How to Seal Around a Basin or Bathtub with Silicone

Learn how to seal a basin or bathtub using silicone or caulk. This process of silicone sealing stops water penetration into joints around wash basins, bathtubs or shower trays.

Steps

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1
Remove any old silicone from the work area.^{[1]XResearch source}
- This can be done with a utility knife or a straight razor.
- Any contaminants like oil and grease could prevent the silicone from bonding so clean the area thoroughly with alcohol.
2
With a knife, cut the tip at 45 degrees, keeping the hole fairly small. This will give you better control over the amount of silicone released. The opening should not be so big that a bead cannot be formed, and it should not be so small that caulk tube seems highly pressurized.^{[2]XResearch source}
- Pop the silicone seal. Most tubes have a thin barrier inside the tube to prevent the caulk from curing. Many silicone guns have a tool to do this built on them. However, if yours does not, then a long nail or something similar will work.
- Load the tube of silicone into the gun.
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3
Silicone sealing can be tricky. Hold the caulk gun over trash and depress trigger to move caulk forward, filling the tip. Caulk should flow out, not squirt or drip. Release the trigger lock to relieve the light pressure inside the tube. You may want to first practice on a test piece if you have never done it before. Use the corner of a cardboard box. This will give you a feel for the gun and the rate of the silicone flow.^{[3]XResearch source}
- The tip should be slightly above the surface, nearly touching. As you begin to press the trigger, watch the flow of caulk. With one steady motion, move the caulk gun straight along seam, creating a uniform bead. Before flow stops, quickly release the trigger and begin to press again as you continue to create a uniform bead the entire length of seam. Do not stop until you reach the corner.
For best results, hold the gun at a 45 degree angle. You want to apply the caulking in an even and steady manner. Be careful not to apply too much as it can be tricky to remove the excess. When you come to the end of the area you plan to seal then release the handle and give it a quick pull to eliminate any strings.^{[4]XResearch source}
Tooling is the process of using your finger to create a seamless, clean bond between the sink and the silicone sealer. Gently pull your finger around the silicone to complete the seal. You may wish to use latex gloves. Now wipe away excess silicone from your finger, and allow to dry. When smoothing the caulk, start in a corner and go 1/2 to 3/4 across. Then start in the opposite corner and meet in the middle. When meeting the already smoothed section, lightly lift your smoothing device so there isn't a hump.^{[5]XResearch source}

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Question
Is it possible to only partially reseal around the bath tub? I only need to replace a short length on the back wall.
Community Answer
The only way to seal both parts together properly would be with heat, which is likely to take more time than replacing the whole thing (as well as potential for burns). Unless you don't mind it looking botched, in which case you can just use some polyfill to seal the joining crease.
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How long should I wait before it's dry?
Community Answer
24 hours will be ample time for the seal to fully cure to its entire depth.
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Question
What can be applied to new GE silicone caulking to prevent future mold problems?
Community Answer
An exhaust fan that's properly piped to the outdoors. The reason for visible mold is lack of ventilation, not the caulk. Vent the area for twice the time the water was used to evacuate excess humidity.
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Tips

If you're caulking a bathtub, fill the tub three quarters of the way full of water to allow the tub to sag while the silicone dries for 24 hours. Otherwise the tub will sag when you get in and pull on the seam, causing possible long-term cracking and breaching.
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Wash your hands quickly after completing tooling. Use a soft soap such as Castile. If the caulking sticks, try using an oil such as tea-tree to help remove it. Use moisturiser to add back softness to your skin.
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Use caulk approved for bathroom or kitchen surfaces. There are choices in color and price. Silicone caulk for kitchen and bath has a mildew preventer built in it.
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