# Forum Home Renovation Concreting  GMC Concret Mixer

## Chipman

I am not sure that this is the right place for this ... 
Has anyone bought one of the GMC concrete mixers currently $289 at Bunnings? 
How do they perform for typical DIY tasks? 
Trying to work out if it is better to buy one or hire a mixer (Kennards $48 per day)  I will need one for several days so if it is any good, it will work out cheaper. 
Regards  
Chipman

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## Burnsy

They are OK but not brilliant, better to buy second hand brand name unit.  Spin a little to fast so you need to make sure morter mix starts wet and you add to it to get it to the right consistency as if it is dry it sticks to the bowl due to the excessive centrifugal force and does not mix.

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## Vernonv

I started out hiring a good cement mixer to do some post holes, I then borrowed a mates GMC to do some more concreting and eventually bought my own GMC (this is the CMX000 model). 
I've done many, many metres of concreting with my GMC and have found that it behaves just like the good hire mixer. The only time I've run into problems like Burnsy had (not mixing thoroughly) was due to the mixer not being on level ground ... once I leveled it up it mixed fine. Not sure the speed is an issue (I didn't think it ran fast??). 
Note that GMC have discontinued the mixer, so if you want one, you need to be quick ... downside is that warranty replacement will be an issue.

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## Chipman

Thanks Burnsy and Vernon, 
Really appreciate the information... It is the GMC cmx000 and Bunnings (Bayswater Vic) had 4 of them. I have bought one and will be using it this wekend so I will let you know how it goes. 
Regards, 
Chipman  :Smilie:

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## Bloss

If it is running too fast then I recall that the pulley on the motor can be changed relatively easily. Levelling up is always an issue too - with all mixers. 
Most el cheapo mixers (and even some dear ones) have simple and poorly designed breaking blades inside the bowl. I have altered a few by simply welding on some addition pieces of steel bar in appropriate places to give more tumbling and better break up of the mix - varies according to the design of the mixer, but a simple job for a mate with a welder (or you if you have one).

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## Chipman

> If it is running too fast then I recall that the pulley on the motor can be changed relatively easily. Levelling up is always an issue too - with all mixers. 
> Most el cheapo mixers (and even some dear ones) have simple and poorly designed breaking blades inside the bowl. I have altered a few by simply welding on some addition pieces of steel bar in appropriate places to give more tumbling and better break up of the mix - varies according to the design of the mixer, but a simple job for a mate with a welder (or you if you have one).

  Yes, I do a bit of welding.... Could you give me a bit more of an idea how you modify the blades inside?. These are simple bars about 30mm wide. Seems to be quite a commonly used setup.  
Thanks, 
Chipman

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## Bloss

I haven't modified a GMC one, but in most instances the issue is that the tumbler bars do not protrude far enough towards the bottom 'corners' of the mixer and as it churns the centrifugal force allows the drier bits to accumulate there. Many are welded onto the side walls of the mixer well up from the base using a single bent piece of steel welded at each end with one or more stand-offs in between. 
I simply cut a suitable length of mild steel plate (the same width as the existing tumbler bar and a similar thickness (usually 5-6mm) so that it extends further into the 'corner' on each one. I have had them go to within about 50mm of the corner. Simply use vice grips to hold it into place and weld. In one case I used vice-grips and did a few mixes just to get the piece in the right place then welded. 
If in use you find that material is getting trapped you can grind the end off a bit or if it needs to go a bit deeper weld another small piece on. On one mixer (an old Lightburn made in SA) I extended to about 15mm from the bottom. 
Of course in use there are a few rules - water in first then aggregate then  sand and cement. Depending on how big the mixer is and your shovel (proportions are important, but so long as you are consistent with the load on each shovel full the ratio - eg: 3:2:1 - is what is important, not the measuring tool) and after while you get to know how much water is needed and will tell by just looking (and hearing the 'right' sound as it mixes). 
Always start with less water then top up to get the right consistency - the mix should be wet enough to hold its own weight with just a little slump most mixes (including from commercial trucks) are too wet. Too much water weakens the resulting concrete although of course makes placement easier (that's why in commercial sites they test every batch for compliance). 
For most residential use this is not so important as even the poorest mix still is strong enough. 
Hope that explains it well enough for you.

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## Chipman

Yes, I understand what you mean.... 
What you say about the actual mixing process is very true and I wish someone had of explained it like you have about 30 years ago! I have come to the same sort of procedure as a result of a lot of trial and error. (have also done a lot of mixing by hand in my time while overseas too) Actually one of the reasons I want to mix this lot myself is it is a bit fiddly and will take a bit of time to place (and in an awkward place to reach) ...I have seen some really poor mixes come from your typical garden supply places but usually the bigger companies are more reliable. 
I will see how the mixer performs and if needs be I will modify the bars. Trying them out with vice grips is an excellent tip 
Once again many thanks, 
Chipman

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## Bloss

My advice came from my dear old Master Builder Dad more than 40 years ago!    :Biggrin:

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## Planned LScape

The angle of the bowl has a lot to do with it too 
If it's pointing too far upwards the mix wont get caught in the bars as much and won't mix properly. On smaller mixers you wont be able to make as big a mix as having it at an angle where it mixes the best will mean that once your mix gets bigger or you put in more water a heap will spill out the front. I usually chock up the handle a bit to stop it if it happens, but not to a point where the mix wont be done properly

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## patty

Nothing wrong with them mate I went halves in one with a mate and we have flogged it at both my place and his and its still going strong, I just give it a good hose out and grease it now and then best 150 bucks ever spent!!

