Homebrew 3:1:1:1 - How to work out how much material to buy?

[4stroker]

Hi all,

Sorry if I have missed this but I did a search and could not find the exact answers I'm looking for.

I'm currently planning a cast WFO in Australia, going to use the Homebrew 3:1:1:1 mix and cast over a sand mold.

The dome will be 1040mm internal diameter, 50mm thick, and I have calculated that the volume of the dome will be approx 0.1m3, or 100 liters.

So from here, how do i work out how much of each material i need to purchase?

For example, do I assume that the 100L just gets split evenly into 6 parts, and therefore I need:

50 liters of sand
16.66 liters of hydrated lime
16.66 liters of fireclay
16.66 liters of portland cement

Therefore total = 100L of dry mix. Or do i need to apply some sort of bulking factor etc, say 20% additional?

Lime/clay/cement are available to me in 20kg bags. So to work out how many kg of each i need, i googled the density of each, and came up with the below:

Sand = 1631 kg/m3 * 0.05 = 82 kg
Hydrated Lime = 2210 kg/m3 * 0.017 = 38 kg = 2 bags
Fireclay = 1702 kg/m3 * 0.017 = 29 kg = 2 bags
Portland Cement = 1150 kg/m3 * 0.017 = 20 kg = 1 bag (will purchase an extra as spare)
Total mass of dry mix = 169 kg

Also, i want to add the SS needles (melt extract fibres).

From various sources I believe i need to add 3% by weight of the dry mix.

Therefore I will need 5.1 kg of SS needles for 169kg of dry mix.

Have i got this right?

Thanks!

[david s]

Hi Mark,

Yes that sounds about right. There are a few things going on here. Firstly dry loose materials are not compacted and reduce volume when packed down, Secondly the finer materials will fill the spaces between the courser ones and finally further compaction occurs once you add water. This means that by volume the 3:1:1:1 mix will not result in a volume of 6.
To explain this better I just did a little test mixing 900 ml of sand with 300 ml lime,300 ml OPC, 300 ml powdered clay which is a total of 1800 ml, but when mixed dry comes to 1350 ml.
On mixing with water to "ball up" consistency it measures 1250 ml (a further reduction and weighs 2194 g, Producing a wet density of 1755 g/L (1755 Kg/m3)
Expect a little further reduction in dry density once the free water in the mix is eliminated.
Hope this helps. If anyone's keen they can make up a table of this info.

Dave

[4stroker]

Thanks David!

So 1800ml of raw materials ended up at 1250ml wet. How much water would you say you added? Do you think it ultimately ends up at 1200ml or thereabouts?

By my calculations that means I need to buy about 150L of total raw materials to make a 100L dome.

So from there I still need to convert that to kg of raw materials because that's how the retailers sell them.

I think that the densities i have gotten off the net are not quite right.

Could you by any chance do another small test please and tell me the weights of the 900ml sand, 300ml lime etc so that I can calculate the densities?

Also, for the SS needles, when they say 2-4% by weight, is it by weight of the total raw materials?

Once we close this out I will gladly turn this into a table or calculator or something for public consumption!

[david s]

Thanks David!

So 1800ml of raw materials ended up at 1250ml wet. How much water would you say you added? Do you think it ultimately ends up at 1200ml or thereabouts?

By my calculations that means I need to buy about 150L of total raw materials to make a 100L dome.

So from there I still need to convert that to kg of raw materials because that's how the retailers sell them.

I think that the densities i have gotten off the net are not quite right.

Could you by any chance do another small test please and tell me the weights of the 900ml sand, 300ml lime etc so that I can calculate the densities?

Also, for the SS needles, when they say 2-4% by weight, is it by weight of the total raw materials?

Once we close this out I will gladly turn this into a table or calculator or something for public consumption!

I did not measure the amount of water added in the test sample.
Dry loose density of materials as follows. Might not be all that accurate as I weighed only a litre of each

sand 1397 g/L
OPC 1109 g/L
clay 742 g/L
lime 620 g/L

SS needle addition is % of total of dry weight of all materials in the mix.

[david s]

Homebrew weights and density.docx

[4stroker]

Thanks David.

