Oiling woes!

[ellal]

Last year (with a lot of help from this forum) built a shiplap cladded workshop, and used Tung oil on it. This year I gave the boards a light sand and applied a couple more coats..

Given that last winter the wood was fine, I'm surprised to find that already this year there is already a lot of mould/discolouration appearing...and I also am getting it on a second building that was constructed this summer, and which had 6 coats applied over several warm weeks!

Any ideas what has gone wrong?...and although I doubt that there is much that can be done before next spring, how could I rectify this?

Photos Here (old and new sheds labelled)

cheers

 

[joe-90]

It's a common problem. The oil is a waste of time. I use acrylic stains these days.

 

[JohnD]

I'm watching this with interest. I treated some external hardwood with linseed oil during the summer, but I gave it several coats of Cuprinol Clear first (rather exposed situation and other treatments have eroded).

My bro-in-law was over from Australia, and told me that fungus growth on oiled timber is common over there.

No mould (yet).

 

[ellal]

the shiplap was 'vac treated' before oiling...

I'm wondering whether this year is a bit different due to the wet warm autumn?

joe-90..what acrylic stain make?..and do they do a clear one, as the main reason to use the oil was to keep the wood natural...(well natural 'yellow', not 'natural' green... )

 

[masona]

Given that last winter the wood was fine, I'm surprised to find that already this year there is already a lot of mould/discolouration appearing

I'm guessing the timber has what is known as Blue stain which come from the interior of the wood, I never buy timber with blue stain on it and it's not always easy to spot it, if it's blue stain then it will not have any effect of the strength of the wood.

 

[ellal]

Given that last winter the wood was fine, I'm surprised to find that already this year there is already a lot of mould/discolouration appearing

I'm guessing the timber has what is known as Blue stain which come from the interior of the wood, I never buy timber with blue stain on it and it's not always easy to spot it, if it's blue stain then it will not have any effect of the strength of the wood.

It certainly does appear blue, but I wouldn't have known how to spot it if it wasn't obvious (I certainly didn't spot any noticeable colouration in the wood at time of delivery)..

It's reassuring about the integrity of the wood, but it's a shame about the discolouration.

So next year, if I sand the top surface and re-oil (or use something else), will the 'blue stain' reappear?

 

[masona]

There's no perfect cure but you might get most of it off with a wire brush, TSP or some type of bleach will lighten the colour but will effect the rest of the timber colour.

Copy & pasted from the website below,

Blue Stain
Certain types of wood get a fungus called "Blue Stain." White pine, which is used extensively in timber framing, is one of them. The fungus that causes Blue Stain begins to grow as soon as the tree is felled and feeds on the sap when the wood is moist. Consequently it affects the sapwood, working inward through the log or timber, but stops at the heartwood.

Blue Stain is not destructive to the wood and will not cause rot or structural damage. In fact, blue-stained wood is used for cabinets because it is considered by many to be attractive. These people are willing to pay a premium for it. A high proportion of timber frame owners also enjoy the blue striations in the timber frame, as it gives it more character.

However, if you do not like the look of Blue Stain, talk with your timber framer about ways to control or eliminate it. They include using winter-cut timbers, which are not as susceptible because the sap is down; or dipping the timbers in a fungus-killing chemical, which will ****** it for a while. Keeping them well-aired while stacked will also help. Scrubbing the timbers with a bleach mixture can reduce the visibility of the Blue Stain. Once the timber frame is erected and the timbers are in a lower humidity indoor environment, the Blue Stain will stop spreading.

More details here

 

[ellal]

thanks for the info...the bit about 'lower humidity' helping probably points to the damp weather this autumn being the trigger for the growth!

 

[joe-90]

Sadolin do a spirit based clear coating in satin finish but it's still a bit yellowish (to stop the ultra violet rays).

 

[ellal]

Sadolin do a spirit based clear coating in satin finish but it's still a bit yellowish (to stop the ultra violet rays).

This I presume?..

But would this help with the 'blue stain' problem (after removing as much as possible by methods mentioned)?

 

[oilman]

I have only had problems with mould where too much oil was applied too quickly and the wood had insufficient drying beforehand. With pine this can be months after purchase. There is no substitute for taking your time if you are using oil I have a shiplap clad wall and wooden frames which are fine, and have had varying quantities of oil, but all of which were allowed to dry for months.

 

[joe-90]

Once you've got that blue mould you are stuck with it. I've had trouble with oil in the past going blue, but never under a varnish (oil or acrylic),

 

[ellal]

I must say that a few areas of the shiplap remained a bit 'sticky' for some time..

I applied the oil with at least a week between coats in warm weather during the summer..

I'm still confused as to whether it's actually mould or 'blue stain' as suggested!

 

[joe-90]

Whatever it is you only get it with bare wood or oiled wood. You don't get it with varnish.