Greenboard and Cement Board
Greenboard is a material used on bathroom walls and is known by several names, including several trademark names.
- gypsum board, and
- plaster board.
There are several generic names used by local contractors based upon the area of the country. In this discussion we will just call the material “drywall”.
The picture to the right is of a bathroom being updated from the 1950s by putting greenboard on the walls.
Drywall was developed as a replacement for lath and plaster construction.
This was a method wherein:
- the studs were covered by wood lath strips nailed to the 2x4s and spaced a half inch or so apart;
- covered with wire mesh;
- covered with a brown coat of plaster – this is the foundation for the wall; and
- then a smooth thin white final coat of plaster was applied.
The finished product looked good, but took several days to cure.
This was a time waster as the worker had to wait for the material to dry. Sometimes there were multiple coats of plaster to get the desired degree of finish. Some of these coats could make the wall several inches thick.
Then along comes drywall to solve that wasted time problem. I have literally seen a wall go from studs to finished product in the same day with fast drying mud compounds.
And if the work is completed correctly, the outward appearance will be very similar.
There are four basic types of drywall.
- the basic paper wrapped for the vast majority of wall coverings;
- greenboard or MR for moisture resistant drywall. (NOTE: moisture resistant NOT water proof);
- Type X or fire rated or resistant, typically 5/8 thick and the newest, paperless drywall; and
- Georgia Pacific brand name is DensArmor Plus. This is a glass mat surface front and back and is the ideal replacement for greenboard.
Drywall is available in ¼, 3/8, ½ and 5/8 thickness.
- ½ inch is the most common size and usually the least expensive;
- Type X is typically 5/8 and is always used in commercial buildings and should be used between floors in multi-story houses to slow the spread of the fire between floors. Depending on which part of the country your home is in, you may or may not have this material installed.
Greenboard is for use in damp environments, but not wet environments. The greenboard surface is coated with an oily waxy material that gives it the moisture resistant” rating. This is NOT the material you want to attach ceramic tiles to.
If the tile grout is porous, the water will seep through and damage the wall behind the tiles. This will cause the eventual failure of the wall system and damage to the interior of the wall.
It may also cause damage to the structure of the home and possibly the growth of mold.
Never use greenboard for ceilings as the material is heavy and will not support its own weight if 16 on center supports are used. If you want to use greenboard on the ceilings, use 12 spacing.
This material comes in ¼ and ½ widths. It is commonly available in 3X 5 boards and sometimes, depending upon the distributor, in 4X 8 sheets.
It can be installed behind shower walls up to the height of the tile where greenboard matches the edges and continues to the ceiling and surrounding walls.
Tape the cement board and seal the seams with cement based joint tape, an alkali resistant Portland cement mortar or thin set mortar. This is to ensure that water does not get through to the wall behind the cement board.
The joints past the cement board are joined with joint compound and sanded smooth for final finishing.
Hanging drywall is fairly easy and can be completed by the average handyman if they take their time and plan ahead. The biggest item is, no unsupported end seams and always split seams on support studs. The fewer the seams, the less work hiding them.
I like to place mud in the seam and then press the paper tape into the mud with at least a 6 knife and let it dry. Come back and add more mud on top of the tape press it flat. Let it dry. Come back again and add more mud. This time use a 10 or 12 knife to smooth the seam out.
TIP: If you are patching the wall and there are some bulges around screws, take a carriage bolt with a rounded head and tap the area smooth or slightly below the current surface to dimple the material. This will allow the drywall compound to flow evenly around the surface and make everything smooth. If done correctly, there is very little finishing required.
If you need information about patching greenboard, go to our Drywall Repair Made Simple page.
I always like to prime the walls to keep the final coat of paint from being sucked into the porous drywall causing blotches and shadows on the finished wall.