Last night I went hunting for hardware to attach my forthcoming wooden light soffit to the plaster soffit that’s already in place. I spent over a half hour scouring the hardware aisle (screws, fasteners, etc.) at my local Lowes and I must admit, for a big box store they have an impressive selection of fasteners. From shelf supports to decorative hardware for mirrors and glass doors, they have much more than you’d expect.
The issue I’m facing with my wooden light box is that it’s going to be completely enclosed with four sides and a plywood bottom (which will hold the new light cans). Therefore, I need some type of fastener that I can drive vertically through the plywood bottom and into the plaster soffit. There are three challenges with this plan.
First, simply driving some type of screw is out of the question because the plaster is like concrete and not accommodating to fasteners.
Second, I’d like to be able to remove the wood soffit in the future, just in case. If I didn’t want to remove, I could simply leave the plywood bottom and right side of the box off and attach the box to the soffit with L brackets. Then, with the box attached, I could slide the plywood into the box and nail the right side in place to enclose the box. This would be a nice option because all mounting hardware would be hidden. The shortfall is that if the wood soffit ever needed to come down, I’d have to remove the right side and then the plywood, certainly damaging the paint.
And finally, since I’m using 1/8” plywood for the bottom of the wood soffit, I’ll need to reinforce the plywood from inside the box to assure the hardware used to attach it to the plaster soffit won’t damage the thin plywood. (I’m using 1/8” plywood simply because it was available in my workshop, leftover from a previous project. If I were buying plywood specifically for this project, I would recommend going with at least 1/4" plywood for the rigidity.)
So here’s my plan... I’ll attach two wood boards perpendicularly to the bottom of the existing plaster soffit, one near each end. Fastened to the bottom face of those two boards will be two 10-24 x 9/32 tee nuts, one near the front and one near the back. (If you don’t know what tee nuts are, stay tuned over the next few days... they’re a fastener you need to know about.) I will then drive 10-24 machine screws up through the plywood bottom, through the support board inside the box, and into the tee nut held by the board attached to the plaster soffit. Since the machine screws can easily go in and out of the tee nut, I’ll be able to lower the wooden soffit should a situation ever arise.
To conceal the screw heads on the bottom of the wood light soffit, I’ll use plastic, hinged screw covers.
I realize that without photos or a diagram that this game plan is hard to follow. Please stay tuned over the next few days to see this plan unfold.