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When you lay the paper tape over a drywall seam, does it make any difference whether the mud you filled the gap/crack under it is hot 20/45 or regular joint compound that comes ready in buckets and takes a day to dry? Also, is it recommended to first fill the crack and wait for it to dry before applying another coat to just serve as adhesive for the tape or can it be done all in one step, meaning apply the tape over a thick (and possibly mushy) layer of mud?

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  • Drywallers will probably have their opinions on the best, but we just used the bucket type. Depending on the size of seam you usually want thinner than thick mud layers. Feather it out more than trying to save mud to a narrow strip.
    – crip659
    Commented Nov 24, 2023 at 20:52
  • There's an ASTM for drywall finishing. C840. For seams wider than 1/8" it requires setting type mud. There's "shall" language asserting that thou shalt not apply a finishing layer over another wet finishing layer, but nothing about putting an initial finishing layer over wet tape. I would expect the tape plus finishing layer to shrink a lot.
    – popham
    Commented Nov 24, 2023 at 21:49
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    USG says either hot or premixed for paper tape. (But setting type for mesh.) usg.com/content/dam/USG_Marketing_Communications/united_states/… Commented Nov 25, 2023 at 2:47
  • @AloysiusDefenestrate is setting type the hot mud?
    – amphibient
    Commented Nov 25, 2023 at 20:45
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    Yes, setting compound = hot mud. Commented Nov 25, 2023 at 21:30

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It is always best to fill any gaps first before applying the tape. This helps the paper to lay flat. Filling the gaps is best completed with hot mud as it will shrink less than regular mud.

Now, it comes down to preference, skill, and available time:

If it is a small scope, or if I'm short on time, I will proceed to tape with hot mud, though with a wetter mix than when filling gaps.

Once tapping is done, I can apply the first coat over the tape. Again, if it's a small scope or I'm short on time, I will do this first coat with hot mud. If I'm almost done for the day, or if it's a larger scope and I don't want to keep mixing up hot mud, I will use regular mud and let it dry overnight.

There are differences between the muds. Hot mud provides a harder finish when dry, which can be beneficial in some locations, but it will also take a little bit more effort to sand if not applied smoothly. Obviously you also have a reduced amount of time to work with it.

General-purpose mud and taping mud can be used for tapping (general-purpose can be used for all steps). Taping mud tends to have more adhesion. However, you can add white glue to your mud for more adhesion if needed

Finishing mud should not be used for tapping.

A great youtube channel for more information and advise is Vancouver Carpenter.

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