Boron wood preserver?

[inventor]

Has anyone experience of using boron products as wood preserver? There are several sites offering them in the UK, and the safety data is great. "Fine Homebuilding" reckons they're wonderful but that they leach out of the wood over time. Anyone know how long boron stays effective in a painted or varnished window? If boron is as good as they say, and as safe as they say, why isn't everyone using it? I note that all the telegraph poles in my road contain boron rods, but they're impregnated with something like creosote as well.

I'm looking for a wood preserver to use with modern softwood windows, which seem to last no time at all - maybe 30 years. And with expensive custom wooden windows, pushing the lifetime from maybe 100 years to 300 years. It has to be really, really, safe and eco-friendly. CCA and insecticide is out!

Thanks!

 

[Newbie_Neil]

Hi Inventor

Welcome to the forum.

I'm sorry I can't help with your question.

Cheers
Neil

 

[MIGNAL]

I used to replace windows. What always mystified me was that I'd be pulling out softwood windows that were near on 100 years old with no sign of decay. Then there were times when I'd be replacing windows that were put in within 20 years. There was a thread on the forum recently about some chap who makes windows and who believes it's down to the modern paint coatings not letting the wood breathe. I think he advocates the use of old fashioned Linseed oil paint, that's the type of paint they use in the scandinavian countries. Perhaps Pekka could chime in.

 

[Nick W]

The LO paint site can be found here

 

[OJ]

I use the Treatex boron preservative. It'll only leach out if the wood is wetted over time. It's mostly for indoor use, but would be fine I think under an exterior finish, preferably linseed as mentioned. The Treatex people are very helpful. Try them and ask about exterior applications. Search the new and old Green Building fora under boron. Also, once you find a product you would like to use, see if it has a BBA certificate which will tell you all of its uses and charcterisitcs. More relevant to the application than a COSHH sheet.

OJ

 

[newt]

I had assumed that the lead in old paint gave the long life to wood.

 

[inventor]

I too find that old windows are rot-free, but new ones rot quickly. I spoke to a structural engineer who specialises in ancient buildings, and he tells me that he was taught that it was the old-growth wood that was critical. More than 25 rings to the inch and it's OK. Less (and that's all modern softwood) will rot. He recommended oak instead of softwood, but that's not always practical, and oak isn't perfect (I'm working on a 500 year old building with plenty of rotten oak right now). I tried out the lead paint idea at
http://en.wikipedia.org/wiki/Talk:Lead_paint
and it might be OK but someone there doesn't think so.

If boron works and is ecofriendly, I'd like to try it. But only if I can find out how long it lasts! Anyone know why it isn't more used? Or how long it lasts?

Thanks, everyone!

 

[MIGNAL]

I'm not sure the structural engineer is right. 25 grains per inch is very fine, you'd be lucky to find that in top grade musical instrument wood. I'm fairly certain that the stuff that I was pulling out was nowhere near that mark, better than a lot of the modern fast grown stuff though. You could try Douglas fir, I've often seen modern doors made of fir which have very slow growth so it must be readily available.
Lead was added to oil paint to speed up drying, not sure if it acts as a preservative.
Borax is an old form of wood preservative but I only know it as being a prevention from woodworm attack although it may well be good for decay.
Here's Biffs take on things:

http://www.biffvernon.freeserve.co.uk

 

[inventor]

There is always the possibility, of course, that the old softwood joinery we see wonderfully preserved was itself treated in some way when it was made. I wonder if it was dunked in boracic acid? Or something else?

Does anyone know whether wood preservatives were used 150 years ago? Was borax?

 

[Wanlock Dod]

OK, rather off topic (and maybe also a bit of a daft question ), but what on earth would cause more recently grown trees to grow so much more quickly and why would this make them more resistant to decay?

Cheers,

Dod

 

[inventor]

In times past, trees were harvested from wild woods, where many trees were well into maturity. Mature trees are tall and don't need to grow fast to get to the light, so they don't. Growth rings are closer together, with the tree putting on less wood than in their youth when they were racing up to find the light in the forest.

More recently, trees have been planted specifically to gain the most growth, the highest volume of harvested timber, in the shortest time, to maximise return on financial investment. As soon as their growth slows at maturity, the trees are harvested. They don't have time to put on timber with fine growth rings.

You can sometimes see the effect of the surrounding trees on modern plantation timber. If the tree starts out from the centre, year zero, with wide growth rings, then suddenly starts creating narrower growth rings after about 20 years, that's when the forest was thinned, felling maybe a third of the young trees.

The rings are formed of earlywood, put on in spring, and latewood, put on later in the year in summer. Earlywood is less dense and is lighter in colour. In general, the earlywood carries the sap through the tree, and the latewood gives the tree strength (although both do both to some extent.) After conversion to timber, most of the remaining moisture sits in the earlywood. Slow grown trees with fine rings seem to have a higher ratio of latewood to earlywood, so are stronger. For rotting fungus to grow, the average moisture content of the wood has to be over 20%, so more dry latewood might make the timber more rot-resistant. I'm not sure why the fungus wouldn't just grow in the earlywood alone, so I don't really understand this. Anyone else have any better ideas?

 

[Wanlock Dod]

Inventor,

I think that I can answer your original question about boron/borate wood preservers. My understanding is that due to their high water solubility (and a general tendency to be highly mobile in situations where water is present) they are not recommended for use in either external or internal applications which would be subjected to significant or repeated wetting. This is due to it being very unlikely that much of the treatment would remain in the wood for very long.

I don't have any direct experience of using them.

Cheers,

Dod