I'm looking at a 3.25 HP, 8-gal and a 4.25 HP, 12-gal shop vac for use in root crown excavation. Is one is more useful than the other? They're the Rigid brand and there's only $20 difference in price. I'm leaning toward the smaller machine mainly because it takes up less room in my truck. But I may need more power and volume. Thanks to all for any advice.

Thanks, Tom

Reply to post by Tom Watson, on August 25, 2000 at 19:58:38:

Hi Tom, OK. you are looking at a 12 gal. capacity shop vac to use on root crown excavations. I wonder about a couple of things here; what size trees are you looking at? were you planning on taking the soil back out of the shop vac after you are done with the examination, and replacing it? In my limited experience, I could easily fill a 12gal. on a 15 inch tree. Also it will not get the rocks, dead branches, chevy bumpers etc; that will not fit through the intake hose. Just a couple of thoughts I had. I have used septic tank "vac trucks" quite successfully, but they were on sites where biggish trees were involved and soil replacement was not required, (read backfill).

James

Reply to post by Tom Watson, on August 25, 2000 at 19:58:38:

James is right, it's a question of scale. A vacume could be very helpful in small trees or small areas of a root system (see link). But be completely overwhelmed by a large scale examination. It sounds like you've zeroed in on the vacume as a useful tool in small scale situations. That said I'd always go for more HP particularly at only a $20 premium. One caution is the amperage draw of that extra HP. Match either the capacity of your generator or the length/guage of your extension cord to the amperage.

Another practical consideration with shop-vacs is noise. They can make you nuts... it's a different kind of noise than a chain saw or a chipper and noise seems to be addressed better with more expensive machines like the WAP, Take a look at Shopvac reviews in builders magazines like "Finehomebuilding."

Reply to post by Scott Cullen, on August 25, 2000 at 19:58:38:

I went with the 12-gal, 4.25 vac as suggested and it performed well. The tree was a 42" dbh, over-mature water oak with hardened, black conks between the trunk flares, a fomes species, I'm guessing. The excavation revealed that the buttress roots had rotted away around half the circumference of the root crown and the fungus was advancing up the stem. The client has arranged for removal as I advised in my report. Scott, thanks for the link to Gary Johnson's stem girdling root publication. It's a great resource. Another advantage of replacing the dirt with wood chips, as he suggests, is that it also allows the municipal arborist handling the removal permit application to easily access the trouble spot.

Thanks once again for the shared experience and the Knothole

Tom

Reply to post by Tom Watson, on August 26, 2000 at 07:29:38:

Tom, would you estimate how deep and how far out from the trunk your excavation was? Was 42" the diameter at grade? What tools did you use? How many times did you fill the vac? How long did it take and how much time did the vac save?

Thanks for the feedback.

Reply to post by Scott, on September 06, 2000 at 00:14:14:

Scott, the tree was 42" at 4.5 feet. I used a garden spade and a small trowel with the point ground down to avoid unecessary wounding. I dug about a foot down, 18" in one area of severe buttress root decay. I excavated, maybe, 2' to 3' feet away from the trunk.

I started on a side of the tree with dried conks between the trunk flares, probably a polyporus species. I immediately discovered extreme decay. All of the major buttress roots on that side were rotted away as close as a foot from the trunk. It was only necessary to excavate the one side to see that the tree, 10' from the house, and with some top dieback, had a high hazard rating.

The vac saved plenty of time and helped prevent further wounding, as it was only necessary to loosen soil and vacuum it away. I spent about two hours on the tree, using part of the time to clear ivy and salvage a few hastas. I could have finished the job faster, but I took extra time to play with the new toy and figure out the most efficient ways to use it. I emptied the vac three times, winding up with a bit more than half of a contractor-size wheel barrow of dirt, which the client wanted for a potting mix.

I plan to use the vac on all future excavations. It saved time, effort and helped avoid collateral damage. I definitely recommend the larger size. The noise didn't bother me. I turned it on only as needed. The Rigid brand I bought works well, but I'm sure other brands will perform as well. I have photos of the operation being processed. I can email images, if you like. Thanks for your interest.

Tom