What joint compound to use?

Gib plus 4 is crap to use compared to other products. We normally use two coats of tradeset 60 or 90 followed by gib trade finish lite. Much easier sanding than plus 4

Edit: is this is for new plaster joins

I was taught plastering by an old Canadian chap, big Andy, his methodology was surprisingly simple. 2-3coats setting compound followed by 1-2 coats finishing (less is pro, more no so).

Add compound like cream cheese on a bagel, then you remember you hate cream cheese so scrape it off.

He also pointed out pros hate sanding and that wet sanding with a sponge was a thing.

And plus 4 sucks. They should remove it as suitable for bedding compound (I mean it is but takes weeks to dry).

Others have touched on what to use but not so much the why.

There are two main forms:

1. Chemical setting compound, "quick set" / "hot mud". GIB Tradeset being an example. Think plaster of Paris with additional ingredients.
2. Air drying - gypsum and glue. Plus4, Trade Finish are examples of this type.

Setting compound:

• Goes hard while still wet, quite quickly - usable working time ranges from 5 to 90 minutes. It goes through a useful slightly plastic stage as it's setting, which you can use to smooth things out a bit/work things around, as long as you're careful. You can recoat as soon as the previous coat is properly set.
• Using hot water will make it set up faster, which can be good or bad depending what you want
• Clean your mixing container well - if there are bits of an earlier batch in there that's set/started to set, it can act as a catalyst, making the new batch kick off faster
• It sets very hard, making it suck to sand.
• It shrinks far less than air dry
• You can adjust the water mix to make it thinner or thicker, depending what you need. The more water, the more it will shrink though.
• It's quite strong in compression, making it the best thing for filling any space between sheets of plasterboard prior to taping, as unlike air drying it won't crumble and fall out of the joint.
• You can add a bit of PVA diluted in water to the mix, making it adhere better. This is great for making really solid repairs of broken board.
• There are variants that include fibrous reinforcing in the mix, eg. fibreglass strands. This acts like rebar/mesh in concrete, making it much much stronger. You can add your own reinforcing material if you have something suitable.
• It's a bit harder to use for taping, but once you have the knack, it means you can prefill, tape, and put on the first top coat in a day.

Air dry:

• Slow to dry - depending on the weather you'll generally need at least a day between coats.
• Generally easier to spread and float out smooth
• Sands well
• Weak compared to quickset
• Not very good in compression - if you use it between sheets of board where there's movement, it will often crush and turn to powder, resulting in joints peaking out
• Shrinks a lot in comparison to quickset

A reasonable process for a DIYer:

1. Prefill with quickset
2. Tape with air dry
3. First coat - air dry
4. Top coat - air dry

Once you're a bit more confident/practiced:

1. Prefill with quickset
2. Tape with quickset
3. First coat - air dry or quickset. If using quickset you may want three top coats, as if any quickset makes it through to the top layer it won't sand well, and you'll get texture differences
4. Top coat(s) - air dry

A further note on taping: mesh tape must only be used with quickset, whereas paper tape can be used with either. Mesh tape has no shear strength, so needs to be embedded in quickset where it'll act like mesh in concrete.

Secondary tip: if you need to do final touch-ups prior to painting, you can mix a little blue chalk line chalk into the mix you're using for touch ups; then you won't have to remember where you did when you need to do a final gentle sand. Blue is recommended because it doesn't seem to bleed through afterwards, whereas other colours can.

Just finished doing half my house, used trade finish lite for all 3 coats. Also decided I couldn't be arsed making a mess sanding so only sanded after the third coat using a drywall sander and vac. Glad I did.