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Corn Cob Blasting on a Budget

Log Siding corncob blasting2003 146We purchased a log sided home in 2003, not really knowing much about log care or treatment in general. I was less concerned about log siding than a log home, because the worse case is to remove the siding and replace it with new, if needed. I now have a better appreciation for the work that went into putting the siding in place. Log Siding corncob blasting2003 197

Our house was built in 1996. From what we can tell has had little to no care of the wood, since it was constructed. This has left the wood in a rough shape, having blackened and showing signs of wear and cracking after exposure to the elements. When approaching re-staining the house, we had the first challenge of removing the existing stain, and prepping the wood for new stain. You can’t really expect to hand sand an entire house of curved wood, so the typical approach is to use some chemicals combined with power washing to remove the stain. There are a few pieces that drove us away from that direction. We didn’t want to deal with chemicals, and masking off the ground and surrounding plant life around the house. We also learned that, depending on what chemicals you intend to use, you may need more chemicals to get the pH of the wood back to a level where it will accept the stain again.

The alternative out there was this process of blasting the stain off of the wood, using ground up corncob. Appreciate that nobody in the area of Rochester had a clue as to what we were talking about, and that perhaps 1 in every 10 people we talked to in the wood industry didn’t look at us cross eyed. Luckily there was enough information on the Internet to get us closer to understanding how to approach the process. Eventually we got in contact with Dick Alger at I Wood Care, who seemed to have the best grasp on the industry and approaching this project. I took a look at renting the equipment from I Wood Care and quickly discovered that this was not for the average home owner. Requiring nothing less than a compressor of biblical proportions, the nozzle system resembled something closer to the size of a fire hose. So I did what I always do, and decided I could build my own system for less money.

Poor Man’s Corncob Blasting

I decided to build my own system, using standard sand blasting equipment, because of the low investment it posed overall, figuring it was small Log Siding corncob blastingDSC07920risk to take in the investment to get the wood repaired. I bought a sand blaster from the mecca of cheap tools, Harbor Freight, and replaced the blast hose with a 30 foot extension. Then ordered what I considered to be a high CFM air compressor from Northern Tool, using points I had earned from my credit card and had a bag of corn shipped up from i Wood Care to give it a trial.

Log Siding corncob blastingDSC08027The system worked, but needed some refinement. Although the compressor was rated at 11.8 CFM At 90 PSI, it didn’t last for longer than a 15-20 seconds before dropping too low in pressure. I also neglected to account for this new thing Log Siding corncob blastingDSC07919called gravity. The further you get up that ladder the more pressure is required to move the blasting media, a progressively painful drop in usable air the higher you went up. I was very fortunate to have a friend at work who had a compressor that put mine to shame, and when I mentioned what I was trying to do, he let me borrow the setup for the months I would need to do the work. The project wouldn’t have happened if that did not fall into place.

The quotes we got from buying the actual bags of corncob were ridiculous. My wife ended up taking a day trip in the truck to go buy it from I Wood Care, because they were the only ones not looking to charge extortion rates for the media. We ended up ordering our stain and bug treatment from them as well.

You can re-use corncob a few times, if you are clever. We were not that ambitious, because we would usually be doing this project after work and did not have time to mess around with collection tarps, etc. Corn Cob Blasting Example

Choosing Stain and Bug Protection

Log Siding corncob blastingDSC08053Many different manufacturers of stain, and many different processes regarding bug treatment. For stain, we went with a stain that did not finish off with a polyurethane coat. Some log processes will take that direction, leaving that outer shell of protection in place. Every few years, you presumably give the polyurethane a re-coat and all is well. The negative is that if you miss the re-application and the stain below takes a toll, you need to figure out how to get stain back onto that wood. There were a lot of non-clear answers on this, all of which sounded like work. We opted to go with a stain that did not use a final protective coat, but could be re-applied as the years go on. Essentially every couple years we apply stain again. It sounds like work, but really we do one side every year, rotating around the house from year to year. The process takes less than an hour for us to re-coat one side, and it has worked out well so far.

