How to Properly Apply Mastic Sealant

Someone uses sealant.
  • 1-2 hours
  • Beginner
  • 20-75
What You'll Need
Tube of mastic sealant
Applicator gun
Sealant application tool
Wet cloth

If your bathroom or kitchen project includes the application of mastic sealant, you will need to know how to apply it correctly for maximum, long-lasting effects. Sealants come in many forms and you can either apply them using a gun fixing or a simple tube that can be purchased from your DIY store.

Step 1 - Choose the Correct Sealant

Of the many hundreds of mastic sealants you will be faced with on the shelves of your DIY store, you may wonder which one is the most ideal for your project. If you are working in a kitchen or bathroom, you will need a sanitary sealant that provides a flexible seal to your project. If you are using the sealant around the edge of a doorframe or other woodwork, you can use a water-based sealant.

Order sanitary sealant

Order water-based mastic sealant

Step 2 - Open the Tube

Using a sharp hobby knife or utility knife, cut a hole in the sealant nozzle. This hole needs to be cut to approximately 45 degrees. The smaller the nozzle hole you cut, the smaller the amount of sealant you will expel from it. Be sure on the size of the gap or edge you are sealing before you cut the nozzle.

Step 3 - Fill Baths

If you are sealing around a bath, it is advised that you fill the bath with water or heavy equipment prior to sealing the edges. When a bath is installed, it has a natural positioning but when it is used, it tends to sink somewhat according to the weight in it. Therefore, filling it first will eliminate sinking when the bath is used.

Step 4 - Use an Applicator Gun

Fit the tube of sealant inside the applicator gun and, using the trigger, bring the barrier to the end of the tube until it is tight, but no sealant comes out. Next, lightly pump the gun trigger until the sealant has reached the very inside edge of the nozzle. This prevents air bubbles from forming in the sealant as you apply it.

Order an applicator gun

Step 5 - Apply the Sealant

Apply the mastic sealant in a straight line along the edge of the bath (or other project) and keep it steady and firm. Do not over squeeze the trigger or the tube will expel too much sealant. Run the sealant along the length of the edge until you reach the end or a corner. Continue around the corner at the same pace you applied the first application. When you have finished applying the mastic sealant, use an application tool (which looks like a small square with a corner cut out of it) to evenly lay out the sealant. Even professionals don’t always get it right the first time and if you have a little too much material in one area, you can use this tool to even out the distribution.

Step 6 - Finish Off

Once your mastic sealant is in place, you can opt to use a wet finger to iron out any small flaws in the work. Finally, leave your sealant to totally dry. You will notice that within about 20 minutes, it will have formed a thin skin. This is the proactive film that will eventually form the hardened but flexible sealant barrier that protects from water leakage.