Painting Plastic Window Surround

[Shadoman]

Hi All, would appreciate some advice about how to approach painting a plastic window surround.
Here are some pics to help set the scene:

https://drive.google.com/open?id=1DFJ9Fl9Ja9wI6Rlxg1KoGpjGr9aMHpll
https://drive.google.com/open?id=1MvPG2q1o9zSPrZAytVL44G2dXaSBSZ4Z
https://drive.google.com/open?id=1NPvgmAzVHEY2g1khkk6NkIbZUABg11YK

Im not sure what these are called but the paint is peeling off the window surrounds and I can see what looks like a plastic base under the paint.
What is the best approach to paint these. Do I need to strip back to the plastic? What paint to use?
Any advice would be great.
Thanks

 

[opps]

Although you have uPVC (plastic) windows the curved feature at the top looks like it is masonry. If it is then masonry paint will be fine.

 

[Shadoman]

Hi, I'm pretty sure it's not masonry because it's completely hollow. I know this because in places there are cracks and I can see that they're not masonry cracks.

 

[opps]

Might it be plaster of paris?

Difficult to tell from the photos, but it does look like the substrate has blistered slightly in some places. If it were plastic I would expect some paint blistering but not for the substrate to blister.

Have you jumped up a ladder and tried to scrape a very small section?

 

[Shadoman]

Ok. I'll take a look later when I'm home. If it was masonry it would feel hard to knock right? Like knocking on brick? When I knock on this it feels completely like plastic. Just so you have a better idea, my door surround looks just like the one here:
http://www.buildingplasticsdirect.co.uk/acatalog/grp_door_surrounds.html
So I was thinking maybe it's grp.

 

[opps]

Sorry, perhaps it is grp. I don't understand why they would have painted it though in the first place.

If it is plastic- sand the rough parts (and key the rest) and just undercoat and gloss. Assuming that the paint is sound there is no need to sand it all off.

If you were painting naked GRP you would need to apply a coat of something like Zinsser Allcoat Exterior first.

 

[Shadoman]

Thanks. Yes, I believe it's definitely plastic . Got up on a ladder and it's completely hollow and where paint has peeled off, you can see the plastic. You are right, I can't see why they painted it in the first place.
Thanks for your advice. Much appreciated.

 

[Shadoman]

I forgot to ask. Which gloss would you recommend? The surface in question gets a lot of direct sun light so I don't want it to yellow.

 

[opps]

Oil based gloss yellows because of a lack of sunlight. Waterbased gloss does not yellow as a result of a lack of UV light from the sun.

My personal preference is oil based Dulux Trade Weathershield undercoat and gloss. I prefer to apply one or two undercoats and then two coats of gloss. You don't need two coats of gloss, I just prefer the depth of finish that it gives.

Assuming that you are only painting plastic (and not wood) then save some money and use a standard undercoat and gloss- there is no need to pay a premium for the Weathersheild paints

 

[Shadoman]

Thanks for the explanation. It all makes sense. Thanks for all your advice. I'm going to make a start next weekend.