What is a Stump Grinder?
A stump grinding machine is basically a large woodworking machine that resembles a circular saw on steroids. A spinning wheel has large teeth attached to it that are designed to sever wood fiber.
- Some are mounted on trailers that are towed behind trucks of various sizes. These grinders stay attached to the tow vehicle at all times.
- Other grinders come as attachments to large excavators or wheeled/tracked loaders.
- Still, others come as self-propelled units that roll off a trailer and are then driven around a homesite.
- In their smallest format, there are stump grinders that are almost “hand-held.” They can be powered by a variety of engines, with a chain saw engine being the most commonly used.
No matter what kind of stump grinder used, they all share a common weakness- they are designed to cut wood. Dirt and rock are literally their mortal enemies. Stump grinder “teeth” are equipped with tips of carbide that are designed to slow this wear process down but there is still no getting around the fact that the “tooth geometry” required to sever wood fiber is much different than the “tooth geometry” required to either scoop soil or shatter rock- and those tooth geometries are not interchangeable.
However, there are ways to factor in stump grinder tooth “decay” into the stump grinding process. More on that subject will come later.
By-products of stump grinding
Depending on exactly where the stump grinder is positioned relative to the stump, the resulting stump grindings will vary in both size and color. The portions of the stump originally above ground will be almost entirely “wood-colored” and will be as long as 7” and the diameter of your index finger. From there the particles will get smaller, right down to 1/4” x 1/4 “ and even sawdust-sized.
As the stump grinder reaches further down into the ground, it will “cut” more soil, resulting in a change of color to the pile as the dirt, darker in color, gets intermingled with the wood chips.
The volume of stump grindings relative to the original size of the stump. The larger the stump, the more the stump grindings. I’ve had many 20’ diameter stumps that produced 3 wheelbarrows full of grindings. On the other end of the scale, I’ve had some large stumps that produced 10 cubic yards of stump grindings. How much are 10 cubic yards? Think large dump truck. For a rough rule of thumb, when you look at a stump, take the volume of what you see and multiply it by ten (10) to arrive at the volume of grindings produced by the stump grinding process. Many are the client who has been left with 2 to 4 cubic yards of mulch. ( A cubic yard measures 3’ x 3’ x 3’)
Where do all the grindings go as they are being made?
The vast majority of stump grinders throw the grindings underneath the stump grinding machine.
While this is a good thing relative to the grinder’s property, it often creates problems for doing a good job.
On almost any job where the stump is larger than 30” in diameter, the machine will generate so many ships that the operator can no longer “see” where the stump actually is. The best way to maintain visual certainty and job integrity is to back the machine off the stump and move the ship pile off the stump. Depending on the machine, this pile removal cycle can occur after every 15 minutes of grinding time.
With the completion of a grind, any chips that have gone “rogue” and flown away from the larger pile must be mechanically brought back to the pile.
What’s to be done with the hole where the stump was and all the grindings?
Unfortunately, there’s no way around it. There is no machine out there that can just vacuum up this material and cart it off. And, stump grinding piles are so varied inconsistency that they do not respond well to being scooped up by the machine. In the end, roughly half of the grindings from any grinding job must be hand loaded into whatever vehicle will carry them off.
On the bright side, is their usefulness. Although not uniform in color or size like commercially available screened mulch, they can be put to the same purpose. Besides, these wood chips can absorb up to 7 times their own weight in water, which renders them a great material for wet garden paths and landing areas.
There are multiple solutions to filling up the hole left from the stump grinding process. The ideal solution is to remove all the grindings from the hole, which is usually 6″ to 8″ deep and then filling the hole with fresh soil. This ensures that the new plant material, whether grass or ornamentals, will have a good shot at thriving.
For those less concerned, the “dirtier” part of the grindings pile can be used to fill in the hole up to 2″ below finished grade, with a 2 ” veneering of fresh soil spread out on top like icing on a cake. Finally, for the roughest resulting look, the grindings can be used to fill the hole, the top layer is then spring raked to remove the larger woody portions. Grass can be started on this but it will extremely weedy, if not barren, for at least a couple of years afterward.
History of StumpGrinding: Dealing with stumps- some history, and the alternatives
Decades ago, as the land was being cleared for new homesites, the stumps leftover from the tree-felling process would often be dug up and trucked away to be deposited in the unused portions of a farmer’s property. These stumps would be packed together, covered over, and forgotten about.
The Farmer would eventually sell off his land in parcels and new homes would be constructed on top of these lands that had been infilled with stumps. Unfortunately, stump decay and deterioration were inconsistent and there have been numerous incidents where sudden sinkholes have appeared on these homesites. Some sinkholes had children falling into them and some sinkholes, much larger, have contributed to the structural failure of the foundation of the homes perched upon them. All told, these incidents have been numerous enough that stumps are now classified as “hazardous waste” and must be disposed of properly.
The modern-day property owner, or homeowner-to-be, has 3 methods for disposing of the stumps that are on their property:
- Stumps can be extracted from the ground using an excavator, then loaded onto a large truck, and then carried to and dumped at an appropriate dumpsite. The large the stump, the larger the excavator need to extract it from the ground, the larger the truck needed to haul it. It is not uncommon to see a $100,000 excavator putting a large stump into a $75,000 truck, which will then haul it to a site that charges by the cubic foot dimensions, to dispose of it.
- A stump can be chemically treated to help the decay process or it can be burned. Unfortunately, in a freshly cut state, a stump contains a great deal of water and will actually extinguish many of the smaller fires that are started on it. To really eliminate the above-ground portion of the stump, any fire started must be kept very hot and must last for hours. The chemical solution is still slower, often requiring months of letting it sit, and even then a fire is often recommended as a late-stage “helper.”
- This alternative requires bringing a machine to where the stump is located and actually “grinding” the stump into a pile of shavings and sawdust at the site. The advantages of this over the other stump removal alternatives are numerous:
a. Minimizing any physical disturbance to the property immediately around and leading to the stump.
b. Eliminating trucking and disposal costs related to putting the stump elsewhere.
c. The creation of a bio-degradable by-product that can be used for various purposes around the property or homesite.
d. The pace of the process involved with stump grinding is such that, from start to finish, the process can be concluded in hours. The intrusion into a property owner’s life is kept to a minimum.
