Polymeric Sand Calculator

What polymeric sand does, and why joint size runs the estimate

Polymeric sand is joint filler: a blend of graded sand and polymer binder swept into the gaps between pavers, then activated with water so it locks into a flexible plug. It is not bedding sand and not play sand. The bedding layer under the pavers is a different material at a different depth, and a sandbox estimate counts bulk volume in an open box. Here the sand lives only in the joints, so the whole estimate hangs on how much joint length and joint depth the surface carries.

That makes the inputs different from any other sand calculator. A cubic-yard estimate for a sandbox needs length, width and depth. A polymeric sand estimate needs the paver module, the joint width, the joint depth and the paved area, because a patio of big 16 inch slabs hides a fraction of the joint length that the same patio in 4 by 8 pavers does. Two jobs with identical square footage can differ by a factor of three in sand.

Manufacturers publish both the limits and the coverage. Alliance Gator's 2025 technical data sheet for Gator Maxx G2 sets a minimum joint width of 1/8 inch and a maximum of 4 inches for traditional installs, with joints at least 1 1/2 inches deep. PolyBind's data sheet caps its sand at 1 inch wide with the same 1 1/2 inch minimum depth, and Dominator XL allows 1/8 to 4 inch joints at least 1 inch deep. The calculator below follows the same logic: count the joints, size them, and report the weight.

Joint width and depth: the limits makers publish

Before any math, the joint has to qualify. The table collects the installation requirements from three current data sheets, with the year each figure comes from.

Three readings fall out of that table. Joints tighter than 1/8 inch cannot take the polymer, so hairline gaps get plain joint sand or nothing. Depths under 1 inch starve the plug, which is why every maker publishes a floor. And gaps wider than 4 inches, or stone set thinner than the minimum depth, are a mortar job, not a sand job.

Measure the joint in several places and use a typical value, not the tightest spot you can find. A 1/4 inch nominal joint that opens to 3/8 in spots needs the wider number, because the estimate scales line for line with joint width.

The math: count the joint length, then the volume

For a running grid of rectangular pavers, every square foot of surface contains two families of joints, one running each way. In a square foot there are 12 divided by the paver pitch, feet of joint in each direction, where the pitch is the paver size plus one joint. Written out:

joint feet per sq ft = 12 / (L + j) + 12 / (W + j), with L and W the paver length and width and j the joint width, all in inches. The volume is that length times the joint cross section, j x d, converted from square inches to square feet by dividing by 144.

Small pavers carry three times the joint length of big slabs, which is the whole story of polymeric sand coverage. Check one row by hand: for 4 by 8 pavers with 1/4 inch joints, 12 / 8.25 = 1.45 and 12 / 4.25 = 2.82, and 1.45 + 2.82 = 4.28 feet of joint per square foot.

Weight comes from volume. A 50 pound bag of bagged sand runs about half a cubic foot, so this page uses roughly 100 pounds per cubic foot for loose sand, the same figure a sandbox estimate uses for dry play sand. Treat the pound figure as an estimate and buy by the bag with a margin, since real joints vary in width and depth along their length.

Worked example: a 120 sq ft patio in 4 by 8 pavers

A 10 by 12 foot patio, 120 square feet, laid in standard 4 by 8 inch pavers with 1/4 inch joints, joints 1 1/2 inches deep to the bedding layer. The steps run through the same arithmetic the widget does.

The label range tells a softer story. Alliance publishes 65 to 85 square feet per 50 lb bag for narrow joints, so the label method gives 120 / 85 = 1.4 and 120 / 65 = 1.8, two bags either way. The joint-by-joint count of 133.7 pounds, 3 bags, is the cautious ceiling because it fills every joint to full depth with no settling. Real jobs land between the two, and three bags covers the spread with a partial bag left for touch-ups.

The same patio at 1/8 inch joints would need 68.5 pounds, and at 3/4 inch joints it would need 365.4 pounds, a swing of more than five times on identical square footage. That is why the joint width field matters more than the area field.

Worked example: a 240 sq ft driveway in 6 by 9 pavers

A 12 by 20 foot driveway, 240 square feet, in 6 by 9 inch pavers with 3/8 inch joints at 1 1/2 inches deep. Bigger pavers and wider joints pull the estimate in opposite directions, which is exactly the kind of job worth running through the numbers.

The label method for narrow joints gives 240 / 85 = 2.8 and 240 / 65 = 3.7, so three to four bags from the label. The joint-by-joint count says 6. On a driveway, where the plate compactor seats the pavers and the joints run full depth, order five bags: enough to cover the label-to-model spread without a sixth bag sitting in the garage. If the joints were speced at 1/2 inch or wider, the wide-joint label range of 22 to 42 square feet per bag takes over, and the count moves toward five or more bags from the label alone.

