Out door wood preservatives.

[Amateur]

I have a pine bench that needs finishing.
There doesn't seem like a lot of options for a clear finish except for wood preservatives.
Does anyone know how they work?
When you paint them on and they are absorbed into the wood does the liquid harden inside the wood grain, like Danish oil?
I'm also struggling to get any info from people who have used this type of product and can say that 5 years down the line they have had (especially pine) furniture outside and it hasn't rotted etc.
Well they are called preservatives, so I would have thought that would have been a minimum requirement?? :roll:
Anyone any comments please.

 

[Woody2Shoes]

Hi, my tuppence-worth:

Pine is essentially not a "durable" timber - if left outside it will decay fairly quickly.

All wood has two main types of enemy which use it as a source of food and protection, destroying it in the process:

1) Fungi (remember that nearly all fungi will not survive/thrive if the timber is kept dry [i.e below 15-20% moisture content]) - so keeping it dry at all times e.g. with an effective varnish/paint system, will keep it rot free.

2) Insects and other tiny creatures.

Most timber preservatives contain chemicals which kill and/or discourage both types of enemy. As a general rule, the more toxic (most lifeforms react badly to the same things) the chemicals, the better they work!

The idea of most timber preservatives is that these chemicals are dissolved in a solvent (e.g. white spirit or similar) which can carry them into the fibres of the timber (mostly via the end-grain). Various mixtures exist and the process of absorbtion can be sped up using hydraulic pressure e.g. the Tanalith process. The solvent then evaporates - many solvents are themselves harmful.

Even using pressure, the central core of a piece of timber is unlikely to be treated, if at all, as thoroughly as the outer regions - this is why cut ends of treated timber ideally need re-treating.

Over time, UV from sunlight probably breaks down some of the chemicals - especially the insecticides I guess - and probably makes them less effective - the same applies to varnish/ paint of course.

If it were me, I'd try and give the bench a good soaking in clear preservative, let that dry and then paint it - starting with an aluminium-based primer (pine is often sappy which undermines other paint finishes) and then exterior grade undercoat/gloss. An alternative to paint would be varnish but I've not found a one which is very long-lasting in this kind of application.

The alternative of course would be to religiously put the bench away in a shed, or under a stout weather-proof cover, when not in use and certainly during the winter months anyway.

Cheers, W2S

PS I forgot to add that a particularly vulnerable bit is where the legs touch the ground - I would try and find something impermeable to put between timber and ground e.g. slate or plastic or something similar

 

[Amateur]

Thankyou for your reply.

I have been looking at some of the outdoor finishes on sale. Some time ago I had a cheap teak type table that I oiled, but I wasn't impressed. The initial finish looked great but after a couple of summers and winters outside they started to retain a dark pigment, as if muck from the atmosphere was building up. I eventually concluded that it was spores making some sort of algae or fungus.
The quest goes on looking at the products available :roll:

 

[blackrodd]

I use Ronseal quite a lot, but, as mentioned softwood isn't good outside untreated, I see quite a lot of lawn furniture now
is sold complete with winter covers, but it's best taken inside for the wet winters we have .
A cleaning kit is available for cleaning deckings and furniture, to help in re coating.
Here's some advice,--
https://www.rhs.org.uk/advice/profile?PID=616

And something like this,--

http://www.wood-finishes-direct.com/pro ... oCHK_w_wcB
HTH Regards Rodders