What could this be from an old oak worktop??

[infowarrior]

Hi,

I work for a kitchen company and my workplace was getting rid of a length of old oak worktop so I claimed it as I wanted to make a chopping board out of it. After doing a bit of research online I found out that you need to clean them, then sanitize them and then finally seal them with a food grade oil such as white food grade mineral oil. As far as I was aware the wood looked raw and didn't look like it had been treated with anything. I started to scrub it with a scourer and water and the water started to turn light brown quite quickly. So I guess I have 2 questions. Is there any natural qualities of certain oaks that would turn the water brown? (doubtful) or does this sound like it's been stained with something in the past and it's leeching out when wet? If it's the latter how deep do you think I'll need to plane/sand it down to be sure of getting it out of the wood??

Cheers in advance for the replies.

 

[WellsWood]

What kind of scourer were you using? Any ferrous content - steel scourers/wire wool etc - will react with the tannins in oak and could give that result.

 

[infowarrior]

No, it was just a normal scourer used for washing dishes. One of the greenish plastic type of scourers that's attached to a small square sponge.

 

[mtr1]

Could you be just rubbing out some oak dust?

 

[yetloh]

I suspect it is natural colour coming out of the wood. After all, natural pine of the sort used in old pine worktops is not the colour (almost white) of an old scrubbed pine table top.

Jim

 

[Sgian Dubh]

Tannin in the oak, water, and iron react and create a brown stain. You say it's an old worktop, so there's a good chance there's plenty of little bits of microscopic steel (with its iron) embedded in the surface.

On the other hand, water alone can leach out the tannin in the oak. If you've ever inspected the inside of a wood drying kiln after a batch of oak has been dried you'll notice much of the interior is coated in a brown stain, in much the same way as the inside of a tea pot after a few brew ups. See below for an example of a wood drying kiln just after seasoning a batch of European oak. Slainte.

 

[infowarrior]

I suspected it could be just a natural colouring of the wood but wasn't sure if that could happen with oak. I've borrowed an electric planer from my mate and was going to take it down a mil or 2 but think I might just leave it now. My concern was mainly that whatever it is that's causing the water to turn brown could leach out onto the meat etc that I will be chopping on the chopping board but could that happen anyway if it's been sealed with the food grade mineral oil after an initial cleaning?? Reckon it's worth me planing a couple of mill off anyway just to be on the safe side?

 

[mtr1]

I haven't seen many butchers blocks made of Oak, they are usually beech with a maple frame around....perhaps beech would be a better choice, its less prone to splintering from chopping to.

 

[Steve Maskery]

I bet it's just tannin leaching out. You would know if it had been sealed, there is no truly invisible finish of which I'm aware.
Wash it, dry it and oil it, it'll be fine.
Unless it's very thick and a skim won't materially affect its appearance, I wouldn't remove any material.
S

 

[bugbear]

If you've ever inspected the inside of a wood drying kiln after a batch of oak has been dried you'll notice much of the interior is coated in a brown stain, in much the same way as the inside of a tea pot after a few brew ups. See below for an example of a wood drying kiln just after seasoning a batch of European oak. Slainte.

Wow. Thanks for that, I didn't realise tannin was so mobile!

BugBear

 

[Sgian Dubh]

I didn't realise tannin was so mobile! BugBear

When I think about it bugbear, it's likely that there had been several batches of oak dried in that kiln when I took the photograph, so perhaps what's visible as a fairly long term accumulation of staining.

However, here's what I hope is a useful tip. If you make a piece of outdoor furniture with either European oak or American white oak, and it's intended end destination is on a concrete or slab base, eg, a patio, don't put it there when it's brand new. If you do you'll find after a while there's a brown stain under the piece. And if you've made that piece for a client they'll sometimes phone up and complain about the stain and ask what you can do to fix it. For the sake of good customer relationships the maker tends to have to go to the client's location and spend a good amount of time cleaning the stains with hot water and detergent, and a stiff brush.

It's generally much easier to deal with the stains if the new piece of oak furniture is placed over grass for a while, ha, ha. Of course, nowadays I'm much more likely to warn the client about likely staining, and then leave it up to them where they site the piece ... at their own risk. Slainte.