How big of a hole in drywall can be fixed by spackle alone?
The previous owners left numerous holes in the drywall. Each hole is the diameter of a coaxial cable, which I want to patch up. Can I use spackle to bridge the gap? Or can I press fit a piece of wooden dowel to form a firm base for the spackle?
I don't think you'll be happy with spackle for anything bigger across than a nail hole. It's not very strong, and also not very sticky. So what tends to happen in your situation is that the spackle will fall through the hole into the wall; if not when you're applying it then it will be likely to do it when you try to sand it smooth before you paint.
I think the solution that's going to get you the best results for holes that size would be to cut a 2" square of fiberglass drywall joint tape and stick it over the hole, and then use joint compound to fill the hole and cover the tape, feathering it out to a 6-8" diameter circle. You can do this reasonably well with a cheap 4" putty knife. Then sand it smooth, being careful not to sand all the way through to the tape.
For something that small the spackle should be fine by itself. You might want to fill the whole with spackle first and let it dry, as some will tend to want to bubble out. Once it is dry sand it down and then put on a second (hopefully final) coat of spackle.
(I am assuming the “spackle” is US for filler.)
Have a firm base for filler does help, as you need to be able to push on the filler to get it well into the side of the holes. However as it is not the end of the world if the filler breaks when you try to send it, I would try the easy option first.
For larger holes I have built up with layers of filler passed into the side of the hole then left to dry for a day before doing the next layer. This sounds like a real pain, however if you have lots of holes and you don’t need them fixed today, you can just walk round your house each day making each hole a bit smaller. The key is to push the filler well into the side of the hole so it grips well, trying not to have it coming to far in front of the wall, so as to reduce the amount of sending you will need to do. (No professional would do this, as it need to many visits, but you have not travel costs to your own house)
Pushing newspaper or a sponge through the hole so it expands behind to provide a base for the first layer of filler has also worked for me in the past. However if the hole is more than about 2cm across, you should be fixing a hard backing of some sort.
For a hole the size of a coax cable, I would just spackle. Any larger and I would use drywall compound. It make take a couple of coats. If its up to the size of a nickle (3/4 of an inch), I would put a piece of fiberglass tape over it like Mike suggests. If its larger than that, I would cut a small piece of drywall and tap it into the whole. Here's two tricks: 1)cust the piece of drywall slightly larger than the hole, then trace around it to mark what to cutout on your wall. Use a razord blade knife or drywall saw to cut your wall, or score and snap. Two, put a drywall screw into the scrap you are adding, to hold it while putting the first coat of drywall compound on.
I have used a wadded up piece of newspaper pushed into a hole this size. It provided a backer for the spackle or joint compound. As mentioned by the other posters, you need several coats then sand it smooth.
Spackle on it's own will work just fine for small holes. For larger holes shoving paper into the hole frequently results in lots of paper inside the wall cavity before you get it sitting just right for patching. At least that's how it goes for me.
For holes that might be too gig for just spackle, yet a bit small for drywall tape, one trick I've not seen mentioned before is to use a use a piece of stocking/pantyhose, say about an inch or two across. Rather than just stuffing it into the hole, put it into the spackle so that it.s well covered, then make a ball out of it and put that in he hole. Once it has gone firm you can put a little more spackle over the top to finish it off. This works much like the fibers in fiberglass.
I'm not sure what you mean by "spackle" but I've had good luck sealing smaller holes with Polyfilla - you might have to do it in a couple of passes, but it'll do a 1" hole without any problems.
This is a two-step trick. You can fill the hole enough to cover it closed but not enough to fill up the 1/2" depth completely, then push it in slightly towards the back. this will plug up the hole, but there will not be too much paste to weigh it down and have it open up again. let it dry, then fill up the rest of the hole.
An interesting trick you could use also is with a cocktail umbrella. Open it up inside the wall, and keep a hand on the handle part. Pull on the umbrella until the underside of its canopy is against the inside side of the wall while you put the paste in. The handle is usually made out of cheap wood or plastic that is very easily cut and sanded down alongside the excess dried plaster.
This is kind of going the other way from what you are asking, but have you considered putting a "remodel box" like this "Super Blue Hardshell" box from Carlon:
and then putting a cover on it, possibly with a blank faceplate or a coax terminal? You would end up cutting a larger hole, the size of the box, then you push the box through and turn the screws to lift up the "flag" (dark blue in the photo above" and pull it towards the drywall from the back to secure it in place.
If you don't have any interest in having coax in these places, perhaps the coax could be used to pull Ethernet network wiring or something else that you'd find useful in these locations?
I did this when we moved into our house, to bring Ethernet and phone to places where we didn't have it before, and these boxes look very nice when done. It looks like any other electrical or phone outlet you'd have in the house.
You can get modular faceplates with one or multiple holes to mount various networking, phone, audio and video cables in, for example this coax/HDMI/Ethernet example from Wisdom Electronics:
