What is the exterior wall of our sunroom made of and how can we repair this section? It’s foam in the center but the outsides of it are slick and it looks like it’s particle board or plywood under that.

Damaged external wall

  • From your images, that looks like a piece of trim with the foam inside. Is that actually a wall surface? Your description made me think of Structural Insulated Panels, sips.org/what-are-sips.
    – popham
    Commented Mar 18 at 17:38
  • @popham that’s exactly what it is!! It’s the interior and exterior wall for the sunroom. How do we go about fixing it!
    – Chris
    Commented Mar 18 at 21:15
  • This is the first time I've ever actually seen the stuff in the wild. My mind sees that striped texture as analogous to engineered trim, so I assume that the scale is about 2" or 3" across the damaged area. Some sort of common item like a coin is nice in pictures like this to clarify the scale. If the damage is less than 6" across, then my first instinct is to fill it with bondo, prime, and paint it. Without more context from a broader picture, I'm uncomfortable saying anything definitive.
    – popham
    Commented Mar 18 at 22:39
  • @popham I just uploaded some more pictures to Imgur. I’m not sure how else to add them to this. I’m hoping these help. They show the extent of the damage in measurements as well as what the wall looks like that doesn’t have any damage to it just to make sure you agree that’s what it is. imgur.com/a/gpDulaJ
    – Chris
    Commented Mar 18 at 22:58
  • I'm familiar with SIPS but I wouldn't have expected what looks like a hardboard exterior sheathing. Can you get some estimates of thickness of the outer panel and the foam? Poke a wire through.
    – isherwood
    Commented Mar 18 at 23:29

1 Answer 1


Exterior walls frequently function as wall bracing. Another common term for the functionality is shear walls. Losing some bracing strength is my main worry with damage down low on the wall like that, but for just an 8" gash I wouldn't worry about the bracing strength.

Without a structural concern, the problem is purely cosmetic. To clean up that surface, Bondo makes a nice two part filler. Clean the gunk out of there and slather Bondo in there. For matching texture, I've had pretty good success by breaking a cedar shim across its grain and using the jagged edge for scratching faux grain into the filler.

Prime and paint.

(That siding looks like some kind of OSB panel product. It seems sensible to adhere a sheet of that stuff to the outside of an SIP to save a buck. Your exterior wall's surface could also just be an OSB panel product with foam incidentally behind the surface at this location. Either way, it shouldn't matter in your case. You could probably figure it out by looking for vertical lines of fasteners attaching the OSB panels to traditional wall studs. SIPs just use adhesive, so there wouldn't be vertical lines of fasteners.)

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.