Drywall repair questions

When repairing drywall and layign multiple layers of speckling over the tape, do I need to sand between each layer, or only the last one? Also, should I do wet-sanding or dry?
Related question: what is the difference between various wall-repair compounds, such as spackling, joint compound, etc? I mean, what is the difference in their composition and how that affects the specific application?
Thanks D
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It's important to "sand" between each application, making sure the feathering is near perfect each time and each succeeding coat wider than the last, EXcluding the taped part; don't rub on that too much.
Also,

Personal opinion, but I like wet sanding. Almost no mess/dust to contend with and for me at least, smoother and faster to work with. Usually I use wash cloths stapled to 2x4 pieces and a couple buckets of water to slide along with me. I got to where three applications at joints was pretty much my norm; dunno how that equates with the experts, but it came out looking good. 1 for a bed, tape it, mud it, sand it, mud again with a wide blade and sand final. Nails/screws I usually do two apps of mud; sanding each of them afterwards to be certain they're smooth. The overall idea is to have to sand as little as possible. I've never used the power sanders/vacuums etc so don't know about those.

Dunno - good question; I just usually read the labels and make sure it describes the job I'm about to do. But hey, I'm just a diy'er; I don't do it for a living.
HTH
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snipped-for-privacy@citigroup.com ( snipped-for-privacy@citigroup.com) said...

Ideally, you should not put so much on each layer that you need to sand it down before the next layer is applied. It is easy on the first or second layer to go overboard and try and make it nice and perfect. Don't bother as you will end up with high spots that need sanding.
Apply it sparingly as you get to the last layer and you will only need a real light sanding at the end, and (if regular mud is used) then you may be able to wet sand it.

Regular mud (compound that comes pre-mixed) only dries, it doesn't set. That means that it can be softened with water, even after it fully dries, so you can "wet sand" it with a damp sponge. The disadvantage is that it is not very strong.
A settable compound comes in powder form and must be mixed when you need to use it. This can include plaster (plaster of paris) or a commercial drywall product like Durabond (Durabond 90, or just "90", seems to be the most preferred in my experience as it has 90 minutes of working time). This sets, which means you cannot re-wet it, but it is much harder and more durable than plain mud.
The contractor I used to tape the drywall in our home uses 90 in the seams under the tape, then uses mud for the rest of the work.
My standard for any repairs and new work is to use 90 for the first coat on all corner beads (I will use plaster of paris, if I don't have any 90 available). This provides a hard and durable layer that doesn't require any sanding. The finishing layers are done with mud, which is easier to sand and can even be wet sanded if desired. I have never had such a corner fail with kids playing and smashing into it.
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