# Forum Home Renovation Brickwork  Core-Fill Grout Mix

## Craigoss

Hi Guys, 
I have a small block wall which needs core filling, they are 200 series blocks, 4 courses high and 5m long. I intend on mixing the grout in a mixer, however I haven't not been able to find the relevant grout mix to use. I know the most logical thing to do is order a truck, but I only need a small quantity of < 1m3, weekend cartage is expensive and I don't have anyone to assist.  
Can someone provide the appropriate mix for the grout? 
Thanks.

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## phild01

I have used 1 cement to 2 coarse river sand.

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## joynz

Most good sand and screening suppliers will have a premixed 'Core fill mix' (screenings and sand mix) for this job that you just add cement to.  They will be able to tell you the amount of cement you need too. 
Check the volume needed.  We work out that you need less than 1 cubic metre (for a 200mm wide block 0.00741 cubic metres needed per block.  For 50 blocks, you need 0.4 cubic metre approximately.

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## Craigoss

> Most good sand and screening suppliers will have a premixed 'Core fill mix' (screenings and sand mix) for this job that you just add cement to.  They will be able to tell you the amount of cement you need too. 
> Check the volume needed.  We work out that you need less than 1 cubic metre (for a 200mm wide block 0.00741 cubic metres needed per block.  For 50 blocks, you need 0.4 cubic metre approximately.

  Thanks I didn't realise you could get premix from landscape suppliers. How much cement do you use with this pre-mix?

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## phild01

2 to 1, was the block makers recommendation with river sand though a coarser aggregate might need less cement.
  Don't forget to rod it.

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## Craigoss

Still having some trouble getting this mix correct.  
Boral suggest:
• Characteristic Compressive Strength 20MPa;
• Cement content not less than 300kg/m3;
• Round aggregate (if any) not bigger than 10mm;
• Clean sand (salts can leach through to the face); and 
I a nice round figure of 1m3 of corefill. So the above would suggest I need 15 bags of 20kg cement. I rung around this morning and Newcastle doesn't appear to have anyone which sells a premix of corefill aggregate. So I need to work out the riversand/10mm aggregate/cement mix.

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## Moondog55

No way I'd be mixing a cubic metre by small tub machine, it takes almost forever
Why not simply use standard  mix using 6mm aggregate and specify 20mPa?
Even counting weekend rate it may workout cheaper, it can even workout cheaper to take a day off work and do it during normal delivery times

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## phild01

> No way I'd be mixing a cubic metre by small tub machine, it takes almost forever
> Why not simply use standard  mix using 6mm aggregate and specify 20mPa?
> Even counting weekend rate it may workout cheaper, it can even workout cheaper to take a day off work and do it during normal delivery times

   Actually a mixer for 1 m3 is good, I did a m3 of concrete in a day using buckets to get it all under the house.  Hard work but the core filling is easier than what I did.  Also you can pace yourself through the day rather than getting it all in one big lump.

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## phild01

20mpa is a not strong mix so I reckon you could stretch it to 2 sand, 2 small aggregate and 1 cement.  At the strength specified, almost anything goes...correct me if I am wrong. 
Re-think
Grouting mix needs plasticity and the delivered stuff has it all worked out with ash and plasticisers.  I would *not use* the aggregate for hand mixing and go with what I originally said.  2 river sand and 1 cement and it needs to flow.  The aggregate will slow that aspect of it.  We barrow mixed until it was runnier than toothpaste (not watery though, if you know what I mean).  The blocks quickly absorb excess moisture and become quite wet at the base.  The walls were 2m high.

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## Moondog55

https://www.google.com.au/url?sa=t&r...B-HGVLSLRfgz1A 
■ Grout is to have a characteristic cylinder
compressive strength (f'c) of 20.0 MPa. Note the
maximum value of grout strength (f'cg) used for
design is 1.3 times f'uc ie, 1.3 x 15.0 = 19.5 MPa.
Where possible pre-mixed grout should be used
and, when ordering, specified that it is for
grouting blockwork incorporating reinforcement;
a minimum cement content of 300 kg/m3 is
required. If the grout is to be site-mixed, it should
be mixed in a tilting drum paddle mixer and must
flow freely without separation of the aggregate.
The aggregate should be rounded gravel where
available and preferably 5 mm to 10 mm in size.
The following proportions should be used:
Cement 1 part
Hydrated lime up to 1⁄10 part
Mortar sand 3 parts
Aggregate 2 parts
Although I don't know why a free flowing standard concrete mix couldn't be used I'm sure there is a good reason, I think that grout recipe mix also needs vertical rebar ( you can get concrete with Stainless Steel wire already mixed in but from memory it is high strength stuff and expensive)

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## Craigoss

Thanks for the information. I've tub mixed 1.5m3 in the past for some deck footings which took a day. 1m3 of 20/20 is about $580 for a saturday rate for a small shed I poured a few years ago. Compared with this wall footing which was poured last week for $220 per cube. Unfortunately I have to mix this myself, I wouldn't be able to fill 200 blocks in the 30mins truck wait time, and I don't have anyone to assist.

