Durock is a cement board manufactured by USG, a company in the US. Building codes in some parts of the US require the installation of cement boards before tiling or finishing bathrooms and surfaces.
Builders normally use cement boards for interior walls, so can you use Durock for exterior walls?
You can use Durock for exterior walls. You can use it for exterior walls because Durock is water resistant and inorganic, so you don’t have to fear mold growth and water weakening its integrity. Durock is made of fiberglass and Portland cement, giving it good durability and a lifespan of up to 30 years.
Can Durock be Used for Exterior Walls?
You can use Durock for exterior walls. Contrary to popular belief, cement walls can survive being wet for extended periods without softening.
The combo of fiberglass and Portland cement enhances its durability and strength. Before cement fiber wall boards like Durock, paper gypsum boards were popular.
But paper gypsum boards were susceptible to water and rot. But cement wall boards do not have such problems.
Here is a physical and chemical comparison between gypsum wall boards and cement boards and why you can use Durock for exterior walls.
#1. Durability
Durock boards are very strong and durable; they are also pest and fire resistant. The average Durock cement wall has an expected lifespan of more than 30 years.
Gypsum boards are also quite durable but have a shorter lifespan than cement boards.
#2. Water Resistance
Durock wall boards are not waterproof but water resistant. Gypsum boards are waterproof, but they are prone to molds and rot. Durock boards do not suffer from water degradation when used for exterior walls.
#3. Ease of Work
Durock boards are easy to measure, and marking the board is easy. You can measure, cut, fix and plaster the cement board without too much trouble.
#4. Weight
Durock wall boards are heavier than gypsum boards, but this doesn’t reduce their worth.
Exterior wallboards need to be firm and able to resist lots of damage. Gypsum boards are flimsy and can easily warp if exposed to sufficient force.
Will Durock Hold up Outside?
Durock boards contain high-quality Portland cement and a fiberglass composite. This special composition makes it resistant to rain and weathering.
Even though Durock boards might get exposed to harsh weather outside, they are strong enough to survive such conditions.
You can reinforce your cement board with silicone and waterproof membrane. Waterproofing your board will significantly extend its lifespan.
Fiberglass, the material used in making Durock boards, is tough and sturdy. Fiberglass is resistant to warping and can stretch without breaking or deforming.
The inorganic nature of fiberglass and Portland cement makes them unable to rot or degrade. Cement walls made with cellulose and organic matter will fall apart quickly.
How Long does Durock Last Outside?
Durock boards come with a 30 years warranty. That is to show you how Durock boards are long-lasting.
They are very few things with a warranty that long. Unlike traditional plaster that cracks, peels, and falls off, cement boards stay intact until the end of their lifespan.
If your Durock board has been properly drilled into the wall and water sealed, it should last for the entire lifespan of the house.
Here is a table comparing the abilities of two cement wall boards.
| Particulars | Durock Board Next Gen | Wonderboard |
|---|---|---|
| Flexural strength (psi) | 1250 | 1500 |
| Compressive strength(psi) | 2300 | 2500 |
| Gypsum free | Yes | Yes |
| Warranty | 30 years transferrable | Lifetime non-transferrable. |
Does Durock Need to be Waterproofed?
Durock wall boards do not need waterproofing. Durock wall boards are naturally water resistant and do not allow mold growth and rot.
Water, although very important, can become a problem for buildings and structures. Key places like bathrooms and toilets with lots of water need a layer of water insulation.
If there’s insufficient insulation, the wall tiles and cement boards will absorb excess water and fall off.
Damp walls also cause paints to peel off and weaken the plaster. Here are some ways you can waterproof your Durock board.
#1. Placing a Membrane
Durock boards might be water resistant, but that doesn’t mean they are waterproof. You must place a waterproof membrane before installing your Durock board outside or inside the building.
A membrane will prevent your mortar or cement from weakening and dislodging your tiles.
#2. Using a plumber Mesh Tape
You can use a plumber Mesh Tape to water seal the gaps between the boards. Then it would help if you sealed the gap with putty cement to get a watertight and fine finish.
#3. Silicone
You can pour silicone on the edges of the Durock boards to get a watertight seal. Silicone finish prevents pests like termites from gaining access to your backboard.
Does it Matter Which Side of Durock Faces Outside?
Durock wall boards have two faces, a smooth and fine face and a rough and mesh face. The face that faces outside depends on the type of adhesive and work you are doing.
You can use either face for your work, but the rough face bonds well with mortar, while the smooth face bonds well with flexible adhesive materials like tile mastic.
Here are some reasons why Durock boards have different faces.
#1. Tiling
Tiles do not adhere properly to smooth surfaces. The rough and water-resistant surface of cement boards is one of the best surfaces to place your tile. Tiles placed on the cement board’s smooth face would not last.
#2. Attaching Surface
The rough and smooth faces in Durock boards are its attaching surface. If you are attaching tiles to the board, you should use a rough face. In contrast, you can paint the smooth face or plaster it directly.
#3. Aesthetic Design
Different types of paints require different surfaces. You can purchase cement boards that you can paint directly.
Durock boards have different patterned boards, and You can place some without needing to tile or plaster.
#4. Reinforcement
Plain surfaces do not generate enough friction to adhere to heavy loads. So if you plan to attach tiles, you need a rough surface with enough friction to hold it in place. Such a surface directly reinforces the stability of the work done on it.
How to Install Durock on Exterior Walls?
You need a certain amount of skills and knowledge to install Durock boards on exterior walls.
Here I will list the recommended ways of installing Durock on exterior walls.
#1. Tools and Materials Needed
It would be best if you get the following tools and materials for installing Durock boards.
- Jigsaw saw or power cutter
- Glass fiber tape
- Measuring tape
- Galvanized roofing nails
- Hammer
- Power drill
- Marking tool
- Wood rasp
- Safety goggles and hand gloves.
- Thinset mortar
After getting all the tools and materials ready.
#2. Measuring and Cutting
To cut the cement board accurately, you must take double measurements of the walls and cement board.
After taking the measurements, mark the Durock board with a marking tool and cut with a power saw. You can also wear the marking line with a knife and snap the board to size.
#3. Apply Thinset Mortar
After cutting the board to the required size, mix and apply thinset mortar on the walls.
If you are boarding a large surface area, mix your thinset mortar in small batches and spread it evenly on the surface.
Making small batches will prevent your mortar from drying before you finish working.
#4. Install the Board
The Durock boards should be installed on freshly applied thinset mortar and softly tapped with a mallet.
Attach the boards to the surface of the thinset mortar. Ensure there are not too many gaps between the boards when installing.
#5. Drill the Board in Place
After installing the boards, it’s time to drill them in place. You can use galvanized roofing nails or ring shank nails.
Use nails that have big heads and can grip the board properly. You can get power drills like this one for as low as $55 on Amazon.
#6. Secure the Board
After installing and drilling the board, secure the ends and edges of the board and close all its gaps.
It would be best if you used glass fiber tape to close the gaps between the boards and thin-set mortar used to seal it permanently.
Conclusion
You can use Durock cement boards for exterior walls. Durock boards can survive harsh winters and summer without cracking and breaking up.
They are water resistant and can stay wet for days or weeks without compromising their structural integrity.
Following this guide and watching DIY videos online will help you easily install a Durock board on your exterior wall.
