I've just bought two pairs of tri-fold exterior doors, the frames of which are made from softwood. The manufacturer places a lot of emphasis on me applying 3 coats of paint/varnish before installation to ensure their warranty. For example ... Finishing must take place before assembly and installation using at least 3 coats of a paint or stain suitable for external joinery. Using any other type of finish (varnish, oil or wax etc) will invalidate your 12-month warranty with us. Please note that this door set is treated with a high-performance preservative which includes a water-repellent material, designed to protect the product throughout its life. Before finishing your door set, please ensure that your chosen paint or stain is compatible with timber treated with a water-repellent. I spoke with my advisers at Brewers, the decorator supplier chain store where I buy paints and finishing products, and they suggested either of the following: Sadolin Classic All Purpose Woodstain as a base coat, followed by 2 or 3 coats of Sadolin Extra Durable Woodstain or Sadolin Ultra Highly Translucent Woodstain. Sikkens Cetol HLS plus as a base coat, followed by 2 or 3 coats of Cetol Filter 7 plus Which of the above would the painter pros suggest? Astramax, that means you! ... but others with good ideas are welcome to contribute to the discussion.
A decent solvent one,like Sikkens Cetol HLS/Cetol Filter 7 Plus,which you mentioned,not sure about Sadolin, there also Osmo Natural Oil Woodstain which is solvent.
Either of the products you have mentioned will give you very good protection, I have used both and would probably lean towards the Sadolin recommdation only because a wider colour choice is/was available. Used the Sikkens system on a exterior oak door using a clear satin finish and it looked superb.
Many thanks to both of you. I'll probably go for the Sadolin as Brewers has a special offer on it at the moment, making it a good 20% cheaper than Sikkens. Every little bit helps!