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Starcrete

Ultra-Light Fireproof Concrete Using Starlite

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Starlite is pretty amazing stuff, but its not very economical to make and use for anything practical as it is.
Previously I've used Perlite and Fire Cement to make a fireproof moulded interior for a Helical Forge capable of melting aluminium, so it seemed a good idea to use Perlite as a filler with another heat resistive binder like Starlite.

I've now completed first tests with some awesome results.

The Perlite performs as an inert bulker that doesnt allow heat to penetrate the interior of the material so it doesnt get hot.

I oven-dried a second batch of tiles and discovered that they are handleable minutes after removing from the oven and perform as well as Starlite dough for a fraction of the cost. Ordinary flour is just as good as cornstarch too, and the finished tiles behave better than expected.

Bonus, smells delicious while testing. XD

Starlite.

According to popular research this amazing stuff has been reproduced. Perhaps not as the original, but certainly works equally well. That seems to be down to its geometry as much as its chemistry, and thats what I'm leveraging here.

Carbon
Starlite is made predominantly of Carbon, with extra Carbon locked up in its structure redundantly that it uses to reinforce itself when it is burned, so it retains structural integrity. It isnt so much fire proof, as flame resistant. The outer surface burns and blisters, making a shield over the core which doesnt even heat up.

Ingredients
For all this carbon, the ingredients are actually simple. Corn Starch provides the bulk of the carbon, with some extra locked up in Sodium Carbonate dissolved into the PVA binder. Corn Starch bulks up during hydration several times its dry volume, so a lot of PVA is needed to make a Starlite dough with an appreciable volume, and its way too thick to apply as a paint so it winds up expensive for large areas.
The PVA however is just a binder and it can be wetted down considerably before it affects the finished product...

Perlite

Perlite is a natural volcanic stone, in fact its a foam of magnesium/aluminium and calcium oxides similar to Meerschaum, which actually floats on water, and used to be used to carve tobacco pipes from. It is used commercially in horticulture because being a glassy foam it holds a lot of water in its structure and works like a sponge in soil, creating reservoirs of moisture to keep it from drying. Perfect for flower pots...
Being volcanic, it is also heat resistant, and when mixed with a binder like a glue it sticks together like a Cocoa Krispie. And that is how the stuff will work with the Starlte...

Starcrete
Experimenting with Perlite and binders before, I established you really need to mix it at something like a 5:1 ratio of filler to binder, so a litre of Starlite will make 6 litres of Starcrete. I'm estimating this of course based on experience, and I also think I should be able to water the PVA down 2:1 for that as well, maybe even 3:1. We will see...

I will experiment with the ratios to make simple tiles and bricks to experiment with, but the use case for mine is my workshop.
This has a 1.5inch cavity wall that I will be filling with Starcrete to insulate and fire-proof it, and I have yet to figure out the volume I'll need.

  • Space Cake

    Morning.Star04/26/2019 at 12:24 0 comments

    The first tiles werent so successful, they turned out to be a little too crumbly to use. They also took a very long time to dry, so I decided to oven-dry them, along with a new mixture.

    This was very carefully measured out at 3:1 Perlite / Starlite, I wasnt so careful and left some Starlite in the cup, plus I added the Perlite in half-cups and it wasnt accurate.

    This mixture ratio holds together much better, but will take longer to dry.

    I pressed some smaller tiles, crushing about twice the volume of the mould into it. This forms a much tougher end product.

    I also tried cramming a bit of poly tube full of it and rammed it down pretty good.

    This makes a material that is slightly flexible. The mixture is kind-of non Newtonian, it can be bent and stretched a bit but is also slightly springy while wet. It could be trowelled onto a surface with a bit of practice.

    After baking the pieces were a bit of a lottery.

    Gas Mark 2 for an hour was more than enough to drive the moisture out of the smaller pieces. They cooled in a matter of minutes and were handleable. Interesting...

    The moulded pieces remained the same shape and didnt deform at all. The surface turned kind of plasticky and its slightly rubbery inside but breaks open under pressure.

    Its more like Flapjack than Cocoa Krispie, smells delicious. Probably isnt... ;-)

    The first pieces crumbled when I tired to get them in the oven. Now they are fully dry they are a bit delicate. This ratio of mix could be poured into a cavity and packed but doesnt support  any weight.

    However, the test pieces behave as I had hoped.

    I hit this bit with a blowtorch for over a minute, and it just looked at me, so far so good.

    Next I turned to a fully-dried piece of compressed tile from yesterday that I left on my bench indoors.

    This dried out to make a chunk that feels like Papier Mashe.

    However it doesnt burn. It doesnt even burn your fingers...

    After the first success I tried the cooked moulding, and it doesnt affect it in the slightest.

    The Perlite simply adds to the bulk and is completely inert. Being a foam it does not transmit the heat inside the Starcrete at all and improves the handling of the original material as well.

    I'm very impressed with the performance. :-D


  • Starcrete is born

    Morning.Star04/25/2019 at 12:27 0 comments

    I managed to get my shit together today enough to make a batch of Starcrete, and now I'm waiting for the test pieces to cure.

    Should be tomorrow I'll get some test results then.

    I decided to use flour rather than cornstarch; in this application I dont think it'll make a huge difference.

    Ingredients

    1 Litre PVA

    200g Sodium Bicarbonate

    1.5 Kilo Plain Flour

    1 Litre cold water

    10 Litres Perlite

    Mix together the Sodium Bicarbonate and a little water to make a paste, then add the glue and mix, then add the water to thin it out. It mixes better this way.

    Then add the flour a little at a time until the paste reaches the consistency needed to glue the perlite together. I found I needed the whole bag of flour to make it gloopy enough, you could add more and make it stiffer but I dont think its necessary.

    We shall see... ;-)

    Take a cup of the stodgy mixture and slowly knead in 2 cups of perlite. This is fun, just like cocoa krispies.

    This ratio of mixture makes a nice solid when compressed together.

    Here I just grabbed a handful and moulded it into a ball with my fingers. It isnt messy now, the glue absorbs into the perlite and coats it, and it all sticks together really nicely.

    I lined a dish with greaseproof paper and piled in some of the mixture.

    The first one I just did with my hands, it works quite well but it wasnt very even. But it stays together when wet nicely and made a decent tile.

    The next one I pressed down with a bit of wood. This crushes the perlite at the surface a bit and makes it smoother, I'm wondering if a press would work even better to produce even more solid bricks.

    Shouldnt be hard to knock something up with some scrap plywood to push tiles out by the dozen.

    Here's how tough the stuff is right after mixing. It performed exactly as I hoped it would.

    When dry, that would be an artificial rock. :-D

    This is using the test ratio of 2:1 Perlite / Starlite.

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