You want to add some bug treatment to the wood, to discourage all of our bug loving friends from making a home in your house. Some of the treatments mix with the stain itself. The system we went with, which was Penetrete did not. It was was applied before the stain. The negative out of this, and perhaps something I would change given the choice to do it again, is needing to allow the bug treatment to setup over 12-24 hours. In upstate NY where ever other day is rain, this proved to be challenging. The best thing about corncob blasting is that the wood is cleaned, dry and ready for stain, which we lost with this process. Many a nights we scrambled to wrap the house in tarps, as we waited for the treatment to set in and crystallize over night.

Lessons

What I learned and what I would offer for anybody approaching this from the same “do it yourself” perspective.

  • Find the largest air compressor you can find. Ideally you will want a construction grade trailer compressor that you would find on construction sites. I will not need to do our house again, but I still watch the classifieds to see if one comes around for a reasonable cost.
  • Get a sand blaster that has a large capacity, or is easy to fill. I wasted a lot of time refilling the corn into the blaster, because I had to go through a funnel. Stretch the budget $100 and get the large easy loading model. If not, consider getting two blasters, and have somebody loading the one, while you are blasting.
  • Keep the bags of corn dry. Consider keeping them someplace with a dehumidifier running. A little moisture made for more challenges getting the spray tweaked just right, than I care to admit.
  • The corn will get everywhere. Keep a set of clothes that you only where for this project and isolate then from the rest of the house, inside. That is about the best you can do.

I recently blasted the final logs, after some reconstruction work on our back wall. I took one HD video of the process itself, to show how nice the stain comes off.

It is amazing to see how the same stain applied to weathered and blackened wood appears, versus new cuts of wood. The house looks like a very dark color, but when applied to new wood, it appears very bright and light colored. If you need to replace one or two boards on a wall, you may be approaching replacing the entire wall, depending on how it affects the look of the house.

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  1. Ted Weaver
    July 1st, 2009 at 13:09 | #1

    Nice write up on our Grit-o’cobs that we manufacture. We supply I-Wood Care.

    Ted Weaver
    The Andersons, Inc.

  2. July 1st, 2009 at 13:47 | #2

    @Ted Weaver
    Thanks Ted,
    I was having trouble finding a link inside of The Andersons website which linked to the Grit-o’cobs product. If you have one to pass along, I can put up a short list of material I used with a link back to the information pages.

    Stephen

  3. Ed Ethridge
    November 7th, 2009 at 07:38 | #3

    I have a similar blast system and need to know the cob media size (2040 fine?), 1040 appears to be too coarse.

    thanks

  4. November 7th, 2009 at 07:51 | #4

    Ed,
    We did everything with 2040 from the start. It felt very fine, but still had very abrasive effects on the wood. I have to admit, I never tried any other grit sizes. I would think it would be hard to keep the wood from etching or excessively furring with a course grit, but I have not tried.

    Stephen

  5. Ed Ethridge
    November 16th, 2009 at 22:21 | #5

    I finally got cob media (2040) to go through the Harbor Freight blaster (as per your recommendation large capacity, easy to fill). I have taken the entire system apart several times to clean out “clogged?” media. The first time there were 2 large 1.5″ long metal shavings clogging the blasting gun. After that the media clogged in the hose, but I was able to get it unclogged by running 1/4″ od copper tubing into the hose from both ends. Finally I got the system pressurized with media coming out the blasting gun over the weekend. So I packed the blaster, the 40# bag of media, and compressor (2HP) and went to my cabin late this (Monday)afternoon, before the rain starts tonight. The hose got completely clogged and I got nothing coming out at all. So I could not perform a cursory test of the system.

    I believe my media (2040) is “dry” it has no indication of being moist. The weather was dry when it was shipped.

    I have a question about “getting the spray tweaked just right”.

    Does the tank pressurize through the “media metering valve”? I suspect that my problem is that I should shut off the “media metering valve” on the bottom of the tank while it is pressurizing. This would keep the media from leaking into the hose. The instructions with the Central Pheumatic Harbor Freight blaster do not say how it should be opperated. Will the tank pressurize with the metering valve shut? Is this, perhaps, my problem. I left it all at the cabin so I cannot test this hypothesis.

    Do you have a recommendation as how to keep media from filling and clogging the hose?

