Category: Patios & Pavers

Every spring I get the same call. The patio has a hump in it, or one corner sits an inch proud of the door threshold, and it wasn’t like that in October. By July it’s mostly gone back down and the homeowner has decided it fixed itself.

It didn’t. It’ll be back in March, a little worse.

Frost heave, in plain terms

Frozen water in soil doesn’t just expand the nine percent that ice expands. What actually happens is worse: as the freezing front moves down, it pulls unfrozen water up toward it from below, and that water freezes into growing lenses of ice. Those lenses can lift a slab several inches.

Three things have to be present. Freezing temperatures reaching the soil, soil that holds and moves water — silt and clay are the bad actors, clean gravel is nearly immune — and a supply of water. Take away any one and the heave stops.

Downtown Appleton has plenty of the middle one. Our frost can drive four feet down in a hard winter, and a patio slab sitting on four inches of sand over native clay is riding on top of all of it.

Why the house doesn’t move but the patio does

Because the house is founded below the frost line and the patio isn’t. Footings here go down to roughly forty-eight inches for exactly this reason — below that depth the ground doesn’t freeze, so it doesn’t move.

A patio slab is a floating element. Nobody digs four feet for a patio; it would cost more than the house’s foundation. So the strategy is different: instead of getting below the frost, you take away what frost needs.

What actually prevents it

• A real base. Six to eight inches of compacted open-graded aggregate, not four inches of sand. Clean angular stone doesn’t hold the water that feeds ice lenses.
• Drainage under and away. The base has to have somewhere to send water. A base that drains into native clay and sits there is a bathtub.
• Grade that falls away from the house, a quarter inch per foot minimum, so surface water leaves rather than soaks in at the edge.
• Downspouts discharging past the patio, not onto it or beside it. This one detail causes more heave than any other single thing I see.

Pavers have a real advantage over a poured slab here — they move as individual units and can be lifted and relaid. A slab that heaves cracks, and a cracked slab stays cracked. If yours is pavers and it’s dipping rather than lifting, that’s a different failure with an easier fix, which I’ve covered in releveling a paver patio that has started to dip.

What repair runs

Pulling up pavers, correcting the base, and relaying: $9 to $18 per square foot, and the number depends almost entirely on whether the existing base can be reworked or has to come out.

Replacing a heaved concrete slab is $12 to $22 per square foot with proper base preparation. Slab jacking to lift a settled section is cheaper at $600 to $2,000, but understand what it does — it corrects the position without touching the cause, so on a heaving slab rather than a settling one it’s temporary.

Frost depth requirements for footings are set locally and are worth checking against whatever anyone proposes to build attached to the house; the City of Appleton’s building inspection division can confirm the number that applies to your address. For a freestanding patio it’s not a code question, it’s a base preparation question, and that’s where the money should go.

Frequently asked questions

Why does my patio lift in winter and settle in spring? Frost heave. Ice lenses form in water-holding soil under the slab as the freezing front moves down, lifting it, then the ground relaxes on thaw. The slab rarely returns exactly to where it was, so it worsens each year.

How deep is the frost line in Wisconsin? Roughly four feet in the Fox Valley for footing design purposes, though it varies by location and local requirements. That’s why house footings go that deep and patio slabs, which don’t, are the things that move.

Can frost heave be prevented on a patio? Yes, by removing what frost needs rather than digging below it — six to eight inches of compacted open-graded stone base, drainage away from the slab, correct grade, and downspouts discharging well past the edge.

A paver patio has no mortar and no slab. What holds it flat is friction between units, and what supplies that friction is the sand standing in the joints. Almost every complaint about a paver patio, from wobbling units to weeds to a sunken corner, traces back to joints that have quietly emptied out.

The patio is held together by what is between the pavers

Interlock is the whole design. Full joints let neighbouring units share a load instead of taking it alone, so a patio behaves like one surface rather than a few hundred separate pieces. Drop the sand level a quarter inch and the units start to rock under foot traffic, edges chip where they knock together, and the bedding layer underneath begins to migrate into the gaps. That is why the yearly job is not sweeping the surface, it is checking the joints and topping them up.

Weeds are a symptom, not the disease

Weeds in a patio almost never grow up from the base. Seed lands on the surface, works into a joint that is no longer full, finds the small amount of organic material that has collected there, and germinates. Pulling them treats the visible half. The joint that let them in is still open, and it will collect the next batch. Refilling joints properly does more for weed control over a season than any amount of spraying, and it fixes the structural half of the problem at the same time.

