City of Burien

Slurry seal is a cost-effective pavement preservation method capable of extending pavement life by as much as ten years. It is a mixture of fine crushed angular rock about one-eighth to one-quarter of an inch (at maximum size) and emulsified asphalt (that may contain recycled rubber tires and asphalt shingles). The mixture is then "painted" on residential travel lanes.

This preservation method "coats" the streets (that are already in good condition or pavement rating) and provides additional protection from long term effects of water penetration, ultraviolet radiation, and oxidation. The slurry seal is very similar to painting your house or sealing a deck for additional protection and longer lasting benefits.

The slurry seal coating, however, is not the same as paving a street. It is only a coating less than one-half inch thick.  It does not correct any warping on streets or any slope issues for drainage.  It only coats/seals the street.  In our case, the slurry seal coating is only applied to vehicle travel lanes not driveways or street shoulders/on-street parking areas (even bicycle lanes).

Slurry seal is typically applied during warm, sunny dry weather to aid the curing process. However tree shading, humidity, and rain can all affect curing. Even extra hot days in late summers here in Washington can soften the coating again (before it has the chance to fully dry) then harden once again.

Slurry Sealing is practice well-used in California, Nevada, Utah, and states in the eastern half of the United States (Virginia DOT). It is becoming more widely used in the Pacific Northwest by cities such as Kirkland, Mukilteo, Bothell, and now Seattle.

Slurry sealing streets saves nearly one-tenth of an asphalt overlay (paving) or one-fiftieth the cost of a total road reconstruction. As an example for 1000-feet stretch of residential street:

• Slurry Sealing - $12,000 (engineering and construction costs)

• Asphalt Overlay - $120,000 (engineering and construction costs)

• Road Reconstruction - $500,000 to $600,000 (engineering and construction costs)

Watch a short video about slurry seal to learn more.

Residents within the project area will receive information in several phases. First, project information will be sent to residents in late spring/early summer informing them of the upcoming work. Next, residents will receive a postcard on tentative start dates for the work. Third, residents will receive door notices at least 48-72 hours before work on respective streets is to begin.

Please note the City uses available address information on record with the City to contact residents via postal mail. It is possible that some addresses will be missed. However the City will do its best to reach out to residents impacted by the work.

On the day of work, the contractor will attempt one last effort to contact residents whose cars are within the immediate work area. Also, temporary "No Parking" signs will be placed along project roadway(s) at least 24-hours in advance. Please note once those signs are in place, parking enforcement per Burien Municipal Code 10.12.030 and 10.15.080 applies. 

Driving on the fresh slurry will damage your car! Please allow for it to dry in 4–6 hours even as the contractor reopens the street. Vehicle and property owners may be subject to repair costs for any damaged work if treated surface is driven upon before reopening of street. 

Streets scheduled for slurry seal will be closed anytime between 7 a.m. to 5 p.m.

The contractor will begin street closures at 7 a.m. The first streets listed will start the slurry application around 8 a.m. The contractor will generally follow the street schedule order. This means your street may not show any ongoing work right at 8 a.m. but later on throughout the day. 

Depending on the street to be treated, the applications can take 15-30 minutes per street. This means at least six streets will be done in the morning and remaining streets in the afternoon.

Once applied, it may take six hours to be dry enough to reopen the street (depending on the weather, tree shading, and resident cooperation). Please note the contractor is required to reopen all streets by 5 p.m.

Driving on the fresh slurry will damage your vehicle and you may be held responsible for the cost of reapplying the slurry. Please plan ahead.

DO NOT PARK in work zones designated by the "No Parking" signs or your vehicle may be towed at vehicle owner's expense. BMC 10.12.030 and BMC 10.15.080.

The contractor will be applying the slurry seal in street blocks beginning anywhere between 7 a.m. and 3 p.m (streets reopened by 5 p.m.).

