Gluing Fibre Cement to underside of steel roof

I have an existing carport with a trimdek roof. I’d like to retrofit some villaboard as a ceiling rather than have the metal showing.

I have limited headroom and live in a Fire Prone area so fitting battens will not be practical (but not totally impossible).

I’m wondering if I can glue the villaboard to the underside of the steel roof. I’ve looked to see if there are fittings that can go up inside the ribs that could hold on to which I could screw the villaboard to but can’t find any. I don’t really want to screw all the way through from the bottom of the ribs and sticking out the top of the roof.

Anyone done this or have alternatives? If it’s all too hard I’ll just have to leave it. Due to other limitations I can’t remove the roof and fit counter battens and I can’t lower the ceiling because technically I need to have 2/3rds of the ceiling height above 2100mm.

Glue definitely isn’t the answer.

What is the spacing between the carport rafters/purlins? Lining the carport with custom orb might be an option if the span is too much for cement sheet.

The spacing is 1500. The custom orb is just as ugly so I wouldn’t use that.

I was expecting that glue/silicone wouldn’t work but I was hoping someone may have had some other solution.

As I said I don’t want to retrofit purlins.

Silicon or one of the Sika products will be the only 2 that will work given your specification. The enemy you have is the heat from the metal roof and the considerable expansion co efficient of the metal roofing. you need a product tolerant of heat that will not loose its adhesive quality or go hard and brittle with time FORGET ABOUT USING LIQUID NAILS that is the worst possible use for it. Look at the glazing sealant that is used for car windscreens, it has to perform to the same environmental that you will get with your carport

I have glued fibre cement sheets up without fixings on a number of projects and it works fine even in extreme high wind exposed conditions We would cut the sheets with a tracksaw and leave 3mm expressed joints between the sheets
Use polyurethane adhesve like Sika 11FC from memory or Soudal makes a “seal and stick”type rather than the seal and flex which is more designed fir movement , we used to buy boxes if the stuff
Just prop the sheets up with batterns and sticks and keave to cure for 24 hours and you are good to go.

This is all subject to your substrate being suitable to take the sheets.

Quote:

---

Originally Posted by viiking

The spacing is 1500.

---

I used 35mm thick polystyrene sheets but the span was only 1m. the purlins were "C" section, I used 10mm ply strips screwed to the underside of the purlins to form support on the backside of the purlins. Maybe thicker polystyrene sheets would work??

Jim

Get in touch with Sika or T Rex and ask which product THEY suggest.

You need one with a bit of flex due to expansion/contraction of the roof sheeting + heat.

My suggestion would be Sika 221 because it holds the panels on buses.

I used T Rex to glue stainless sheet to concrete 5 years ago and no problems, and it is in the sun for the better part of the day.