How to reseal your bathroom with new silicone: a step-by-step weekend job

Photo: Frank C. Müller, Baden-Baden, Wikimedia Commons, licence CC BY-SA 3.0 (cropped)

Weekend DIY #1 · Every Saturday a new DIY job in and around the house 

Black edges along the bath, a crack next to the shower tray, a sealant line that comes loose? Then this is your weekend job. Autumn is the perfect moment: you'll be spending more time indoors, and the bathroom works hard in the damp months. In this first edition of Weekend DIY we show you step by step how to remove old sealant and apply a neat, watertight new joint. With the time it takes, the difficulty, a materials list and safety tips.

When should you replace the sealant in your bathroom?

Sealant joints age: they discolour, weather and get mould. According to sealant manufacturer Soudal, once a joint is damaged, replacing it is the only lasting solution. Watch out for these signs:

• Black or grey spots that won't wash off. Mould removers sometimes help, but according to the Dutch association for adhesives and sealants (Vereniging Lijmen en Kitten) the result is often disappointing and the mould returns faster and faster.
• Cracks, holes or loose edges. Severe mould can make a joint weak, so it no longer stops leaks.
• Sealant that feels soft or has shrunk away from the tile.

Good to know: a mouldy joint is mainly an aesthetic problem, not a hygienic one. But the damp and warmth that cause it are a sign your bathroom needs more fresh air.

Can you put new silicone over the old sealant?

No, never. New sealant does not adhere well to old sealant, so it will soon come loose, and the mould underneath comes back quickly. Soudal puts it this way: new sealant only adheres to a fully clean, dry and grease-free surface, and even small residues can make a new joint fail early. So the old sealant has to come out completely.

Which silicone sealant should you choose for the bathroom?

Choose a sealant that says on the cartridge that it is suitable for sanitary use. Then there are two main types:

• Acetic (acetoxy) silicone releases acetic acid while curing, so it smells of vinegar. According to manufacturer PENOSIL, it fits perfectly in bathrooms with ceramic tiles, glass and anodised aluminium.
• Neutral silicone (oxime or alkoxy) smells sweet or hardly at all. Use it next to bare metal, because acetoxy can make metal corrode, and on cement-based surfaces, where acetoxy doesn't adhere well. PENOSIL's advice for beginners: when in doubt, choose neutral.

Got natural stone (marble, travertine) in your bathroom? Then choose a sealant that is specifically made for natural stone, to prevent stains. And remember: silicone sealant can't be painted over. Do you want to paint the joint? Then you need acrylic sealant, which is meant for dry spots such as walls and seams.

What do you need for this job?

• Snap-off knife to cut the old sealant loose
• Scraper for the residues
• Silicone remover for stubborn thin residues (optional, but it saves a lot of scraping)
• Degreaser (or a mild cleaning agent), a bucket of lukewarm water, a sponge and clean cloths
• Masking tape
• Sealant gun
• Sanitary silicone: according to Bison, one cartridge does about 8 to 15 metres of joint, depending on the width
• A spray bottle with an acid-free soap solution and a sealant spatula (or your finger) for smoothing
• Work gloves

Step by step: how do you reseal your bathroom?

1. Prepare. Open a window or switch on the extractor fan. Clear the edges of the bath and shower. Check the temperature: the STALCO sanitary silicone may be applied between +5 °C and +40 °C.
2. Cut the old sealant loose. Use a sharp snap-off knife and cut along both sides of the joint. Careful on acrylic baths and plastic shower trays: a sharp knife scratches them easily.
3. Pull out the old strip. Grab one end and pull the sealant out in one long strip. Scrape the remaining pieces off calmly with a scraper, without damaging the surface.
4. Dissolve the last residues. Apply a silicone remover to thin residues. Soudal advises letting it work for at least 10 minutes. According to Fila, Zero Sil dissolves hardened silicone in about 20 minutes. Then scrape again and test the remover on a hidden spot first if you have natural stone or plastic.
5. Clean, degrease and dry. Remove all remover residue, because it reduces adhesion. Degrease, rinse with clean water and let the joint dry completely. This step decides how long your new joint will last.
6. Fill the bath with water (if relevant). According to Kitcentrum, a bath often sags slightly under the weight of the water, so the joint is at its widest. Seal it in that position and the sealant won't tear later. This isn't necessary in every situation.
7. Tape the edges. Apply masking tape on both sides of the joint, a few millimetres from the corner. That's how you get a perfectly straight line.
8. Prepare the cartridge. Cut the tip of the cartridge open above the thread, screw on the nozzle and cut it at an angle. Bison advises an opening of about 6 mm, and a joint of at least 6 mm and at most 20 mm wide.
9. Apply the sealant. Hold the gun as straight as possible on the joint and work slowly in one steady movement. Press the sealant into the joint, not just on top of it. Fill the joint completely.
10. Smooth it within 5 to 10 minutes. Spray the sealant with an acid-free soap solution and smooth it in one movement with a wet finger or sealant spatula. Make the joint slope slightly, so water runs off and doesn't stay on it.
11. Remove the tape immediately. Do this before a skin forms, pulling the tape back over itself and away from the joint.
12. Let it cure. Silicone cures with the moisture in the air. The STALCO sealant forms a skin after about 20 minutes and cures 2 to 3 mm per 24 hours. Keep the joint dry and don't touch it: most silicones need 24 hours before you use the bath or shower again.

How do you keep your new sealant free of mould?

Mould grows almost only in damp, warm rooms. The checklist of the Vereniging Lijmen en Kitten helps your new joint last as long as possible:

• Ventilate during and right after showering, so damp and warmth can escape.
• Rinse soap residue off the joint with clean tap water and dry it, because soap residue feeds mould.
• Avoid aggressive cleaning agents such as chlorine and bleach. They break down the top layer of the sealant, so mould comes back sooner. Plain tap water cleans best.

Milieu Centraal also advises keeping tile joints in wet rooms clean and never mixing your own cleaning products with soda, bleach or chlorine.

What safety tips should you follow?

• Always cut away from your body. Slide the blade out no more than one segment, lock it, and slide it back in after use. Snap off a blunt segment with the snap-off function of the handle or with pliers, not with your fingers.
• Wear work gloves when scraping and when using silicone remover.
• Ventilate well. Milieu Centraal advises ventilating extra when you do DIY jobs. Acetic silicone releases acetic acid while curing, which you'll notice from the vinegar smell.
• Test chemicals first on a hidden spot: not every remover is suitable for natural stone, plastic or painted parts.
• Never mix cleaning agents.

Which Saniso products do you need for this job?

Everything for this weekend job, from cutting loose to the last smooth stroke. The essentials (knife, scraper, tape, gun and one cartridge) together cost €16.01.

What is the delivery time at Saniso?

Order on a workday before 15:00? Then your order is delivered the next workday, as long as it fits in a parcel. Pallet shipments have a different delivery time. Saniso has thousands of products in stock in the Netherlands.

How do you order at Saniso if you're not a customer yet?

Your first order is easy to place:

1. Create an account via register.
2. Already have an account? Log in here with your email address or phone number.
3. Choose your product and click "Add to cart" or go straight to "Buy now".
4. Check out: all prices include VAT. Rather not pay shipping? You can also pick up your order for free in our showroom.

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Frequently asked questions about resealing your bathroom

Weekend DIY is a new series: every Saturday morning a fun, doable job in and around the house. This is edition #1, and next Saturday brings a new job.