Birch worktop going black

JimmyL

Our Birch kitchen worktop is going black behind the sink where it gets wet.

Tried sanding but looks like it is going into the grain probably a fungus/mold. Is there anyway of getting rid of it and keeping it away (other than regular maintenance - I used to oil it (with Danish oil) once a month, then twice a month, etc.

kadman

Hi Jimmyl,

Just a couple of questions Jimmyl,

How long has the worktop been fitted.
Was it kiln dried when you bought it.
Was it a manufactured top , or did you join it.
Did any cement/plaster get onto the top during building work.
How long was it in before it turned black.
Are there any steel screws in that area.
Is the bottom of the top finished.
Is there a good seal around the sink.

How long is the top, and how thick.
Is the colour definitely black, or maybe dark green, or blue.

How deep have you sanded at this stage.
I'm a bit confused why you are oiling it twice a month.

Sorry for all the questions, but different problems require different solutions.

kadman

rooferPete

Ahaaaaaaaa kadman another victim ?

Errrr Customer

One question I see missing is was the timber around the cut for the sink painted or treated before the sink was fitted into place ?

Well with all his questions I'll throw in another, was the sink set in a silicone that has anti fungicide properties ?

kadman

Rooferpete,

Get out the calculator quick, its after nine o'clock....so we're on night rates he.he.

Stains could be from a number of sources here, depending on a few things,

Black stains ( if they are black) could be iron oxide staining from steel reacting with the timber, and moist conditions. Depending on how severe, it is possible to remove with Oxalic crystals ( DEADLY POISON NOT RECCOMMEND FOR DIY USE ) diluted in warm water. This would have to be treated by a professional restorer.

Could also be staining from cement plaster dilutions into unfinished timber surface. Sanding, or in severe cases, removing the top and thicknessing. Depending on the width, this would be an awkward repair.

Could also be mould growth. But If the top was finished top and bottom, and as Rooferpete rightly pointed out, all cut surfaces with at least 5-6 coats of Danish Oil, this could not have happened. Danish oil is an extremely deep penetrating, durable and water proof finish and would prevent this.

Could also be blue sap stain.This condition occurs when the timberwork is allowed to get wet and remain damp for long spells. It is the result of a chemical reaction, between fungal elements and characteristics of the timber. The longer this is allowed to persist, the deeper the penetration into the timber. Only cure here is to remove the stained timber part and replace with good timber.

So it is possible to either remove the stain or replace with good timber, depending on the cause of the problem.

My feeling is that the finish was not properly applied, and that you will have to remove the top, rout out the stained timber to a depth of about 15 mm. Prepare a new piece of timber insert. Glue into position. Refinish new timber, and all the cut surfaces. Replace top.

kadman

JimmyL

Quick reply before I start working.

It was just over a year since the (manufactured) worktop was fitted. I wasn't around when it was done but was assured that it was properly oiled (By the way, I didn't oil it twice a month. It should have been once every two months - just increased that to six). Don't think the bottom is finished and don't think they used anti-fungal sealant (I'll try that) - should have done the job myself.

Apart from ripping the kitchen apart. Is there anything else I could do?

Another thing, the oil does not seem to soak(?) into the dark areas (no shinely finish) and it is also happening on a solid Beech drainer. Could there be something in the water?

JimmyL

P.S. Thanks for the help.

kadman

JimmyL wrote:

Quick reply before I start working.

It was just over a year since the (manufactured) worktop was fitted. I wasn't around when it was done but was assured that it was properly oiled (By the way, I didn't oil it twice a month. It should have been once every two months - just increased that to six). Don't think the bottom is finished and don't think they used anti-fungal sealant (I'll try that) - should have done the job myself.

Apart from ripping the kitchen apart. Is there anything else I could do?

Another thing, the oil does not seem to soak(?) into the dark areas (no shinely finish) and it is also happening on a solid Beech drainer. Could there be something in the water?

