I would be scared to remove sandtex and black gloss paint from sills by way of heat gun as this can warb the pvc or by using a chemical paint removal stripper which could also damage the pvc i would test area dry scrape the sandtex and key into the black use a pvc paint over with a few coats.
How to remove paint from plastic guttering.
Step 5 scrub the area.
Knowing how to repair plastic gutter seams early on reduces the chance of further damage and possibly a major repair.
Repairing the seal in a plastic gutter seam will keep the water from pouring into your woodwork.
When the paint starts to wrinkle scrape it off using the plastic putty knife.
Use a rag to scrub the area until the paint is removed.
Paint the edges with a brush and the majority of the gutter and downspout with the roller.
Strip off the old paint with a plastic putty knife.
A plastic putty knife is ideal as it will not scratch the gutters like a metal or steel wire brush might.
To remove dried paint from plastic start by applying some rubbing alcohol to the paint which will help loosen it so it s easier to scrape off.
Try to get off as much of the old paint as you can.
Scratch off old paint on the gutters with the putty knife putting pressure on the knife as you scrape off the paint using long strokes.
The roller makes the job go much faster and produces a smooth finish.
Before painting the gutters wash them with warm water.
Oil based paint works very well on plastic and does not require a primer.
Apply the paint with a brush and a small 4 to 5 inch roller.
Then hold a straight edge like a paint scraper your fingernail or a flathead screwdriver at an angle against the paint.
After removing a significant amount of the paint on the surface of your plastic pour warm water on a sponge and add some detergent.
Occasionally gutter seams or joints open producing major leaks.
This paint does not require a primer and it works well on plastic.
Next scrape the straight edge across the paint continuing until all of the.
It is best to paint the gutters and downspouts with oil based glossy paint.