How much compaction can I expect from my screenings when setting Cambridge Ledgestone XL pavers? The pavers are large and heavy (25lbs+ per sq ft) so I expect it will be much different than laying 6x9 pavers. I just want to plan accordingly as I am preparing to begin filling the hole this week. Will it be a negligible amount or might it be something like a quarter of an inch (especially after running the vibratory plate over the finished patio at the end? The patio is bordered by the house and a course of retaining wall around the outer edge which has already been set, so I need to be sure the finished level of the patio meets the tops of the boarder caps. I don't want to be in a spot where I leave a 2 3/8" void only to have the pavers set down a quarter of an inch or more. Thanks in advance for any assistance!

Chris

 

The gravel base should be well compacted as you place it, and if properly done, will not compact further when you place the pavers. The sand layer is generally an inch thick on top of the base. It will compact a little when you place the pavers, but not much. When you run the compactor over the pavers once they are placed you can expect them to settle in around a quarter inch, maybe a little more, depending on size of pavers and how much space is between them. This is because some of the sand will push up in the spaces between the pavers as you compact them.

Then, over time, you can expect things to settle maybe another quarter inch. I always aim to end up with the pavers a little high, maybe a quarter inch at most, after compaction for that reason. So I start with them 3/8 to 1/2 higher than desired finish height.

 

I thought that the consensus was that gravel doesn't compact well, at all. Did I miss something?

 

You don't use plain gravel, you use paver base material, which is a mixture of sizes from 3/4 inch down to stone dust. Because of the mix of sizes, it compacts very well. You wet it down during compaction to lubricate it and compact no more than 4" at a time. It makes for a rock-solid base that can still let water drain through.

Straight gravel is not recommended for under pavers. It doesn't compact well (as you said) and the spaces that remain between stones allow the sand from above to gradually sink in, and allow the soil from below and along side to gradually migrate in, causing uneven settling and poor stability. It's ok under concrete, but not pavers.

 

A contractor whom I worked for never used gravel, of any sort under pavers. When sand was used, it was mixed 3 parts sand to 1 part Portland cement. That mix may have been on top of concrete which some argue won't allow water to drain or top soil but never gravel. I've seen pavers laid on top of dirt where weeds eventually appeared.

 

Pulpo - your ex-boss just did it totally wrong. A 1" sand setting bed is screeded and leveled over a compacted base (vibratory plate compactor). No Portland Cement is added to the sand. The paving surface is finished off with a vibratory plate compactor to draw sand into the tightly set joints and to even out the finished surface. Take a look a ICPI (Interlocking Concrete Paving Institute) or the NCMA (National Concrete Masonry Association) installation instruction. - Each has the complete instructions and material specifications.

If the pavers are laid before the edge restraint is put in (for large areas or large curves) the edge restraints can be placed before the setting of the pavers or after the set pavers and saw cut to the edging for curved paved areas. After the edge restraint is lightly sanded and vibrated.

Dick

 

Okay & what about the gravel? No gravel, right?

 

Gravel is a fuzzy non-specific term. I suppose if you want to get technical gravel is rounded, water worn stones which are probably not good for a base. What Carbide Tipped called "paver base material" is called "crusher run" around here and is available in a variety of blends. It's a mixture of crushed stones varying in size all the way down to dust. The angular shape of the pieces prevents them from rolling and slipping past each other so it holds once compacted. The variety of sizes makes for very few voids as the smaller bits fill in the space around the larger ones locking everything in place.

 

Thank you all for the assistance/education! So if I want to set the top of the pavers at 3/8 or 1/2" above the desired finished height, am I to do so with extra screenings (more than an inch here) or with extra compacted base (more than the planned 5" here)?

Chris

 

Extra base - the sand stays a 1" layer on top of the compacted base.

 

Thanks, that's what I assumed, but wanted to be sure.