I'm not convinced that the surface was finished properly, for a couple of reasons.

It sounds very like your builders have applied oil over a damp surface .
Was that top oiled immediately before fitting and allowed to dry, or was it done immediately after fitting. It sounds like it was not sealed quick enough.

The scenario seems to go like this.
Builder fits top. Builder and mate has a cuppa. Cups washed up, and left on drainer. Top allowed to soakup water. Next day builder wipes dust off top, and oils.
If something like this has happened. Where the damp was on the top, the oil will not take to sufficiently to form a proper seal. Subsequent oilings will not seal it either , if the top was damp, and not fully dry. After long periods of water ingression, fungal attack seems to have started , hence the stains.

Depending on the severity, you may have no option but to rout out the offending timber affected ,and replace with new timber or replace the top.
Again if the stains are widespread, and have penetrated deeply .and you consider replacing the whole top, I would go examine the possibility of thicknessing the top to a lesser thickness. You would need to visit a joinery first to see do they have a wide enough thicknesser for this. This would have to be considered as a last resort.

Personally I would rout out the stained areas. Was the drainer routed with a number of slots to drain water towards the sink. Maybe you could rout in more through the stains, to remove them.

Danish oil is extremely water proof, when used properly. I have pine sheeting in my bathroom down to bath level, after a 5 year period with only two quick coats, and there is not one mark on it any where.
Sounds like poor sealing to me.

Can you post a pic maybe to get a better idea of the severity.

kadman

JimmyL

Hi Kadman,

There was definitely one coat of oil after installation on the day. How well that was done, I don't know but I am sure I put on another coat very soon after that.

Anyway, cann't really do a proper job on this (taking the top off is out of the question - it's about three meters long and I would have to remove the splash back as well).

The area is not very noticeable - it's only 20mm wide behind a ceramic sink. Would varnishing help? It won't get rid of the stain but would it stop it from getting worse?

Unfortunately, I am way behind with the digital photo thing... and no scanner.

P.S. The Beech drainer is made from slates and I'll probably give a good sanding or plane it.

kadman

JimmyL wrote:

Hi Kadman,



The area is not very noticeable - it's only 20mm wide behind a ceramic sink. Would varnishing help? It won't get rid of the stain but would it stop it from getting worse?



P.S. The Beech drainer is made from slates and I'll probably give a good sanding or plane it.

Hi Jimmyl,

The staining can only get worse if the area is not properly sealed, and keeps getting a supply of moisture. You need to make sure the timberwork is thoroughly dry before further applications of oil/varnish.

In an earlier post you said the solid beech drainer was also staining, so I'm a bit confused with the last quote.

It all points to inadequate sealing, further compounded by applying oil , on what was thought to be dry timberwork. Is the bottom of the top in that area stained also.


kadman

JimmyL

Haven't look underneath - will do when I get a chance but I suspect it would be obscure by the cabinets.

How long does it take to dry out properly?

The drainer is removable (it comes with the sink) and is not part of the worktop (sorry for the confusion). Once, I remove the stains, I'll reseal it.

kadman

Depends on how damp it is, and how well you protect it from further water, does it feel damp to the touch. Good ventilation and a warm room should dry it out in a bout a week, if its not too damp. If you could hire a small moisture meter, that would tell you instantly the condition. You could take a reading at the stain, and at the end of the top. In a warm condition you would expect to get a reading of about 8-10 % moisture content in the top.
This would be the reading of a kiln dried board in a kitchen.

Is the worktop staining where it makes contact with the drainer.

kadman

JimmyL

Unfortunately, the sink is in use everyday and it usually gets wet behind it (where the stain is) when doing the washing up (some things just can't go into the dish washer).

I'll let it dry out properly when I am away on holiday in the summer (for a couple of weeks) and reseal it after I am back.

Thanks for all your help, Kadman, much appreciated.

Jimmy