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Old 02-13-2013, 03:34 PM
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Location: Tochigi Prefecture, Japan
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Default Home brew concrete and cast-in-place concrete.

With all the combined knowledge in this forum, why no discussion on home brew concrete. Always concrete is "ready mix" or "from the bag"!

A call from someone in the concrete business to give simple recipes for making your own. Also some discussion of cement to water ratios and importance of proper mixing.
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Old 02-13-2013, 05:31 PM
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Default Re: Home brew concrete and cast-in-place concrete.

I'm not in the business, but have been around it just a little.
Do a Google search on formula for concrete mix.
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Old 02-13-2013, 06:03 PM
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Default Re: Home brew concrete and cast-in-place concrete.

Mikku,

If you want to see a fine example of a perfectly smooth v-crete, looks at Gulf's build. Yours is looking good too.
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Old 02-13-2013, 06:34 PM
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Default Re: Home brew concrete and cast-in-place concrete.

Gulf,
I did just that- the results are either "way" to simple with no strength data, or "way" to complicated to cause the "glaze over eye effect".

A "happy medium" approach, like something found in these forums, where anyone would tackle mixing their own, instead of relying on the premix, and feel confident with the end results.

Wow! I did check out your build album... been around it a bit is a real understatement. Really like your template for the pericrete! Also all your detailed brickwork.

I think you really have it right, put the oven somewhere under cover, then you never need to worry about drying out phase once you are completed. And the oven can be used any weather conditions!
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Old 02-13-2013, 07:13 PM
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Default Re: Home brew concrete and cast-in-place concrete.

Quote:
Originally Posted by mikku View Post
Gulf,
I did just that- the results are either "way" to simple with no strength data, or "way" to complicated to cause the "glaze over eye effect".

A "happy medium" approach, like something found in these forums, where anyone would tackle mixing their own, instead of relying on the premix, and feel confident with the end results.

Wow! I did check out your build album... been around it a bit is a real understatement. Really like your template for the pericrete! Also all your detailed brickwork.

I think you really have it right, put the oven somewhere under cover, then you never need to worry about drying out phase once you are completed. And the oven can be used any weather conditions!
I am not very open to discussions on concrete. I am probably a little set in my ways and there are others who can Pie-R-Square me slam off of this forum. The simplest/nearest formula (on the web) to what I was taught for general purpose concrete is 1-2-3. One portland-two sand-three gravel. If thee is no gravel or simular large aggregate to be used, you would be better off adjusting to 1 portland and 3 sand.
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Thank you very much for the Kudos on the build. I have always thought that I could build any form for concrete that I set my mind to. The form you built for your precast has me wondering now if I might have been a little cocky about that subject .
You formed your pcrete insulation much the same way that I did my vcrete. You described using a grout float to use as a floating form and a your hand as a depth guage. You applied a base layer and then built upon that as it set up. The only draw back to applying the p/vcrete in full 4" layers is the amount of water which has to be removed. I air dried mine for months and was sure that it was dry before I rendured. I did purposefully leave a hole (vent) in the apex of mine just in case. I got a lot of water out of moisture out of the vent during my Karagi Dude Heat Bead Cure. Several dome clearings later there is no moisture or heat coming from this vent. I am installing a permenant vent cover in this hole for future problems.
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Last edited by Gulf; 02-13-2013 at 08:00 PM.
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Old 02-13-2013, 07:35 PM
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Default Re: Home brew concrete and cast-in-place concrete.

That kind of recipe I can follow.
When I did little projects, setting posts, some small pads etc. I would use: 1-5gallon bucket filled with sand, 1-5gallon bucket crushed rock, 1/3 bag portland cement (but our cement comes in 25kg sacks). I found this nice to work with, looked like something that the ready mix guys deliver and happy with it in general. It would work up a nice cream, and when you stripped any forms, looked nice and dried to a nice light gray finish.

I did not know the strength though.

When starting my slab, I checked a little at the ready mix place. After a bunch of long divisions.. Same ratio: 1- 5 gallon bucket sand, 1- 5 bucket crushed rock (pea to 1"), and 10 kg portland. From their chart, it made about a 5000psi mix. They had another mixure component...some kind of air-entraining stuff, but I was not happy with the way it mixed in.

That kind of recipe; anyone can use without the Pie-R-Square intimidation factor- only need a plastic bucket, and weigh one time the portland in a different bucket and mark height with a magic marker. Future batches come out always the same. I have trouble with shovel fulls--same as making coffee. My wife says my coffee is too strong. Level vs heaping/same measure.
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Old 02-13-2013, 07:42 PM
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Default Re: Home brew concrete and cast-in-place concrete.

It depends on what you want your concrete to do. While the 3:2:1 is a standard reliable recipe, if you are after high strength concrete then there are other considerations. Admixes can be added to increase strength, make the concrete waterproof and control the rate of hardening. High strength concrete should be measured by weight rather than volume and water added should be exact (a super plasticiser is usually required for this because too much water in the mix weakens it.) Temperature range the concrete will be subjected to may also determine the type of cement and aggregate to be used. There is tons on the net about concrete recipes. Start with "concrete by weight". Placement method, vibration, setting time and temperature are all further considerations.
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Old 02-13-2013, 07:54 PM
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Default Re: Home brew concrete and cast-in-place concrete.

Like I said!
A good place to start a discussion.
Tried and true are the recipe's I'm looking for!
Something that a WFO builder would use! That is the first job most builds require, making the base!
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Old 02-13-2013, 08:19 PM
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Default Re: Home brew concrete and cast-in-place concrete.

I use bulk deliveries for big jobs, mix my own from the sand, gravel and cement for small jobs.
In my opinion, 3:2:1 "Government Mix" is fine for just about any home job, including supporting ovens.
I don't buy the premix bags of sand gravel and cement. When I read the labels on these, they are usually something less than 3:2:1 and say they are for garden paths and post holes, not structural concrete.

The only thing I will say about mixing your own is that most home concreters I know who mix their own get carried away on the water addition. I believe this is due to wanting to keep the first mixer full of concrete from going off before the last one is poured.

The proper approach is to have so many helpers that you can't keep up with spreading it and screeding it before the next barrow load arrives.

Last edited by wotavidone; 02-13-2013 at 08:30 PM.
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Old 02-13-2013, 09:19 PM
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Default Re: Home brew concrete and cast-in-place concrete.

A couple things about diy concrete...Mixing your portions by volume is by far easier than by weight for homemade concrete. Make sure you gauge your portions the same per batch. For the 1:2:3 mix you want to use 1/2 part water by volume of your mix which you can adjust +/- depending on the water content of your sand. I also use an acrylic or polymer admix in my homemade mixes, and they act as water reducers, which help with flowability without weakening the mix. It also helps control with shrink cracking during the cure. I replace about 10-20% water volume per batch with polymer.

A 1:3 ( portland/sand) would make a poor concrete..that ratio is used as a building mix for stonework usually ( which isn't great either). If that's all you have, you are better off reducing the sand to around 2 or 2.5 at the most. Acrylic or polymer is essential to a mix like this...otherwise you will get plenty of cracks.

Your aggregate should be sharp grained...sand and crushed stone alike. Rounded gravel or sand makes very weak concrete. Simply put, because the sharp shapes lock together much,much better than rounded ones. Usually, concrete sand has 1/8" to fines and is the best choice for the sand portion. Crushed washed stone 3/4-1/4" is really nice for the aggregate part if you can get it. But any graded crushed stone is better than washed bank run, which is usually rounded. Hope this helps.
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