How to Use Joint Compound with Plasterboard

What is joint compound?

Also known as plasterboard joint filler, joint compound has the same consistency as mud and is primarily used for the installation of new drywall and large-scale repair jobs. It is created from a mix using limestone and gypsum, as well as other materials including starch, clay, perlite and mica. Despite its main use for bigger repairs, drywall joint compound can also be used for plaster walls to fix smaller problems, such as filling small holes and smoothing out wall dents. There are 4 different types of joint compound.

1. Quick-setting joint compound

An effective solution for tackling big repairs, this type dries quicker than its counterparts. It is particularly useful if you need to apply a number of coats in one day. Quick-setting joint compound is a drywall filler which works well for deeper holes and cracks in plaster. For humid working conditions, this compound will be set by a chemical reaction in damp environments instead of water evaporation. Depending on which quick-setting joint compound you buy, setting times can range from 5 minutes to 90 minutes.

2. All-purpose joint compound

A popular option when it comes to taping and finishing fasteners, wallboard joints and corner trims. All-purpose joint compound is easy to work with and provides low shrinkage for both the second and finishing coats. It is effective for all stages of drywall finishing, such as skim-coating and texturing, in addition to embedding filler and joint tape. Also, the all-purpose joint compound is lightweight but weak compared to the topping compound - the drying time is also slower.

3. Taping joint compound

This joint compound is used over drywall tape. It is an effective choice if you need to cover cracks in plaster as well as when crack resistance and superior bonding are needed, such as around window and door openings. The drying time is fast and sanding proves more difficult than topping and all-purpose types. For laminating drywall panels on ceilings and multi-layer partitions, taping joint compound is the best option to complete these jobs.

4. Topping joint compound

In conjunction with the taping compound, the topping joint compound is spread onto a wall as a final coat with 2 additional coats of taping compound. It is low-shrinking, is applied smoothly with high workability, and provides a tough bond. However, you should not use this type for embedding joint tape. Although it is less convenient than an all-purpose joint compound, you are able to mix as much as you need with water and save the remaining compound for future projects. But if it is applied correctly - compared to lightweight joint compounds - the sanding time should be reduced.

Things to consider before using joint compound

Before you buy a plasterboard filler to complete the job, it is important to make sure you have the right materials and have thought about any potential problems. Here are 3 key considerations to think about. 

Choose the right joint compound

As outlined above, there are different types of joint compound for certain jobs and situations. Therefore, you should do your research into which type of joint compound will work best for your project. For example, you will find an all-purpose joint compound is more flexible to work with than a topping compound - particularly for embedding tape. 

Budget restrictions

If you are working on a small project or your budget is restricted, an all-purpose joint compound will be the best option. It is cost-effective and works as a comprehensive solution. But, because all-purpose joint compound has high shrinkage and can be tough to sand after drying, you will likely have to apply multiple coats to fill any cracks and holes.

Invest in a power mixer

Before you start applying joint compound to the plasterboard, be sure to invest in a power mixer, a useful tool if you are mixing the compound yourself. This will prove useful if you are working on bigger projects and need to mix large amounts of joint compound. For smaller amounts, you can use a power drill for the mixing, but investing in a power mixer will prove to be convenient and save you time. 

Benefits of using a joint compound for plasterboard

Joint compound is versatile and can effectively be used for a vast range of tasks. This includes skim-coating ceilings and walls and repairing cracks. Here are 3 top benefits of using joint compound for plasterboard. 

Time-sensitive

Particularly true if you decide to use a ready-mixed joint compound, you will save a lot of time instead of having to prep and mix the compound yourself. Plus, it is handier if you need to finish the job on a tight schedule. Generally, joint compound will harden at a fast pace and is easy to sand which will also save you time. 

High-quality finish

Because joint compound is manufactured to provide a smooth texture, the coverage will appear level once applied. The need to smooth out any imperfections to the surface will be minimal. A top tip when you apply a skim coat is to use a paint roller for a perfect finish - it goes on quickly and the clean-up is limited. Be sure to replace the roller cover if it slides and becomes stuck. 

Things to consider when using a joint compound for plasterboard

Although there are some clear benefits of using a joint compound, you should also consider the potential risks and how they can be overcome.

Potential health issues

Because the joint compound is produced from materials including silica, mica and gypsum, builders and other construction professionals are at risk of developing irritation of the throat, eyes and nose. If the exposure continues, the irritation could lead to further health problems such as similar breathing issues to asthma and continuous airway and throat irritation. Particularly when silica is present, the risk of lung cancer and silicosis is increased.

Problem mixtures

You may run the risk of mixing the joint compound too thinly if a lot of water has been added. If this happens, you should add an additional dry mixture and use a power mixer to make the compound stiffer. Plus, if too much water has been used, the thin combination will take a long time to dry. When painting - if you choose a high gloss paint - it may not bond well with the plasterboard joint compound. 

How to use joint compound

Once you have weighed up the benefits and risks, it is time to get started. Here are the 5 steps to correctly apply plasterboard jointing compound. 

Step 1 - Prepare tools and materials

To make sure you are fully prepared, be sure to collect all the materials and tools you will need throughout the job. Below is a checklist. 

Now is also a good time to gently dust off the plasterboard - it will help the compound and plasterboard to work well together. Also, use this time to cut your jointing tape to the required length.  

Step 2 - Seal any joints

After you have mixed the joint compound, you should start to fill the plasterboard joints with a scraper or jointing knife. When doing this, it is important to make note that joints should be no larger than 1mm wide. If the joints are bigger, you may need to use mortar before the joint compound. A generous amount of joint compound should be applied, starting from the top and working to the bottom. Be sure to cover the area around the joint with compound. 

Step 3 - Use jointing tape

With the cut and measured jointing tape, fold the length in half - you may find the tape has a printed side which should be placed against the plasterboard. Start with the outer corner and stick the jointing tape to the joint compound which should still be wet. This process is also known as tape and jointing. Again, the tape should be applied from top to bottom. With your jointing knife, go over the tape with moderate pressure to tackle air bubbles and remove any excess compound. 

Step 4 - Apply a second layer

Depending on which type of joint compound you have decided to use, you may need to wait anywhere from 6 hours to a few days before applying a second layer. Check out the manufacturer’s instructions before moving on to this stage. But once the joint is ready for a second layer, follow the same method as the first application. Then you will need to go over it with your jointing knife and make sure the surface is completely flat. Once dry, apply a third and final layer, covering a wider area than before and smooth everything out with your jointing knife. 

Step 5 - Sand down the joints

To ensure a smooth finish, sand the compound down after its drying time using a sanding block. This ensures a smooth finish - you only need to apply light pressure when sanding. If you are planning to paint over the joint compound, think about using a primer. 

Joint compound vs spackle: What are the differences?

Below is a table outlining the key differences between them which will help you determine the best choice for your project. 

Joint compound products available at competitive trade prices 

We supply high-quality joint compound and other dry-lining products. If you are a construction professional with a Building Materials Nationwide trade account, you can use your cash or credit trade account to pay for the tools and materials you need. When you shop with us, quick UK-wide delivery is available so you receive your order ready for the job. Apply for a trade account online or give us a call for a friendly chat.