Questions about my first Rocket Mass Heater

Hello, my name is Juan (John), I' from Mar del Plata, a city in Argentina, in here we have a cold winter.
Me and my wife are moving soon to our new house and I am beginning to build a RMH and I have some questions that maybe some of you can answer.

First of all, I'm not an English speaker!! you will have to read with patience.

My first question, later I will upload some photos and more questions:

Here the fire bricks are expensive, I bought them anyway, buy now I wonder if a made a mistake (I can return them), maybe there is a cheaper ( and equally good or better) alternative?, I'm thinking about the heat riser, if I make it with to shit metal tubes and insulation between (perlite and clay) it would work the same? or perhaps with thinner fire bricks? here you can buy them, buy I was afraid that they where too thin (3/4 of an inch)

Thanks
Juan

The first question is what kind/quality of clay you have available. Is your soil sandy or clayey?

If you have good clay easily available, you can do without most of the firebrick. Do you have any experience working with clay? With building or making things? If you are generally good at making things, you should be able to use clay/cob for most of your build including the hot zone. If not, you would be safer using the firebricks to easily make the whole hot zone.

The two metal pipes with perlite/clay between them will make a good heat riser. You want them to be at least 4"/10cm different in size to get a good thickness of insulating perlite/clay. The inner pipe will burn out over time, leaving the perlite/clay inner surface and the metal outer shell to hold it together.

Have you studied the information here about RMHs? Do you have Ianto Evans' book Rocket Mass Heaters?

Thanks Glenn, I have experience with clay, but not much.
Yes, I have the book, the 3rd. edition, have read a lot of posts from permies and all the videos I found but I still feel insecure
Here there are some photos of the RMS so far:
This are the fire bricks:

This are the smaller ones:


What do you think is my best option:
The thicker bricks?
The thinner ones?
Do something with clay? (I think the clay I can get from my yard is good, maybe tomorrow will upload a small video showing this,I would like to know your opinion)
Or I may go with the two metal pipes? (I will upload the pipes photos tomorrow to)
I would love to know your opinion about the options, some pros and cons maybe!

Metal inside the heat riser doesn't work in a properly running rocket.


Look at this!

https://www.youtube.com/watch?v=7RyvsZD1_CU

ok, so the metal sheet inside the heat riser is not a good idea, what do you think about the thinner fire bricks, they are 2 centimeters width

Metal as a permanent part of the inner liner of the riser is doomed to fail; if you are just using it as a form for perlite/clay insulation, that will still be sound when the metal liner burns away.

It looks like you have a good handle on building the J-tube with firebrick, so it would probably be good to continue with that. You want the full bricks in the main feed tube and burn tunnel for durability. The thin bricks should work for the riser if you wrap them well with insulation, or the round riser of perlite/clay might be more efficient and would allow considerably more space between the barrel interior and riser exterior. You would want a good cutting method for the firebricks so you don't have all the "fins" sticking out of the corners, if you go that way.

Thanks Glenn
Firebricks and refractory bricks are the same thing?
If they are not the same, which is the one in the photo?
With these bricks, how mach perlite/clay insilation do I need?

Yes, they are the same. Probably about 2"/5cm of perlite/clay would be good. It depends partly on the size of your system - the bigger it is, the thicker the insulation should be.

ok, made it with fire bricks, good so far, also made the outer shit metal to contain the insulation.
Now iam looking for some advice about the floor of the RMH, I have searched in the book and in the videos and not sure about how to continue, here is a photo to try to explain my self:

Maybe someone can point me to a photo, video or explanation about how to follow from now?

And here are some more photos, maybe you have some observation/correction/advice: