Wood treatment for summer house

Question

How to treat wood on a new summer house, for which a natural look is desired?

1. Oil/solvent or water based treatment? The manufacturer of the summer house recommends the former, but various online sources claim modern water based treatments are equally good and better for health/environment - I am not sure, though, to what extent these claims are unbiased.

2. I presume treatment is only needed for the exterior? (Any interior treatment would definitely have to be low VOC as children will play inside).

3. Must treatment be applied in two layers, some sort of rot prevention followed by a barrier layer, or can a suitable product can do both together?

Answer 1

1. IMHO, the water based stuff should be fine. The walls of a summer house should be protected by the roof and eaves, and shouldn't touch the ground, so they have a relatively easy life (compared to a fence/gate/bench). Oil based products like creosote will smell strongly for months, can leave oily marks if you brush against it, and only comes in one colour. Sometimes that doesn't matter, sometimes it does. Look around your neighbourhood to see what works and what doesn't, as everyone's climate is different.

2. Interior wood is worth protecting, but you can use something with a nicer finish. The goal here is to fill the pores in the wood so they don't fill with dirt. Modern water-based stains and varnishes are pretty good indoors, or you could use some sort of teak-oil or wax, even a smear of cooking oil will keep it looking nice much longer than untreated wood.

3. If the preservative says to use two coats, follow the directions. OTOH you do not need to apply a preservative and then a layer waterproof paint. Rot is caused by bugs that need moisture, so applying a poisonous preservative will prevent rot, as would a waterproof paint. The problem with waterproof paint is that cracks and pin holes inevitably allow water through, and once behind the paint, it never dries. Good preservatives shed water but still allow the wood to dry out, much like Goretex fabric.

Probably the most important thing for long life is to keep the walls dry. Maintain the roof and gutters, to keep rain off the walls. Ensure the ground level doesn't get built up, and regularly check that nothing (like bushes, piles of leaves, or other junk) can trap moisture against the walls.

Answer 2

I still lean to oil based , yes for years I have heard water based is just as good but my results do not agree with how long they last. You will need to apply additional coats in the future, some last 5 years some, 7 years after having natural cedar finish on 2 homes nothing lasts as long as they advertise, the weather in the Pacific Northwest, has a lot of rain, some low 20 deg F and even - temps every few years with high summer temps in the low 100 range so we get it all. Eves only overhang 2’ for most homes and the bottom 1/2 or better gets weather beaten, I found extra coats on the bottom 1/2 at the same time I was treating the entire wall(s) held up the best and the lower 1/2 did not discolor even after 20 years 2 applications so far with another one needed soon but I don’t live there any longer. I only use 1 product if natural clear make sure it has an UV inhibitor this will reduce sun fade.