A neat bead is easy once the joint is right. Most of the work, and most of the failures, happen before you pull the trigger. This is how we apply sealant, from an empty joint to a cured bead.
Before you start
- Right sealant for both surfaces. Acetoxy silicones (MP, 802) aren't for natural stone or uPVC; silicone can't be painted. See which sealant to use.
- Right temperature. Pereseal AF, Pereseal N and Pereseal 802 gun from −20°C to +50°C. Pereseal MP and Pereseal 702 need +1°C to +30°C; Pereseal FR, +5°C to +30°C.
- A cartridge in date. Silicones keep 12 months unopened, acrylics 24 months. A cartridge that is hard to gun or lumpy goes in the bin.
- Read the SDS. Gloves, eye protection and ventilation, especially with acetoxy silicone in a small room.
Prepare the joint
Cut out any old sealant completely; new sealant won't bond to it. Remove dust, loose material, oil, wax and soap film. Both faces must be sound, clean and dry. 702 can go onto damp surfaces, but not wet ones. Silicones need dry.
Primer is rarely needed with our range. 702 and FR bond without primer to aluminium and most porous building materials. AF, N and 802 bond without primer to most materials. On an unfamiliar surface, run a short test length and pull it once it has cured.
Fit backer rod and masking
In a movement joint, push closed-cell backer rod in to set the depth and stop the sealant sticking to the back. Don't puncture it. For how deep, see joint design basics and when to use backer rod.
Mask both sides if you want a crisp line, keeping the tape off the faces the sealant needs to grip.
Gun one continuous bead
- Cut the nozzle at an angle, to about the width of the joint.
- Hold the gun at about 45° and push the sealant ahead of the nozzle, rather than dragging it behind.
- Keep steady pressure and a steady speed so the bead fills the joint and touches both sides with no gaps or air pockets.
- Finish each run in one go where you can. Stopping and starting leaves weak spots.
Tool it before it skins
Tooling presses the sealant into the joint and against both faces. It isn't just for looks. Tool AF, N and 802 within 5 minutes. MP skins in about 7 minutes, 702 in about 20 and FR in about 25.
Use a spatula and leave a smooth, slightly concave face. The 702, FR and MP data sheets allow a soapy water solution for tooling; use it sparingly and keep it out of the unfilled joint. Pull the masking tape straight away, before the skin forms.
Clean up and let it cure
Wipe off uncured silicone with MEK or toluene, following the solvent's own safety instructions. Clean fresh 702 with white spirit. Once cured, silicone can only be cut or scraped off.
Keep the joint dry and undisturbed while it cures. Acrylics need 24 hours before water. AF, N and 802 cure about 10 mm deep in 7 days. Details are in how long does sealant take to cure.
Which Pereseal for your joint?
Tell us the two surfaces, the joint size and whether it's inside, outside or in a wet area. We'll recommend one.
Ask us
