Puddles on a court: what the birdbath test tells you

A court was resurfaced, and a few weeks later the owner called to say it had puddles. Resurfacing does not make puddles; it reveals them. Here is what a puddle on a court means, how to measure whether it matters, and what we do about it.

The birdbath test

Wait an hour after the rain stops, or after the hose, with the sun on the court. Water that is still standing is in a low spot, which the trade calls a birdbath. Lay a nickel in it. If the water covers the nickel, the low spot is about a sixteenth of an inch deep and will dry on its own; it is a cosmetic flaw. Lay a quarter in it. If the water covers the quarter, the spot is deep enough that it will hold water after every rain, grow algae, wear faster than the court around it and, in winter, freeze and lift the color. That one gets leveled.

The construction guides put the tolerance for a new court at a sixteenth to an eighth of an inch under a ten-foot straightedge, depending on which guide and which year, which is the nickel's order of magnitude. Older courts do not meet that and do not need to; the quarter is the working rule.

Where puddles come from

• The base settled. The commonest cause on a court more than ten years old: a soft spot in the subgrade, often where water has been getting in through a crack, lets the slab sink a little. The puddle is usually near a crack.
• The paving was not planar. A new court is supposed to be one plane with a one percent fall. A paver that stopped and started, or a roller that sat, leaves a dip that the first coating shows up. This is a construction defect and the contractor who built the court owns it.
• The slope is too flat. Courts built at a half percent or less hold water everywhere after a hard rain and take hours to dry. There is no spot repair for this; the court plays wet until it is overlaid at a proper fall.
• Net posts and drains. Footings and drain boxes settle at a different rate from the slab, and the surface dips toward them.
• The surround. Water from a lawn that slopes toward the court runs across it and sits at the low side. The fix is a swale outside the fence, not anything on the court.

Leveling

A low spot up to about half an inch is filled with acrylic patch binder, a mix of acrylic, sand and cement, applied in lifts of an eighth to a quarter inch, each one feathered out past the edge of the puddle so there is no ridge, and each one dry before the next. We mark the spot by flooding the court, chalking the water line, and flooding again after each lift until the quarter stays dry. Then the court gets its resurfacer and color, and the patch disappears. Deeper than half an inch, the spot is cut out and repaved, or it is a sign that the court needs an overlay.

This is why we flood-test on the first walk and again after the washing, before any color goes on. A puddle found after the color coats means a leveling day and a color coat over it; found before, it is an hour's work.

Water and the color

Besides looking bad, a puddle wears the court. The acrylic stays wet longer there and softens; grit collects and grinds; algae grows and holds more water; the color is the first to go. In winter the ice in a birdbath lifts the surface around its edge. A court with three birdbaths will need resurfacing a year or two before an identical court with none.

What to do

Walk the court after the next rain with a quarter in your pocket. Chalk any spot that covers it, and photograph it with the chalk. Send me the photos: if the spots are near cracks, we bridge the cracks and level the spots in the same October visit; if the whole court is holding water, it is time to talk about the slope.