Polymeric sand, and where it disappoints people

Polymeric sand carries a binder that sets after wetting, so it resists washout and suppresses germination better than plain sand. It also has narrow installation requirements, and this is where it goes wrong. The joints have to be filled deep, the surface has to be swept genuinely clean before watering, and the watering has to follow the manufacturer method rather than a guess with a hose. Residue left on the pavers cures into a haze that is unpleasant to remove, and an under-filled joint sets shallow and cracks out within a year. Done properly it is a real improvement; done in a hurry it is worse than the sand it replaced.

Washing without emptying the joints

The fastest way to undo a good patio is an afternoon with a pressure washer on a narrow tip. High pressure strips joint sand out in seconds, and once it is gone the units lose interlock immediately. A wide fan tip, moderate pressure, and an angle that keeps the stream off the joints will lift dirt and biological growth without excavating the patio. Plan on refilling and recompacting the sand after any thorough wash, because even a careful one takes some out.

The two hours a year that keep it flat

Early in the season, walk it and look for units that rock, low spots that hold water after rain, and joints sitting below the chamfer. Sweep in fresh joint sand, work it down with a broom, and settle it with water or a plate compactor on a protective mat. Deal with an edge restraint that has shifted before it lets a whole run of pavers spread. Done annually, this is a short job. Skipped for five years, the same patio needs lifting and relaying.

Frequently asked questions

How often does joint sand need topping up? Check every spring and refill wherever the sand has dropped below the chamfered edge of the pavers. On a patio with plain sand joints that is often an annual job; polymeric joints can go several years but still need inspection.

Will sealing stop the weeds? Only partly. A sealer can help lock joint sand in place and slow surface soiling, but it does not substitute for full joints, and it needs reapplication. Sealing over joints that are already empty locks in the problem.

Can I pressure wash a paver patio? Yes, carefully. Use a wide fan and moderate pressure and keep the stream out of the joints, because concentrated pressure blasts out the sand that holds the patio together, then plan to refill and recompact afterwards. If a condenser pad shares the patio, keep the spray off the coil: an HVAC contractor in Roswell would rather clean it properly than straighten bent fins later.

My grandfather laid brick, my father laid brick, and I laid it for forty years before my knees retired me to giving advice. The job people call me about most now is a paver patio that has gone wavy, one corner sunk, a lip you catch your toe on. Folks assume the pavers are bad. The pavers are almost never bad. What failed is underneath them, and if you fix the surface without fixing the base, you will be doing it again next year.

Why patios sink in the first place

A paver patio is only as good as the base it sits on. Sinking and heaving come down to a handful of causes:

• A base that was too thin or never compacted. The most common one. Pavers set on loose or shallow base settle unevenly under traffic.
• Washed-out base. Water running under the patio, from a downspout or poor grading, carries the base material away and leaves voids.
• Soft or organic soil left under the base that keeps compressing.
• Tree roots lifting a section from below.

Down in Springfield and the older Jacksonville neighborhoods, the sandy soil and those hard summer downpours make washout the usual culprit. Water is patient, and it always wins if you give it a path.

The right way to relevel

Fixing it properly means going back to the base, not just lifting a paver and shoving sand under it. The real repair runs like this:

• Lift the affected pavers, keeping them in order so they go back the same way
• Dig out the failed base down to solid ground and find out where the water came from
• Rebuild with proper compacted crushed stone in lifts, not all at once, compacting each layer
• Reset a bedding sand layer, screeded flat, and relay the pavers
• Sweep in fresh polymeric joint sand and compact

Keeping those joints full afterward is what protects the repair, which is the routine care I cover in sealing and maintaining a paver patio.

Fix the water, or don’t bother

If a downspout or the grade sent water under the patio once, it will do it again. Before you close everything back up, redirect the downspout, correct the slope so water runs away from the patio, and make sure the finished surface still drains. Skipping this is why so many “repaired” patios sink a second time. Hardscape base and installation standards are published by the Concrete Masonry and Hardscapes Association.

What it runs

Spot repairs of a sunken area commonly run a few hundred to about $1,500 depending on size and access; if the whole base was done wrong, you are closer to a partial or full rebuild. Either way, insist the fix goes down to the base. Anyone who wants to just lift and re-sand the surface is selling you next year’s repair too.

Sunken versus heaved: read which way it moved

Before you lift a single paver, figure out whether the section dropped or lifted, because they have opposite causes and different fixes. A sunken area, low in the middle or at an edge, almost always means the base compacted, washed out, or was never thick enough, so the repair is to rebuild that base deeper and properly compacted. A heaved area, pushed up into a hump, is a different story: down here in Florida it is usually a tree root growing under the patio, but in colder country it is frost lifting a poorly drained base. Fixing a heave means dealing with the cause, cutting and redirecting the root with care, or improving drainage so water is not there to freeze, not just relaying the surface, or the hump comes right back. Run a straightedge or a string line across the patio to see the true shape; the eye exaggerates small dips. Knowing whether you are chasing a sink or a heave tells you whether the problem is under the pavers or coming from something growing or freezing beneath them.

