Sealant, often referred to as silicone, mastic or mastic sealant is a waterproof flexible rubber-like material that is applied to baths, sinks and around kitchen worktops.
It’s also used outside, usually around Upvc window frames and plastic roofline boards such as fascias, soffits and bargeboards.
This page contains a guide to removing mastic sealant from a bath and how to reseal it professionally so it lasts for years to come.
You can also apply our guide to any other surface, from sinks and worktops to window and door frames.
On this page you’ll discover:
Tools You’ll Need
While a Stanley knife is sharp enough to cut out mastic sealant, there’s a very real chance of it slipping and damaging the bath.
Instead, we recommend using a scraper.
If you’re still concerned about scratching the bath, you can use masking tape to protect it.
Here are two photos showing how a scraping tool works:
List of Tools We Recommend
Here’s a list of all the tools we think you’ll need to remove mastic then and re-seal a bath professionally:
- Multi-purpose scraper tool (as seen above)
- Removal fluid/gel
- Masking tape (optional)
- Mastic gun
- Mastic sealant
- Stanley knife (for cutting the nozzle on the sealant tube)
- White spirit (to clean off the removal gel)
How to Remove Bath Silicone Sealant
If you’re using masking tape to protect the bath, first apply this to the edge of the bathtub:
Now use the scraper tool to gently remove as much of the silicone as possible.
You won’t be able to remove all of it but you should aim to remove as much as you can without damaging the bath.
Now you’ve removed most of the sealant, use the removal fluid to loosen up any that remains.
Once all of the sealant has been removed, the entire area should be thoroughly cleaned and dried with the tissue.
It’s essential that the bathtub is bone dry.
Next, rub done the area with a tissue and a small amount of white spirit. This is to remove the silicone remover gel, we don’t want it to remove the new silicone!
The bathtub is now ready to be re-sealed.
(There are more photos further down the page)
Difference Between LMA, LMN and HMA Silicone Sealers
If you choose the wrong sealant then one the following will happen:
- it will fade and turn yellow over time
- it will peel off
- green and black mould will grow on it after a few months
To prevent this from happening, you should choose your sealant carefully:
LMA (Low Modulus Acetoxy) is a general purpose mastic sealant that can be used indoors and outdoors. It works best on smooth non-porous surfaces. Low modulus means it’s very flexible.
LMN (Low Modulus Neutral) is often used outdoors around window frames, doors and on roofline fascias, soffits and bargeboards. It has better adhesion than Acetoxy on porous materials such as bricks, blocks and concrete.
HMA (High Modulus Acetoxy) can be used in bathrooms and kitchens. It isn’t as flexible as the other two options and will dry to form a harder sealant. This makes it more suitable for rigid structures that don’t flex such as gaps between tiled walls, sturdy cast iron bathtubs and the like. It doesn’t stick so well to porous materials such as bricks and blocks.
I recommend using LMN outdoors on window frames.
For baths and showers, HMA is generally best. Although if your bath is made from a very thin and flimsy plastic, an LMA might be best as it’s more flexible.
All sanitary sealants should contain a fungicide to prevent mould growth.
For general-purpose sanitary sealing such as baths, sinks and shower units, Dow Corning 785 is a great option.
Just choose your colour carefully, it comes in grey, clear, white and several other colours too.
How To Silicone Seal A Bath Like A Pro
Just follow these steps and take a look at the photos:
- Ensure the edge of the bath is bone dry and will remain so for at least the next 24 hours (that means no bathing or showering for 24 hours).
- Fill the bath with cold water up to the halfway point. This is ESSENTIAL if you have a flimsy plastic bath that flexes. If you don’t do this, when you go to fill the bath for the first time, the mastic may tear or split as the bath flexes under the weight of all the water.
- Choose the best sealant for the task (see notes above).
- If you’ve never used a mastic gun before, go and practice somewhere else, perhaps under the sink in your kitchen or under the stairs, anywhere where it’s hidden from view.
- Cut the nozzle at an angle with a sharp Stanley knife (see photos).
- Apply masking tape if you are worried about making a mess (optional).
- Apply the mastic by squeezing the trigger smoothly and consistently.
- You can smooth off the mastic with saliva on your finger, the more saliva the better but make sure you don’t put your finger in your mouth as the silicone may be harmful if swallowed.
- Leave the window open for ventilation and avoid showering/bathing for the next 24 hours.
Here’s a selection of photos I took while sealing a bathtub in the house I recently purchased:
Dow Corning 785:
Cut the nozzle at a 45° angle with a 5-8mm hole for the silicone to come through.
It took me less than 10 minutes to remove most of the silicone with the removal tool.
I then applied the removal gel and waited for three hours before spending around 5 minutes removing the final traces of silicone and rubbing the area down with tissue and white spirit.
Resealing only took a few minutes, but I have many years of experience using silicone guns.
If you’ve never used one before, I strongly suggest you practice somewhere else first, it looks easy but it can get messy if you don’t have a steady hand.
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