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Looks like sawdust on the underside of a hardwood ceiling board


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Give us some clues, eh?

Was the ceiling covered with plaster until recently? Which room of the house, age of house, number of planks affected. I agree with Marc that it looks more like a fungus growth, but if it is wood powder, then you should see some tiny holes where the mature insects have emerged.

 

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Thank you so much!! For some reason, the system did not notify me of a response. It is in an unconditioned garage, 90 years old, hardwood. The surface has been exposed since the garage was constructed. It's damp in there, and firewood was brought in and left nearby. 1 plank infected. 

I can sweep off the dust  and have a look to see whether there are holes. I was thinking powder beetle, but haven't removed the dust.

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I did. The wood is solid, but has a LOT of sawdust on the underside. So much that it is difficult to sweep it down to the wood. I don't see any bore holes from insects, but there is a lot of dust there. It is as if someone is sneaking in and sanding the underside of the wood. It is just part of one plank.

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I guarantee that it's not an insect and it doesn't look like any fungus that I've ever seen. The powered is following the growth rings. 

My best guess is that it's the wood equivalent of efflorescence. Brush it off and forget about it. 

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Whatever it is, it's very strange. There is a good 2cm of dust on there. It seems to come back after wiping it, and that board has a hollow sound. But jamming a screwdriver in it doesn't break the wood. It's very good wood, that is for certain.

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Assuming you are in the East USA, as you have hardwood ceiling planks 90 years old, and assuming that the sawdust is not from insect damage*..... then it could be a fungus growth that attacks Eastern hardwoods (that may have been present in the plank from day one).

There are a few rot organisms that break down wood fiber into dust. I think there is a standard fungacide treatment, but I'm personally not familiar with that one.

*The Eastern Powder Post Beetle leaves a huge hole you can't miss.

 

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On 5/29/2017 at 4:07 PM, pm124 said:

Whatever it is, it's very strange. There is a good 2cm of dust on there. It seems to come back after wiping it, and that board has a hollow sound. But jamming a screwdriver in it doesn't break the wood. It's very good wood, that is for certain.

Two cm? No way. Maybe two mm. 

I've seen moisture move through wood and leave mineral salts behind - just like what happens in concrete -- and I suspect that's what's happened here. 

It just seems implausible that a fungus or insect could produce that much product without causing the wood to deteriorate to a noticeable degree. 

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Well, whatever it is, it is definitely weird. There is a LOT of dust. And it seems to be spreading in real time (days, not years). I'm going to try to spray it with Timbor because it is cheap and non-toxic. The dust could be obscuring the holes. Not sure what else to do except spray it with fungicide next.

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When you rub it between your fingers, is it gritty and coarse, or smooth like talc? 

If you're brave, taste a bit of it. Does it have a salty/sweet/mineral taste, like efflorescence? Or is it bitter and piney, like tree sap? 

In one small section, use a brush and a spray bottle of water to thoroughly clean it. Do you see holes? 

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It is smooth like talc. I'm not brave enough to taste it. My plan is to get a shop vac out there and clean up the boards to see if there is a hole. I did brush a section, and no hole. It was  LOT of sawdust, however. So, I think I will try a shop vac. Thanks again.

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3 hours ago, pm124 said:

It is smooth like talc. I'm not brave enough to taste it. My plan is to get a shop vac out there and clean up the boards to see if there is a hole. I did brush a section, and no hole. It was  LOT of sawdust, however. So, I think I will try a shop vac. Thanks again.

Try brushing some into a small beaker of water and stirring. If it completely dissolves you're looking at efflorescence. 

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5 minutes ago, Marc said:

How does efflorescence form on wood?  What is it?

It's the formerly dissolved minerals that are left behind when water evaporates from a surface. In order for it to form on wood, mineral-saturated water would have had to have been present in the wood and evaporated from the surface. I've seen it when wood is in contact with wet masonry or concrete and in industrial settings when liquid chemicals have leaked onto wood platforms. 

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14 hours ago, pm124 said:

It's a big layer of sawdust on top of the water. No dissolution. 

So when you stir it or shake it, the dust doesn't get wet? If so, that sounds like a fungus. Many of them are water repellent. It might be interesting to drop some onto an agar plate to see what happens. 

I'd use a whisk broom to brush off a large section and then watch to see if it returns. 

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