this mould discolouring has recently appeared on some oak posts for a porch I built in the summer , any ideas of the cause and possible remedies . I expected ageing and changing of colour to silverish overtime , but not this sudden unsightly mould
cheers Jim

Seems normal. The untreated oak gate and gate posts I put in also went black first. Took three years to go silver and even then the surface is slightly flakey.

I have some other oak posts treated with Dainish Oil. They developed a similar pattern to yours except where you have mould they went white and mouldy. The rest remained a honey colour similar to yours.

If you want them to go silver I believe you just have to wait. If you want them to stay honey colour they will probably have to be sanded back and treated.

I suspect aswell that you've included sapwood and it's that that's discoloured. Sapwood is NOT DURABLE, & should be excluded from external work. Sorry James, I know it's too late!

Try Oxalic Acid crystals and then neutralise and oil.

be careful - its poison.

I've just had a load of holm oak trunks planked to be used as decking. Where does sapwood finish and heartwood start? I sort of presumed there's one or two outer rings of sapwood which eventually transmogrifies into heartwood? Education please.

I think biff is right James, lay back and enjoy, it's nature. If it really troubles you, instead of going down the route of bleaching etc., which will never equalise the colour, perhaps your only solution to a "equalised" colour is to darken them all over. Ammonia fumes react with the tannin in oak to blacken the wood, not like a surface dye but really goes deep into the timber structure. Constructing a polythene "tent" around each of the posts may tackle your imagination, though not impossible. You could then regulate the darkening effect with the ammonia strength. First idea is best I think, just leave it alone.

Oh well, if it's only a mere customer...
You could say:
a) If you wanted a plastic post why didn't you say so?
b) Ah yes, perfectly normal, you'll find that the whole post will turn the same colour eventually.
c) Oh we deliberately leave a little sapwood on the arrises. Eventually it erodes to a softer texture giving a gentler aspect to the line. Similar results are evident on much of the work by Morris and Co. You may have to wait a century for the full effect to become evident.

Hi James,

Definitely an issue of sapwood, I would suggest that the amount of sapwood included by your sawyer is completely normal - cutting all the sapwood out is very wasteful and pushes your timber price up considerably. There are some jobs which would require sap free to ensure joints or other details aren’t compromised when the sapwood disappears but in this case a simple post will work fine with or without the help of the sapwood corners :-) The mould could be particularly active if the tree was felled in spring/summer as this is when the sapwood is performing its most important function of transporting food and nutrients around the tree - winter felled oak suffers far less from this problem. I would suggest leaving it alone as it will equalise soon enough - attempts to bleach and oil will only slow the process down. Oxalic acid (without the oil) would be a good option if the customer 'needs' something to be done, I don't think the mould would reform as the sapwood has probably dried significantly since then? If you do go down the oxalic route you will need to neutralise otherwise it will 'burn' your posts a funky colour!! (and it is a neurotoxin so take care).... anyway, just a few thoughts to confirm what others have said :-)

@ dickster - holm oak isn't durable I'm afraid - best not use it in an exposed location like decking. The BS codes say that if you cannot distinguish between sap & heart wood by eye then you class the whole section as not durable. For Holm oak is would be fair enough, spruce heart for example is more durable but you still need to class it as a non-durable timber because there is no colour variation between heart and sap.

Not boring, just Robur-like- solid and true!

Mills will cost for oak on the basis of anything between 40% and 60% "scrap". The mill I worked at always assumed 60% and still has a reputation for being expensive amongst those who don't appreciate that the "extra" cost is a guarantee of quality and durability.

The "scrap" was used for garden timber products, like gravel boards and cladding (waney-edge, feather-board fencing), offcuts for hardwood logs.

Until you made the first cut you could never be sure how consistent the heartwood would be along the length. A good guy on the primary saw could make a pretty good assessment by eye, but taking off another inch just to eliminate a foot of sapwood half an inch deep would have made the boss a very unhappy bunny. Most of the regular customers accepted the risk, such as it was. It's what gives a beam its character over time, and most joiners can work around what they've got because they know that a bit of sapwood is the least of their worries once central heating is turned on or the piece is exposed to the environment. But then those shakes are somehow accepted as a 'normal' characteristic of oak, whereas discolouration isn't. Still can't get my head around that.

Mind you, a bit of sapwood is nothing compared to what we found in one load from the Enville estate. Bullets. The estate had been used by the army for live-firing exercises during WW2. A bullet to the heart took on a whole new meaning!

There's a vast amount of non-plantation timber incl hardwood that's not economic to harvest so landowners may even pay to get it taken away usually for firewood or just rots. Must surely be worth it to someone who's invested in a portable sawmill, if he can keep that busy going from place to place. Plank it up on the spot so easier to transport away than whole trunks. This non-plantation stuff AFAIK isn't included in assessments of national timber production. I asked a TRADA expert about it once and it was so off her radar that I think she thought I was a crazy.

Robur, you don't travel much do you.

I found your post to James very informative and I dare say, despite Biff's boredom, many others did too.

Unfounded speculation is another kettle of fish.

Posted By: RoburComing back to the question of Holm Oak durability - I have had a chance to look through TRADA & BS-EN tables now and it doesn't get a mention so hard to confirm either way. ...Holm Oak is undoubtedly used in the Mediterranean, from where it originates, for a certain amount of construction but durable in Spain doesn't translate to durable in the UK?

Indeed. I guess there's so little holm oak available in the UK that the data are hard to find. But there are some trees and we have a poster who is using it for decking. What references I've found support the idea that it should be regarded as durable but it would be nice to know for sure.

Spain is, of course, a different place - less damp and more capricorn beetles. Swings and roundabouts.