Ceiling Panels and Intumescent Primer

Goodbye, ceiling insulation! Hello, an almost finished surface?

I want as many nice, clean, flat surfaces in my house as I can manage, so when it came time to choose a material to close in my ceiling, I did not go with the knotty pine tongue and groove boards that so, so, so many tiny housers choose. 

No, I went with plywood. So glamorous, right? Not...

But before it went up, I gave it a coat of something even less glamorous (at least in name): intumescent primer. I bought a five-gallon bucket of the stuff from Home Depot for more money than I care to mention (okay, it was upwards of $350), but hopefully the peace of mind it brings will be worth it. 

You see, most houses have interiors clad in drywall, which is a somewhat fire-resistant material. My house, not so much. Intumescent coatings are a way to make surfaces more fire-resistant because when the coating is exposed to oh-crap-a-house-fire temperatures, it puffs up into an insulating layer of foam, thereby shielding whatever surface is beneath it from heat. 

I figured it would be a pain in the neck, literally, to coat the ceiling once the panels were installed, so after cutting 5 sheets of 1/4" interior-grade plywood to size, I took to them with roller and brush. 

Because the plywood isn't perfectly smooth, I actually found the brush made it somewhat easier to get complete coverage. 

I only used a small fraction of the intumescent primer at this stage. Once I apply the wallpaper liner, I plan to paint the walls and ceiling with as many coats as it takes to use up the whole bucket. The thicker the coat, the thicker the insulating layer of foam and the better the fire protection. This first coat on the ceiling panels will help make those next coats a lot easier, since the plywood surface is already looking a lot smoother and more roller-friendly! 

Here's the ceiling before installing them, by the way:

 

One disadvantage of using the foam boards is that I then had to go through and cut out channels for the cables to run along, in addition to the notches in the rafters. The original idea had been to push the foam boards up high enough so that there would be a good inch of space between the insulation and the plywood ceiling panels, but somehow that inch didn't make it into the final configuration. 

It's not shown in that photo, but I covered the notches in the rafters with steel plates to prevent accidentally puncturing the electrical cables. You can see them in the first photo of the post. They worked much better than the big hammer-in staples for holding the cables in place!

The storage loft is a cramped place to work in. Here I am preparing to lift the last panel in place with my head and foot as I staple it to the rafters...

(Side note: those Arborwear pants are the answer to my work-pants-for-ladies prayers. Double front from knee to upper thigh, 12 oz. cotton duck, and--get this--they don't need a belt!)

And done!

Alas, the 1/4" plywood has very little structural integrity, so it is already sagging between the rafters. As long as it's flexible enough that I can push them flat and hold them there with trim pieces, we'll be fine.

P.S.: What does intumescent primer do when it meets a propane blowtorch? A semi-scientific examination:

Plain plywood, burned with a blowtorch.

Primed and blowtorched. Note slight raised texture.

What was the damage? Primed plywood...

If nothing else, I definitely learned that my idea to add more coats of the primer is a good one! The spare first coat helped a little, but as you can see, the protective bubbling was quite minimal.

Unprimed plywood... much more wood was burned away.