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## Moondog55

Uni Grout 
No idea how the cost compares

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## Craigoss

> Uni Grout 
> No idea how the cost compares

  Unigrout is $25 a bag (20kg), 100 bags per cube or $2500, plus you have to mix yourself.

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## Moondog55

> unigrout is $25 a bag (20kg), 100 bags per cube or $2500, plus you have to mix yourself.

  *ouch!*

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## joynz

I think you are estimating for too great a quantity of core fill unless your blocks are like the TARDIS.

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## Tools

> I think you are estimating for too great a quantity of core fill unless your blocks are like the TARDIS.

  I agree. For 50 blocks you will only need about 0.4m3 
Tools

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## Craigoss

> I agree. For 50 blocks you will only need about 0.4m3 
> Tools

  Not sure where the 50 block count came from, but I have 220 blocks in total, but they are a mix of 100 and 200 series sizes. I have calculated the correct amount based upon the boral specifications.

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## phild01

> Not sure where the 50 block count came from, but I have 220 blocks in total, but they are a mix of 100 and 200 series sizes. I have calculated the correct amount based upon the boral specifications.

  _"small block wall which needs core filling, they are 200 series blocks, 4 courses high and 5m long" _ 5000/400x4=

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## Pulse

http://premierconcrete.com.au 
in wallsend does a trailer mix. I'm sure they'll mix up what you want.  
I'd buy an electric vibrator from eBay, $80 mine was, does the trick, get a mate or two, the trailer mix goes hard quick   
Sent from my iPhone using Tapatalk

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## phild01

> Premier Concrete | Home 
> in wallsend does a trailer mix. I'm sure they'll mix up what you want.  
> I'd buy an electric vibrator from eBay, $80 mine was, does the trick, get a mate or two, the trailer mix goes hard quick   
> Sent from my iPhone using Tapatalk

  Used them once, try a quiet day because the trucks get priority.

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## Tools

> Not sure where the 50 block count came from, but I have 220 blocks in total, but they are a mix of 100 and 200 series sizes. I have calculated the correct amount based upon the boral specifications.

  From this:
I have a small block wall which needs core filling, they are 200 series blocks, 4 courses high and 5m long 
5m long is 12.5 blocks x 4 courses = 50 blocks. 
Even if we forget that the cores are only a percentage of the block, total wall volume is 5 x 0.19 x .8 = 0.76m3. Is your wall bigger than what I have just calculated? 
Tools

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## Pulse

great way to get 0.5m3 though  
Sent from my iPhone using Tapatalk

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## Craigoss

> From this:
> I have a small block wall which needs core filling, they are 200 series blocks, 4 courses high and 5m long 
> 5m long is 12.5 blocks x 4 courses = 50 blocks. 
> Even if we forget that the cores are only a percentage of the block, total wall volume is 5 x 0.19 x .8 = 0.76m3. Is your wall bigger than what I have just calculated? 
> Tools

  Yeah sorry I didn't provide all the detail, I listed a 5m section just to provide the scale of the project (small job rather than building a house/extension). I have about 30 linear meters of dwarf block wall to construct (some walls are 4 courses high, some walls are only 2 courses). See picture below with the footings poured, I have 6 different levels with a mix of the 90mm and 190mm wide blocks.

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## Tools

ahhhh, that makes more sense. 
Tools

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## Moondog55

So not a load bearing wall?
If not load-bearing why does it need filling?

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## Craigoss

> So not a load bearing wall?
> If not load-bearing why does it need filling?

  The 200 series blocks are loading bearing (verandah floor and tin roof load), I'm building as per engineers specifications. As usual they specified over the top requirements in order to meet the mine subsidence board.  400 x 400 footings with no loose ends for a 2 course high garden wall  :Doh:

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## Craigoss

Just an update for you guys. Got the blockwork done on saturday, there was one bricklayer and 2 laborers. The core filling took about 6 hours to complete by myself. The materials ended up costing about $200. 
0.8 gravel
0.5 sand
16 bags of cement

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## phild01

Well done, looks like you have plenty more work to do now.

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