavy dense firebricks that can be cut only with a diamond wheel on a grinder or with a brick saw? (and not by a hand held hack saw for instance)

    By Dom — Permalink

  28. Hi Rado,

    We are looking into specifying a pizza oven for a job in Tasmania and suppliers of the pizza oven (Zesti) have recommended purchasing the vermiculite locally the product that they us is a vermiculite/perlite mix 100L fine bag. The pizza oven is to be fitted in wall and to be fully covered over with vermiculite/perlite.

    My question is will straight vermiculite say grade 3 or 2 be sufficient in this role?

    Could you please respond at your earliest possible convenience.

    Kind regards,

    added by Rado:
    Grade # 3 Vermiculite is what i use. It is a good size also for mixing with a bonding agent(s).

    Yes if the oven body is behind a wall, and if it’s also fully boxed-in by the other remaining 3 walls, then just use the Vermiculite to fully cover it. It is much better to create a honeycomb effect on top, by mixing the vermiculite with just a little of Portland cement say 6:1 or 7:1 only for the particles to stick together. That way the hot air doesn’t soak upwards as much between the particles, the heat loss rate gets much slower and the oven retains heat and stays hot for longer.

    Vermiculite particles can be mixed also with the water glass (called also liquid glass, Sodium silicate, Na2SiO3 – it is basically cheap stuff but most places blow its price to astronomical level don’t know why or how come they get away with it.)

    If you mix it; do not add too much water, mix semi-dry and pour it also semi-dry in like that, without tapping it down! Here are ideas on mixing Vermiculite – it is the refractory thermal heat resistant insulation page.

    By Steven — Permalink

  29. Rado,

    Thank you for the response. Where do I access your email address. I will send the pictures.


    added by Rado:
    Hi Dom, email them to my: kangarado (at) g m a i l . c o m
    More details to see the better, also from the back.

    By Dom — Permalink

  30. I just sent a few pics of the structure. Let me know if they came through and what you think. Your help is greatly appreciated!

    added by Rado:
    Hi Don,
    Yes the images came through fine, good to see the details. All clear. Nice stone structure actually otherwise. As is right now, it can be only used for instance for cooking or grilling directly on an opened fire or over red hot embers. The structure cannot retain much of the heat as to perform like an oven does. There are a few reasons for this;

    1. Most importantly there isn’t the entrance throat in the front to stop the hot air running out through the front opening. The entrance is big, it should be smaller. This way there is no system as to limit the heat from escaping freely out instead of being absorbed by the walls, floor and vault inside.

    2. The flue opening at the back right corner; it just sends the heat from inside the chamber away from there. Like from an opened fireplace which has purpose only to radiate a bit of heat out from the source.

    3. When you make the entrance changes, and possibly block the currently existing flue pipe, insulate the oven on the outside by applying a thermal insulation layer-s. There are several insulating options – ceramic blankets or mixed insulation usually from exfoliated Vermiculite or Perlite – more about how to do insulation.

    Please see these two pages to see how to change the front. You can add it in as an extra to the front area. It would be the best if the vault was completely removed and new oven was put in there made out of firebricks instead. Please see these two pages for full sequence:

    MTo design firebrick part entrance.

    MTo design hood flue area.

    You can view there also other pages with all necessary oven building stages.


    By Dom — Permalink

  31. I want to make ecological stoves with this material, could you give some prices about this vermiculite? For the moment I need 100L amount.
    I’m from El Salvador, Central America.

    By Roberto Gonzalez — Permalink

  32. I am making two small portable ovens on metal stands with wheels, and weight is an issue. My choice for bases is either mold a cement-vermiculite mixture to size or use lighter weight calcium silicate blocks, which is more expensive, but easier. What do you advise? How to do mixing vermiculite with cement?

    Chuck, Lake Tahoe, CA

    added by Rado:
    Hi Chuck,
    Why not the lightweight layer would function also as the thermal insulation which goes under the dense heavy part for better efficiency and performance. I use Vermiculite cement in ratio 5:1 which is basically lightweight concrete with great insulation properties while still being strong to position the heavy-dense part on top that.

    But for the insulation over the top you can make the mix a lot weaker, meaning adding lesser amount of cement into a Vermiculite volume, could be 10:1 or even 12:1 vermiculite with cement mix. See these pages for how I make the layer and the second link is for how I mix Vermiculite with cement:

    From here navigate to the link/stage for the layer which goes under the top hearth slab.

    Insulation – properly mixing the 5:1 ratio of Vermiculite with Portland cement manually and quickly simply and easily by hand.

    What is the density of those calcium silicate blocks in question, how do they insulate, are they any good?

    Email me photos of the structure how you progress I will have a look at it.

    By ChuckPermalink

  33. I was searching for information on mix ratio for insulating cement and vermiculate. Your site had so much great information which I was looking for that I had to comment and thank you for the effort and time you so abundantly contributed for the benefit of others. It is information like this that make the internet worth having.

    Thank You,

    By insulating cement and vermiculatePermalink

  34. Kindly give me the proportion of cement and vermiculite to be used for pools and such. I also want to know whether water proof compound is to be mixed?

    By Latha — Permalink

  35. G’day from New Zealand.
    Having one or two volcanoes we have a lot of pumice available cheaply.
    Do you have any experience using this in an oven insulating mix?
    If so, what is your recommended brew?

    By Insulation — Permalink

  36. I’m trying to build a tandoori in a 55 gallon steel drum and I’m confused by how to use vermiculite as an insulation, do i need to add cement to it or could I put a layer at the bottom of the drum and just dump the vermiculite on the top too as the top layer has terracotta pot, pls help, thanks for the answers I’m expecting.

