Drywall Joint Compound

There are many brands and types of joint compound available and the choices can ebe confusing, but they all fall into one of two categories; drying-type compounds and setting-type compounds.

Drying Type Compound

The most common compound is drying type joint compound. This is the stuff that comes in 1 or 5 gallon buckets at the hardware store. It can be in pre-mixed or powdered form. A one gallon container is good for patching and small touch up jobs, whereas a 5 gallon bucket will be enough to finish a typical 12 by 12 foot room.

Compounds of the drying type are vinyl-based and dry via water evaporation. They must be allowed to thoroughly dry between coats. Time required for drying is highly dependant on air, drywall surface, and compound temperature, as well as ambient humidity and airflow. A good rule of thumb is to allow 24 hours for drying, under optimal conditions.

The premixed compound has the advantage of being ready for use straight out of the container, as well as having a good consistency of mix, as it is controlled at the factory. You also get the benefit of being able to reseal the bucket to keep your compound fresh for later use. However, an opened container will go bad after about a month at room temperature.

The powdered form drying type joint compound has the benefit of longer storage life. As its name implies, it comes in dry form and needs to be mixed with water prior to use. It's use and workability are otherwise the same as the premixed form.

Depending on what you are working on, you will probably be regularly using three kinds
of drying type compound; topping compound, taping compound, or all-purpose compound. They all come in dry or premixed.

    Topping: Use this for the final thin coat, because of it's ease of workability, the smooth way it feathers on a surface, and it's smooth finish after sanding.
    Taping: Use this as a first coat, to capture the joint tape, and as second coat filler. It has superior bonding ability, is crack resistant and a low shrinkage coeeficient after drying.
    All Purpose: Can be used for any stage of drywall joint taping. It is the most commonly used because of the convenience, but you give up the better strength and bondability of the other types as a tradeoff. Good for smaller and patch up jobs.

Setting Type Joint Drywall Compound

This kind of compound dries by chemical reaction rather than water evaporation, and, as such, their advantage is that they harden much quicker than drying type compounds. They will set completely in from 20 minutes to 6 hours, depending on the type and brand. This allows working in cooler or humid situations, not to mention the fact that you have less downtime in between coats. They also have the advantage of having better bonding, anti-shrinkage and anti-cracking properties. This is the compound of choice for rush jobs.

The big disadvantage with setting type compounds is they are quite a bit harder to sand than drying type. As a consequence, getting a smooth finish while applying it is of the utmost importance. Otherwise, you will spend more time sanding. In addition, it does not come premixed, as mixing initiates the hardening reaction. This means that it can't be stored and reused later, so you need to be good at estimating how much to mix for your job.

The best way to use setting type compound is as a first coat, to embed your joint tape, and even as a second filler coat. For a final finish coat, it recommended you use topping or all purpose drying type joint compound.

How Much Compound do you Need?

Rough estimates for how much drywall joint compound are required for typical three coat jobs are:

    Premixed drying type: 11 gallons per 1000 square feet of drywall surface.
    Powdered drying type: 80 pounds dry compound per 1000 square feet.
    Setting type: varies by brand, by roughly 3 bags of dry mix per 1000 square feet.