Silicone or adhesive will not stick – which primer helps

Problem solving 7 min read Difficulty: easy Baustoff-Held editorial team · reviewed on 30.09.2026

At a glance

If a joint or bond comes away from the substrate, the sealant is almost never the cause, but the bonding surface. What matters is whether the substrate is absorbent (concrete, plaster, natural stone) or non-absorbent (PVC, metal, paint, tile): for smooth surfaces a clean primer is usually enough, absorbent mineral substrates need a barrier primer. Without pre-treatment an adhesion failure threatens – the joint tears cleanly away from the edge.

Contents

Step 1: diagnosis – how exactly is the joint failing?
Step 2: the three most common causes of missing adhesion
Step 3: which primer for which substrate?
Step 4: how to prepare the substrate properly
Common mistakes – and how to avoid them
Frequently asked questions

What you need

Quantities adjustable

OTTO Cleanprimer 1101 adhesion cleaner for metal and plastic 100 ml Version: 100 ml aluminium bottle · choose another version €13.95
OTTO Primer 1227 plastic primer bonding agent for many plastics 100 ml Version: 100 ml aluminium bottle · choose another version €29.49
OTTO Primer 1105 mineral primer and blocking primer for absorbent substrates 100 ml Version: 100 ml aluminium bottle · choose another version €20.49
OTTO Primer 1102 sandstone primer for natural stone silicones 100 ml Version: 100 ml aluminium bottle · choose another version €12.29

When a joint or bond comes away from the substrate, it is almost never the sealant that is at fault but the bonding face. What matters is whether the substrate is absorbent (concrete, plaster, natural stone) or non-absorbent (PVC, metal, paint, tile) – because that determines the primer. For smooth surfaces a clean primer, which cleans and activates in one step, is usually enough; absorbent mineral substrates need a barrier primer that regulates absorbency. Anyone who seals critical substrates without pretreatment risks adhesion failure – the joint tears cleanly away from the edge instead of tearing itself.

Clean primer being applied to the substrate before sealing

Step 1: diagnosis – how exactly is the joint failing?

Before you buy a product, take a close look at the damaged spot. The pattern of damage tells you whether a primer is the solution at all:

Pattern of damage	What it means	Solution
Joint comes away cleanly from the substrate, back smooth and glossy	Adhesion failure – the sealant never bonded properly	Create adhesion: clean, roughen if necessary, primer
Joint tears through the middle, remains stay stuck on both sides	Cohesion failure – the joint is overstretched, too narrow or too deep	Correct the joint geometry, do not prime
Joint comes away together with paint, plaster layer or old silicone	Substrate is not sound	Remove the loose layer completely, then rebuild
Joint adheres only in places, coming away at grease or dust zones	Contamination, release or preservative agents	Clean and activate – clean primer
Dark edges next to the joint on natural stone	Edge-zone discolouration through plasticiser migration	Barrier natural stone primer plus suitable silicone

Only rows 1, 4 and 5 are primer cases. If the joint tears through the middle, it is down to the geometry – read Silicone joint keeps cracking on that. If it comes away over a wide area from the wall, Silicone joint coming away from the wall helps narrow it down.

Step 2: the three most common causes of missing adhesion

Release and preservative agents on new goods

Plastic profiles, window frames and painted components carry release agents, oils or preservatives from the factory. They are invisible and cannot be removed with water. It is exactly on these that the sealant later slips off.

Substrate that is too absorbent or sandy

Fresh plaster, aerated concrete or weathered concrete draw the moisture out of the sealant unevenly and bring loose particles into the bonding face. The sealant then adheres to dust, not to the component.

Smooth, dense surfaces without mechanical grip

PVC, metal, glass and paint offer no pore structure for the sealant to dig into. Here adhesion has to be created purely chemically by an adhesion promoter.

Step 3: which primer for which substrate?

Substrate	Product	Flash-off time	Special feature
Metal (coated and uncoated), plastics such as PVC	Clean Primer 1101	no flash-off required	Cleans and improves adhesion in one operation
Plastic surfaces, e.g. PVC window profiles	OTTO Primer 1227	min. 30 minutes	Further processing within 24 hours
Mineral, absorbent, porous: concrete, plaster, masonry	Primer 1105 barrier primer	approx. 30–60 minutes	Viscous, regulates absorbency
Absorbent natural stone, especially sandstone	OTTO Primer 1102	approx. 30 minutes	Prevents edge-zone discolouration
Smooth, non-porous surfaces: plastic, metal, paint	Soudal Surface Activator	quick flash-off	Cleans, degreases and activates in one step

All application temperatures lie in the range +5 °C to +35 °C (Soudal Surface Activator: +5 °C to +25 °C). Below +5 °C the primer does not dry off reliably – in that case wait instead of improvising. You will find an overview of all products in the category Primers & adhesion primers.

