Understanding Drywall Joint Compound... How To Choose It
What is drywall joint compound, or "mud"?
Drywall compound is a water-based paste that is used to cover seams, holes and make repairs in walls, ceilings and, in some cases, even painted woodwork! It is available premixed in containers up to 5 gal., or as a powder that is mixed with water.
It is a combination of some or all of the following materials: limestone, dolomite, water, perlite, vinyl polymers and crystalline silica. The combination of these materials gives drywall compound good adhesive properties, limited flexibility, and a hard, smooth surface for painting. When primed and painted, it is almost indistinguishable from the drywall it has been spread on!
Prior to 1980, many joint compound formulations contained asbestos, which is a known carcinogen under some conditions and for some people. Though modern compounds contain no asbestos, care should be taken when doing repairs that might raise dust in older buildings.
Two Types of Pre-Mixed Drywall Joint Compound...
There are two versions of premixed drywall compound on the market today, standard joint compound and so-called lightweight joint compound.
Standard drywall joint compound is the original product for finishing drywall seams and nail holes. It dries very slowly, especially under cool conditions. It is very soft when applied but dries very hard. Because of its initial softness, it has a tendency to sag badly if applied heavily. Thus, it is not the product of choice for filling holes or seams unless tape is used.
Lightweight drywall joint compound is quite a different animal. Due to its different composition, it is much firmer out-of-the-can than standard joint compound and can be used to fill cracks or holes with little sagging. This property makes it ideal for wall repairs. However, when dry it is not as hard as standard drywall compound so many drywall installation professionals prefer to use standard joint compound for everyday use.
Both these products are available in dry formulations that you mix with water. For the average homeowner or handyman, though, I see little advantage in purchasing the powder when using the premixed product is so dang easy!
Quick-Setting Drywall Compound... or "Hot Mud"
Sheetrock® Brand Easy Sand (from USG) is a powder that you mix with water. Now, this is a different animal! Many professionals love this product because it sets much more quickly than either standard or lightweight joint compound. A skilled taper can easily do a complete room in a day! (Okay, half a day, Superman!)
You can purchase it formulated with various setting times... 20-30min, 30-60min and 60-120min. USG also markets a powdered accelerator that can shorten setting time to as short as 10 minutes! Obviously, this is too short for doing entire rooms, but it can sure speed up small wall repairs. (Be sure to read the instructions if you try the accelerator... improper mixing will negate the effect, according to USG!)
Guess what the main ingredient is??? Plaster of Paris (POP)! Okay, stop the applause. Yes, I have been using Plaster of Paris for quickie repairs for years on both plaster and drywall. I suppose you'd call this product POP on steroids!!
Based on the ingredients, the main difference between hot mud and POP is the addition of limestone, dolomite, perlite and other materials, which make it somewhat easier to sand than POP which is very hard to sand.
The main problem with all drywall compounds is the dust. As mentioned earlier, asbestos was removed from all joint compounds by 1980, though care should be taken when making repairs in older buildings. Nevertheless, inhaling dusts of any type in quantity can pose respiratory problems. Minimizing sanding through good application techniques, wearing quality dust masks, collecting dust using vacuums and masking rooms with tarps all help to control the inhalation of dust and movement of dusts through the home during repairs.