Black Walnut Slab - PLEASE HELP!

[Matthew Gelb]

Hi. I am a complete beginner when it comes to woodworking. I bought a black walnut slab almost a year ago and it has been haunting me ever since. This slab is meant to become a free standing countertop/long table.

Upon arrival I began sanding it beginning with coarse grits, working all the way up to 320. I decided I wanted to keep the bark on to keep the color contrast. Controversial I know, especially because even from the beginning I noticed small potato-bug-like beetles ending up on the ground beneath the slab accompanied by small piles of sawdust. I sanded the top and bottom probably to 180 before I filled some cracks, holes, and crevices with epoxy, the west systems stuff. By the way this is over the coarse of up to 5 months at this point, I ran into many issues and wasn't sure how to solve them so this slab stayed idle for weeks at a time sometimes. Over the winter it remained in my attic, I sanded a few times, and also began smoothing out the bark on the sides.

Throughout this whole time, holes would pop up from those critters, mainly at the joining of the bark and the wood, although since then small holes have shown up elsewhere in the wood. I finally decided to just finish it in the hopes of suffocating the bugs.

After sanding to 320 I decided to poly it using a water-based Miniwax polyurethane (polycrilic), clear satin. I didn't want to use stain of any sort as I only wanted to bring out the natural color of the walnut. I've put on between 5 and 10 coats on both sides, sanding lightly between every few coats until I began using a special water-specific applicator which left it smooth enough.

Holes! More holes kept appearing, so I injected the poly into them if they were large enough, some on the bark, some on on the wood surface. Since then it has stood idle for a week or so, then another coat or 2, then more holes, and this process keeps repeating.

Sorry for the length, it's been about a year and I wanted to detail the process so I could get some specific advice. I need the bugs to die since they keep affecting my finishing process. Once they are gone, a few more coats to fix it up and I'll be set.

Also, at some points during the finishing process poly has dripped onto the top side, creating small bumps of extra poly. These, I've found, are difficult to sand out, and sanding affects the the surrounding area, scratching it up when I only intend to get rid of the bumps. Any advice here?

Eventually I plan on drilling holes in the underside for 3-4 hairpin legs.

Pictures of the slab, and examples of holes and rough patches attached. Having trouble attaching all of them, more to come.

Thanks for any advice and insight!

[Dan Hahr]

Well, with it being sealed, I'd say heating it to kill the powder post beetles is probably not going to work, (without damaging the finish, anyway). I'd find someone with a walk-in freezer that gets well below 0 degrees F. I'd leave it in there as long as you can stand it. That should do the trick.

Dan

[John K Jordan]

Throughout this whole time, holes would pop up from those critters, mainly at the joining of the bark and the wood, although since then small holes have shown up elsewhere in the wood. I finally decided to just finish it in the hopes of suffocating the bugs.

Are the holes tiny, 1/8" or smaller? If so, look up "powder post beetles" (there are several different varieties). They mostly get into wood that is not dry and can live in the wood for a long time. Here is one article: https://www.doyourownpestcontrol.com/powderpostbeetles.htm

You can't usually get rid of them by putting something in the holes. There are things you can do to prevent a board from being infested, but the best thing to kill them in the wood might be to heat and dry the board. Some people will get it heated/dried in a kiln. I've heard of people wrapping the wood in plastic and setting it in the sun but I've never tried that. The article mentioned above indicates some pest control companies can fumigate the wood. If I have wood with PPBs I usually get rid of the wood, but most of mine is smaller turning stock, not a large slab.

BTW, someone gave me some 2x2 walnut turning squares once and I put them on a shelf in the shop. One day I heard a faint "scritch, scritch, scritch" and looked just in time to see a PPB chew its way out of the wood! What are the chances?!

JKJ

[Mike Heidrick]

Take it to a kiln and bake it. Then refinish.

[Bob Bouis]

There are only a few types of beetles (which aren't very common) that can actually infest dry wood. What you're seeing are probably larvae that got into the wood when it was wet. They've matured into beetles and the holes you see are them exiting the wood.

If it's dried out by now the odds are that it will be inhospitable to future infestations and that the larvae will either leave or die off by themselves. Just takes time.

[Scott T Smith]

Heat sterilization is the only approved method to kill any bugs in the wood. The core of the lumber needs to be heated to 133f or greater.

FWW magazine had an article a few years back about an easy and inexpensive home built sterilization chamber that you can make in order to sterilize your lumber. If you send me a pm with your email address I'll forward a copy of the article to you.

[Danny Hamsley]

Powderpost beetles can live in the wood for several YEARS before they bore out, so get the slabs heated like Scott says. Better safe than sorry.

[Bill Adamsen]

Having been the victim, I agree with what the others say. Heat and refinish.

