Need advice on what is the best method when installing the insulation blanket please?

[Wheels1974]

I have almost finished the dome of my wood fire oven, which is made using fire bricks. After the dome is finished I was ALWAYS going to put the INSULATION BLANKET (Insulfrax) which is approximately 1 inch thick over the fire brick dome followed by some chicken wire and then I was going to add a 4 to 5 inch thick refractory mortar over the insulation blanket and last of all a 1 or 2 inch layer of a cement type render.
However recently after speaking to a few people from the shop I purchased ALL my stuff for my wood oven, they told me that I should first add the 4 to 5 inch thick refractory cement layer over the fire brick dome and after that then add the 1 inch thick "Insulfrax" INSULATION BLANKET followed by some chicken wire over the insulation blanket, then followed by the final layer of a cement type render. Hence to say that I am now confused. PLEASE help?

My query is, does it make a huge difference regarding what way you install your INSULATING BLANKET and if so what way have you ALL gone about it and which way works best?

P.s. I will just add that the foundation I have done has a 4 inch concrete base, followed by another 4 inch refractory cement layer on top and lastly a
1 inch insulated board, which is where the fire brick floor has been laid.
I know it's probably over kill but I would prefer to over insulate rather then under insulate.

Your advice is much Appreciated

Regards
Dean

[nissanneill]

Re: Need advice on what is the best method when installing the insulation blanket ple

Dean,
you are getting yourself into a confused state with your plans and what people are advising you to do!
Firstly and foremost, you need to understand that refractory cement is not insulation but will absorb the heat and will increase your relative heat retention of your oven, ie. increasing the thermal mass of the oven!
Read through my build, as I explain in detail and support it with photos of how I built my 40" Pompeii with half cut firebricks, (4 1/2" long) then laid a 1" superwool blanket over the dome, covered it with chicken wire and then plastered this with 3 one inch thick layers of vermiculite cement insulation.
I then finished it with a 1/2" layer of render which waterproofed it and will be the base for my ceramic tiles once I get around to sourcing them and tiling the dome.
By increasing your thermal mass, it will take considerably more time and wood to heat up BUT it will hold much more heat for much longer (provided that you thoroughly insulate the dome) for baking 3 or more loads of bread, roasts etc.
A 1" "Insulfrax" INSULATION BLANKET will not be sufficient and you need to at least double this and preferably triple it to work properly. 2" of vermiculite cement is the equivalent insulation value of 1" thermal insulating blanket!
Because heat rises, many people put an extra layer of offcut blanket over the top of your dome. When my oven is over 500˚C for an hour or so, the outside top of my dome is cold, not even warm!

Neill

[Wheels1974]

Re: Need advice on what is the best method when installing the insulation blanket ple

Thanks Neill,
So what do you suggest would be the best method since im not using Vermiculite and only SHERLITE which is the refractory cement.
Do you think I should use the 4 inches of Sherlite directly on the firebricks Oven dome and then purchase say four 1 inch insulation blankets on top of the Sherlite/refractory cement and then finally cover it with the concrete render?

Regards
Dean

[dmun]

Re: Need advice on what is the best method when installing the insulation blanket ple

When you say refractory cement, there are thousands of specific refractory products. The "lite" in sherlite seems to indicate that it might be an insulating castable, but I don't know.

If it is an insulating product, you should be fine.

[Wiley]

Re: Need advice on what is the best method when installing the insulation blanket ple

From our own archives:
http://www.fornobravo.com/forum/f7/q...ixes-7550.html

It appears that Sherlite is an insulating refractory. Also a Google of "Sherlite refractory" gives a few more references on the product. Be sure to add "refractory" to that search or you will end up with lots of entries on a walking staff.

Hope this helps,
Wiley

[DimTex]

Re: Need advice on what is the best method when installing the insulation blanket ple

Wow, that is a new approach. All I did for my oven was wrap the oven dome with the insulfrax blanket, I bought three boxes of the stuff for my 36 inch oven because after all the work in building the stand and dome I wanted to get on with my life and start cooking. Three boxes gave me enough material to wrap the entire dome in four layers (4 inches) of the stuff. I then wrapped chicken wire (open wire mesh) around the whole thing shaping the dome. Then I started the three layer stucco process (scratch coat, 2 top coats) and voila I was done. To be candid I was hesitant about the insulfrax blanket because of the cost but now that I have used the oven a couple of dozen times I am sold on the stuff. I've had interior temps in excess of 950 degrees F and the stucco dome outside temp was the same as the air temperature.

[Wheels1974]

Re: Need advice on what is the best method when installing the insulation blanket ple

When you say refractory cement, there are thousands of specific refractory products. The "lite" in sherlite seems to indicate that it might be an insulating castable, but I don't know.

If it is an insulating product, you should be fine.

Firstly thank you ALL for your comments. Dmun yes mate that makes total sense and I will call the shop I purchased it from to confirm, I know when I first went to the shop and asked about purchasing VERMICULITE that they told us about SHERLITE being basically the same as VERMICULITE apart from it being later technology and above all because it is allot easier to apply.

Hypothetically speaking lets say it is a insulating castable, then what would be the best method regarding when to lay the INSULATION BLANKET (Insulfrax) should I put the 4 inches of SHERLITE refractory cement directly on the fire brick dome and then the INSULATING BLANKET over the 4 inch SHERLITE followed lastly by a layer of render?
I was always going to do it this way until the people who sell the stuff told me otherwise as explained in my initial post.

Regards
Dean

[Wiley]

Re: Need advice on what is the best method when installing the insulation blanket ple

Dean,
Interesting question on order of placement. Whether the highest quality insulator should go on first or last? For my two cents: I would think placing the insulating blanket over the dome followed by the more rigid castable insulator would provide:

1) a more flexible layer so the bricks can expand and contract with less chance of cracking as a result of being restrained by the more rigid castable insulator.