    By ron — Permalink

  37. I’m interested to find out if vermiculite can be used for external purpose? I intend to build a concrete roof and replace the sand by the light granules. Does it make sense? Will the roof have lighter mass/weight if the vermiculite is used and what sort of ratio mixing do I have to work with?

    By Perrodo — Permalink

  38. I need to find out if vermiculite can be used for external purposes and also I’m trying to build a light weight concrete floor for my house out of some insulation materials. Any recommendations on what to use?

    By kandicer — Permalink

  39. We mine raw vermiculite of all grades in Zimbabwe and keen to collaborate with international distributors and exfoliators of vermiculite. Our resource is quite huge.
    If keen kindly contact me on
    tel: +2637 7232 5666
    and email: cpaul [at] earth [dot] co [dot] zw

    By Paul Chimbodza — Permalink

  40. I have a 36×40 inch barrel shaped pizza oven which the oven interior ceiling is firebrick the exterior top of the firebrick has a 2 inch fire clay mortar clad on top of it and the exterior of the roof is framed and shingled. There is a 6 inch space between the top exterior brick to the roof frame. I left the top row of shingles out for examination. I added 6 inches of vermiculite there and during a test fire I got a lot of hot steam. Coming from the roofs peak, and it smelled like the vermiculite was cooking … what am I doing wrong?

    By Phil R — Permalink

  41. Phil, the vermiculite is not cooking, it is simply only the chemical water fumes from the dense layers, steam, being driven out with the higher temperature. Soon it will stop. Second or third firing should be free of the smell in the air. Did you just use loose vermiculite insulation or did you mix vermiculite with something?

    By Rado — Permalink

  42. Hi Rado,
    Thanks for sending the downloads again. Managed to get them onto a disc this time.
    Can I use vermiculite board under the oven as the insulation layer? My local stockist has them so no delivery charge! Not sure about price though. It comes in various thicknesses from 20mm to 75mm. They also have vermiculite bricks of various sizes. Would these be OK to use for the layer of insulation behind the flat back firebrick wall? Would we still need insulation blanket and chicken wire etc?

    By Nancy Flavell — Permalink

  43. Hello Nancy,
    Is it possible to find out how much weight the Vermiculite board with cope with per surface area? I would have a look at it with that information. If OK I would choose the thicker board option for under the oven. yes it could be used as backup insulation for the back wall but the thermal vermiculite board would need to be positioned tightly, meaning no air gaps between this insulation and the flat concrete dense part there, for the insulation is efficient.

    By Rado — Permalink

  44. Hello again Rado,
    Is there any issues using sawdust in place of fly ash?

    By John — Permalink

  45. Saw dust would burn like a wood once high the heat reaches it. Sometimes people add by mixing-in saw dust into a refractory insulation, say 10% portion in total volume sense, and apply it with the saw dust in it. Later the saw dust burns out (burns out either gradually within more than one firing or right away in the first firing as it depends on the structure and conditions) leaving the insulation layer that much more airy – meaning better insulating properties. The bonding agent(s) of the insulation mix has to be proper, refractory so it remains solid as expected. But this needs to be done in a way so it does catch on fire, but safely in a controlled environment so to speak because it smokes. At time we do this for ovens, pottery kilns or other kilns and furnaces.

    By Rado — Permalink

  46. Big Hello from Puerto Rico! BTW, in PR to obtain perlite or vermiculite for making the light-weight concrete mix; you can buy perlite and vermiculite at garden centers and/or agricultural supplies distributors here.

    By Juan — Permalink

  47. My uncle has a vermiculite mine. He asked me to find out how he can use it produce concrete.
    Do you advise him to sell processed products of vermiculite or to use the vermiculite to produce concrete and make money from it?
    And i would like to know is it different to make concrete with vermiculite or other aggregates? If yes what is the different process?
    And can vermiculite be used as an aggregate itself or does it need any addings?

    By Shahriyar — Permalink

  48. G’day Shahriyar,
    Logical approach. Please read content on the thermal insulation, lightweight concrete on the insulation page. It’s in the second part/half on the page in the area where it’s being dealt with how to mix vermiculite and cement containing lightweight concrete. You have there described the process of hand mixing with cement, and also water quantity/ration for volume of vermiculite of standard vermiculite based lightweight concrete. Easy to make and even test it by yourselves in your production. When you do something like this, you need regularly make industry tests, a small amount used, of each batch you mix. This is required to assure for the proper consistency each time you package new lot. You can then ship us one whole container of it.

    By Rado — Permalink

  49. Hi Rado,

    Can you please answer a question for me?

    I have some 25mm thickness ceramic fiber board for thermal insulation, would you put it down first under the hearth slab floor? Or on top of the hearth slab and place your fire brick floor on the ceramic fiber board?

    Thanks in advance.


    By Shane — Permalink

  50. Good day Shane,
    The ceramic fiber board prevents heat conduct. For my purpose for instance, I would only place it under the heart slab. This way the heat could travel down through firebrick hearth soaking into the slab as well thus increasing heat absorbing capacity/mass. this is of course if you intend to store more heat in these dense parts, which also absorb and retain the heat energy. For example useful for baking or roasting long term (5 hours) in stable temperatures not having have to reheat the structure. This is the same as with the cladding layer around the firebricks in sides and top. once the dense part absorbs and retains the good heat amount several batches of breads can be reloaded without reheating it.

    However, say if you wanted to store this heat only in the firebricks, e.g. to use only a thinner dense shell (for instance when the oven is used with ongoing fire heat source inside or for a simple shorter time baking etc. purposes), then the slab could be separated that way from the firebrick layer. Also, the ceramic board should be fine to cope with the firebricks’ weight so they do not squash it. What is it’s density?

    Warm regards,

    By Rado — Permalink

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