• Nick Veilleux

Why we switched to an Open Graded Base!

There are numerous ways to lay a patio, some hold up over time better than others. The main two methods to prep a patio are using a dense graded base or an open graded base.

What is a Dense vs Open Graded Base
  • A Dense Graded Base Consists of 6" (or more) of 3/4" gravel, mixed with crushed stone fines. Topped with 1" of washed sand as a bedding layer

  • An Open Graded Base consists of 6" (or more) of 3/4" clean angular gravel, topped with 1" of 1/4" clean angular gravel as a bedding layer. This base does not have any fines or sands mixed in.

Problems we have experienced with Dense Graded Base

A Dense Graded Base does not allow water to freely percolate through it. Since water doesn't drain freely, it will shed off the base and as the water sheds off, it brings the stone fines and sand layer with it. This erosion causes movement of the patio pavers. Majority of the problems we encounter are due to this:

  • Because of the water shedding off the base it is common for sand washout. This happens frequently on raised patios and along the edges of patios causing sinking and settling.

  • Since the bedding layer and stone fines in the base layer absorb water, during freeze and thaw cycles the pavers shift and settle causing lips, cracks, and failure of the polymeric sand.

  • Sand and stone fines are a very welcoming home for weeds, grass, and ants. . This obviously isn't destructive, but is something that without constant maintenance can overtake your beautiful patio.

Benefits of an Open Graded Base

By design an Open Graded Base allows water to freely flow through its base with the use of clean angular gravel.

  • Due to water flowing freely through this base there is not a risk of pavers sinking during freeze/thaw cycles.

  • With a dense graded base, the crushed stone fines and sand can easily wash out and erode if it rains prior to the completion of laying the pavers. With an open graded base, there is not a risk of washout during un-predictable weather.

  • Permeable Nitro sand can be used within the paver seams to prevent washout around the patio. This sand allows water to drain through the pavers unlike traditional polymeric sand. Nitro Sand can only be used with an open graded base.

  • The 1/4" bedding layer compacts at a higher percentage compared to bedding sand. This higher compaction prevents minor settling.

  • Due to the base being all coarse gravel there isn't a concern with pests, weeds, and grass growing in the paver seams.

So How Do We Install Our Paver Bases
  1. Dig the Area Out: We remove 10-14" of subsoil

  2. Lay geo-textile fabric: In order to keep our sub base from migrating into the subsoil we lay geo-textile fabric throughout the entire project space

  3. Install a drain (as needed): Since we encourage water to drain through our patio we install a french drain to move the water away from the patio.

  4. Dump and Compact: We bring in 6-8" of 3/4" clean angular stone and compact it every 2-3". This ensures the entire base if fully compacted and will prevent the pavers from settling.

  5. Screed: On top of the 3/4" clean angular stone we spread about 1" of 1/4" clean stone to get the perfect slope.

  6. Lay the Pavers

  7. Install Sand: We use 2 products; Gator Maxx polymeric sand and Alliance Gator Nitro Sand. For open graded base nitro sand is by far the superior product and we typically push for this sand installation.

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