New log cabin - what to do about wet weather

29 Nov 2015
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United Kingdom
I've just built a log cabin and it needs fire retardant and preservative but the weather is rubbish right now. Drizzling every 30 mins as it was put up and no doubt rained over night.

From what I can tell all of the wood preservers have to go on dry wood and the fire retardant too but not sure how long I can leave exposed to the elements before it becomes damaged? It could be 2 weeks before it stops raining long enough for the wood to dry.

I didn't manage to get the roofing on before it got dark, but presume ok to felt over damp wood?

Also, was going to use insulated boards on the walls inside but again, should I wait to preserve on the inside first?

Any advice really appreciated. Don't want to get this one wrong, it's 30sqm so an expensive waste if I do!

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For the roof I would get a plastic tarp. and tie it over , just to keep the rain off. The sides I would leave until the weather gets better too. I understand your concern but I would leave it all bare until the weather improves. IMHO it's better to put preserver/finish onto dry wood- and the wood won't deteriorate much at all over the winter. You will get patchy drying if you go for it now. Just bide your time and all will be well. Weighing up any damage from weather vs. the timber drying naturally ;)
Do you want the fire retardent to work, or do you want to be seen applying it to satisfy building control.

For it to actually work it must be applied to dry timber, you must ensure that the preservative is compatible with it, and you want evidence for it's durability on external use (that is indipendant test evidence, not glossy leaflets). You also need to apply it as per instructions, some brush applied fire retardents fail to achieve the required loadings when applied vertically.

There are some dodgy products out their, and some that are good but need specific application conditions to actually perform as tested (as above), AND maintained (only pre-pressure fire retardents are proven to be durability without regular maintenence, anything you brush on WILL need maintenence).

As to preservatives.

Yes it won't be that effective applying preservative to wet wood (the treatments are waterbased, so applying to wet timber is trying to fill already full cells)

But you may want to apply a bit to stop mould growth (mould does not harm the timber but looks horrible) and then re-treat properly when the timber is dry.

For long term protection the timber structure must be above ground contact (so the cabin base should be on footings/upstand of some kind), able to drain, with fully sealed and protected end-grain.

Brush on preservatives are going to give you minimal protection under the best of conditions due to lack of penetration, so good detailing is essential if you want it to last and last.
Thanks both for your replies, really helpful.

Re the fire retardant - I want it to work AND satisfy building regs :) It came with the log cabin so hopefully not dodgy but thanks I will check how to apply.

I've seen some preservatives advertised as having micro particals or some such to maximise penetration - do you have any thoughts on if they're just a sell or actually work?

Also Aron when you mention fully sealed end grain - these are exposed - do you mean with something other than preservative?

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The micro particles to maximise penetration is 'kind' of nonsense. It may help to increase penetration, but multiply a fraction by a fraction and you still have a fraction.

The lowest pressure/vacuum applied preservative schedule is 3mm of penetration, maybe this gives you an idea how superficial any brush applied treatment will be. That is not to say brush on treatments are useless, but they absolutely depend upon frequent maintenance of coatings (brush on preservative treatments MUST be coated over, or be part of the coating system).

Typical log cabins have exposed end grain on the corner joints, liberally apply preservative to the end grain, then use an end-grain sealant(below) before applying any final coatings.

The difference doing all this to the durability of the structure will be significant.
Oh, also most fire retardents cannot be painted/stained or otherwise treated over, so you will want a fire retardent coating as the final finish (be very very wary of any brush applied fire retardent that claims to work with other products without test evidence to demonstrate this).

Any varnish will have a short life, so pigmented finishes are better.

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