Best shed floor preservative

[1974stephen]

Just bought a new shed and even though it comes with a 10 yr guarantee the instructions state that the underside of the floor must be treated with a high-quality oil or solvent based wood preserver, presumably as a get out of their warranty.

It's T&G softwood on approx 40x25mm bearers which have already been coated in the factory finish 'bright orange' preservative treatment. Google comes with a bewildering amount of solvent or oil-based finishes, most of which come in 5l tins. The sides of the shed are being treated/painted with Cuprinol's garden shades, which is water-based, and mainly to make it a nicer colour.

What's the best thing for the underside of the base?

 

[JohnD]

fresh air. Ventilate it well to prevent damp.

Raise the bearers off the ground on paving slabs or something. Timber in contact with the ground or with water rots quickly. Protect from rainsplash and use gutters and downpipes.

Don't bother with ornamental stains intended to make it look lurid.

Buy a preservative treatment.

usually about £25 - £30 per 5 litres. I still like the spirit-based ones which penetrate deeply. Apply on the timbers after they have been sawn and drilled, on all edges and surfaces, before final assembly. if you set up a couple of trestles and lay the boards out it is easy to turn them over, and any drips or spillage will go on the boards below and not be wasted.

look at the safety bulletin documentation to check what chemicals it contains. Preservatives are intentionally poisonous. Protect your skin, and especially eyes. Own brands may be copies, or identical, to big names. You might find the same chemicals in several treatments. I have been happy with Cuprinol and Wickes own-brand (currently not listed)

Some examples:
https://www.screwfix.com/p/sika-wood-preserver-clear-5ltr/47030?_requestid=481449

https://www.screwfix.com/p/no-nonse...tr/36237#product_additional_details_container

https://www.wickes.co.uk/Products/G...Treatment/Wood-and-Fence-Preservers/c/1000773

https://www.everbuild.co.uk/product/wood-preserver/

https://www.diy.com/search?Price=20..30&Price=30..40&term=wood+preserver

I actually like the green-coloured ones, because long ago, there was a product called "Cuprinol Green" containing copper-based chemicals, and it was very easy to see where it had been used, and if there were any bare sawn edges. When using a coloured one you have to stir it well before and during use, as the pigment tends to settle.

Preservatives don't usually contain water repellent coloured waxes as used in fence stains, so for surfaces exposed to rain, you may need to stain them after the preservative has thoroughly dried.