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## Terrian

About time I bought a mixer I think, was looking at Westmix (I know they are good) but for around the $500 mark for a 2.2f3 I might just go for the GMC (if they have any left) the price is right, and comments here seem happy with them...

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## Chipman

> About time I bought a mixer I think, was looking at Westmix (I know they are good) but for around the $500 mark for a 2.2f3 I might just go for the GMC (if they have any left) the price is right, and comments here seem happy with them...

  Bunnings in Cantebury Road still had 3 left last Sunday afternoon... 
Chipman

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## GraemeCook

> Of course in use there are a few rules - water in first then aggregate then  sand and cement. Depending on how big the mixer is and your shovel (proportions are important, but so long as you are consistent with the load on each shovel full the ratio - eg: 3:2:1 - is what is important, not the measuring tool) and after while you get to know how much water is needed and will tell by just looking (and hearing the 'right' sound as it mixes).

  OldBoss 
I have always put in water, then cement, then aggregate, then sand as they seemed to mix best in this order. 
But I do not do a lot of concreting so I was wondering how important was the order of mixing. 
Thanks 
Graeme

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## Vernonv

From http://www.concrete.net.au/viewpdf.p...retebasics.pdf   

> 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. NEVER USE A SHOVEL AS A MEASURE AS VOLUMES CAN VARY WIDELY. Mix materials together until there is no visible sand in the mix.  Add enough water to get a workable mix.

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## Chipman

> From http://www.concrete.net.au/viewpdf.p...retebasics.pdf

  Hi Vernon,
I found this info from the same website  http://www.concrete.net.au/viewpdf.p...pdf/Volume.pdf   _With mechanical mixing, two thirds of the water_ _is added first, followed by the coarse aggregate,_ _sand and then cement. After a uniform colour is_ _achieved, add the remainder of the water slowly_ _until a workable mix is achieved, and continue_ _mixing for at least two minutes._ 
This is the way I have always done it. 
It would be nice to know which is the correct way!! 
I always assumed the "mix all dry ingredients and then add water" was the hand mixing method 
Cheers, 
Chipman**

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## Vernonv

There you go, even the "experts" are confused ??? ... the description you provided seems like a more thorough description of the process than mine. If I had to pick one to put money on, I would probably go with yours.

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## GraemeCook

> There you go, even the "experts" are confused ??? ... .

  
Does that mean we are all wrong?   Or are we all right?? 
Graeme

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## Chipman

Well I used the GMC today and it worked well (mixed 0.5 cubic metres) Some water, gravel then cement and add water to get the consistency right. 
I think the bars could be widened in the corners (Oldboss) and the motor got quite warm after 6 loads but wasn't a problem as I had to get the next part boxed up. I wonder what would happen on a hot day working it continuously) 
It was every bit as good as the one I hired last time. 
Chipman

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## Terrian

> Bunnings in Cantebury Road still had 3 left last Sunday afternoon... 
> Chipman

  Yep,was there Saturday morning and saw them, was wondering how stable there were when mixing though (borrowed the father in laws 3.5f3 for this weekends job though, was cheaper than buying one  :Smilie:

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## Chipman

Once it is set up, it is quite stable. I had no problem with it wanting to tip over or anything like that. Now moving it around on uneven ground, then yes it is a little unstable.  Maybe longer axles would help but it is not a big enough problem at the moment to worry about.  
Chipman

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## Vernonv

As Chipman has said, they can be a little unstable when moving them over rough ground, but are more than stable once set up. 
As for running time - I've had mine running non-stop for more than 8 hours (and numerous times for 4 to 5 hours) and didn't have any problems (I didn't bother to feel the motor to see if it was hot). Although I would suggest that any motor doing that job would get hot.

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## Terrian

> As Chipman has said, they can be a little unstable when moving them over rough ground, but are more than stable once set up. 
> As for running time - I've had mine running non-stop for more than 8 hours (and numerous times for 4 to 5 hours) and didn't have any problems (I didn't bother to feel the motor to see if it was hot). Although I would suggest that any motor doing that job would get hot.

  
will let you know later today how warm / hot the motor gets after I have made up about 2.5m3 in the FILs' mixer  :Smilie:  
I have seen other bolt together mixers that would wobble about as the barrel turnered, not a good sight !

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## Terrian

only got about 1.2m3 done today (damn rain) but the motor was warm, but you could easily hold your hand on it and not suffer any burns...

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## emptybucketman

I had a GMC mixer on order at my local hardware since the end of last year but heard nothing.  I saw one second-hand GMC mixer go for over $300 in January on ebay.  Thanks for the heads-up Chipman.  What sort of grease did you use on it?

