Recently a small exterior board fell down from above one of the uPVC windows in my house. and even though it mainly seems to have been there for cosmetic purposes I would like to put it back up. The fall has broken it in two but I've been able to recover both parts.

I would like to glue the board back together but the problem is I'm not sure what material it is made from and therefore cannot be sure which adhesives are suitable. When I searched online the main suggestions seemed to be uPVC, aluminium or wood. It's too light to be the first two - from some simple tests it seems to be less than half the density of water. Whilst if feels like it could be some type of light wood the cross section on the damaged area is completely white which would suggest it's not wood

I've added a photo to hopefully make it easier to identify the material

I am from the UK which would probably be relevant in determining which materials are most likely to be used.

Large piece

small piece close up

Edit: I’ve just realised that one side appears to have some sort of smooth laminate but the other does not. This is hard to show in photos as the colours are similar to each other

  • A photo with better lighting might help more. That looks like outdoors in the sunglight.
    – Huesmann
    Jan 19 at 13:27
  • Running a finger nail over the broken section is hard like plastic or softer like foam?
    – crip659
    Jan 19 at 13:30
  • @Huesmann: apologies, I've added another photo although I was struggling to get good light with macro mode on my phone
    – James
    Jan 19 at 13:44
  • @James the seond pic sure looks to me a lot like what PVC molding looks like when it breaks.
    – Huesmann
    Jan 19 at 13:45
  • That small piece in the 2nd photo is 4.5” wide at the widest part and 1/4” thick, yet it only weighs 11g. This doesn’t seem right for PVC. I’ve also just realised it has some sort of laminate on the side facing out
    – James
    Jan 19 at 13:59

2 Answers 2


That fractured piece looks an awful lot like PVC to me. I don't know what kind of tooling is used in the factory to get such nice edges on the finished product, but whenever I cut into a PVC molding it looks like broken polystyrene as in the pics (even when I make a straight cut).

  • Obvious suggestion: if this looks like it's a standardized length, getting a replacement piece might be less hassle, and more reliable in the long term, than trying to weld this one together again without the joint either failing or being visible. Some things really are best treated as disposable.
    – keshlam
    Feb 29 at 19:32

As light as you indicate that it is and with surface laminates, I'd suggest that it's some sort of "foam core" board. This stuff has a very light foam core (hence the name) and a veneer of paper or plastic on the surface to protect it.

It's often used by architects to build 3-D models of structures they're designing so they can see them in the real world. It's often used (here in the US) as a backdrop for a diorama or presentation, or sometimes presentation material is directly attached to the foam core.

I'm not aware of it being used as exterior trim, but, perhaps, it is used that way in the UK. Maybe there's a kind that's weatherproof enough for this use.

At a minimum, I'd take it (or at least the small part) to a local home center/DIY supply place (I believe B&Q is one example, any other competing retailer should do) and ask them to help you identify it. Odds are good that purchasing a replacement part might be a cost effective solution and may be much easier than attempting to repair this one.

While there, ask about how to finish/protect it from the weather. I'm not sure if there may be special paints/treatments that need to be applied to weatherproof it, or if it's sold ready to be installed and weatherproof as is.

  • Yes I think you might be right because it does remind me of polystyrene a bit except it seems much stronger than I'm used to. I've had some success with gluing expanded polystyrene with a specialised two part glue so might try that and if it doesn't work I'll have to find a replacement
    – James
    Jan 19 at 15:33

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