I wanted to get my son a large chalkboard for his room because he likes to draw on a large scale. Unfortunately for him I'm horribly cheap and infinitely bored. Real, good quality chalkboards of any significant size are rather expensive so here is how i made a decent quality one for relatively cheap.
Step 1: Materials
There isn't much required.
48 x 48 piece of 5/8" plywood
48 x 48 sheet of 24 ga. sheet metal
Step 2: Plywood base
I already had a 48 x 48 piece of plywood in my garage so that was the size i decided to make the board. Next, I picked up a piece of sheet metal from the local sheet metal union wear I work. You don't NEED to use sheetmetal for this project but it is necessary for another project I'm working on for later. I need the board to be able to hold strong magnets. I then trimmed the metal to 45 x 45 so that there would be a 1.5" border of exposed plywood around the edge. Lastly, I used liquid nails to secure the metal to the plywood.
Step 3: Poof! Chalkboard.
After the liquid nails set I painted the metal with some Glidden chalkboard paint from the hardware store. This paint is the most expensive part of the project. It is about $15.00 per pint. It is important that you follow the drying and curing instructions on the can. If you try to rush the paint it wont give you the nice smooth surface you need. Also, you should use a dense foam roller rather than a brush.
Luckily when I did this the humidity in my area was in the single digits and the temperature was low 90's. The paint dried and cured sufficiently within 2 days.
Once the paint was cured I dry fit some inexpensive wood base board for a nice frame.