    Ed

  6. November 17th, 2009 at 05:52 | #6

    When the gun clogs, it is only clearable by getting the wrenches out and taking the tip off. It clogs quick when the media is running heavy.

    2 Main nozzles on the blaster. (besides the one that shuts off all of the air) The media control at the bottom of the tank, and the direction of flow at the top. I would need to adjust the valves every time I started a new bag, and typically once or twice before going through a full tank of media. The weight of media in the tank affects how much things move.

    Media Nozzle
    I always started with the media control valve closed, and opened it up until I could get some media to start coming out. It was typical that the moisture in the tank would clog this up before I started, so I would open and close the valve very quickly the entire way a handful of times to attempt to shock or break loose the media.

    Flow Control
    The flow control valve became a balance. It hovered around half, but I could manipulate that valve when the media was really stubborn, to add more pressure to the tank. Sometimes I would similarly send all of the pressure to the tank in a quick jolt to help break the media loose in the bottom. The reward (or more appropriately the curse) was a wad of media that would clog the nozzle.

    Perhaps worth noting, is that I had replaced my blast hose with a 30 foot hose. It was actually a Parker “quick connect” hose that I grabbed at hydraulics place. I am not sure if this made a difference in how much media reached the nozzle at once. It would give me time to react, as I could hear the flow coming up, after my media control valve rapid “shock” attempts.

    If I had to do it again, I would entertain looking at other “non-harbor freight” blaster setups. I know the harbor freight one was cheap enough to get me working, but there has to be an easier way. I spent so many hours with the tank, that I got used to the problems and acquired a feel for what it was doing. I can’t count how many times I had to un-clog the nozzle. The few minutes of “dialing-in” the pressures would be easier with dry media, but still a challenge regardless.

  7. Ed Ethridge
    November 17th, 2009 at 07:32 | #7

    Thanks, it is not my nozzle per se that is clogging. It is the hose. Past times I had an 18″ obstruction. Last night I started trying to clear the hose again, virtually the entire 8′ length is clogged. I will probably get a new longer (~15′) hose. I’ll also get quick disconnects to put on. We have a good industrial supply store that handles all kinds of pneunamatic and pressure water hoses.

    The key seems to be to keep the media flow valved closed or just cracked open to prevent unnecessary excessive flow of media. Just learning.

    Thanks.

  8. November 21st, 2009 at 08:28 | #8

    The hose I got was a Parker branded hose, with their labeling of the “quick connect”. In hydraulic world, that means you don’t need an industrial crimping machine to put the ends on. I may have confused the statement by putting that in there, as the hose itself does not have quick connect fittings on it.

    Definitely go conservative on the media feed rate, just enough to get the corn to flow. You will re-adjust when the tank gets half empty and open it up a little more, as you will find the weight of the corn helps that feed process.

    Stephen

  9. February 28th, 2010 at 12:32 | #9

    Thanks for your post. Are you from MN? I am from Owatonna and have been cob blasting for over 15 years. I am sitting on about ten pallets of the 2040. I have decided to get more agressive on using it up by marketing our service to the log home industry. We have used the cob blasting on factory ceilings. I have found that the 2040 is very dusty and the dust by static electricity wants to adhere to the surface. That dust needs to be removed prior to painting at least when it applies to steel/metal surfaces.

  10. February 28th, 2010 at 17:40 | #10

    We are in upstate NY. I feel like the amount of adhesion of the dust seems to be dependent on the humidity for the day. Only in areas where the wood was over-weathered did we need to dust off the boards before applying stain.

  11. brian boudreau
    May 23rd, 2010 at 08:43 | #11

    @Stephen

    hi stephen-

    i am considering building my own corn cob blasting setup. wondering if you would be available for 15 minutes by phone so i can learn about your setup.

    thanks

    brian

  12. Ron VanBibber
    June 5th, 2010 at 10:00 | #12

    Hi thanks for posting this, going down this road, looking at harbor freight, do you have a complete list of the parts I need? estimate of costs to do a whole house? I know it depends on house but just some general figure. I’m in wv plenty of humidity in summer. Where do i get the nozzle? looked like a fan shape on one video. thanks for you help, priceless.
    Ron

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