Resealing and Restriping an Ageing Car Park

Five blue bays, a 1998 layout, and a purchase order for paint

The request that arrives in March is four words long: seal and stripe it. The site is an office park off a ring road, built in 1998, two separate lots either side of the building — 148 stalls in the visitor lot at the front, 96 in the staff lot behind. The surface is grey rather than black, there is map cracking through the south-facing bays, and the lines are ghosts. Five bays across the site carry a wheelchair symbol, three at the front and two at the back, every one laid out to whatever the striper's chalk said twenty-eight years ago.

The trap in the four-word brief is that the paint is the cheap part and the paint is also the part that carries the obligation. Once the old layout is scrubbed off and a fresh black field goes down, the crew is not restoring a layout — they are establishing one, against the standard in force this year. The Department of Justice's technical assistance under Title III of the ADA has long treated restriping a parking lot as an alteration rather than as maintenance. What governs on any given site is the accessibility code the local authority has adopted, and the owner's counsel; this page is about finding the number before the machine is loaded.

So the sequence runs backwards from the paint. Count what the standard asks for. Establish whether the existing bays can be reused where they sit. Check the slope where they would move to, because that is a paving question with a lead time. Only then do the crack work, the sealer and the striping become a schedule with quantities against it. The other order produces the familiar outcome: a beautiful black lot, a letter in September, and a second mobilisation to grind off paint that is six weeks old.

Finding four more bays without losing a row

Four extra accessible spaces and two van conversions come out of the existing field, which is a geometry problem inside aisles you are not moving. Section 502.2 sets a car space at 96 in wide minimum and a van space at 132 in, with the exception that a van space may be 96 in where its access aisle is 96 in. Section 502.3 puts the aisle at 60 in minimum, running the full length of the space it serves, and lets two spaces share one. A pair of the 1998 layout's 9 ft stalls is 18 ft of frontage; a car space plus a 60 in aisle is 13 ft, and two car spaces sharing an aisle is 21 ft. The conversions are not free in stall count, and telling the owner the front row loses three general spaces is an April conversation rather than a July one.

Position is scoped too. Section 208.3.1 puts accessible spaces on the shortest accessible route to the entrance they serve, which here means the four nearest the lobby doors rather than the four nearest the fence where there happens to be room. Section 502.7 adds that a parked vehicle must not obstruct the required clear width of the route beside it, ruling out the tempting move of putting the aisle where a walk already runs and calling the walk the aisle. And a van route carries a headroom requirement under Section 502.5 that a car route does not — 98 in minimum at the space, the aisle and along the vehicular route — so a van space cannot be tucked under the canopy a barrier arm was hung from in 2006.

Then there is the state code, which often wants more. California's Building Code Chapter 11B is the example most managers have heard of; its parking provisions differ from the federal ones in dimensions, in aisle markings and in signage. ICC A117.1, referenced by the IBC, is the technical standard behind many state adoptions. The federal table is the floor. Find out what has been adopted before the layout is drawn, because a bay drawn to the floor and built somewhere stricter is a bay you paint twice.

One in forty-eight, in every direction, and paint has no opinion about it

Section 502.4 requires accessible spaces and their access aisles to be at the same level and to comply with the surface provisions, which permit slopes no steeper than 1:48 in all directions. That is 2.08 per cent, and it is the commonest reason a relocated bay fails on the day it is measured. A 1998 lot was graded to drain, and the fall need not be much steeper than nominal before a stall corner breaks the limit — particularly on the diagonal, where a two per cent cross-fall and a one and a half per cent longitudinal fall combine to two and a half.

Take a rotating laser or a digital level to the four candidate locations before anything is promised, read each along the stall, across it and diagonally, and record the readings against a sketch. A seal coat is a film a fraction of a millimetre thick and marking paint is thinner again; neither moves a level by an amount an instrument can find. A bay location reading 3.4 per cent is milling and a patch, or a small area of regulating and a new surface — a paving contractor with a lead time and a cure period before sealing. It is the one item here that cannot be compressed into the week the lot is closed, which is why it belongs at the front of the programme rather than in the snag list.

What the cracks are telling you before you price anything

Walk the lot with a wheel and a clipboard and record distress by type, not by adjective. ASTM D6433 is the practice for pavement condition index surveys of roads and parking lots, and it exists because owner and contractor otherwise negotiate over the word tired. Which of three patterns dominates decides the job, and only one of the three is the job that was requested.

Straight cracking — transverse across the bays, longitudinal along a construction joint, and the wide-spaced block pattern from binder shrinkage — is what a seal-and-stripe is for. The surface has oxidised and shrunk, water is reaching the base through the cracks, and sealing them and coating the field buys years. Fine block cracking over a whole panel is a warning shot rather than a green light: the binder has hardened to where the surface sheds its own aggregate, and a sealer over that buys a cosmetic year, honestly described as such.