Frequently asked questions

Why did my paver patio sink? Almost always because of a base problem: too thin or uncompacted base, or a base washed out by water from a downspout or poor grading. Soft soil and tree roots can also cause it. The pavers themselves are rarely the issue.

Can I just add sand under the sunken pavers? No, that is a temporary patch. If the base failed or washed out, adding sand on top does not fix the cause, and the area sinks again. A lasting repair rebuilds the compacted base and corrects whatever water problem caused the failure.

How do I stop my patio from sinking again? Fix the water. Redirect downspouts, correct the grade so water flows away from the patio, and make sure the surface drains. Combined with a properly compacted base and full joint sand, that is what keeps a repaired patio stable. Condensate lines are a quiet contributor to that, and a Tarrytown HVAC contractor can reroute one away from the patio in an afternoon.

The summer I finally replaced the cracked concrete slab behind my Decatur house, I thought the hard part would be the digging. It wasn’t. It was standing in the yard with two sample pavers in my hands, a clay brick paver in one and a concrete paver in the other, trying to decide which one I’d still be happy with in fifteen years. I chose, I laid the patio, and I’ve had a few years to judge. Here’s the comparison I wish someone had handed me first.

I’m a homeowner who restored an old brick house, so I’ll admit a bias toward real brick. But bias aside, each material wins in different situations.

What you’re actually choosing between

Clay brick pavers are fired clay, the same basic material as traditional building brick but denser and made for walking on. The color goes all the way through and comes from the clay and the kiln, not a coating. Concrete pavers are molded from cast concrete with pigment added, and they come in far more shapes, sizes, and colors, everything from tumbled cobbles to big modern planks. Both sit on the same kind of base: excavated soil, compacted gravel, and a bed of sand. The base, honestly, matters more than the paver.

Cost and installation

The two are closer in price than people expect. Installed, concrete pavers commonly run about $10 to $20 per square foot, and clay brick pavers about $12 to $25 per square foot. Material is only part of it; most of the cost is excavation, base preparation, edging, and labor, which are similar either way. Concrete pavers have a slight edge in ease because the uniform sizing and huge range of interlocking shapes speed up the laying. Clay brick, with its classic running-bond and herringbone patterns, takes a bit more care to keep the lines straight.

Whatever you lay, budget for a real base. A patio that skips proper compaction and edging will heave and sink no matter which paver sits on top.

How they age

This is where my bias earns its keep. Clay brick holds its color essentially forever, since it’s baked in, so a clay patio looks much the same in twenty years as the day it went down, just mellowed. Concrete pavers can fade over time as the surface pigment weathers and UV works on it, and a chip shows the lighter concrete underneath. On the other hand, concrete pavers are generally more uniform and, in many product lines, slightly more resistant to cracking under point loads.

Both can shift, stain, and grow weeds in the joints if you ignore them. Both benefit from polymeric sand in the joints and occasional attention; I go into that in sealing and maintaining a paver patio, because maintenance affects longevity more than the material choice does. For guidance on base and installation standards for segmental concrete pavers, the Concrete Masonry & Hardscapes Association’s hardscape installation resources are the reference I kept coming back to.

Which one for your yard

I’d choose clay brick when the house is traditional or historic, when I want a color that never fades, and when the patio is a focal point I’ll see up close. I’d choose concrete pavers when I want a specific modern shape or a large format, when the budget is tighter, or when I need a color or pattern that clay simply doesn’t come in. For my own backyard, off a 1920s brick house, clay brick was the obvious match; it ties to the house and it’ll outlast me. If my house were a contemporary build, I’d probably have gone the other way without regret.

Either way, the patio you’ll love in fifteen years is the one built on a proper base and maintained a little each year, not simply the one with the pricier paver.

Frequently asked questions

Are clay brick pavers more expensive than concrete pavers? Slightly, but they overlap. Clay brick pavers commonly run $12 to $25 per square foot installed and concrete pavers $10 to $20. Since most of the cost is base prep and labor, the material choice is a smaller part of the total than people assume.

Which lasts longer, brick or concrete pavers? Both can last decades on a good base. Clay brick keeps its color permanently because it’s fired through, while concrete pavers can fade and show lighter concrete when chipped. Concrete pavers are often slightly more crack-resistant. Maintenance matters more than the material.

Do paver patios need sealing? Sealing is optional, not required. It can deepen color and help resist stains, but its main practical benefit is stabilizing joint sand and slowing weeds. Many patios do fine with just polymeric joint sand and periodic cleaning instead of a surface sealer. Freeze-thaw country shifts that calculation: a Pittsburgh concrete driveway contractor will push sealing harder on anything that gets salted every winter.