MasterSeal NP1

NP 1 sealant is for homeowners and contractors sealing expansion joints and gaps around aluminum or wood window frames. You get a weather-resistant polyurethane that comes ready to gun, with no mixing. Concrete and masonry typically need no primer, which saves a preparation step on those surfaces.

Sika makes NP 1. Kaspar Winkler founded the company in 1910. Its work includes sealing, bonding, damping, reinforcing and protecting.

Choose the package for the amount of work

The cartridge suits scattered repairs. The larger ProPak suits longer runs because you get more sealant between reloads, and its packaging reduces job-site waste. Both need a professional-grade caulking gun suited to the package. Match the ProPak to a gun set up for sausage packs.

Primer depends on the surface and the job

NP 1 is considered nonpriming, but some substrates and circumstances require primer. Concrete and masonry typically bond without it; immersion and green-concrete applications have specific primer requirements, listed in the table below. Check cured-sealant adhesion on representative project joints before and during application.

Around painted windows, the coating needs an adhesion test to establish whether it will hold the sealant or needs a primer. Sealant depends on the surface underneath it staying attached. Scrape loose paint from wood to bare wood, leaving it clean, dry and sound. Remove scale, rust and loose coatings from metal to expose a bright surface.

Where primer is required, let it dry before applying the sealant. Prime and seal on the same day.

Control the depth before filling the joint

Packing a deep gap full wastes sealant and gives you poor control over the bead’s shape. Use closed-cell or soft backer rod to control depth. Under optimal conditions, sealant depth should be half the joint width, with the depth at the center kept between ¼ inch and ½ inch. Where the joint is too shallow for backer rod, use a polyethylene bond breaker to prevent adhesion on three sides.

Finish preparation before opening the package. Fill from the deepest point toward the surface, keeping the nozzle against the back of the joint. Tool the bead dry to establish its shape and contact with the joint faces.

Allow time for the cure

Plan around approximately one week for full cure. Published timing assumes 75°F, 50% relative humidity and a joint ½ inch wide by ¼ inch deep; temperature and humidity change the timing. Skin formation comes overnight or within 24 hours under those conditions. Allow room in the schedule for the full cure.

Immersion work has its own primer requirement and a listed service time of 21 days under those reference conditions.

NP 1 is paintable and compatible with non-rigid coatings. Plan the finish around that coating type.

Product specifications

Detail	Specification
Current product name	Sikaflex NP 1
Sealant type	One-component, non-sag, moisture-curing polyurethane
Cartridge size	10.1 fl oz (300 ml)
ProPak size	20 fl oz (590 ml)
Immersion primer	Sika Primer-173 or Sikaflex Primer-429
Green-concrete primer	Sika Primer-173
Unopened cartridge shelf life	15 months in original packaging
Unopened sausage-package shelf life	18 months in original packaging
Storage	Original, unopened containers away from heat and direct sunlight; elevated temperatures reduce shelf life

Frequently Asked Questions

What is NP 1 polyurethane sealant used for?

NP 1 seals expansion joints and gaps around aluminum and wood window frames. You can also use it around partition perimeters and cut-outs, where it cures to rubber and helps reduce sound transmission through gaps. Fill the joint from the deepest point toward the surface, then tool the bead dry to establish good contact with the joint faces.