A GOOD JOINT STARTS WITH GOOD PREPARATION
Before you open the cartridge, take a few minutes to prepare. The sealant will bond better, the joint will look cleaner and it will last longer.
REMOVE THE OLD SEALANT
Do not apply new sealant over old silicone, PU or other residues.
Remove the old material as thoroughly as possible with a knife, scraper or spatula. Take off any loose material along the joint edges as well.
ImportantThe new sealant must bond to a sound substrate, not to old material.CLEAN AND DEGREASE
Remove completely:
- dust
- grease and oils
- residues of old sealant
- cement dust and loosely bound particles
- cleaning agent residues and other contamination
After mechanical cleaning, degrease the substrate with a cleaner suitable for the material.
On concrete and other porous substrates a wipe with a rag is often not enough — the dust has to be removed from the surface itself.
CHECK THAT THE SUBSTRATE IS DRY
Do not seal over:
- a wet substrate
- a visible water film
- condensation
- a frozen surface
After cleaning, let the substrate dry.
TipWorking outdoors, watch the early morning hours — the surface can look dry and still carry condensation.Always observe the temperature and humidity requirements stated for the specific product.
CHECK THE WIDTH AND DEPTH OF THE JOINT
In movement joints the sealant needs enough width to absorb the movement between the two elements.
Rule of thumbAs a practical guide, many elastic construction sealants are used at a width : depth ratio of about 2 : 1. For a joint around 12 mm wide, a sealant depth of about 6 mm is often appropriate.Do not make the sealant unnecessarily thick. A deeper joint is not automatically a stronger joint.
ImportantThis is a general principle. For façade, floor and movement joints the dimensions must follow the technical data of the specific sealant and the expected movement of the structure.USE A BACKER ROD IN DEEP AND MOVING JOINTS
When the joint is deep enough, fit a polyethylene backer rod. It does three important things:
- it sets the correct sealant depth
- it reduces unnecessary material consumption
- it prevents the sealant from bonding to the back of the joint
A correctly formed movement joint must be bonded to the two side faces, not to three faces at once.
The rod should be slightly wider than the joint so it stays firmly at the required depth. Do not puncture it when fitting — use a blunt tool, not a sharp object.
If the joint is too shallow for a rod, a suitable bond-breaker tape can be used at the back.
CHECK WHETHER A PRIMER IS NEEDED
Not all surfaces behave the same. On materials such as:
- concrete
- aerated concrete
- natural stone
- some metals
- painted and aged surfaces
a pre-treatment or a primer may be required.
A primer, however, does not make up for poor cleaning. On a doubtful substrate run a small test and check adhesion after the sealant has fully cured.
PROTECT THE EDGES WITH MASKING TAPE
Apply tape on both sides of the joint before application. It helps you get:
- a straight line
- an even width
- clean edges
- less clean-up afterwards
After application and tooling, remove the tape before the sealant forms a surface skin.
- Applying over dustThe joint can look fine at first, but the sealant is bonded to the dust rather than to the substrate.
- New sealant over old siliconeResidues of old material can seriously reduce adhesion.
- Filling the full depth with sealantMore material does not mean a stronger joint. In movement joints the wrong geometry limits the sealant ability to deform.
- Three-sided adhesionIf the sealant bonds to both sides and to the back, its movement is restricted and the risk of tearing or debonding increases.