Coverage per 50 lb bag: what the labels say

Manufacturers publish coverage ranges rather than single numbers, because paver height, joint width and joint depth all move the answer. These figures come straight from the data sheets.

Compare those ranges with the joint-by-joint model on a standard surface. For 4 by 8 pavers at 1/4 inch joints and 1 1/2 inches of depth, the model puts a 50 lb bag at 44.9 square feet, under what the labels promise for narrow joints, and the model errs in the cautious direction. Bigger pavers stretch a bag further, because the same square footage hides less joint: the model gives 98.0 square feet per bag on 12 by 12 slabs and 130.0 on 16 by 16 slabs, as the second chart shows.

For the third row, 100 square feet of 12 by 12 slabs with 3/4 inch joints: the model gives 1.88 joint feet per square foot, 1.47 cubic feet, 147.1 pounds and 3 bags, while the wide-joint label range of 22 to 42 square feet per bag gives 100 / 42 = 2.4 to 100 / 22 = 4.5. A wide joint wanders more than a narrow one, so the order splits the difference at four bags.

Whichever method you trust, buy one partial bag of margin. Cutting a bag open costs nothing; running out mid-joint on a dry day, with the surface half activated, costs the finish.

Watering and curing: the step that decides the job

Every failed polymeric sand job fails at the water, either too much, too little, or at the wrong moment. The manufacturers agree on the sequence even where their numbers differ, and the sequence starts dry.

• Start dry. Pavers and joints must be completely dry before the sand goes down, and rain should not be in the forecast. Dominator's data calls for temperatures above 50 F for 48 hours before and after installation.
• Sweep dry. Spread the sand, sweep it into the joints with a hard bristle broom, and compact with a plate compactor with a protective pad so the sand seats to the bottom. Repeat until the joints stay full, then sweep the surface clean of residue.
• Water with a shower setting, never a jet. Alliance's 30-30 method showers at least 30 seconds per 30 square feet, starting at the lowest point of the slope, and stops when the joints repel water and it begins to pool. PolyBind works 100 square foot sections and waters each one three times, waiting 2 to 3 minutes between passes.
• Never let a wetted section dry out during activation, and keep feet off until the surface dries. Dominator allows foot traffic right away and vehicles after 48 to 72 hours.
• Watch the clock on rain. Alliance lists Gator Maxx G2 as rain safe 15 minutes after activation for traditional installs, and 24 hours for overlay applications. PolyBind sets within an hour of activation and asks for one dry hour after.

Too little water leaves the bottom of the joint loose, and the plug shears off the first time a car tire turns on it. Too much washes the polymer out of the joint and leaves a haze of binder on the paver faces. Both failures look the same a week later, so the timing discipline is the product.

Mistakes to avoid, and when to use mortar instead

The recurring failures are mechanical, and each has a cheap fix:

• Installing on a wet surface. Damp joints activate early, cake before they seat, and cure with voids. Wait for a dry stretch; the Oregon State University Extension paver guide makes the same dry-surface point for ordinary joint sand, and polymeric sand is less forgiving still.
• Joints too tight. Under 1/8 inch the water cannot reach the bottom of the joint, so the plug never forms. Sweep in plain dry joint sand instead, or open the joint if the pattern allows.
• Joints too wide or too shallow. Past 4 inches wide, or with less than the maker's minimum depth, use mortar. Flagstone set on thin bedding is the classic case.
• Overwatering. A jet nozzle blasts sand out of the joint and leaves polymer streaks on the surface. Shower setting, timed passes, stop at pooling.
• Skipping the compactor. Hand tamping leaves the bottom half of the joint empty, which is why the surface looks full and the joint fails in a season. Compact, top up, compact again.
• Using it as bedding. Polymeric sand goes in joints only. The bedding layer is washed concrete sand, as the extension guide describes, and mixing the two ruins both.

Kept inside those limits, polymeric sand resists washout, ants and weeds far better than loose joint sand, which is the reason it exists. Plan the watering pass before the first bag opens, because the job gives you one window to activate it. For the quantities of bedding and base material under the pavers, the paver calculator and gravel calculator size the layers below the joints, and the concrete calculator covers an edge restraint pour. The installation requirements and coverage figures on this page come from Alliance Gator's Gator Maxx G2 technical data sheet, PolyBind's sand data sheet, and the Oregon State University Extension paver installation guide.