The author provides some good starting points for people to understand their options, but I want to make some clarifications.
Regarding the field test for the presence of coal tar sealant, please follow the recommended safety precautions listed on this blog (link to field test). This is toxic stuff and it should be handled with care. I understand that is an ironic statement given that we have (and most still do) let our kids play on this for decades, but the sooner we minimize our collective exposure to this, the better.
The process for removal is shotblasting" not sandblasting. It uses little bb sized steel shot that is simultaneously shot onto the pavement and then vacuumed off of the surface. The major principle at work here is that the sealant removal should not to create a bigger mess on your property than when you started. The equipment used should have an industrial grade, HEPA filtration attached. Otherwise you will coat your whole neighborhood with this toxic dust.
I've got some reasonable quality video of a parking lot being stripped below, but the above from youtube gives a clearer picture. This can be a very effective removal technique. I would be leery of the success if the condition of the asphalt is poor. It may break up the asphalt into smaller pieces and destroy the pavement altogether.
Here is are a few pictures of stripping a sealant:
|Metal shot for sealant removal|
|A strip of sealant removed.|
|Close up of sealant removed at top and not at the bottom.|
One other important issue. Every state has a different interpretation of how this dust can be safely disposed of. It ranges from bagged and thrown in with regular municipal waste to being sent to a special landfill ($$$$). Please check with your local officials first.
Now about sealing over the top of a coal tar pavement surface. In some ways this only covers up the problem and no sealcoat will last forever. It will be gone in a few years and back to a coal tar surface.
I have only seen one product that works with new or thick coal tar seal coats and that is CarbonPlex or Carbonyte. It has been successfully used over coal tar sealants in Austin. The product may be difficult to get, but the company is out of Sacramento, California. Others have said with a specialty primer any asphalt sealant could work over coal tar, but I haven't seen it.
While neither of these techniques addresses the potential problem if coal tar sealants have contaminated adjacent land, but they begin to address the source of the problem.