I have a 40′ x 45′ patch of blacktop in my backyard. I want to install pavers. Can I install right on top? If so should I use a sand bed on top of the blacktop or should I use adhesive on the pavers and stick them to the blacktop. The blacktop is in fairly good condition, it slopes away from the house and water runs off. Any help would be great.
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No...No...Noooo.... (unless you want it to look like crap)
Even if the blacktop was flat enough for the pavers to sit evenly on top (and it never is), it would be a mistake. It WILL crack and move over time and wreak havoc on the pavers. If you are going to go through the trouble, do it right.
I'm going to assume you are located in an area that get some amount of frost in the winter (but this only matters marginally). A proper paver installation that recieves only foot traffic and not vehicle loads would consist of a 4" - 6" crushed gravel base, compacted in lifts, a 1" layer of bedding sand, and the pavers on top, compacted into the sand.
Now, a well done blacktop installation would have a similiar compacted gravel base under it. If your existing blacktop is in good condition, it might indicate that a proper base was installed beneath it. The other concern is the existing subsoil...is it clay, loamy, or sandy? Dig a hole along side your blacktop and try to get a sense of the installed base depth and the subsoil conditions. If it is adequate (3" - 4" base over sandy subsoil, 5" - 6" base over clay) then your best bet is to remove the blacktop and install the pavers over the existing base.
After the blacktop is removed, use a straight 2x4 as a screed to flatten the base into an even plane. Spray a light mist of water on it. Make one pass over the surface with a vibratory plate compactor. Now the base surface should be flat and firm. Lay 1" Dia. pipes (galvanized plumbing pipes work well) on top of the base surface and fill clean, washed concrete sand between the pipes. Pull a straight 2x4 accross the top of the pipes and you will be left with a perfect 1" sand layer to lay your pavers on. Move or slide the pipes as needed to cover the entire area and fill in the voids left by the pipes with sand.
Put and edge restraint around your finished surface and run the plate compactor over the top of the pavers. No, you won't break them (maybe a couple). Sweep sand over the entire surface, let it dry, and then compact again.
Get out the grill and a cooler of beer and enjoy your new patio...
You got freeze and thaw cycles, whats the slope, how even is the ashpalt need more info.
I've installed 1000's of this material over the last 20 yrs. give me more info and I'll give you the answers.