Screw 1' x 4" x 8' Furring strips across the 24" on center ceiling joists. Then crown staple 1/4" Luan/Flooring plywood to furring strips. the furring srtips press in the ceiling tiles that a bellying and the 1/4" ply gives you a nice flat surface to glue the tile to without adding a lot of weight to the existing ceiling. Purchased at www.antiqueceilings.com/ Hope this helps.
I did see they were not listed on their website so I called and they said the website was undergoing some changes those products where omitted. They are in stock and available on Amazon www.amazon.com/dp/B0BK6JP54L/?coliid=I35HGZYJOIZZNS&colid=3R3RO91JI0ACV&ref_=list_c_wl_lv_ov_lig_dp_it&th=1 If you live nearby their showcase you can pick up and recieve a discount, Hop this helps.
Am i the only one who thinks the luan plywood on the ceiling looks better than these Styrofoam panels? Heres my takeaway....considering he had to install luan plywood to the ceiling to compensate for the uneven ceiling. Wouldn't it had been sort of comparatively just as easy to install new sheetrock? Thereby avoiding just another cheap looking alternative like these Styrofoam panels. Installing new sheetrock really isn't that difficult, and the results are so much better!
Not sure about the fire rating but these are sold on Amazon as well as Lowes now. The mobile home I installed these in had a massive roof leak and home owner said there wasn’t any staining or discoloration.
www.antiqueceilings.com Need to call them. Website is being revised and the planks are not in the products. Also on Amazon. 39"x6.5" Foam Ceiling Planks - 12pc Pack - Covers 21.1sqft - Glue Up Application - Easy DIY - Choose Your Finish - Decorative Ceiling...
The mobile home ceilings were 24” on center and bellied quite a bit. When I tried applying the planked tiles to this , they appeared to wavy. I furred the ceiling and crown stapled 1/4” plywood to get a flat surface. If your ceilings are flat you don’t need to do the plywood. Hope this helps answer your question.
Might want contact the manufacturer at www.antiqueceilings.com It is polystyrene and I know it is paintable. Should wash up well with a mild soap solution.