# Forum Home Renovation Concreting  Mixing rapid set and regular bagged concrete?

## Micky013

Hi guys  
Maybe a dumb question but ill ask anyway..... Doing a 30m run of post and rail fencing and i need about 45 bags of premix concrete. To save on cost can i mix rapid set with the cheaper stuff (half price) and expect it to work??

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## Pulse

probably not, I'd use dirt packed around base to hold temporarily then backfill the rest of the hole with regular concrete. You could use rapid set in the base but I wouldn't mix them. I've found rapid hard to work with, can't mix it conventionally in a mixer  
Sent from my iPhone using Tapatalk

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## Micky013

Thanks. I did the back fence a couple days ago and used all rapid set. Worked well but pricey. This fence is nearly 3 times longer so much more expensive. Might just have to use the normal stuff

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## Marc

Rapid set is rubbish, (non structural) If you must have the concrete set quicker, just add a little bit of accelerator with emphasis on "little"  :Smilie:

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## Micky013

Im talking baston quickset hightstrength 40mpa - bunnings of course. Where can i find this accelerator?? Cheers

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## Marc

Any hardware store would stock it.

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## sol381

just buy a half m2 of concrete blend and 4 bags of cement.. always the cheapest way to make concrete..30m run of fence is about 13 posts. so id say bag and a half per post anyway...20 bags..

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## Moondog55

Speaking from experience and some expert advice from concrete packaging companies adding ordinary mix to rapid set works if its 1 bag of rapid set to 2 bags of normal concrete mix but it is much cheaper to batch it up from scratch and if you want 40+ rating you can just add a 5 litre bucket of builders cement to each batch of premixed
Easiest way to get strong concrete is to use the correct recipe and batch mix with minimum water.
While most people would start with the gravel the correct method is to start with the cement and fines, add the water and additives mix until smooth and creamy then add the correct amount of gravel
For a fence I would be using stabilised earth anyway heavily rammed

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## Random Username

Calcium chloride (the Damp-Rid stuff you can find in Bunnings) at a maximum of 2% cement volume works as an accelerator. 
Simply shovelling the dry mix into the hole and letting it hydrate over time, will, surprisingly, give you a strong enough concrete for post purposes.  ASABE Technical Library :: Abstract 
and  http://www.renovateforum.com/f211/dr...od-use-100858/

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## Bloss

mmm - not sure what happens in Adelaide, but in Canberra (not known to be a cheap place for building supplies!) Bunnings sells ordinary QuickSet for $7 a bag Australian Builders 20kg Quick Set Concrete | Bunnings Warehouse , Regular Concrete mix for $7.50 a bag Australian Builders 20kg Concrete Mix | Bunnings Warehouse and the Bastion High Strength for $8.45 Bastion 20kg Quick Set Hi-Strength Concrete | Bunnings Warehouse. 
But if this is a simple post and rail fence as it seems then regular rapid set is fine - why would you use a high strength mix? But as I said in another post the Sika from is a good choice here too Sika 979ml Post Fix | Bunnings Warehouse at $27 a little dearer than the three bags a hole (if the holes are dug to the proper depth & size) , but especially for one person a really easy option.

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## Bloss

> Rapid set is rubbish, (non structural)

  Not rubbish - it is fit for its intended purpose which is specifically non-structural, but great for fences and other places where is is recommended for  use. A time saver and plenty strong enough when used as per instructions.

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## Bloss

> Speaking from experience and some expert advice from concrete packaging companies adding ordinary mix to rapid set works if its 1 bag of rapid set to 2 bags of normal concrete mix but it is much cheaper to batch it up from scratch and if you want 40+ rating you can just add a 5 litre bucket of builders cement to each batch of premixed
> Easiest way to get strong concrete is to use the correct recipe and batch mix with minimum water.
> While most people would start with the gravel the correct method is to start with the cement and fines, add the water and additives mix until smooth and creamy then add the correct amount of gravel