[Ron Citerone]

I would verify the temp needed to kill bugs. Perhaps a Minivan in the sun on a hot day might achieve that temp. I baked a piece of white oak in my oven that was the top for a jewelry chest and haven't had a problem so far.........1 year ago.

[Nicholas Lawrence]

I used a hatchback in the hot sun once. We had a series of very hot days, it was in direct sun, and the boards were directly under the window.

My advice is to stop what you are doing, get it out of your house, and don't bring it back inside until you have done something to be sure the bugs are dead. The peace of mind is worth it. You don't want to spend the next twenty years wondering if they have now infested the framing of your house.

[Bill Dufour]

I suppose theoretically you could bag it up and fill the bag with any gas other then oxygen such as CO2 or N2. I have no idea how long this would take and I am sure even longer for the eggs. A vacuum would do the same. Freezing I doubt it.
Maybe you could put it inside a house being tented for termites.
Bill D.

http://www.powderpostbeetles.com/cold-temperatures/freezing-temps-beetle-larvae.html

[David Helm]

First thing to do is get rid of the bark. wood boring beetles lay their eggs in the bark. When hatched they enter the wood and start doing damage. At maturity, they bore out (hence the holes) and start the cycle all over again. The beetles you have are likely Lyctids. They generally infest hardwoods. You can remove the bark with a relatively dull draw knife (I work with live edge all the time and that is my go to tool). Keeping the bark on is a BAD idea.

[Matthew Gelb]

Thank you for all the advice, it seems like the best way to move forward is to bake it and refinish it. I will try to get more pictures up tonight, I'm not sure why that wasn't working.

[Matthew Gelb]

First thing to do is get rid of the bark. wood boring beetles lay their eggs in the bark. When hatched they enter the wood and start doing damage. At maturity, they bore out (hence the holes) and start the cycle all over again. The beetles you have are likely Lyctids. They generally infest hardwoods. You can remove the bark with a relatively dull draw knife (I work with live edge all the time and that is my go to tool). Keeping the bark on is a BAD idea.

This is something I would like to avoid considering all the work i put into keeping it on. I actually used glue, epoxy, and poly, in various stages of this project, where the bark contained cracks and crevices or was detaching from the wood. If I could bake it properly, won't that take care of anything left inside?

[Bob Bouis]

Bugs that got into the wood when it was green probably don't present a danger to the dry wood in your house. Generally speaking, bugs that eat hardwood don't eat softwood and vice versa. Likewise with bugs that attack wet wood vs dry wood. In fact, I don't think I personally have ever seen powderpost type beetles infest wood that was truly dry. I'm not saying they don't exist, but they aren't likely to come in with a piece of wet wood.

[John K Jordan]

Bugs that got into the wood when it was green probably don't present a danger to the dry wood in your house. Generally speaking, bugs that eat hardwood don't eat softwood and vice versa. Likewise with bugs that attack wet wood vs dry wood. In fact, I don't think I personally have ever seen powderpost type beetles infest wood that was truly dry. I'm not saying they don't exist, but they aren't likely to come in with a piece of wet wood.

Unless I missed something, all we know about the type of insect in the wood is there are holes. A positive ID would be a big help here to assess the potential for spread.

From the link I gave earlier, "Various anobiid beetles attack seasoned wood in the United States. These beetles range in size from 1/32- to 3/8-inch long; however, those that attack structures are 1/8- to 1/4-inch long. " They mention anobiid powderpost beetles can infest hardwoods or softwoods.

Perhaps interesting: I once watched beetles land and start to dig into the end grain of some green wood. I was outside my garage cutting some maple logs into chunks and waxing the ends with anchorseal. The sweet smell from the wood was strong. I looked up to see a cloud of tiny insects flying towards me from the direction of the woods, I assume attracted by the smell. (It wasn't actually a "cloud" but it sure was a bunch, many dozens or hundreds.) They were tiny beetles and they started landing on the freshly cut end grain and digging holes, more than one on each piece - I was surprised at how quick they were to get holes started. (Were they digging holes to lay eggs?) The anchorseal didn't stop them. I ran and got some insecticide and sprayed the wood then put all the pieces inside and closed the garage door. If I had left the pieces outside all the pieces would probably have gotten infested, assuming they were some type of powderpost beetle. By the time I thought about collecting some for ID it was too late.

JKJ

[Bob Bouis]

If you read my post carefully, you'll see that I qualified it as best I could. I don't doubt that bugs exist that can attack dry wood, or maybe even softwoods and hardwoods both. Anobiid is an entire family of bugs. I don't know how many species are in it, but I bet it's a lot. I've never heard of a bug that infests both hardwood and softwood. Doesn't mean they don't exist, but they aren't common. And, yeah, I've had logs (or 20" cherry slabs, those*^#@ers!) that have been attacked exactly like you describe, by bugs that flew in seemingly out of nowhere right in the middle of a suburb where I live, and bored into the end grain of wood right after I cut it. But I've also got dry hardwoods and softwoods that have been stored outside, on the edge of a forest, for decades and have never been messed with.

