How often are seal coats applied to parking lots

[jgailla]

I am looking at a report on parking lots for a client with about fifty school facilities done by another engineering firm. The report contains a repair forecast.
The report has most of the parking lots to be resurfaced within the next few years. The resurfacing is to consist of milling 1.5" and repaving. I haven't seen most of the parking lots but this seems reasonable for the age of the facilities.
The thing that strikes me as strange is that the report calls for sealing (I assume asphaltic slurry sealing) three years after the resurfacing and every three years thereafter.
I only have access to part of the report and this is about all of the information that I have, so I'm mostly just curious.
I've done asphalt remediation before from study to recommendation and construction, but I don't recall ever recommending a seal coat every three years.
If the construction is performed properly I would think a seal coat would not be necessary for 7 to 10 years depending on conditions, but I haven't looked at this issue for a while.

Does anybody have an opinion or web resource that might be helpful?

 

[cvg]

we seal our private street about every 3 years. our current estimate from a paving contractor as of yesterday recommended that we dont need to seal this year, even though it is scheduled. so 4 or more years is possible. we plan on mill and overlay approximately on a 20 - 25 year basis.

cost is $0.03 per sq ft counting sweeping, sealing cracks, sealing pavement and re-striping so it really is not a big deal

 

[jgailla]

That's interesting. I'm getting costs off RS Means of about $2/square yard, which is 7 or 8 times higher than $0.03/square foot. The $2/square yard is also in line with the costs that I remember from a few years ago, but my memory's not that great.
Is it possible that I am thinking of a slurry seal when what they are proposing is an emulsion seal coat? I would expect the emulsion seal coat to be more in line with your numbers, cvg.
I've never recommended those because it's basically like painting the pavement without providing any real benefit, although I can't say I've seen any serious research done. I suppose there is some very short term protection against moisture intrusion.

 

[cvg]

i'm sorry, I didn't total the entire bid, more like 10 cents a square foot. see attached. you might be looking at slurry seal cost or more likely Means is just not that good at estimating. you need a hard bid. we had another bid that was higher than this and it is highly dependant on oil prices.

 

[jgailla]

Thanks cvg. I appreciate the response. The attachment is helpful.
These costs are forecast out to past 2020, so it is at a very conceptual level. Who knows what oil will be in five or ten years?
I don't like Means much either, but I have a couple of bid sheets with unit prices that are pretty close to what Means is giving me in this case.

 

[Ron]

jgailla...you are correct. No need to sealcoat every three years. They are probably recommending an emulsion coating (paint it black with coal tar crap)to keep it looking similar over the years. Waste of money.

Your costs are a bit high but not completely out of line with properly applied slurry seal coat or microsurfacing. Spray-applied emulsion "sealcoats" are cheap but not worth the money....keep in mind that they also lower the skid resistance as compared to asphalt slurry seal coats which can be used to enhance skid resistance.

Routine seal coats are not necessary. Only use to prevent top-down water intrusion such as with cracks or to renovate the surface. You'll likely need mill and overlay prior to needing seal coat for oxidation repair.

 

[eea]

I agree with the commenters, but offer these thoughts.

We had a major industrial client ask us to do a review of their intermediate surface coating and found that even crediting the pavement with some amount of extended life by surface treatment coating, the rolled up costs back to year zero were essentially the same. They had us look at the same 20 years for a straight 1.5" mill and overlay versus say 25 for the same but with periodic seals.

The other part of the equation not to miss, AESTHETICS. It looks nice and fresh, so to 99% of the public they have a "new" parking lot every four years. Even though you have to re-stripe the parking stalls, normal paint would probably age at the same frequency. All and all I'm neutral on it from engineering warrants but can see the benefits for retailers and the sort.

 

[MiketheEngineer]

I do my driveway with "sealer" about every two years -- looks great!! Big driveway - costs a couple hundred bucks just for the dealer.

 

[jgailla]

Thanks to all for your responses.
Ron, I appreciate the confirmation. Hope everything's going well for you.
eea, that's a good point about the aesthetics. I don't think it applies to schools, but being an engineer I always need to remember there are other things beside function.

 

[Ron]

jgailla....going well...hope the same for you. Extremely busy...no complaints! Tell DS "hello".

 

[ACtrafficengr]

Years ago, I knew an engineering professor who was asked a similar question. He found that the sealants of the day continued to protect his test patches long after they had worn off the high points and had oxidized to match the color of the surrounding pavement. But, by then, the cooperative extension agent that had asked the question originally had moved on, so he never wrote up his results.

I suspect the sealant industry wouldn't like him if he did.