I am on the Board of Directors of a small townhouse community (156
houses) and am responsible for providing information to the board
concerning the infrastructure needs of the community.  For what period
of time will sealing otherwise maintained asphalt parking lots in a
mid-Atlantic state be extended.  We are concerned with 15,000 sq. yds.
of parking lots.

Hi David,

First, my research indicated that sealing is primarily for cosmestic
purposes.  Even the Asphalt Institute (a self-described "...U.S. based
association of international petroleum asphalt producers,
manufacturers, and affiliated businesses."  notes on its site, "...A
well designed and constructed low traffic volume pavement, such as a
driveway or parking lot, should not require sealing for approximately
2 to 5 years – depending on severity of climate and quality of
original work."

http://www.asphaltinstitute.org/faq/mrfaqs.htm#Crack%20Sealing

The FAQ goes on to note... "Sealing is effective to renew old asphalt
surfaces that have become dry and brittle with age, to seal small
surface cracks and surface voids, and to inhibit raveling (loss of
surface aggregate). So, sealing should be done as soon as any of these
distresses are noted."

However, certainly your Association wants to maintain the appearence
of its parking lots for your community, and the general consensus I've
found on the Web was that sealcoating an asphalt driveway or parking
every three to five years can help improve protection from the sun,
which can deteriorate the binder and expose the aggregate. Probably
more of a concern in a mid-Atlantic state, sealcoating may also help
to prevent water and ice from getting into the paving and causing it
to crumble. However, you should note that if you're sealing primarily
for cosmetic purposes every year, the sealer can build up and will
eventually peel.

A complete asphalt driveway sealing job should includes crack fillers,
sealer, hole patch mix and spot sealer for oil stains. Warranties can
range from one to up to 10 years (using an airport-grade sealer).

It's important to know what type of sealer your vendor will be using,
according to my research. You want to make sure that they're using
pro-grade sealers and/or fillers, either coal tar- or asphalt-based.
Coal tar sealers are more reportedly durable and much more resistant
to oil or gasoline penetration than asphalt. However, asphalt is
better for the environment, but is more expensive.

Whether coal tar- or asphalt-based, according to Rick Noon, technical
director at SealMaster, the more solids in the formula, the better the
sealer quality and the more expensive it will be. You get more solids
in better - or best - grade sealers. The better, and top, grade
sealers typically cover 250 to 350 square feet, depending on the
condition of the surface.

Lower-grade sealers will only last a season, especially in severe
weather conditions. The top-grade sealers

For an in-depth view of these points, see, "The HandyMan Club" site,
at...

http://www.handymanclub.com/document.asp?cID=70&dID=755

regards,

rico

Search strategy

sealing asphalt driveway length time 

://www.google.com/search?sourceid=navclient&q=sealing+asphalt+driveway+length+time

Professional sealcoating warranty

://www.google.com/search?hl=en&lr=&ie=UTF-8&c2coff=1&q=Professional+sealcoating+warranty&spell=1

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Clarification of Answer by rico-ga on 08 Aug 2002 07:44 PDT

Sorry, the next-to-last paragraph of my response was truncated, and
should read...

"Lower-grade sealers will only last a season, especially in severe
weather conditions. The top-grade, airport-quality sealers can last as
much as a decade."

This is an excellent answer.