How to seal gaps and joints with sealant

Short answer: you seal a gap or joint up to about one centimetre wide with sealant. Indoors, on surfaces you want to paint, choose acrylic sealant. In wet rooms and in places that keep moving or get wet, choose silicone sealant. If the gap is wider or deeper, first fill it with polyurethane foam or a backer rod and then seal it. A good sealant joint bonds to two sides, is roughly half as deep as it is wide and is applied in one movement and tooled straight away.

Read this article in Dutch as well: Hoe dicht je naden en kieren af met kit?.

Which sealant goes where?

Most mistakes happen because the wrong sealant is in the wrong place. Acrylic sealant can be painted but cannot handle permanent moisture. Silicone sealant is waterproof and elastic, but paint does not stick to it.

For indoor painting jobs use a fast-curing acrylic sealant or a lightweight flexible acrylic sealant. In the bathroom choose a sanitary silicone sealant. For glass, metal and plastic a transparent neutral universal silicone works well. How to reseal a whole bathroom is explained in our blog on resealing a bathroom with new silicone.

⚠️ Draughts around a window can also come from worn draught strips, a warped window or rot in the frame. Sealant is not the answer then. Have rotten wood and leaking joints on the outside assessed by a professional, because they often need frame repair or an exterior sealant with the right build-up.

What do you need?

• A sealant gun or a sturdy silicone sealant gun for even pressure.
• The right sealant, see the table above.
• A multifunctional scraper and a universal knife to remove old sealant and loose paint.
• Fila Zero Sil silicone remover for the last traces of old silicone.
• blue painter's tape for crisp edges.
• A 12-litre bucket with lukewarm water and a drop of washing-up liquid to tool the joint.
• For wide gaps: a polyurethane foam gun with polyurethane foam cleaner.

Working safely

Sealant and silicone remover quickly end up on your hands. Wear work gloves with nitrile coating, and wear a safety goggles when scraping overhead or using foam. Polyurethane foam sticks stubbornly to skin and clothing and expands a lot. Make sure there is fresh air and read the label before you start.

Sealing a joint step by step

1. Remove old sealant and dirt. Cut out old sealant and scrape the joint clean. Remove silicone residue with a remover, otherwise the new sealant will not bond.
2. Make it dry and dust-free. Vacuum or brush out the joint. The surface must be dry, clean and free of grease.
3. Check width and depth. If the gap is deeper than about one centimetre, first fill it with foam or a foam backer rod. This gives the joint the right depth and it only bonds to the two sides. A joint that also sticks to the bottom tears sooner.
4. Mask off. Apply tape on both sides a few millimetres from the joint. You will get a crisp, straight line.
5. Cut the nozzle. Cut the nozzle at an angle, slightly smaller than the width of the joint. Better too small at first, you can always trim more.
6. Apply the sealant. Hold the gun at an angle of about 45 degrees and apply in one steady movement. Press the sealant lightly into the joint.
7. Tool the joint. Smooth it straight away with a wet finger or a sealant spatula. Use water for acrylic and soapy water for silicone.
8. Remove the tape. Pull off the tape while the sealant is still wet, at an angle away from the joint.
9. Let it cure. Let the sealant cure as stated on the label. Only paint acrylic sealant once it is dry.

Wide gaps: foam first

A gap around a frame or a pipe penetration is often too wide for sealant. Shake the can of foam well, lightly moisten the gap and fill it about halfway: the foam still expands. Cut the cured foam flush with a knife and then seal the joint with acrylic or silicone. This makes the connection airtight and neat. After use, flush the gun with cleaner, otherwise it will be stuck next time. If you carry on working on the wall, read our blog on painting a wall.

💡 Never apply sealant in frost or on a cold, damp surface. Ideally work at room temperature. For window frames on the outside, wait for a dry spell without night frost.

👷 Are you dealing with frames with wood rot, large joints in the facade, connections between roof and gutter or joints around gas, water and electrical penetrations? Then call in a professional. They know which build-up of sealant, backer rod and seal belongs there. If you are unsure whether the seal around pipes or cables is safe, have it checked by a certified installer.

Frequently asked questions

Can I use acrylic sealant in the bathroom?

Only in dry places, for example at the ceiling or a window frame outside the shower zone. Around the shower, bath and washbasin you need sanitary silicone sealant.

Why does my sealant joint come loose?

Usually there was still grease, dust or old silicone on the surface, or the joint was too thin or too deep and bonded on three sides. Remove everything, clean the joint and seal again.

Can I paint over silicone sealant?

No, paint does not stick to silicone. If you want to paint the joint, choose acrylic sealant. More about painting can be found in our blog on painting a door.

Where can you find everything for this job?

At Saniso, the online store for DIYers and professionals, you will find tools, materials and personal protective equipment for your job.

• Browse our construction tools and our workwear and safety.
• Create a customer account and order easily.
• Working on a bigger project or want to hand over the job? Request a project quote.
• Book a showroom visit, at least 24 hours in advance.
• Not sure which material suits your job? Get in touch with us.

In doubt about the approach? Feel free to call in a professional.

Saniso – Build your home with Saniso.