Setting Block Sizing and Glass Thickness Measurement Guide

Glass thickness gauge  · 

Measure thickness before you order anything

Setting block and packer sizes follow the glass, so measure the glass first. For monolithic glass, use a caliper or a glass thickness gauge on an exposed edge, and take readings at more than one point. Nominal thickness is not exact: float glass has a tolerance set by ASTM C1036, so a lite labelled 6 mm can read slightly off nominal. Record what you measure.

An insulating glass unit is different. A caliper across the edge gives you the overall unit thickness, but it cannot tell you the thickness of each lite or the air space. Read those from the unit’s spacer marking, the glass supplier’s order or the unit’s spec sheet. An optical thickness meter or a gauge made for insulating units can read individual lites, so check what the gauge you plan to buy says it can measure.

Also calculate the weight. Float glass is about 2.5 kg per square metre per millimetre of thickness (roughly 0.5 lb per square foot per millimetre), so a 1.2 m by 1.5 m lite of 6 mm glass is about 27 kg. Confirm against the supplier’s figure.

Where setting blocks go

Pilkington’s general glazing guidelines say each lite should sit on two setting blocks centred approximately at the quarter points of the bottom edge. When that is impractical, the guideline allows the block end to be moved a limited distance from the quarter point, and the limit is stated in the document itself, so read it for your glass type.

The blocks carry the weight of the lite and keep the glass edge off the frame. They must not block the weep holes. The AGMT study guide from the glazing certification body lists proper selection and placement of setting and edge blocks, and keeping weep holes clear, among the knowledge points for installers.

With an insulating unit, the block has to bear on all the lites of the unit, so a block that supports only the inner lite is a defect.

Material and hardness

Tristar Glass Products states that EPDM or silicone setting blocks of 80 to 90 Shore A durometer hardness are placed at the quarter points. H-O Products notes that ASTM C864 governs dense elastomeric compression seal gaskets, setting blocks and spacers, with Option I normally the one called for on setting blocks, typically 80 to 90 Shore A per ASTM D2240. C864 covers the material and does not set the block’s length or width.

That distinction matters when you shop. A block labelled Shore A 80 to 90 and EPDM or silicone meets the common hardness expectation. A soft foam spacer does not. Keep setting blocks and face cushioning apart in your head. Pilkington calls for continuous cushioning of Shore A 65 plus or minus 5 for face clearance, such as neoprene, and says intermittent face shims should not be used.

Length and width: get them from the glass maker

Block length is normally tied to the area or weight of the glass, and different manufacturers and glazing manuals state different rules and minimums. Use the rule from the glass maker’s glazing guide, the insulating unit manufacturer’s instructions or the project specification, and do not guess from a rule of thumb you remember.

Block width depends on the glazing channel and the glass thickness, with space left so the block does not touch the sides of the channel and block drainage. The block must also be thick enough to give the clearance the system requires. Pilkington’s guidelines point out frame limits that affect all of this: a maximum 1/8 inch difference in diagonal lengths for squareness and 1/16 inch bow in any four-foot length. If the opening is out of tolerance, a thicker block will not fix it.

Packers, edge blocks and what to buy

Setting blocks carry vertical load. Edge blocks and spacers keep the glass centred in the opening side to side. Do not substitute one for the other, and do not use a setting block as a face shim.

Before ordering, write down: overall thickness or lite make-up, weight of the lite, glazing channel width, required block hardness and material, block length from the applicable rule, and quantity (two per lite, plus edge blocks as the system requires).

Compare EPDM glazing setting blocks only after checking the glass maker’s requirements against each listing’s stated hardness and dimensions. A product search does not establish that a particular block fits your unit or frame.

Compare EPDM glazing setting blocks

A thickness gauge is worth buying if you handle mixed stock regularly. Check its range covers your thicknesses, whether it reads monolithic glass only, and whether it can read insulating unit lites. For occasional work, a caliper plus the supplier’s specification does the job.

FAQ

How many setting blocks does a window lite need?

Pilkington’s general glazing guidelines say each lite should sit on two setting blocks centred approximately at the quarter points of the bottom edge. Check the same document for how far they may move if the quarter points are impractical.

What hardness should setting blocks be?

Tristar Glass Products specifies EPDM or silicone blocks of 80 to 90 Shore A durometer, which matches the typical ASTM C864 Option I material range. Always confirm against the glass or unit manufacturer’s instructions for your job.

Can I measure each lite of an insulating unit with a caliper?

A caliper reads only the overall edge thickness. To learn each lite and the air space, use the spacer marking, the supplier’s order details, or a gauge designed to read insulating unit lites.