I think my original densities were a fair bit out, after doing some more googling your densities are pretty close to some other info i can find online, so i think they are right.

Going off your densities your 1800ml of total loose materials would have weighed 1999g, and then after mixing with water it weighed 2194g, so you mustve added about 195ml of water. Does that seem right?

I've expanded on your table and turned it into a calculator, see attached.

If you think it's right ill post the excel version which has all the formulas etc.

[david s]

Thanks David.

I think my original densities were a fair bit out, after doing some more googling your densities are pretty close to some other info i can find online, so i think they are right.

Going off your densities your 1800ml of total loose materials would have weighed 1999g, and then after mixing with water it weighed 2194g, so you mustve added about 195ml of water. Does that seem right?

I've expanded on your table and turned it into a calculator, see attached.

If you think it's right ill post the excel version which has all the formulas etc.

Good job Mark. I hope your boss is not reading this forum, you must be doing plenty of oven research at work
You have the dry density wrong "assumed 1200ml final dry density"
It will probably be more like 1700g/L I kept the sample and currently curing it, so when that's done will let it dry completely and reweigh it to let you know.

[4stroker]

Haha you can get a lot done in a lunch hour

Ok awesome I was hoping you would say that about keeping it and weighing it etc!

My wording isn't correct there with "1200ml final dry density". What I did was (most likely incorrectly!) assume that the original 1800ml of material ends up at 1200ml volume once cured, ie a "bulking factor" of 1.5 which needs to be applied to your dome volume when calculating how much loose dry material you need. Thats why the 93.4 litres in the table goes to 140.1 litres.

I will wait until your experiment is complete and revise the table and notes from there.

Thanks again for all your help.

[4stroker]

Any updates david s ?

[david s]

Hi Mark. I did repeat the test and the dry materials weighed 2015 g for a mixed volume of 1360. This time I measured carefully 400 ml water to mix the brew to ball up consistency resulting in a weight of 2371 g for a volume of 1260 ml.
I used different (course) sand (density 1525 g/L, a fair bit denser than the fine sand) as my other stuff was damp which would skew the measurements. Also there would have been a slight loss with material stuck to the surface of the barrow and tools.
I have also been drying samples to get a final dry weight. The samples are losing around 30 g/day. The first sample having lost 264 g down to 1930 g from 2194 g.I’ll let you know the final dry density when the numbers flatten out.

[4stroker]

Awesome, thanks!

[Mullster]

4stroker is it possible to repost the r revised spreadsheet? I’m contemplating a last minute switch from my amateurish gym ball vermicrete dome thanks to the guys in here

[4stroker]

Yes I will do, once the testing described above by david s is complete

[david s]

Hi Mark. I repeated the tests 3 times with more carefully measured volumes and weights. For a batch of 900 ml sand, 300ml OPC 300 ml powdered clay, 300ml hydrated lime, I used 400 ml water. The average wet mixed vol was 1260 ml with an av mass of 2412g (density 1914g/L or 1914kg/m3)
on drying for 7 days (no more water loss after weighing each day) the samples av mass was 2162g (density 1716g/L or 1716 kg/m3)
Of the 400ml water used the loss on drying was 250ml, so 150ml used up chemically in the hydration process. That figure could be higher if the samples had been allowed to damp cure for a week rather than dried quickly. Hope this is useful for your spreadsheet.

[4stroker]

Many thanks david s

For those interested, please see attached revised table.

I will wait for a QA review from David before posting the excel version!

david s , if the attached is correct, I only need 1 bag each of the clay and lime. In a Covid-19 induced episode of panic buying, I went out and bought 2 bags of each last week, for fear of further lock downs etc.

If I have extra it's no big deal, they aren't that expensive, but my question is this; if I do indeed have extra, should I:

1. Build a thicker dome. Ie if the table is correct, I could easily now do 75mm thickness with the materials I have. Is there any benefit to this though, eg strength, retained heat? Are there any negatives?
2. If Option 1 is not advisable, I may keep the additional materials for a future smaller oven for my self (this big one is my father in laws build). What is the shelf life of the materials? It would be some time before I ever got around to the second one... Will I need to store in a vacuum bag or something?

Thanks again for all your help. Hopefully this helps out others too.