Using Porland/Fireclay cement for a Chiminea? Outdoor Fireplace Design Discuss Using Porland/Fireclay cement for a Chiminea? in the Outdoor Kitchens and Living Rooms forums; Matt. There are times when you just have to get your hands into the mortar i have been using a ...

[fornax hominus]

Matt.
There are times when you just have to get your hands into the mortar i have been using a product called gloves in a bottle , hand blocker it really helps and a trick I learned about 1/2 way through my oven , when you stop work , rinse your hands in plain vinegar.. it seems counter-intuitive but the vinegar seeks out all the bits of lime in /on your skin and neutralizes them .. it works!
tim

[mourits]

Another update.

I am writing a full how-to for instructables.com so just a few quick notes here.

I just applied the second batch of cement today and finished the second half of the sphere and the chimney.
I just have to wait for it to cure and attach a spark-catching hood on top of the chimney and we can do a first burn. (see pictures)

• I decided to take cvdukes's and the guy at Wellington's Ablaze firewood emporium's advise and went for normal Portland cement. No, fireclay or other additives.
• I added iron oxide to color the concrete black. The end result is more dark gray but it's fine for this version 1.0
• Don't get 'concrete' ready mix. It contains gravel (duh) which makes it impossible to push the mix in the mesh. I had to sieve it out.
• I made the mesh way to thick. I made ridges in the chicken wire to give it more volume but that was not necessary and made it harder to get a smooth finish.
• When the chicken wire is flat and straight it is actually very easy to apply the mix (I tried both a wet and a drier mix, both were fine) and the result is incredibly strong for such a thin layer.
• Unfortunately the concrete will only stick where the chicken wire forms a nice even surface. Just pushing some scrunched-up wire in an opening and hoping the mix will stick to it will not work.
• Working with chicken wire is very painful! Every bit you cut of and every piece of metal wire will try to cut you and for some reason the cement mix creates nasty infections.
• The skippy ball had to go straight away, you really need two hand (in gloves) pushing fromt both sides.
• Of course you need 2,5 times more cement than you thought. I will be making the chimney lower because of this.

So, next post will be the complete story with all considerations included.

As of now, assuming the chimenea will not explode or fall apart after the first burn, I think ferro cement is good technique for such a project with two reservations:
- Preparing the chicken wire mesh should be done with a lot of care to get the surface as smooth and even as possible.
- Prevent having to cut the chicken wire. It is like working with a pin cushion. (with the sharp end pointed outwards)
- Do a trial pour to see if you like the texture and color of the concrete (many colors are available). Rough concrete by itself is butt ugly.

Matt

[david s]

The mixture cvdukes suggests for the inside can be improved with the addition of lime. I use equal parts of sand, cement, lime and clay. If you want the mixture to be white, say for coating the inside of a dome, then use white ingredients ie white or silica sand, white portland cement, lime, kaolin.

[mourits]

Thanks David,

I agree that the finish needs work.

I would recommend to anyone who makes his first attempt and building such a thing (from either cement or bricks) to make a cheap, trail version first to see what works and what looks good.

I am very happy with my slightly rough and cheeky looking result as it was cheap to do and very educational. For a next version (that would probably stand in our, yet to aquire, garden in Amsterdam) I will be paying much more attention on the innner and outer coating and color.

One question: How thick would such a coating be and how should the main wall off the room be prepared for the coating to stick properly?

Matt

[david s]

The coating for the inside, as suggested, just apply by painting on a good thick paint-like layer.

[david s]

The outside is bound to get some fine cracks fire it up and see how it goes. You could try a flexible acrylic render on the outside. Simply water it down so you can paint it on then give it several coats.With a chimea you want to try and avoid flames which will heat it up too fast and cause cracking. Better to stick to coals, heatbeads or charcoal.

[mourits]

David,

so, a couple of questions. (partly important for the howto i'm writing to give the next ovenistas some good tips)

- Do you (or anyone else who like to chip in ) think you could build a medium (one and a half foot diameter) structure from just 'refractory mortar' and a support structure like chickenwire? How much stronger (percentage wise) is 'pure' concrete (Portland & sand) compared to the refractory mortar mix? : ( from High Heat Primer (High Heat Mortar Primer)

* 1 part Portland cement
* 3 parts sand
* 1 part lime
* 1 part fireclay

Is it more brittle than regular cement? Why would you and wouldn't you use it?


- You mention "flames which will heat it up too fast" and then say "Better to stick to coals, heatbeads or charcoal".

In my (subjective and scientifically unfounded experience) a coal or charcoal fire burns hotter then the boiler room in Hell while a small wood fire burn much more mellow. I am talking about charcoal that is 'burning' (being help with a stream of fresh oxided like the wind or upwards draft). I am mistaken and are wood fires hotter then coal? Why would a blacksmith use coal instead of wood?
__________________

[david s]

I'm sure you could build a structure using the home brew ref mortar. It wil not be as strong as ferro cement though (whole boat hulls are sometimes built using this method.) Portland cement breaks down when it reaches 300C and that's where the lime takes over because it can handle the heat, but doesn't have the strength on cement. Lime is also good because it is slightly elastic and leaves the end product porous so moisture travels in and out more easily.
Sudden heat from direct flame impingement is likely to cause too rapid a rise in temp. possibly resulting in thermal shock failure (cracks) The blacksmith uses forced air (oxygen) to get the fire really hot. When I said coals I meant the gentle burning coals left after the flame of a wood fire.

[mourits]

It's done!

I have finished the constructing and fired the little devil a couple of times with much success.

A very extensive how-to, which much attention to material and construction considerations can be found on Instructables.com:

Outdoor fire place (Chimenea) from ferrocement

I hope you find the information useful and since I plan to build another, better version I am very eager to find any experiences of your... er, experiences here.

Matt

[david s]

It looks fantastic. I would be very careful about firing it with flames coming out the chimney. You risk creating cracks. would love to know how it holds up after 20 firings.