Field Notes

A utility knife lifting a long strip of old yellowed sealant away from a shopfront window frame
Stripping Old Silicone Before You Re-Seal
New silicone does not stick to old silicone. How to get a joint back to bare substrate, what to keep off it, and why a thin film left behind is... Read more...
A glazier tooling a fresh grey silicone bead into the joint between an aluminium storefront mullion and glass
How Long Does Silicone Take to Cure? Skin, Through-Cure and Load Are Three Different Days
Tack free in under an hour, through-cured in days, safe to load in weeks. Three different numbers that get quoted as one, and what each one means on a glazing... Read more...
A four-sided structurally glazed curtain wall with flush panes and narrow silicone joints reflecting cloud
DOWSIL 795 — ASTM C1184 Sealant, Case of 16
The one sealant on this site that carries ASTM C1184 and C920 Class 50 by name. What that means on a submittal, and when nothing else will do. Read more...
A box van loading a pallet of cartons at a New Jersey warehouse bay with the Manhattan skyline behind
Where to Buy Glazing Supplies in the New York Metro
Six ways to get sealant, backer rod and shims in the NY metro, what each is good at, and where each one costs you a morning. Written by one of... Read more...
Trays of stock on a steel warehouse shelf with receiving dates written on the carton edges in marker
Silicone Shelf Life: What an Old Sausage Does
Sealant ages quietly and you find out on the wall. How to read the batch date, what heat costs you, and the twenty-four hour test before a facade. Read more...
A gloved hand peeling a cured strip of sealant back off an aluminium test plate to check the bond
Do You Need a Primer? Test the Adhesion First
Most neutral cure silicone needs no primer on clean glass or aluminium. The ten-minute field test that tells you about your metal, and how to read the break. Read more...
A glazier sealing a shopfront joint on a snowy New York street in winter, breath fogging in the cold
Sealing in Cold Weather: What Actually Goes Wrong Below 40F
New York seals through the winter whatever the data sheet says. What cold does to cure, adhesion and joint width, and how to work with it. Read more...
A cordless driver setting a self-drilling screw into an aluminium storefront frame, metal swarf curling from the point
Self-Drilling Screws for Storefront: Point Size, Length and Why 410 Stainless
The drill point is sized to the metal, not to the screw. Get it wrong and the screw work-hardens the hole and snaps. Point, length and material. Read more...
Gloved hands working a professional sausage caulking gun along a window sill on a building site
12:1 or 18:1? Choosing a Sausage Gun for Structural Silicone
The ratio is leverage, and thicker sealant needs more of it. What the number means, which ratio suits which grade, and why sausages beat cartridges. Read more...
An old sealant bead cracked and pulling away from a window frame, with a dark gap opening behind it
Why Sealant Joints Fail: Five Causes, Four of Them Avoidable
Most failed beads did not fail because the sealant was bad. Three-sided adhesion, wrong joint shape, a dirty substrate, or the wrong temperature. Read more...
A stack of red, blue and black horseshoe shims with an anchor bolt standing through the slot and a tape measure beside it
Horseshoe or U Shim? Measure the Anchor, Not the Shim
The two shim lines look alike and are not interchangeable. The bolt hole decides it: 7/8 inch for horseshoe, 1/2 inch for U. Which your job takes. Read more...
A sealant joint running down the vertical mullion of a glass storefront, the street reflected in the glass
How Much Sealant Does a Joint Actually Use?
Linear feet per sausage for every common joint size, the arithmetic behind it, and the two things that push real site usage above the table. Read more...
A gloved hand sorting blue, red and black plastic shims spread across a workshop bench
Horseshoe Shim Colours: There Is No Industry Standard, and That Is the Problem
Blue is 1/16 inch here and 1/8 somewhere else. There is no industry standard for shim colour. Our chart, and how to check a box you did not buy. Read more...
Close-up of the corner of a dark aluminium window frame meeting glass, with a tooled sealant bead along the joint
Neutral Cure or Acetoxy? On Aluminium There Is Only One Answer
Acetoxy silicone gives off acetic acid as it cures and attacks coated aluminium. What actually happens at the bond line, and what to use instead. Read more...
A glass curtain wall seen from street level at dusk, the sealed joints between panels forming a grid
Structural or Weatherproofing Silicone? They Are Not Interchangeable
One holds the glass on the building, the other keeps water out. How to tell them apart, and what to do when the spec calls for ASTM by name. Read more...
A gloved hand pressing a grey closed-cell foam backer rod into the gap of a window joint on site
What Size Backer Rod Do You Need? A Chart by Joint Width
Measure the joint, then take the rod one size up. A chart of rod diameter for every common joint width, and why a loose rod is worse than none. Read more...