I'd like to put up a small shelf. I have never tackled any kind of DIY project before so this is a first (I don't even have the necessary tools yet!) and I have a rather newbie question: Having read a few how-to guides, I've learned it's important to know the type of wall onto which you're mounting the shelf. But I really have no idea how to tell. How do I determine what kind of wall it is?
Find an opening in the wall. Start with the easy ones, telephone and cable wiring. Other options are under the sink were plumbing lines come through. Utility rooms are another good place to look. And finally, you can try checking under the insulation in the attic.
Typical drywall will be two layers of paper and a white plaster in the middle and is often 1/2" thick inside the home (a little thicker when fire code requires otherwise). Drywall is attached to the studs only and the back side will often be a brown paper.
Plaster walls will have horizontal wood slats behind the plaster and will often be thicker than 1/2".
Masonry is hard and should be obvious.
There are basically two things you have to determine - what is the supporting structure and what is the surface material.
First the support - in most private homes this is commonly wood frame, such as two by fours (boards, called studs, nominally 2 inches wide by 4 inches thick, but actually about 1.5 inches by 3.5 inches). These run floor to ceiling and are most commonly spaced 16 inches apart, but in a few cases, 24 inches apart.
In some private homes and in recent apartment construction, the support is sometimes steel studs. In cross section, these are thin walled boxes of steel that imitate, in size, function and placement, the wooden studs listed above.
In heavier construction, the support may be masonry - brick, poured concrete, concrete block, cinder block or tile blocks. These types of support are usually continuous across the whole wall.
Now the surface - in most recently built homes this is wallboard (also called drywall or plasterboard) ranging from about 3/8 inch thick to 3/4 inches thick. Most often, this is a layer of plaster with paper surfaces on both sides. Some newer constructions use paperless board.
In some older homes and in large buildings, the surface may be solid plaster that has been applied wet over either thin wooden horizontal slats or metal mesh.
In a few homes, the surface may be panelling of some sort, usually a type of plywood. Some very old, cheaper construction may use a cardboard-like material that has very little strength (not common).
Determing the type - You can carefully remove the cover at a wall switch or outlet to see if the material is obvious at the edge of the box holding the switch or recepticle. Turn off the power to that outlet (or the whole house, if you are not sure) before removing the cover. If you see a paper surface on front and back, with plaster in between, it is wallboard. If you see an indication of wood strips or metal mesk behind the plaster, it is a solid plaster. If it is plywood, you have paneling.
Perhaps more important in hanging things is to determine the supporting structure. Again at an outlet or switch, you may be able to see either wood or masonry behind the surface material, but this is often difficult.
An alternate method (that will help you later in hanging) is to see if there are hollows behind most of the surface material, indicating a stud structure. This can be done by poking a series of small holes horizontally in an inconspicuous area with an awl or small drill (with plaster walls, do not use the awl method). If you hit something solid after you are through the surface material, move three or four inches to the side and try again. If it is still solid, you probably have some form of masonry. If it is hollow, you probably have a stud structure (wood or steel).
If it is a stud structure, you need to find out if it is wood or steel - if the awl or drill can be pushed (with some difficulty) deeper into the stud, it is probably a wooden frame structure. If it seems very firm, it is probably a steel stud structure.
Once you determine the nature of the wall, you then can make decisions about how to hang (but that is another question).
In most residential construction, there aren't too many options. Off the top of my head:
In 99% of all cases with any house build in the past century, you're looking at one of the first two options.
In both cases, the wall may be covered with a wall surface...typically wall board (sheetrock) or plaster and lathe.
So, how can you tell what it is? Well, start by looking at it. Then knock on it. Sheet rocked walls sound more hollow than plastered walls (the plaster is stiffer and typically thicker).