As far as what kind of bugs this guy has, again, I was careful not to say that I knew for sure. But I'd be willing to bet dollars to dimes that the bugs in his natural edge walnut slab won't mess with the framing of his house, and that they got into the wood while it was wet.

[Paul K. Johnson]

I suppose theoretically you could bag it up and fill the bag with any gas other then oxygen such as CO2 or N2. I have no idea how long this would take and I am sure even longer for the eggs. A vacuum would do the same. Freezing I doubt it.
Maybe you could put it inside a house being tented for termites.
Bill D.

http://www.powderpostbeetles.com/cold-temperatures/freezing-temps-beetle-larvae.html

I've wondered about that as well. But I was thinking put wood in the bag, put a bug bomb inside, set it off and seal the bag. Then just let it stay that way for a week or even longer if you don't need the wood yet.

I have no idea if it would work but it seems like a pretty good plan. The only thing I worried about is if the bomb will mess up the wood such that even if the outer layers were planed away the wood would still be no good.

[Bill Dufour]

I would assume each type of bug will have a different tolerance to poisons and temperatures. So you have to use extra just in case. And lots of time to make sure it reaches the interior of a thick board. Remember car exhaust is a good source of inert gas that will not support life or promote oxidation of paint and varnishes.
Bill

[Mike Matthews]

Hi Matthew,

If / when you refinish, you may want to consider using some sort of oil-varnish blend. Oil based finish will penetrate the grain more and bring out the natural beauty of that slab. Water based finish dries quicker and doesnt penetrate as deeply (much less "deep sheen") - after all the hard work you're putting in you ought to unlock the full potential of that piece!

-Mike

P.S. be careful where you've used epoxy or poly to seal areas of the wood. The new finish won't penetrate into those areas and could give you some undesirable variations in tone.

[lowell holmes]

I would start over by running the slab through my planer to remove the finish, then treat the wood for beetles.

Then re-finish the board.

[Jacques Gagnon]

... as mentioned by Scott Smith, wood infested with insects can be treated with heat. The international standard calls for the core of the wood piece to reach 56 C (or 133 F) for 30 minutes. The treatment, developed for the sawmill industry (lumber; pallets; dunnage; etc), aims to eliminate live insects (either in the bark or deeper in the wood). In an industrial setting the treatment of large volumes of wood requires many hours in the kiln, to a large part because wood takes a long time to heat up.

Too bad they do not make microwave ovens as large as this slab! :)

However, some people have tried alternative approaches, including painting steel containers black and letting them heat up under the sun in order to generate sufficient heat inside. In your context, you might want to try a similar approach (maybe aluminium sheets painted black or brown?) whereby you slab would be heated for long enough the reach temperatures sufficient to kill the insects. I would not be surprised if your efforts so far with finishing were going to be vain, but this may be the price to pay to accelerate the process of getting rid of the exit holes created by the emerging adults.

[Wes Ramsey]

If you think about the life cycle of PPBs they aren't hard to get rid of, but you have to either bake them or cut them out. PPBs lay their eggs on the surface of wood so they prefer rough-sawn lumber and bark. The eggs tend to survive better in the nooks and crannies of rough-sawn lumber. Not that they can't survive on a planed surface, but the eggs are easily removed by planing and sanding. The holes you see are from the larvae that hatch on the surface eating their way to maturity. Once they are inside a piece you have to either kill them with heat or chemicals or cut away all holes. If you cut away all the bug holes and plane or sand the surface you will completely remove the bugs at all stages of life from that piece of wood.

But if you want to keep the natural edge your only choice is heat or chemicals.

Another option is to replace the piece with another that is not infested. If you're anywhere close to north-central Arkansas, stop in for a visit. I have a stack of natural edge walnut slabs that might hold a suitable replacement or two. I will have several more stacks just like it before I ever get around to using all of this one.

[roger wiegand]

If you have a facility nearby that does ethylene bromide fumigation that is a very good, non-destructive method for eliminating all kinds of bugs. It's often used for valuable antiques that have woodworm. There's a facility near here that is used to fumigate whole loaded semi-trailers full of pasta or grains, I'm told that they will include small pieces on request.

The powderpost beetles I had in my barn were perfectly happy to infest dry wood, I certainly wouldn't bring an known-to-be-infested board into the house. They are not as pernicious as the European woodworms, but can certainly do a lot of damage. (Spraying the entire interior of the barn with a borate product (Boracare) seems to have pretty well eliminated them.)