Size of concrete mixer and water to add?

Posted by scorpionleather on July 7, 2009, 5:37 pm

I'm a newbie to pouring larger quantities of concrete/mortar/cement. I have
a batch I'll need to mix of 3 100 lb bags white portland cement and 5 100 lb
bags of tiny pebbles. What is the smallest size mixer I can rent that will
do this batch all at once? The local rental has 6 cu ft and 9 cu ft
tow-behind mixers. How much water should I add initially? I am afraid of
accidentally adding too much water or if I'm too cautious and add it too
slowly maybe it would take away a bit from my troweling working time. How
long to leave it spinning round the mixer?

Posted by Colbyt on July 7, 2009, 6:50 pm

> I'm a newbie to pouring larger quantities of concrete/mortar/cement. I
> have a batch I'll need to mix of 3 100 lb bags white portland cement and 5
> 100 lb bags of tiny pebbles. What is the smallest size mixer I can rent
> that will do this batch all at once? The local rental has 6 cu ft and 9
> cu ft tow-behind mixers. How much water should I add initially? I am
> afraid of accidentally adding too much water or if I'm too cautious and
> add it too slowly maybe it would take away a bit from my troweling working
> time. How long to leave it spinning round the mixer?

Considering you need sand also I doubt you will get it in one mix.

Without looking it I can't recall the recipe but something like 400-600
pounds of sand (or more) is needed for that much Portland.

BTW Portland is 94 lb bags.

Got up and got the book off the shelf.

A 5 cubic foot batch is:
105 pounds of cement
51 pounds of water
231 pounds of damp sand
315 pounds of stone

Water weights about 8 pounds per gallon. Start with less and temper it with
more if you need to.

So as you can see, you may want to revise your recipe a little.

--
Colbyt
Please come visit www.househomerepair.com

Posted by scorpionleather on July 7, 2009, 7:09 pm

I should clarify: the tiny pebbles appear to be the sand. The grains of
these "pebbles" are no more than 1mm to 2mm wide. So it's like a very
coarse sand. I didn't come up with the recipe; I picked up all the bags
from the warehouse according to their formula for a certain appearance.
Unless somehow they made a major goof up and forgot to give me some fine
sand. But I'm pretty sure that what they call "mini pebbles" is actually
the coarse grain sand.

With this clarified, how large of a mixer to rent?

Posted by Jon Danniken on July 7, 2009, 9:07 pm

scorpionleather wrote:

> I should clarify: the tiny pebbles appear to be the sand. The grains
> of these "pebbles" are no more than 1mm to 2mm wide. So it's like a
> very coarse sand. I didn't come up with the recipe; I picked up all
> the bags from the warehouse according to their formula for a certain
> appearance. Unless somehow they made a major goof up and forgot to
> give me some fine sand. But I'm pretty sure that what they call
> "mini pebbles" is actually the coarse grain sand.
> With this clarified, how large of a mixer to rent?

Since you have what seems to be a specialized mixture, you might want to ask
the company from whom you obtained the "recipe".

Jon

Posted by ransley on July 7, 2009, 6:54 pm

> I'm a newbie to pouring larger quantities of concrete/mortar/cement. =A0I=

have

> a batch I'll need to mix of 3 100 lb bags white portland cement and 5 100=

> bags of tiny pebbles. =A0What is the smallest size mixer I can rent that =

will

> do this batch all at once? =A0The local rental has 6 cu ft and 9 cu ft
> tow-behind mixers. =A0How much water should I add initially? =A0I am afra=

id of

> accidentally adding too much water or if I'm too cautious and add it too
> slowly maybe it would take away a bit from my troweling working time. =A0=

How

> long to leave it spinning round the mixer?

No sand?, save money and have it delivered mixed.

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