Testing Fire Resistance: Alabaster, Putty, Sand, Cement




I tested fire resistance of some materials such as putty, alabaster (plaster), sand, cement. The purpose is to determine the best refractory for my new smelting furnace project. I decided to try different proportions of widespread materials which could be a good refractory for the walls of metal melting furnace.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Making Samples

As a mould for tested materials, I used plastic cups.

I’ve made such samples:

1. Putty – 100%

2. Putty 50%/Sand 50%

3. Alabaster 50%/Sand 50%

4. Cement – 100%

5. Cement 50%/Sand 50%

6. Alabaster 33%/Sand 33%/Cement 33%

7. Alabaster 70%/Sand 30%

...and of course added some water to every sample.

As I know, a lot of such materials are used by home melters for crafting their foundries.

Samples were drying 1 day in a shadow and after that 2 days on the sun.

Step 2: Using Blowtorch

When they were enough dry I prepared gasoline blowlamp to test samples heat resistance.

Step 3: Heat Resistance Results

During the experiment all samples crashed. The best sample is №3 (alabaster 50%/sand 50%). This sample had the worst surface before blowlamp test. Though, it didn’t have the best look it got only small cracks. All other samples were highly damaged.

I’ve decided not to use these materials as refractories because in my opinion, their low temperature resistance won’t let to use them for the furnace walls for a long time.

In the next test I’ll use materials which should sustain much higher temperature.

I am planning to use fire clay (sustain 1600 °C (2912 F)), grog powder (sustain 1600 °C (2912 F)) and graphite dust (sustain more than 4000 °C (7232 F)).

Be the First to Share


    • Made with Math Contest

      Made with Math Contest
    • Cardboard Speed Challenge

      Cardboard Speed Challenge
    • Multi-Discipline Contest

      Multi-Discipline Contest

    8 Discussions


    2 years ago

    nice but cement for example needs 28 days minimum

    for mostly complete chemical reaktion

    inside moist is what cracks the material earlier

    and should be kept moist for that time!

    1 reply

    Reply 2 years ago

    Yep wsmwsm. I understand this. My purpose is to find the solution where I wouldn't have to wait too long. :) And as you see the result is similar even for materials such as alabaster which becomes solid very quickly. That's not a science of course, just an experiment :) For the second experiment I will use other materials and an oven to dry samples better but enough slowly to prevent damages.


    2 years ago

    I like your sound, methodical approach and analysis of materials, and also your conclusions. They represent real world conditions any home foundry enthusiast would use in the pursuit of the craft, well done!

    3 replies

    Reply 2 years ago

    Thank you very much Hank! Just try do to everything step by step. :) I hope that you're right and some of my home experiments will be useful for others. I saw a lot of videos where people said how they did some things but didn't say, that for instance, furnace made of plaster and sand would be damaged after first melt or the most after several times. It's good to find out that something doesn't work before you spend a lot of time and money :)


    Reply 2 years ago

    Looking forward to your next round of investigation of more suitable materials too.


    2 years ago

    That gasoline blowtorch is really neat, I've never seen one before!

    1 reply

    Reply 2 years ago

    Yes. It's enough old thing. :) Nevertheless, still works fine.