Clean Primer 1101 adhesion improver in the 100 ml aluminium bottle

Clean Primer 1101
Metal and plastic, no flash-off time

OTTO Primer 1227 adhesion promoter for plastic in the aluminium bottle

OTTO Primer 1227
Plastic and PVC, 30 minutes flash-off time

Primer 1105 barrier primer for mineral substrates

Primer 1105
Concrete, plaster and masonry

Step 4: how to prepare the substrate properly

Remove the old sealant completely

Remains of old silicone are the most frequent hidden separating layer. No primer adheres to it. How to work without leaving residue is explained in Removing old silicone without leaving residue. Check: run your fingernail along the flank – nothing rubbery may roll up any more.

Clean the bonding faces – differently depending on the type of substrate

Release agents, preservatives, grease, oil, dust and water have to go. Non-porous substrates are treated with a cleaner and a clean, lint-free cloth (flash-off time approx. 1 minute). Porous substrates you clean mechanically, for example with a wire brush or grinding disc, until no loose particles are left. Check: wipe test with a white cloth – it must no longer pick up dirt.

Apply the primer thinly and evenly

Work in one direction with a brush or application cloth. Stay sparing: excess primer forms a film and reduces adhesion instead of improving it. Do not apply beyond the edges of the joint – otherwise visible contamination arises on the surface of the component. With the clean primer, work with sufficient pressure so that the cleaning effect arises.

Clean primer being applied to the bonding face with a cloth

Observe the flash-off time – and use the time window

The Clean Primer 1101 needs no drying time; the OTTO Primer 1227 at least 30 minutes, the barrier primer 1105 30 to 60 minutes depending on the substrate. After that the following applies: With Primer 1227, further processing must take place within 24 hours. If the surface gets dusty in the meantime, the work step was in vain. Check: the surface is matt and no longer tacky.

Test beforehand on a sample piece

Because of the multitude of possible influences in processing and application, a trial application is expressly provided for – especially with unknown plastics and coated surfaces. After curing, lay a test bead and pull on it: it must tear, not peel off.

Common mistakes – and how to avoid them

Too much primer. A thick application forms a film on which the sealant slips off again. Thin and even is the rule.
Primer as a universal solution. If the joint tears through the middle, the joint geometry is to blame – a primer changes nothing about that.
Wrong primer on natural stone. A standard primer does not protect against edge-zone discolouration. For that a barrier natural stone primer is needed, combined with the suitable silicone – see Which silicone for natural stone?
Time window missed. Primed surfaces that are left open overnight attract dust and have to be treated again.
Working below +5 °C. Both primer and sealant need the minimum temperature. In an unheated new build in winter this is a real source of error.
Leaving opened packs open. Primers react with humidity. Close immediately and use up promptly; the shelf life unopened is 12 months (Soudal Surface Activator 9 months) at +5 °C to +25 °C.

How to carry on cleanly afterwards is shown in Applying silicone – the complete instructions.

Frequently asked questions

Do I need a primer for every silicone joint?

No. On clean, sound standard substrates such as glazed tiles or sanitary ceramics, a suitable silicone adheres without pretreatment. A primer is necessary when the substrate is strongly absorbent, sandy, carries release agents, or when coming away has already occurred once.

How do I tell that adhesion and not the sealant was the problem?

From the point of failure. If the joint comes away cleanly from the flank and the back is smooth, it is adhesion failure – an adhesion problem. If the joint tears through in itself and remains stay on both sides, it was overstretched.

How long does a primer have to dry?

That depends on the product: the Clean Primer 1101 needs no flash-off, the OTTO Primer 1227 at least 30 minutes, the barrier primer 1105 30 to 60 minutes depending on the substrate and the natural stone primer 1102 around 30 minutes.

Can I still seal a primed substrate the next day?

With the OTTO Primer 1227, further processing should take place within 24 hours. With the Clean Primer 1101 the period until further processing can amount to several hours, provided dust is avoided. In case of doubt, better to prime again than to risk it.

The primer leaves a white haze – is that a fault?

With the Soudal Surface Activator a slight white haze can remain visible after application. The adhesion effect is not impaired by it.

Which primer do I take for concrete or plaster?

For mineral, porous and absorbent substrates such as concrete, plaster or masonry, a viscous barrier primer such as Primer 1105 is the right choice. It regulates absorbency and creates an even bonding base. The Soudal Surface Activator is expressly not intended for these substrates.

Not sure which primer suits your substrate? Give us a call: +49 (0) 2831 - 916 77 03.