A GOOD JOINT STARTS WITH A CORRECTLY CUT NOZZLE AND AN EVEN FLOW OF MATERIAL
CUT THE NOZZLE AT AN ANGLE
Cut the tip at roughly 45°. The size of the opening must suit the width of the joint.
If the opening is too small:
- you will have to move the gun more slowly
- you will apply more force
- the material may stay on the surface instead of filling the joint properly
If it is too large:
- the quantity is hard to control
- you waste material
- tooling becomes harder
Practical ruleCut a smaller opening first. You can always enlarge it. You cannot put it back.KEEP THE NOZZLE IN THE JOINT
Do not work from a distance above the surface. The tip should travel close to the joint and direct the material into it.
The aim is continuous contact with both faces, with no voids.
In a corner joint the angled tip helps drive the material straight into the corner.
WHERE POSSIBLE, PUSH THE MATERIAL AHEAD OF THE NOZZLE
On many construction joints you get better control when the nozzle pushes a small amount of sealant ahead of itself. That presses the material against the joint faces and lowers the risk of air voids.
Do not drag the nozzle quickly over the surface, leaving a thin ribbon behind it.
Watch the joint, not just the strokeWhat matters is full fill, good contact with the substrate and no air voids. The technique can vary slightly with joint geometry and the specific product.KEEP THE PRESSURE STEADY
A good joint is made with an even flow rate. Do not squeeze the gun abruptly or compensate for speed with a sudden increase in pressure.
The targetConstant speed plus constant pressure gives an even bead.If the material starts to come out with difficulty, check:
- whether the nozzle opening is too narrow
- whether the product is too cold
- whether a skin has started to form inside the nozzle
- whether the gun suits the viscosity of the material
WORK IN ONE CONTINUOUS PASS
Where possible, run the whole section without stopping. Every stop and restart can leave:
- a thickening
- a void
- a visible joint
- an area that is poorly tooled
On long joints, plan where you start and where you finish before you begin.
If you have to stopWhen you restart, make sure the new material bonds well to the still-fresh end of the previous run.TOOL BEFORE A SURFACE SKIN FORMS
Do not wait for the joint to start drying. Tooling has to happen within the working time of the specific product.
It does two jobs: it shapes the joint, giving a clean, even profile; and it improves contact, because the tool presses the sealant against the joint faces. Tooling is not cosmetic.
ImportantDo not rely on a blanket rule such as 5 to 15 minutes. Some products skin over quickly, others take much longer. Check the skin-over time and the working time in the data sheet.DO NOT OVERDO THE TOOLING LIQUID
Some sealants allow a suitable tooling liquid, but only if the manufacturer permits it. Do not flood the joint with soapy water.
An excessive amount can:
- get between the sealant and the substrate
- weaken adhesion at the edges
- leave residues on the surface
- change the appearance of the joint
RuleThe tooling liquid is there to help the tool, not to wet the substrate under the sealant.DO NOT PRESS TOO HARD WHEN TOOLING
The aim is not to scrape out half the material. Too much pressure can leave the bead too thin in the middle and reduce the material needed to absorb movement.
Shape the profile in one smooth pass with moderate pressure. If you keep collecting large amounts of material on the spatula, you have probably applied too much.
REMOVE THE TAPE WHILE THE SEALANT IS FRESH
After tooling, peel the masking tape off before a skin forms. Pull it smoothly at an angle, back and away from the fresh bead.
Do not wait for the material to start curing. Otherwise the tape can:
- lift the edge
- tear the surface
- leave a ragged line
Once the tape is off, do not keep working the joint.
- NOZZLE CUT TOO SMALLIt needs excessive force and makes filling harder. Fix: match the opening to the joint width.
- THE NOZZLE ONLY RUNS OVER THE SURFACEYou get a neat line on top and voids underneath. Fix: direct the material into the joint itself.
- UNEVEN SPEEDThe bead runs thick then thin. Fix: move the gun evenly and control the flow.
- TOO MUCH TOOLING LIQUIDIt can contaminate the bonding faces. Fix: use the minimum, and only if the product allows it.
- TOOLING AFTER SKIN-OVERThe surface drags, wrinkles or tears. Fix: work within the working time.
- PRESSING TOO HARDYou push too much material out of the joint. Fix: tool with moderate, steady pressure.
- REMOVING THE TAPE TOO LATEThe edge tears. Fix: peel the tape immediately after shaping.
HOW TO CHOOSE THE GUN
Not all sealants have the same viscosity. A light acrylic and a stiff PU do not demand the same effort. Guns with a higher mechanical drive ratio reduce hand force and suit more viscous materials.
- lower drive ratio — lighter materials and more direct control
- medium or high drive ratio — stiffer silicones, PU and hybrid sealants
- very high ratio — heavy materials, but dosing needs more care