  Mixing different cement mix types is recipe for not knowing what is the strength and performance of the resulting concrete so IMO is not a good idea. Likewise simply adding cement in the hope of getting to some higher strength final result is guesswork and again not a good idea. If you really need to get a known strength then you need to use ready-mix specced to give it (and contracted to a performance level), use a rated pre-mix to the Australian Standard AS3700, or if you know what you are doing mix yourself to proportions recommended by the published standard. 
As to mixing - not so much 'minimum water as the correct amount. And trying to mix in a cement mixer using fines & cement (i.e.: not using packaged concrete mix) then water then aggregate is likely to end in tears. I have never seen any professional do it that way. In a mixer water (not all!) would be first in then gravel/ aggregate (the actual amount varies - I have seen all go in) then half (or whatever chosen) of fines/sand then all cement, mix well then add remaining sand/gravel. Water is added as needed to get the right mix - often done by sight and so experience as the fines (and to a much lesser extent aggregate) can vary in moisture content - so very dry fines needs more water, wetter fines needs less. I know some prefer to put gravel in first then water then fines & cement and so on, but my experience (and my Dah & his!) is that the miser stays cleaner and it is easier get water in first. 
If mixing in a mixer using bagged mixes then again add around half the water in first (having worked out whether your mixer can take two or three bags and the relevant amount of water), put in the dry mix and mix for a few minutes then add more water as per the instructions on the bag. In this case the mix will be very dry so no need to vary. Note that mixers can be vicious so take care putting anything into a moving drum. 
When having to barrow and place concrete as a one person job then after the mix has been poured into the barrow a fresh lot of water is added to the mixer which is left to run while the barrow is emptied. Then when the gravel is added and then some sand then cement and so on. The sequence of water, then coarse then fine then cement reduces the likelihood of lumps and mix sticking to the lower parts of the drum. Having the water in while emptying the barrow means the mixer drum stays wet and any remnants do not stick or dry up inside the drum or on the paddles/ mixer arms. 
If you buy AS3700 Builders or GP cement then it complies and does not need any added cement, but will need to have the posts supported for at least 24 hours. Rapidset/quickset will allow you to get on with rails the same day.

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## Marc

Rapid set = rubbish ... I say so because when it seems ok at first, if you can work as quick as it sets, the reality is that it cracks later, and there is a long winded explanation as to why. I am sure it has it's market or they would stop selling it. 
I agree with your way of mixing with a cement mixer absolutely. Half the water and half the gravel or gravel and sand mix if you use that product. Starting with water and cement first is likely to leave a lot of cement caking the bottom of the mixer.  
As far as the original question by the OP, considering rapid set is just ordinary concrete mix with accelerant, there is clearly no harm in mixing a couple or even 3 ordinary concrete mix bags with one rapid set. The end result will be a faster curing mix. By how much is anyone's guess, but experimentation with a measuring cup is not rocket science. The final strength of the concrete will be just the same as the original bags separately and considering it is fence posts and not a lintel, clearly it does not matter a bit. And I venture to say that the final product will be a much better one then rapid set on it's own. 
But that is just my taking.

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## Bloss

With Rapid Set it is important to follow the instructions - and that means NOT mixing with water and then trying to use as though it is regular GP concrete, but putting water in the hole then pouring the dry mix in to it.
See for e.g.: Rapid Set Concrete - Cement Australia 
Trying to ix it up like general purposes concrete is why many people get into trouble with it. Likewise cracking is rare when used properly and according to instructions , but happens often when too much angular force is out onto posts too son after using the concrete. 
Of course reading instructions is against all male instinct until after a failure . . . . :Redface:  :Wink:

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## Marc

Instructions? what instructions? ... ha ha

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## Moondog55

What is common practice with making concrete on site Bloss is not actually best practice and never has been
Best practice is as I described The fact that most people still manage to make strong concrete is merely showing how strong ordinary concrete actually is in practice and how easy to work with and points out that most cement mixers on sale are rubbish and built to a price point
Maybe most of those on sale should be described as mortar mixers
Minimum water and maximum mixing is much stronger even with low cement ratios

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## Marc

Hi Moondog, To mix bricky mortar in a cement mixer is actually very difficult. Mortar mixers are a different beast. Mortar is too sticky (or should be) for concrete mixers.
PS
Just googled "how to mix concrete" to find an illustration to post ... mm ... too funny. I spare you the pain.
The best must be the one who tells you ... open the bag of concrete mix, poor in the mixer, start it and then add water. Love it! And he says it with a straight face after stating he has mixed 400 bags that way ...  :Smilie:

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## pharmaboy2

> What is common practice with making concrete on site Bloss is not actually best practice and never has been
> Best practice is as I described The fact that most people still manage to make strong concrete is merely showing how strong ordinary concrete actually is in practice and how easy to work with and points out that most cement mixers on sale are rubbish and built to a price point
> Maybe most of those on sale should be described as mortar mixers
> Minimum water and maximum mixing is much stronger even with low cement ratios

  "Minimum water"?  - are you a civil engineer? 
i ask, because while that's a common statement, concrete strength is a combination of factors, and how well it is worked is critical - dryish mixes make compaction and void filling extremely difficult.   Other aspects such as grading of aggregate and shape of aggregate make a large difference as well (not to mention, concreting sand) 
all in all, site made concrete is only good for minor work - all critical work (suspended slabs and beams) should be highly specified from specified suppliers and placed correctly. 
too much water makes  concrete difficult to finish, as all on the ground concretors are well aware.  All these arguments are pointless however when talking about a small mixer on site, because a mixer can't make enough concrete to complete any important structural work.

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## Marc

> ...a mixer can't make enough concrete to complete any important structural work.