2) The render would have a more rigid layer (castable insulator) to affix to and be supported by. This is the usual sequence, blanket first then vermicrete/perlcrete then render.

Just my thoughts, I don't know if anyone has ever run any tests or calculations on which order is actually more efficient or if it matters.

Hope this helps,
Wiley

[Wheels1974]

Re: Need advice on what is the best method when installing the insulation blanket ple

From our own archives:
http://www.fornobravo.com/forum/f7/q...ixes-7550.html

It appears that Sherlite is an insulating refractory. Also a Google of "Sherlite refractory" gives a few more references on the product. Be sure to add "refractory" to that search or you will end up with lots of entries on a walking staff.

Hope this helps,
Wiley

Wiley & Dmun,
Thanks guys you both were correct. Neill had me worried something chronic mainly because of my foundation which has 4 inches of SHERLITE on top of the 4 inch normal concrete and that's the last thing I wanted if it was going to do the opposite. Although I think that's my fault because Neill most likely got confused because I said that this SHERLITE stuff is a refractory mortar in my original post, sorry mate.

I just called the manufacture and the SHERLITE is a INSULATING CASTABLE not a REFRACTORY MORTAR, im not exactly sure what the diffrence is as im very new to all this.
What they said was once this SHERLITE sets and if you were to look at it under a microscope it literally looks like a honey comb and its light as opposed to Portland cement.
The reason they recommend to spread the 4 inches of this SHERLITE directly on the fire bricks is only because it will give the oven more mass.
They said either way will be fine, but the manager does recommend the SHERLITE directly on top of the firebricks and then the insulating blanket simply because of the mass.

However I totally understand where Wiley is coming from regarding having the insulation blanket first, as it would give the fire bricks more ease when expanding and contracting simply because the insulating blanket is soft and more of a lose fit.

P.s. I'm not sure which way I'll go as yet but thankfully my mind is at ease now. I will post some photo's shortly.

Regards
Dean

[nissanneill]

Re: Need advice on what is the best method when installing the insulation blanket ple

Dean,
that's the advantage of this forum. You have questions and we have answers.
When you speak of refractory 'cements' these normally increase the thermal mass but if they were called refractory insulators, well, that puts a totally different light on the subject.
I agree with Wiley in the order for your insulating layers and let me add that it will work out easier, cheaper, quicker and better because you will have a nice hard solid surface to render, tile or paint to finish your dome.
Sorry if I worried you, but sometimes these things slip through but at least they get sorted out.

Cheers.

Neill

[Wheels1974]

Re: Need advice on what is the best method when installing the insulation blanket ple

I have never posted a photo here so I hope it works. It's just a couple of quick photo I took of the WFO so far. As you will see from both photo's I used foam as a guide for my fire brick dome and it worked perfectly.
The second shot shows a top view of the top of the dome just before I complete the dome, you can see how the foam was used as a guide.
There was a fair amount of cutting fire bricks involved and we also used fire bricks that were tapered so this really made the fire bricks sit really tight with very little Refractory mortar needed to join the bricks together from the inside only a millimeter or two im guessing.

P.s. I purchased a brand new cheap 16 inch blade Wet Brick Saw (WELLQUIP) from eBay which cost me $800 delivered to my door and it worked a charm and saved us a ton of time. It's not worth renting a brick saw for the price they charge here in Australia especially if you want to take your time building the WFO like we are.
I would recommend anyone wanting to purchase a brick saw to get a cheap one from eBay if it's only going to be used for just the odd job although I don't see why it wouldn't work for big time jobs as it cut through these Fire Bricks like a hot knife would through butter and I used the crap dry blade that came with it, although I used the brick saw always with water as it keeps the dry blade cool and makes it last longer, it also saves all that brick dust going everywhere while using the water when cutting. I would be very surprised if this blade that came with the saw costs more then $30 so I could only imagine how it would cut with a proper diamond blade.

After I have totally completed the WFO I think I will sell the brick saw, so if anyone is interested in purchasing a Wet Brick Saw from Melbourne Australia just email me and when im ready to sell it and if some one wants to buy it then I can even give them a demo of how easy it cuts through these Fire bricks or any brick/concrete I would imagine. Although it could be a while before this wood oven is completed as we are taking our time. The front arch and flu is the next part. More photo's posted shortly.

Regards
Dean

[Les]

Re: Need advice on what is the best method when installing the insulation blanket ple

Wheels - I do not profess to being a mason, but this is a bad practice. If the mortar joint gets compromised (heat expansion) there is nothing to keep these in place. You want a consistent taper pointed down. If the bond does break, the worse thing that can happen is the brick will slide down a bit. I would hate to see you go through all this work and have bad things happen.

Les...

[Wheels1974]

Re: Need advice on what is the best method when installing the insulation blanket ple

Wheels - I do not profess to being a mason, but this is a bad practice. If the mortar joint gets compromised (heat expansion) there is nothing to keep these in place. You want a consistent taper pointed down. If the bond does break, the worse thing that can happen is the brick will slide down a bit. I would hate to see you go through all this work and have bad things happen.

Les...

Les,
I understand what your saying mate but what your seeing is two texter marker lines as a guide for the flu. All tapered points are facing down, meaning wider up top and taper in towords the bottom. I will remove the marker lines later , but if you have a closer look you will see that the tapered end is down on ALL arch bricks.

Regards
Dean

[Les]

Re: Need advice on what is the best method when installing the insulation blanket ple

Very cool! My bad.... After you pointed it out, I can see the cuts. Good luck with the rest of the build!

Les...