The first time you venture out to the store to purchase drywall compound also known as mud, chances are you will find a bewildering display of products from which to choose. There will be two or more buckets of pre-mixed compound dry stuff you can mix yourself.
The type of product you will buy will depend on your needs. The powdered, setting type of joint compound is great for small projects or any time you would like to get multiple coats finished in one day. Using this type of drywall compound you can literally finish the board one day and paint it the next right after the final sanding. The setting type compounds do cost a quite a bit more than regular drywall compound but sometimes the speed of setting is worth the cost.
Setting type drywall mud comes in two distinct varieties, sandable types like the SHEETROCK® EASY SAND™ Lightweight Setting-Type Joint Compound, and SHEETROCK® DURABOND® setting-type joint compounds. All setting-type joint compounds are chemically-setting powder compounds. A chemical is added to the powdered gypsum which causes it to set and harden long before it is fully dry. It will have a somewhat green tint, very similar to green concrete until it is fully cured.
The DURABOND® type of products are not sandable, will set up like concrete in your bucket, tray or on your tools. Its primary use is for filling outside corners before the application of the finish coats. It may also be used for filling larger voids that may need to be prefilled before the tape bedding process can occur.
The DURABOND® compounds are available in a range of formulations that provide a range in setting times. DURABOND 20 sets in about 20-30 minutes; DURABOND 45 in 30-80 minutes; DURABOND 90 in 85-130 minutes; and DURABOND 210 in 180-240 minutes. The 20 is ideal for fills in old plaster applied directly over the lath or to a sound substrate. For outside corners and voids I prefer to use the 45. Usually stores like Lowes and Home Depot only stock the 20 and the 45 which leads me to conclude they are the better sellers in the product line.
The SHEETROCK® EASY SAND™ Lightweight Setting-Type Joint Compounds are sold in an equally wide range of setting times: EASY SAND 5, 8-12 minutes; EASY SAND 20, 20-30 minutes; EASY SAND 45, 30-80 minutes; EASY SAND 90, 85-130 minutes; and EASY SAND 210, 80-240 minutes. Once again the 20 and the 45 are my favorite two choices and the one most often sold at the box stores.
With any of these products you "time to set" will vary based on the water temperature, amount of mixing, air flow within the area and the number of times you trowel it on and skim it off the wall. Once it starts to set it is unusable. We suggest small batches until you get a feel for how much you can spread before it sets.
Regular old premixed drywall compound:
Also known as drying-type drywall compound is the work horse of the trades. It is still made and sold in three flavors: bedding, general purpose, and topping. It is sold in one and five gallon buckets and in boxes lined with plastic. I prefer the buckets as they are far easier to use and store.
Unless you have a rather large project there is no need or reason to purchase anything other than general purpose. It works fine for bedding tape and with the addition of a little water to the mix when topping it also works fine for the topping coats. In a large project a bucket of topping mix might save you enough time to make the purchase worth the effort. Topping mix should not be used for bedding tape or general finishing.
When using drying type compound you should allow one day for the bedding coat to dry before the addition of extra coats. This usually winds up being three days of finishing though the time each day is less than the day before. So the setting type compounds can save you some serious time.
