Need advice on chimney and outer arch construction

[stonecutter]

Re: Need advice on chimney and outer arch construction

If you build an enclosure around the oven, do you still need to build a chimney around the clay flue liner? It seems I have seen a couple of youtube ovens where they did not build a chimney, but just left the flue alone.

Thoughts?

No, you don't need to build a chimney around a clay flue...but you want 4" min air space from combustible surfaces.

[david s]

Re: Need advice on chimney and outer arch construction

The small air gap you'll have between the firebrick and facade will be much more effective if you don't fill it (especially with hi temp silicone). Also on the lateral chimney support, I just put in a couple extra pieces of rebar down the holes in my side chimney bricks and again at an angle on the outside embedded in the insulation cladding (perlcrete for mine). Seemed to tie it all together quite nicely.

I fill the gap between the outer decorative arch and the entry with vermicrete. It is slightly flexible so it can work as an expansion joint as well as a thermal break. Some builders cover the gap with some stainless sheet as this area gets some rough treatment.

[SableSprings]

Re: Need advice on chimney and outer arch construction

I believe most places have codes regarding leaving an air space/gap between the chimney and any flammable objects (i.e. plywood roof/wood joists). I built a brick chimney around my double flue liner primarily for looks. I also felt a little uncomfortable looking at the tall stack of liners with all those seams that could get damaged or fail over time...the external brick chimney gave me piece of mind (and made it easier to build the roof/chimney interface).

[fabby]

Re: Need advice on chimney and outer arch construction

If you build an enclosure around the oven, do you still need to build a chimney around the clay flue liner? It seems I have seen a couple of youtube ovens where they did not build a chimney, but just left the flue alone.

Thoughts?

[brickie in oz]

Re: Need advice on chimney and outer arch construction

Fingers cracking and burning.
I think it is the clay that does it, the lime wouldnt help thou.

Working for years as a brickie with the same mix of mortar day in and day out the only time my fingers cracked and burnt was during winter when it rained more.

Where we are has a very reactive clay subsoil, when it gets wet the clay sticks to very thing, if you walk through it, it gets on your clothes, tools and equipment.

[Bacterium]

Re: Need advice on chimney and outer arch construction

I use vinegar afterwards..... funny enough it does work.
Although it does attract jokes about fish and chips

[Gulf]

Re: Need advice on chimney and outer arch construction

Back when my hands were accustomed to brick laying, I kept them coated in mineral oil. In those days I had no finger prints . Lately I have become fond of disposable latex exam gloves. They are relatively cheap, if you can get them in the box of 100. I still use a scented variation of mineral oil, though . It is called "baby oil" .

[mrchipster]

Re: Need advice on chimney and outer arch construction

Max, since you are going to be working with lime and home brew mix I suggest you pick up a gallon of cheap white vinegar. After working with any cement/lime mix, wash your hands with soap & water and then give 'em a good rinse & rub with the vinegar. (I find that even wearing gloves I end up getting my bare fingers involved somehow with the mix or components...) The mild acid neutralizes the lime (base) component that's still on/in your skin and really helps keep your hands from cracking & hurting.

Another trick is to use a good hand moisturizer prior to, and intermittently while doing the work (Ask your social director which one she uses). It will help but not prevent irritation.

Chip

[Massimilliano]

Re: Need advice on chimney and outer arch construction

Thanks Mike
That;'s good advice. I always wear gloves, but still end up getting cement and other nasties on my hands. Maybe I will use balsamic vinegar and claim it is a new kind of after-shave.
Incidentally, I have been sent photos from a guy who has retrofitted a clay chimney to his oven. He shaped clay around a wire skeleton, which obviates the need for a mould (mold in American?) It looks a bit "rustic", but I imagine it could be finished nicely with a coat of render.
Cheers
Max

[SableSprings]

Re: Need advice on chimney and outer arch construction

Max, since you are going to be working with lime and home brew mix I suggest you pick up a gallon of cheap white vinegar. After working with any cement/lime mix, wash your hands with soap & water and then give 'em a good rinse & rub with the vinegar. (I find that even wearing gloves I end up getting my bare fingers involved somehow with the mix or components...) The mild acid neutralizes the lime (base) component that's still on/in your skin and really helps keep your hands from cracking & hurting.

[Massimilliano]

Re: Need advice on chimney and outer arch construction

Thanks David
I'll give it a go as I have a cubic metre of clay from a brickworks
Max

[david s]

Re: Need advice on chimney and outer arch construction

Try using the search button. The recipe is 3:1:1:1 sand,cement,fire clay, lime. You can use bricklayers clay in place of fire clay it is much cheaper and works ok. I find it's best to apply the stuff with a trowel and hands, but the lime is vicious so use a good barrier cream or rubber gloves. If you have a cut on a finger you'll know all about it.

[Massimilliano]

Re: Need advice on chimney and outer arch construction

Thanks David
Excuse my ignorance but what is home brew? I presume you are not talking about beer.
I have heard that I could mix a little sand, cement, and lime with the clay to 'set' it.
Does anyone have experience with this?
Max

[david s]

Re: Need advice on chimney and outer arch construction

Max,
You could form the clay pipe inside the PVC pipe and allow it to dry. Around 25mm should be a good thickness. It will shrink away from the pipe as it dries and you will be able to remove it easily. If you form over the pipe it will shrink as it dries and make removal difficult if not impossible and if allowed to dry completely will probably crack. Depending on the type of clay and the grog content, expect around 5% shrinkage from plastic state to dry and a further 5% after firing. However there is an alternative which does not involve making the pipe in two pieces. You can wrap and tape the PVC pipe in a layer of plastic, form your clay around the outside of the pipe and then roll the whole lot over a few times. This will increase the diameter of the clay pipe and you can then slide out the PVC one. It will be quite difficult to fire the clay pipe to 1000 C safely without cracking it, especially if you intend using a wood fired kiln. A clay pipe of this diam should be quite servicable but to avoid cracking it you should insulate it. Not good to have it cold on one side and hot the other. You'd probably have more success forming one using home brew over a sand mould. You could cast the whole vent and chimney in place at the mouth of the oven. It works I've done it. When done remove the sand.you just need to get the mix right so you can hand form it so it stands up vertically. Make it around 25 mm thick and add some stainless steel fibres and polypropylene fibres ( not absolutely necessary) if you can get them.
Dave

[Massimilliano]

Re: Need advice on chimney and outer arch construction

Thanks for that good advice. A problem we have in New Zealand is that it is almost impossible to buy the sort of products you are talking about. I guess this is a drawback of having such a small population.
Most of our local brickworks have either closed down or make decorative bricks. When is comes to pipes it is just about all plastic. The few clay pipe suppliers have all said their products won't stand the heat.
I think I will have a crack at making my own from a clay cement, sand, and lime mix I have been advised works well for making pizza oven domes (as a substitute for fire bricks). Your idea for a mould is brilliant.
Cheers
Max