To understand which mixer will fit your application we have put together a quick tutorial on how cement is made. This guide will help you make a more informed decision on which machine is right for you. When making cement you want to start off with one bag (usually 80 lbs.) of Portland cement. Next you add sand gravel and water to your mixture. The breakdown of this combination is as follows:
1 bag of Portland cement (80 lbs) Sand (180 lbs) Gravel/P-Gravel (240 lbs) ______________________ = 500 lbs of material
Please note: 1 bag of Portland cement is equal to about 6 (80 lb) bags of Pre-mix (Pre-mix is a mixture of Portland cement, sand and gravel to which you only add water to)
When buying a mixer you must take into consideration the overall cubic feet of the unit. Most manufacturers will say that the total volume of the drum is 9 cubic feet or the capacity is 9 cubic feet. This 9 cubic feet is really about 6 cubic feet of batch output for your pour (remember concrete mixers do not mix straight up and down they mix on an angle which means the entire drum is not used all at once, only about 2/3 of the capacity will be used).
Another way of understanding how much the unit can mix is to take a look at the total weight the cement mixer can actually mix in one batch. If a cement mixer is rated at 250 lbs, then you must remember that 1 bag of Portland cement requires 500 lbs of material. This means that the machine will be able to handle 1/2 a bag (80 lb) of Portland cement plus sand, gravel and water in the cement mixer.
BE CAREFUL: Some people get confused between Portland cement and Pre-Mix and some manufacturers will base batch capacity on Pre-Mix for their concrete mixers since a lot of consumers will purchase Pre-Mix from their local Home Depot or Lowes. Pre-Mix is more efficient for almost all jobsite applications.
So you must ask or realize that if the machine has a rating of 1-2 bags and it is only a 5 cubic foot cement mixer it is based off of pre-mix bags. Because 2 bags of regular cement or (Portland cement) would require a 1000 lbs of mixing material to complete the job and no towable mixer can handle that, only an industrial sized batch plant.
Other things to consider is how the machine is powered, do you need a gas or electric mixer, that all depends on how or where you plan to mix. If you are on a jobsite and power is not easily accessible then gas is the way to go, if you are mixing indoors or have a generator on site, electric is a great alternative as its quiet and requires a lot less maintenance then a gas engine.
Concrete Mixing Tips:
Volumes & Weights of Materials
* 1 Bag of Cement = 88 lbs.
*1 Cu ft. Sand/Gravel = 85-100 lbs. * 1 Cu. ft. Plain Concrete = 140-150 lbs. * 1 Cu. ft. Water = 62-65 lbs. * 1 Gallon of Water = 8.33 lbs. * 1 Cu. Yard = 27 cu.ft.
* Average maximum load = 200 lbs. * 2 cu. ft. = 6 sq. ft. 4" thick * 2 cu. ft. = 8 sq. ft. 3" thick * 1 yard = 27 cu. ft. * 1 yard = 80 sq. ft. 4" thick * 1 yard = 108 sq. ft. 3" thick * 1 80 lb. bag = 2/3 cu. ft. * 1 80 lb. bag per fence post
How to Mix Sand & Gravel
* Use an 8-1/2 x 12" square point shovel. * Portland cement, gravel or round stone and masonry sand. * Start mixer in motion. * Put in 2 gallons water. * Add 6 shovels full of gravel or round stone. * Add 2 shovels full of Portland cement. Slowly add 4 shovels full masonry sand * NOTE: WATER WILL VARY ACCORDING TO MOISTURE CONTENT OF SAND & GRAVEL.
How To Mix Concrete
* You will need approximately 2-1/2 gallons water. * Two 80 pound bags pre-mix concrete. * Start mixer in motion. * Put in 2 gallons of water. * Add one 80 pound bag of pre-mix concrete * NOTE: MIXTURE WILL BE VERY SLOPPY * Slowly add 2nd bag of 80 pound pre-mix concrete. * Add 1/2 gallon water slowly to obtain desired thickness.
Buying a mixer is a large investment, if unsure of what size machine you will need, try renting one from a rental house, Home Depot or Lowes. This way you can also speak to an expert about the costs of ownership for replacement parts or what customers near you are purchasing and what the sales have been on certain machine sizes.