When placing concrete or hardscape it is critical to have the soil you are going over to be in an acceptable condition for your project and while things like water migration, possible erosion and other factors are really important, the most important aspect of site-prep is compaction! All your efforts at placing a great slab, building a beautiful house, all fall apart if the foundation you are building on fails!
On building sites there are usually two choices that contractors will use to accomplish soil compaction -
A “Rammer” or sometimes referred to as a “Jumping Jack”, these units are designed to jump up and down vertically on a small plate or 'shoe' area at the base of the unit which impacts the soil to achieve compaction.
Or you can use a “Vibrating Compaction Plate” unit to create soil compaction, These units vibrate the soil migrating the particles around and finally “locking” the particles into a non-moving compacted state.
RAMMER COMPACTION PLATE
Both these machines basically do the same job - they compact the soil, but each unit has their own advantages and disadvantages - especially when it comes to soil types and project space limitations. Lets look at each in a little more detail...
SOIL is the first consideration to consider when choosing the right compactor unit - and to keep things simple -soil types can be grouped into 2 major types...
this is soil being made up mostly of clay, silt, very fine particles that are mostly too small to see. This material is easily molded when moist and holds its shape and becomes very hard when dried. (ever have a dirt clod fight with your brother growing up? You probably could have called it a COHESIVE SOIL fight.) when compacting Cohesive soil, a Rammer works best as its ramming action compacts the soil removing air pockets and locking the soil together.
- this is soil consisting of visible chunks of rock, pebbles, sand as well as finer particles. Unlike Cohesive soil Granular soil does not hold together when compressed and easily falls apart when agitated but really compacts well. For this type of soil, you would use a Vibrating Compaction Plate because it works so well at shifting the different sized grains into a locked, compacted state. In almost all cases you would not want to use a Rammer as the vertical compaction force will not compact Granular soil, it tends to displace the soil to either side instead of compacting.
AREA TO BE COMPACTED IS ANOTHER CONSIDERATION.
- Trenches and smaller areas and edges:
A Rammer works best for these areas as the smaller footprint and mobility makes a Rammer a great option.
- Large areas:
A Compaction Plate is best as it can compact at a rate if 3-4 times as fast. And gets you a smoother, more consistent finish.
- Amount of “LIFT” or layer of material being compacted:
commonly you want to compact only about 6” of material at a time with a Vibrating Compaction Plate but with the smaller footprint you get with a rammer it makes it possible to compact a greater thickness of lift, around 10” at a pass.
CONCLUSION - WHAT TO CHOOSE?
RAMMER or COMPACTION PLATE?
The reality is this, there is no “one or the other” choice of compactor when it comes to compaction. As a professional contractor you should invest in BOTH Rammers and Plate Compactors in order to be prepared to address the various types of compaction projects/needs you will have on your job sites.
Think about it like this... If I was trying to decide if I should have a Phillips head screwdriver OR a Robertson head screwdriver in my toolbox - the answer would be - have BOTH! The same applies to your compaction tools... Both are essential for the contractor pro.