Alligator cracking is not a coating problem at all. Interconnected polygons in a wheel path mean the section has been flexing beyond what it can carry — a wet base, or a layer too thin for what drives on it. Sealing over it is the most visible way to waste an owner's money, because the pattern reappears through the fresh black inside one winter and the owner reasonably concludes the sealer failed. Measure those areas, mark them on a plan and price them as full-depth repair before any coating figure is quoted. Here there were 1,150 sq ft, all in the two aisles the refuse truck uses.

The walk also produces the crack length, and it produces it in two piles rather than one. Cracks wide enough to be sawn and sealed — a quarter of an inch and up — came to 1,700 linear ft. Narrow map cracking through the sunniest bays, too fine to open up and better handled with a banded cold-applied filler, came to 640 ft. Two products, two crews, two lines on the estimate, and the reason to separate them on the clipboard is that nobody separates them afterwards.

The order the lot goes back together in

Almost every seal-and-stripe failure is a sequencing failure rather than a material one. Sealer will not bond to dust, to vegetation growing out of a crack, to a diesel spill or to a sealant that has not skinned; paint will not bond to a sealer still curing; and none of it happens below the temperature floor on the data sheet, which for most waterborne traffic paints sits near 50 °F (10 °C) surface temperature and rising, with a humidity ceiling beside it. The programme below is the order those constraints impose, and the cure gaps in it are the schedule. Two steps have lead times that will not fit inside a closure week and have to start earlier — the full-depth repairs, because a fresh patch has to cure before it is sealed, and the sign posts, which are foundations with a concrete cure of their own.

1. Survey: distress by ASTM D6433 type, crack length split into sawn and banded piles, levels at every candidate bay location.
2. Scope the accessible count per lot, draw the corrected layout, and confirm it against the accessibility code the local authority has adopted.
3. Cut out and replace the full-depth repairs, and mill and re-lay any bay location over 1:48 in any direction. Leave both to cure.
4. Kill and remove vegetation from the cracks, sweep and blow the lot, then degrease the oil-spotted areas and prime them with the sealer maker's spot primer.
5. Saw the reservoirs, blow them clean and dry, install backer rod where the crack runs deep, and place the hot-applied sealant with its overband.
6. Band the narrow map cracking with cold-applied filler, then let both crack products cure for the period on their data sheets.
7. Mask the concrete, curb faces and building plinth, and phase the closure so half the lot stays in use if a full shutdown is refused.
8. Seal the whole field, then put the second coat on the aisles and entrance run only, respecting the recoat window on the drum.
9. Let the sealer cure to the data sheet's traffic figure — commonly 24 to 48 hours, longer in humidity — and keep vehicles off for all of it.
10. Chalk the corrected layout from the pre-works record, walk it, park a van in the van space with its side door open, then run the striper.
11. Stripe the 4 in lines, the 6 in lines and the hatching, then the stencils, then drop beads where the specification calls for them.
12. Set the sign posts, mount the identification signs, hand over the as-built drawing, and record the sealer and paint batch numbers.

Signs, and the things paint cannot do

Section 502.6 requires accessible spaces to be identified by a sign carrying the international symbol of accessibility, van-accessible spaces to be designated as such, and the sign to be mounted with its bottom edge at least 60 in above the ground surface. The height is what gets missed on a repaint, because the existing posts were set at whatever suited 1998 and nobody measures a post they are not replacing. Measure all nine before the crew leaves, and expect the van space to need a different sign rather than the same sign with a sticker on it. The standards do exempt very small facilities from the identification signs, but that provision is about lots with a handful of spaces and has nothing to say to a 148-stall field.

A post at the head of a bay is a foundation rather than a fixing, and it stands in the worst place on the site — in front of a bumper and in the path of a plough blade. Set it beyond the vehicle's reach, wall-mount it where the bay backs onto the building, or give it a sleeve so the next replacement is a fifteen-minute job. Wheel stops earn the same scepticism here as anywhere: a trip hazard on a route that specifically has to be usable by somebody with limited mobility.

The last thing to hand over is the drawing: bay counts by row, the corrected accessible layout with its aisles dimensioned, the slope readings at each of them, the full-depth repair locations, the crack sealant type and the paint and sealer batch numbers. In two or three years, when the sealer has worn through the aisles again, the next person to price this lot otherwise starts from a wheel and a clipboard on a surface that shows none of it. The only thing that makes the second cycle cheaper than the first is a record of what the first one found.