Troublesome exterior wooden window frames, new paint peeling

[MisterBoy]

We have old, frequently repatched wooden frames. They were looking tired - the sills were down to bare wood in places - so we got them painted 2 years back. The paint started to come off the next year; far as I can tell the painter must have just painted on top without priming or prepping first

I sanded back and reprimed last summer and painted on top using some generic exterior trade paint from screwfix. This year, it's coming off again and I'm a bit unsure what to do:

Clearly I need to scrape these bits but I was wondering about trying a different product that might help with my lack of skill!

I was looking at https://www.sadolin.co.uk/products/sadolin-woodshield-superior-flexible-paint-for-wood/ which seems slightly mis-named, far as I can tell it's really a paint not a stain.

Or is there some better preparation I should be doing other than just priming? It is definitely the parts that were bare which have the issue and I am assuming the wood got damaged (it is still sound though)

 

[Chivas69]

I think you'd have noticed straight away if your painter hadn't used primer on bare wood.
Also was any undercoat involved anywhere?

 

[MisterBoy]

I think you'd have noticed straight away if your painter hadn't used primer on bare wood.
Also was any undercoat involved anywhere?

Possibly I mean undercoat when I say primer, though as an amateur many products seem to be both. I didn't get the impression he did much prep based on how quick it was and how little old paint was lying on the ground after being chipped off, and vague memories of asking him but not knowing what it all meant.

Either way whatever he did, I stripped and sanded problem areas last summer and painted a primer/undercoat (it specifically said it was both) and gloss on top. I thought I had done a fairly thorough job rather than cutting corners but clearly something went wrong!
I have seen advice not to use water-based primer/undercoat which I'm sure this was, but I was still pretty surprised to see it cracking and peeling so badly.

 

[sparkwright]

For an oil-based gloss traditional finish, I tend to use aluminium wood primer on bare wood, and ensure all gaps, holes and cracks are filled. Undercoat(s), topcoat.

For a water-based finish, I tend to use Sadolin Superdec as a primer, undercoat and topcoat. Again, all holes and cracks filled.

Sanding and preparation essential.

 

[MisterBoy]

How do you decide when to use water/oil based?

 

[sparkwright]

I use the water-based outside for quickness, as you can get three or more coats on in a day.

Also, when it comes to re-painting in years to come, it seems easier to sand and prepare. The Superdec resists cracks and blistering, and isn't as shiny as oil-based gloss, so preparation generally seems quicker.

However, if I want a more traditional, glossy and impressive look, I would use oil-based gloss, and spend more time with all the long drying oil-based primers, undercoats and topcoats.