  A chinese/bunnings mixer maybe not, but I remember contracting a concreter to pour the concrete for a two storey building. Footings, columns, first floor slab, more columns and second floor slab/roof. All done with a medium size mixer of some 10 buckets capacity, filled by hand with buckets filled by hand with shovels by a team of 6. Concrete lift up and distributed with wheelbarrows by another 2 or 3 guys.  
No concrete trucks and no pumps. Building still standing with no cracks nor leaks 30 years later

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## pharmaboy2

> A chinese/bunnings mixer maybe not, but I remember contracting a concreter to pour the concrete for a two storey building. Footings, columns, first floor slab, more columns and second floor slab/roof. All done with a medium size mixer of some 10 buckets capacity, filled by hand with buckets filled by hand with shovels by a team of 6. Concrete lift up and distributed with wheelbarrows by another 2 or 3 guys.  
> No concrete trucks and no pumps. Building still standing with no cracks nor leaks 30 years later

  Jeesus!  Not a bunch of 457 visa workers by any chance?   :Wink:  
anyway, cement concrete aggregates asutralia specifically recommends for site mixing 
"When site mixing, begin by loading a MEASURED AMOUNT of coarseaggregate into the mixer drum. Add the sand before the cement, both in measured amounts. "

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## woodbe

Aren't "BUCKETS" a useful measure?

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## pharmaboy2

Buckets are acceptable, shovels are not. 
the former has much opportunity for on site rhyming poems... Must try that in front of the kids as a replacement I think.

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## Bloss

This is a useful guide http://www.elvingroup.com.au/wp-cont...ete_basics.pdf

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## PlatypusGardens

Lots of different methods here....interesting.  
I always get the premixed "builder's mix" (sand and 10 or 20mm stones mixed) by the ute load and allow the best part of a bag GP per mix for fence post holes. 
16-18 shovels of mix, put half in first, lots of water, add the cement dust, more builders mix, mix it up really wet and "dry it out" towards the end with the last couple of shovels of mix. 
Was shown that method by an old brickie years ago and it works for me.  
When mixing in a barrow (very rarely happens) I use the mattock/pick rather than a shovel so I can get right down the bottom of the barrow and mix everything.
I make a "pond" at one end, fill it with water, drag the stuff through, add more water at the other end, drag it through again and it's more or less done.  
Buckets....ain't got time for that. 
When in doubt make it stronger.
Never had anything fall over/crack yet.   :Wink:  
Rapid set....ok for a letter box maybe.    :Smilie:

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## Marc

> Jeesus!  Not a bunch of 457 visa workers by any chance?   
> anyway, cement concrete aggregates asutralia specifically recommends for site mixing 
> "When site mixing, begin by loading a MEASURED AMOUNT of coarse aggregate into the mixer drum. Add the sand before the cement, both in measured amounts. "

   Nee ... probably all illegals. They even stole the electricity hooking a cable to the 3 phase off the street pole. Fun to watch.

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## Marc

After filling in more tons of footings I care to remember, I discovered the existence of sand and gravel mix. 
I remember asking the scruffy looking dude at the landscape supplies what was the ratio they used to mix it, to what he replied, 3 gravel 2 sand.
Beauty I said ... 3+2 would add to more or less 4 in volume right?
The answer came rather quick and included bloody wogs and other niceties, ha ha
But I was correct of course and 4 in volume with one volume of cement will give a strong mix of 3/2/1.

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## Micky013

Just having a read through .... Some helpful stuff in there.  
Anyways, did the job yesterday and bit the bullet and just bought 40 bags of high strength rapid set. Reason for buying the high strength is purely that it was only .45c dearer per bag than regular rapid set and seeing as the fence was 2.1 and another 2.4 in areas i didnt think it would hurt being 40mpa.  
I had to fix up a crappy path that the neighbour had, that i broke in process of fencing. All i had was one bag of rapid set and two bags of the conpac $4.50 rubbish. It went off in 30 mins. So i guess i could have gone down that road but for the sake of $200 and not knowing if there would be any repercussions for mixing concrete types, i figured it was best to just go with what i know.  
I will save the 3,2,1 mix ratio though. Next time ill buy the premix sand and gravel.  
Thanks!!

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## PlatypusGardens

> Bastion High Strength for *$8.45* 
> Bastion 20kg Quick Set Hi-Strength Concrete | Bunnings Warehouse.

  Good for you.
We pay NTH QLD tax on that....      :Shock:   
Can't find the "Australian Builders" products you mentioned.
The Sika goo is the same price here though.... 
go figure    :Unsure:

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## Micky013

Wow, thats crazy.

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## PlatypusGardens

Yep 
The price we pay for living in paradise.....

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## woodbe

> Buckets are acceptable, shovels are not.

  Marc said:   

> filled by hand with buckets filled by hand with shovels

  So unless he didn't mean what he wrote, the mixer was filled with BUCKETS, not shovels. 
Or are you not supposed to fill the buckets with shovels? lol.

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## PlatypusGardens

> Marc said:   
> So unless he didn't mean what he wrote, the mixer was filled with BUCKETS, not shovels. 
> Or are you not supposed to fill the buckets with shovels? lol.

  
As long as you do it all by hand it should be ok   
I think.

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