How to Re-Silicone a Mouldy Shower

Do you have a shower or bath with old, black, mouldy silicone? Is the silicone damaged and is the shower leaking as a result? Sometimes the best bet is to start again – this means removing all the old silicone and re-applying new silicone properly.

Tools for the job

As usual there’s affiliate links below – they don’t cost you a penny extra and help me to make more independent helpful guides for you. Here’s a selection of tools I would take on a job like this:

  • HG mould spray
  • Fugi former / profile kit
  • Silicone remover – e.g. No Nonsense Sealant Remover
  • A selection of plastic scrapers
  • Sharp metal scraper
  • Narrow scrubbing brush
  • LOT of blue roll
  • Methylated spirits
  • Hair dryer
  • Cloths
  • Dow 785 Anti-Bacterial Silicone
  • Dust sheets
  • Bucket for rubbish

Obviously you don’t need all of the above but this is what I’d generally take with me and it covered most scenarios.

Caulk in a Shower
Don’t use caulk in a shower – use silicone instead!
Mouldy Silicone in a Shower
This silicone has been badly applied and needs to be replaced

Limescale in a shower?

If the aluminium or chrome of your shower is covered in limescale this will need to be removed. Silicone can’t get a good seal over limescale and ultimately the joint will fail.

Limescale in a Shower
Limescale will need to be removed to prevent future leaks

How to remove limescale in a shower?

The limescale can be used with household vinegar. This is acidic and should dissolve the limescale. PLEASE NOTE vinegar can damage the finish on aluminium or chrome. Test in a hidden area first. In my own tests I left the vinegar on for around 30 minutes. This softened the limescale enough for it to be easily scraped off and didn’t cause any damage to the aluminium. No guarantees this will work for you! Keep an eye on it and if you notice any surface damage from the vinegar remove it immediately with a damp cloth.

Limescale on Silicone
Limescale can be removed with vinegar-soaked toilet paper

Remove all old silicone

It’s essential that old silicone is completely removed before you apply any new silicone. This is a laborious process but if you don’t do it the new silicone won’t stick properly. Two basic rules about silicone:

  1. Silicone doesn’t stick to silicone
  2. Silicone doesn’t stick to damp surfaces

Rule number 1 isn’t strictly true. Silicone can stick to silicone, but it’s not a good idea to leave old silicone under the new silicone. Remove ALL of the old silicone first.

Using a silicone remover

I normally just use No Nonsense Sealant Remover and it works fine. I apply it before doing anything else and leave it for around 30-60 minutes to work. The instructions say to leave it for 15 minutes but I’ve found the longer you leave it the easier it is to get the old silicone off. I’ve never had any problems with this but if you’re unsure test it on a hidden area first.

Then use your selection of scrapers to remove all of the old silicone. Avoid metal scrapers on plastic or GRP shower trays / baths as they can scratch the surface. Use plastic scrapers where at all possible. In troublesome areas you may have no option but to use the metal scrapers. Just be very careful – apply very light pressure to avoid scratches. Multiple applications of the silicone remover may be necessary.

Clean everything down

Once all of the old silicone is removed it’s time to clean everything down. Try not to get things too wet (see rule number 2). If there’s black mould you’ll need to apply a mould remover first. I use the HG Mould Spray and it works well. I’ve also had good results with Detol Mould & Mildew Remover and even regular houshold bleach. Leave it for 30 minutes or so to completely kill the mould and then wipe everything down with a clean, damp cloth.

Dry everything thoroughly

Since silicone doesn’t stick to damp surfaces you now need to get all of the joints BONE DRY. This is an essential step that a lot of people miss. If the joints aren’t completely dry the silicone won’t stick properly. I use a hair dryer to speed up the drying process. Then if possible leave it for another 30-60 minutes to air dry.

Clean everything with meths

I then clean all joints with methylated spirits (denatured alcohol). This acts as a degreaser and gets all the joints perfectly clean ready for the application of new silicone. Again, this is an essential step if you want the silicone to last.

Apply your new silicone

Use whatever colour of silicone is required. I’ve always had good results with the Dow 785 anti-bacterial silicone. Use the Cramer Fugi kit to profile the silicone.

Leave it 24 hours to dry and that should be everything done! Check for leaks the first time you use the shower.

Shower Silicone
New silicone between the shower frame and tray
Shower Silicone
Silicone profile by using the Fugi kit
Shower Silicone
New silicone in all edges

Tips to avoid mould in showers

Now that you have nice shiny new silicone you probably want to keep it that way. Here are a few tips:

  1. Avoid storing bottles etc. on top of the silicone – leave a good air gap so that it dries out properly between showers.
  2. Ventilation, ventilation, VENTILATION!
  3. Try to keep a window slightly open or on ‘vent’ in your bathroom
  4. Keep your shower doors open when not in use
  5. Leave the bathroom door open when it’s not in use
  6. Don’t use abrasive cleaners on your silicone

Do all of the above and your silicone should last for many years. Best of luck with your re-silicone job!

Andy Mac