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## Chipman

> I had a GMC mixer on order at my local hardware since the end of last year but heard nothing. I saw one second-hand GMC mixer go for over $300 in January on ebay. Thanks for the heads-up Chipman. What sort of grease did you use on it?

  Why don't you try some bunnings stores... they might have one, that is where I got mine.  Gave it another good work out today and no problems so the way I see it, at the price I paid, I only need to get another 3 days work out of it and after that, it will be free!  (by comparing the purchase price to the daily hire fee) 
I just used what grease I had... it was the white zinc oxide grease... I am told it is a good water resistant grease. 
Cheers, 
Chipman

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## Feralbilly

Hi All. Have had a GMC mixer for about two and a half years now and done a lot of work with it without any problems. Initially I found that the mix tended to stick to the bowl and not tumble. Cured this by cutting about 5 mm off the bowl stop. Doing this did not noticeably reduce the maximum capacity. I use agricultural machinery grease on it. It is a dark red stuff and sticks like s**t to a blanket. 
Bill

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## Bloss

I am a bit puzzled - my description of mixing concrete matches the description on the website quoted by Chipman. 
Mixing the water then aggregates and sand then cement usually works best as they get thoroughly mixed to take in the cement - a fine dust that can not absorb water well if just thrown in with the water alone and can form lumps that do not unclump easily. 
So in my view the order is important although I have no doubt that on most occasions it would mix OK in any order so long as water is on first - doing the aggregate and sand first when dry tends to have them go to the bottom corner of the bowl and stay there. 
As I said measurement is very important - I just disagree  that it cannot be done with a suitable shovel. I have poured more cubic metres of concrete than I want to think about from mixers loaded with a shovel and have not had a failure. That said novices can as easily use a bucket or other suitable container to get a more consistent accurate, but so long as the volumetric proportions are maintained then a shovel is fine.

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## Terrian

> I
> Mixing the water then aggregates and sand then cement usually works best as they get thoroughly mixed to take in the cement - a fine dust that can not absorb water well if just thrown in with the water alone and can form lumps that do not unclump easily.

  I have always added water first, then 1/2 the stone, then 1/2 the sand, then 1/2 the cement and then repeated, always add the sand & cement slowly, adding extra water to stop the mix getting too dry... 
On another note, got my new mixer last night, a 'Super Mix' 2.2 cubic feet model, 1/2 hp electric motor, nice birthday present (along with an ipod touch) nice wife & inlaws & kids I have (the missus was looking at a new 7x5 tandem trailer, but wasn't exactly sure what I was after, and didn't want to outright ask  :Smilie:

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## Chipman

The GMC got another good work out today... works fine but it IS unstable on uneven ground.... it fell over! 
Nice one Terrian with the birthday present but it means more work! 
Now if I can just persuade the wife to buy a Woodfast lathe..............   
(Actually she told me to go and get one and it is on order) 
Cheers  
Chipman :Smilie:

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## Terrian

> The GMC got another good work out today... works fine but it IS unstable on uneven ground.... it fell over!

  bugger, make mental note, use only on stable ground !   

> Nice one Terrian with the birthday present but it means more work!

  na, not more work, just means I don't have to borrow the FIL mixer  :Smilie:    

> Now if I can just persuade the wife to buy a Woodfast lathe.............. 
>  (Actually she told me to go and get one and it is on order)

   :Clapping:  damn fine missus you have there  :Smilie:

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## Vernonv

Chipman, did the mixer fall over while you were moving it or while you were using it (ie it was stationary)? 
I've certainly aware of it's instability while moving it, but have never had a problem while using it (as long as you make sure it is set up level).

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## Chipman

> Chipman, did the mixer fall over while you were moving it or while you were using it (ie it was stationary)? 
> I've certainly aware of it's instability while moving it, but have never had a problem while using it (as long as you make sure it is set up level).

  
Hi Vernon, 
I have never had any problem while mixing with it, only when moving it.  When I get the chance, I want to widen the axles. 
Regards, 
Chipman :Smilie:

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## Planned LScape

My old westmix mixer had the gong the other week, the handle that you use to empty it snapped off....weak welds and thin tubing. 
I looked at new westmixes and other brands, which were all $650+, I ended up with a Taskmaster from my local garden yard for $345, works a treat! Seems to be made more sturdily, good motor, mixes well, and is very easy to move around. 
I've used it flat out on the last few jobs, probably done close to 60 mixes...hasnt missed a beat yet

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## Theremin

I had a few DIY concreting jobs to do, so I bought one of those GMC mixers from Bunnings.  It did everything I needed it to do.  When I was done, I sold it on ebay for $11 less than I paid for it!  :2thumbsup:

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## Chipman

I was at Bunnings in Bayswater (VIC) buying more radiata and noticed they still have one GMC concrete mixer left for anyone in the Eastern Suburbs who might be looking for one. I have used mine for more than 5 separate days so in comparison to hiring one, it has already paid for itself and like Theremin, I can always sell it on ebay! 
I am not in a hurry to get rid of it... might be useful for mixing mulch and top soil for my garden or washing pebbles.....  
or even wash my clothes when my wife says they are too dirty to put in the washing machine :Biggrin:  
Chipman :Smilie:

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