Please consider parking your car anywhere "outside"of the work zone where it can still be accessed when needed. This can be at the next street corner or a neighbor you know who lives on a street not being considered for the slurry seal.

If you work during the day, chances are you will leave before the work begins and come back home after the street reopens. If you do not plan to leave, then please park your car in the driveway or as far away from the street travel lanes as possible. If no driveway or shoulder, please ask your neighbor if you can share (temporarily) in their driveway or off-street parking. If you decide to stay parked in your driveway, you will not be allowed to drive on the slurry until the contractor allows it.

Please keep in mind when the weather is good, then the slurry seal tends to dry quicker. Streets can then be re-opened sooner.

Driving on the fresh slurry will damage your vehicle and you may be held responsible for the cost of reapplying the slurry. Please plan ahead.

We hope by providing as much advance notice as possible that you will schedule or reschedule appointments around the designated work dates. We are also easing the burden by closing only a few streets at a time for each project day.

Postcards are sent out a month or two in advance to inform residents of this work. The project website is typically updated to inform residents of the selected contractor, tentative schedule of work, and any project schedule changes.

Also, 48 to 72 hours before, door notices are delivered to remind residents of scheduled work dates and to make preparations.

If there are no plans to leave your home before 8 a.m. on the day your street will be sealed and you need to use your vehicle later in the day, please park your vehicle on an adjacent street that has not been designated as a "NO PARKING" zone.

As a reminder, the slurry seal when first applied, is like fresh paint on your wall. If touched, it will have to be redone and getting the work done will take longer. Also, the slurry mixture is brown and sticky and can damage vehicles and bikes if driven on. People and pets should also avoid touching the slurry coat because it may cause some irritation to sensitive skins.

Driving on the fresh slurry will damage your vehicle and you may be held responsible for the cost of reapplying the slurry. Please plan ahead.

So the slurry seal work is done and it does not look the same as it was before. Why?

Street paving is an entirely different construction process. About two- to six-inches thick of hot-mix asphalt (HMA) is used and compacted (on top of an already compacted gravel road base) by large vibratory rollers. When it is rolled and compacted, it is a smoother finish. Even from that effort of construction, asphalt pavement may still fail because environmental conditions, traffic volumes and loads shorten its useful life. Pavement construction is a significant cost and therefore an asset worth protecting.

Slurry seal coating is not paving. It cannot be compacted. It is a wet mixture with small sized rocks which add strength (and in some instances better traction for better winter driving). Being a wet mixture, it is applied with a similar type but much larger “paint brush”. And how smooth a paint or lacquer finish is depends on the brush used. The slurry seal machine used (called a spreader box) applies the mixture much like a giant paintbrush. One difference is that this type of paintbrush or spreader box has small rocks in it.

The benefit of the slurry seal application can be hard to see in the first few weeks after the streets first receive slurry seal. The newly treated surface will be gritty, where it may have once been smoother. This is because of the small angular rocks used. It will be coarse and might even sound “louder.” The initial grit is expected and it is not permanent. Over the course of a week after the treatment, three weeks after that, and two months later, the treated streets will be swept.

Small sized rock or aggregate is used because it makes the emulsified (liquid) asphalt stronger just like sand and gravel is added to cement to make stronger. Over time, vehicle traffic will dislodge shallow aggregate (on the surface). Months of tires rolling over the coating daily in and out may also push remaining aggregate deeper into the coating.

The ridges seen are generally the result of overlapping the coating (during application). We try to minimize this as much as possible but it can be difficult maneuvering trucks to make this happen. To work around this, squeegee hand rakes are used by contractors to work out any “gaps” and ruts caused by the application trucks.  It is not a perfect process.  And just like any lacquer finish to wood, sometimes streaks are there and have to be fine-sanded. With slurry sealed streets, time is the only way to “fine-sand” some of the streaks in the road.

Within a year or so, the smooth road should mostly return to the street that residents remember, only with an added three to seven years of extended life.