Home brew concrete and cast-in-place concrete.

[mikku]

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.

[Gulf]

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.

[UtahBeehiver]

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.

[mikku]

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!

[Gulf]

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!

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.
Just Say'in
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.

[mikku]

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.

[david s]

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.

[mikku]

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!

[wotavidone]

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.

[stonecutter]

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.

[mikku]

Re: Home brew concrete and cast-in-place concrete.

Same here, but concrete is not my business- all kinds of little to bigger carpentry jobs are. But it always pops up. Sometimes you must have small batches of concrete and delivery cost really eats up money fast. For around the house stuff, I have had sand and stone delivered - 3 to 5 m3 loads. Anything left over, instead of leaving a pile, I put into 5 gallon-size UV resistant mesh sand bags. Just put the bag into a 5-gal plastic bucket and fill to the top and tie it closed! Crushed stone sells for about $24 per ton.

These bags of sand or crushed stone can be easily stacked up out of the way.
When I need some concrete for any little job. One sand, one stone, 1/3 bag portland and I get 1/30m3 mix of concrete. By weights- the sand is 27kg, stone is 31kg, 8.3 kg portland. And there is another bucket that is marked for water. Mostly consistent concrete--variable is if it rained and the sand/stone is wet. Really have to be careful.

I don't have a mixer but use a heavy-duty rubber 65liter bucket, plaster people sometimes use them here. Mix with a Toshiba heavy duty drill (actually designed only for mixing).. That was about $400 several years ago but over time has mixed a lot of stuff. Just the right speed to blend. Always start with water, then portland to make slurry, then sand, finally crushed stone. 1 container takes about 3 to 4 minutes to mix??? Really don't know-- but you have to place it near where you are working because you cannot carry it full. Just mix and dump.

For better concrete, can add some finer sand and portland, always watching the water. Using this drill however, you are stuck with a slightly wet mix.

[david s]

Re: Home brew concrete and cast-in-place concrete.

I think it is good planning to make the supporting slab waterproof by adding an admixture.this prevents water wicking up from the base after torrential or extended rain periods.

[mikku]

Re: Home brew concrete and cast-in-place concrete.

David S- Hello!
What material would you use as an admixture to do that?

[mikku]

Re: Home brew concrete and cast-in-place concrete.

Gulf- Hello!
David S warned me about getting the water out as well! I finished the main insulation this afternoon (other thread) and was B.S. ing with an electrician friend--telling him all about WFO's and did a quick calculation. Yesterday and today- I plastered on about 80 liters of water in this pericrete mix. That is over 20 gallons of water! Wow!!!! I even wet the dome so that the water would not immediately suck out of the mix...where the water hit yesterdays' work--zap and it was gone!

Tomorrow, I have to put the heavy wheels on and roll the entire thing next to the garage door, some sun and wind. With a chimney in place and the rest of the insulation in place --by next week, I was thinking about some kind of an initial dry-out. I saw the "Kanagi Dude- Heat Bead Cure" thread, and for the life of me could not figure out what a heat bead might be. After looking at the photos--what it looked like are "charcoal briquettes"--Is that an area name for the same thing?

What is the "real poop" on them? Too hot they burn up firebrick or refractory or what?

I did not read your entire thread--I will have to and pick up the tips mixed up in the text.

(Other note): The formwork just takes a little time, playing around with a compound slide miter box. Once the angles are set- the ring cuts are the same, inner form and outer form. Just the length of the leg changes. It can be laid out with a template on plywood, by simply dividing to make a 16 side figure. No magic.

Really I was just playing with the form and once it was completed, thought it was a waste of time not to fill it with refractory..That is when this all got started!

A very-very long time ago, I did some refractory work at a site that processes taconite ore into pellets. Their kilns are huge! I worked many weeks on making a form for the "dam" inside one of these kilns--at that time, it was the first time an APGreen contractor ever poured this section in one piece. There were probably thousands of bags that went into this single casting. On top of that, the form had to be made then disassembled to a size that would fit into the kiln opening door! As a "refractory carpenter", I got an "adda boy" thumbs up when the form held and a reminder to get back to work on a special form for a recuperation duct. Funny how some work experience gives a little confidence to try a new hobby.

[david s]

Re: Home brew concrete and cast-in-place concrete.

David S- Hello!
What material would you use as an admixture to do that?

The stuff I use is called Xypex C 1000 NF, it does a number of things, one of them being to make the concrete waterproof. This brand may not be available to you, but something similar should be. It is expensive.