I'm stripping sash windows back to bare wood before painting - what grade sandpaper would be best to finish the preparation off - I've been around with 40 grade - should I go around again with something finer?
TIA
Definitely.
And also use something like 240 wet and dry after priming and after first undercoat.
Course or medium wirewool as the final.
If you're back to bare wood, I'd take this opportunity to "harden" the wood, certainly on the bottom 25% of the lower sash. I use ordinary 2 part fibreglass resin from Halfords rather than the overpriced Ronseal stuff . Leave it overnight and then give it a light sanding. Once you start painting you'll see what a difference it makes.
Interesting - does it soak in and go rock solid?
That's the idea. Unlike solvent based coatings, there is no reduction in volume when it cures, so you shouldn't over apply it. Although it's fairly viscous, it soaks into porous material quite well.
Whats the advantage? I can only think of a disadvantage.
NT
The main advantage is it gives the paint a firm foundation on which to form a proper film, without which the whole exercise is a waste of time. Ever tried painting a loaf of bread?
Exactly. Painting wood has a lot of stages. If you understand them, you can cut corners.
1/. Use knotting to stabilise any resinous knots in the wood. This puts and impermeable layer over them. 2/. use filler to gill any cracks or dents.3/. sand whats left as flat as you can.
4/. Apply a primner. This is to provide a key to the wood sop that further paint wuill adhere properly. Sand afterwards5/., Apply filler primer. The idea here is to get a dead flat grain free surface. As many coats as are necessary. Sande between coats.
6/. Apply undercoat. The purpose of this is to build up the correct pigmentation. Apply as many as are neccesary to get a flat even color. Sanding between coats.7/. Apply one top coat. This is essentially there to give the final washproof glossy (or otherwise finish) and forms the most protection.
Do it right and wood looks as good as a factory finished steel car body.
The polyester resin coat takes the place of the knotting and the primer. Good idea.a
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