Should I Put Gravel Under My Deck Blocks?

Hey there! I know you‘re wondering whether gravel is necessary under those deck blocks you just bought. Short answer – yes, absolutely use gravel! It might seem like extra work, but gravel provides critical support and drainage that protects your deck for years to come.

Let me walk you through all the details on why gravel is so important under deck blocks, how much you need, what type to use, and step-by-step how to do it right. I‘ll even share some pro tips I‘ve learned from installing decks over the years!

Why Use Gravel at All?

I‘m sure you‘re anxious to get building, but trust me, taking the time to add gravel is worth it. Here are some of the big benefits gravel provides:

Sturdy Base

Gravel compacts into a solid base that won‘t erode or shift around over time. This keeps your deck blocks firmly in place so the structure doesn‘t settle or become unleveled. No one wants a wobbly deck!

Drainage

Water drainage is crucial for the longevity of your deck. By allowing water to drain away, gravel protects the wood from moisture damage. Otherwise puddles and soil saturation can cause major issues like rot, warping, and mold.

Frost Protection

In cold climates, gravel insulating the blocks from below helps prevent frost heaving. This is when water in the soil freezes and expands, pushing blocks upward. Not fun to deal with!

Erosion Control

Bare soil easily erodes away, especially on slopes. Gravel contains the soil so your blocks maintain a stable foundation over the years.

Flat, Level Surface

It‘s much easier to create a flat, even layer with gravel than with bare ground. This allows you to perfectly level all your blocks in every direction.

So in summary – gravel equals stability, drainage, frost protection, erosion control, and makes leveling a breeze. That‘s what I call peace of mind!

How Much Gravel is Needed?

Many homeowners don‘t use enough gravel, so let me give you some guidelines:

• For typical, well-draining soil – go with a 4 inch gravel base.

• With denser, clay-like soil that doesn‘t drain well – use 6 inches of gravel for improved drainage.

• For larger decks, it‘s smart to use a full 6 inch base. This prevents sinking or shifting over greater spans.

• Add an extra 1-2 inches of gravel to create a sloped base for better runoff.

Of course soil conditions can vary across your yard. I recommend digging test holes to check moisture levels across the deck area. Water should sink in within a minute or two – if it‘s just sitting there, that soil will need more gravel for proper drainage.

It‘s better to use more gravel than less. Proper base preparation is key to a long-lasting deck. Don‘t skimp here – you‘ll regret it down the road if your blocks start sinking or heaving on you!

What Type of Gravel is Best?

Not all gravel is created equal. Here are some tips on picking the right stuff:

The best type of gravel is crushed stone, sometimes called clean stone, which has angular edges. This locks together for solid support vs rounded pebbles that shift easily.

Ideal sizes are 3/4 inch or 1 inch gravel. Anything larger than 1 inch is difficult to level. Anything smaller compacts too densely for proper drainage.

Aim for a uniform gravel size rather than mixed. The individual pieces will lock together better.

Washed gravel is ideal because it won‘t contain silt or clay that can clog the drainage capacity.

The strongest rock types are granite, basalt, limestone, and traprock. So check with your local quarry or landscape supplier about these crushed stone options.

Avoid soft types of gravel like limestone screenings or crushed concrete – they break down too easily.

I prefer to use a geotextile fabric in addition to the gravel – this extra layer prevents the gravel from sinking into soft soil or getting contaminated by the dirt over time. Definitely use fabric if you have very loose, muddy soil.

Tip: Take a look at the Types of Gravel guide at www.landscapingrocks.com for photos and more examples.

Preparing the Ground

Laying down the gravel properly is just as important as choosing the right type. Follow these steps to set up a solid base:

1. Excavate the area, removing grass/plants/debris. Dig down 6 inches minimum.

2. Check the soil stability. Does it hold form when squeezed? If it‘s loose fill dirt, remove another few inches and replace with compactible soil.

3. Use a plate compactor to compress the soil down to a hard, flat layer. This prevents settling later.

4. Shape the compacted soil to allow for 1/8 inch of slope per foot run. Use a leveling tool or transit to check slopes.

5. Install geotextile fabric if needed, overlapping the seams by 6 inches. This adds a moisture barrier to problematic soil.

6. Start spreading your washed gravel in 2 inch layers. Compact each layer fully before adding more.

7. Use a board with level to check flatness across the entire area as you build up layers. Adjust low spots with extra gravel as needed.

8. Compact the final 4-6 inch layer down to a near concrete hardness. Solid compaction = solid support!

Pro tip: If you‘re installing a large deck, renting a plate compactor with detachable base plates will make quick work of this. Don‘t skip the fabric for poor drainage areas – I learned that lesson the hard way!

Installing the Deck Blocks

Once your compacted gravel base is prepped, it‘s time to set the blocks:

1. Start by laying the perimeter blocks first. I recommend using the blocks with built-in tabs to grab the edge boards.

2. Use shims and a level to adjust each block until its perfectly level in all directions.

3. Stake the perimeter blocks in place temporarily. This prevents them from shifting while laying the interior blocks.

4. Fill in the remaining block pattern based on your joist layout plans. Maintain proper spacing between blocks.

5. Continuously check for level and flatness across all blocks as you work. Make adjustments.

6. Confirm final leveling before moving forward. Nothing else matters if the base isn‘t right!

7. Install treated joists and beams, securing them to the blocks per code requirements.

8. Start decking installation. Protect the wood and maintain stability by leaving the gravel exposed.

9. Celebrate with a cold beverage – you‘ve secured a solid foundation for years of backyard fun!

Gravel vs. Other Base Options

What about using crushed stone, sand, landscape fabric, or wood chips instead of gravel? Here‘s a quick comparison:

Crushed Stone

• Harder and more uniform than gravel.
• Excellent compaction but doesn‘t drain quite as well.
• Angular shape resists erosion.
• More expensive than gravel.

Sand

• Shifts and erodes too easily.
• Poor drainage leads to moisture issues over time.
• Hard to keep perfectly level.
• Best used under pavers, not blocks.

Landscape Fabric

• Helps prevent gravel from sinking into soft soils.
• Needs proper shingled overlaps to work effectively.
• Can tear during installation or later.
• Adds cost but improves stability long-term.

Wood Chips / Mulch

• Quickly decompose leading to settling.
• Invite pests like carpenter ants.
• Not advised under deck blocks – temporary use only.

For most soil conditions, crushed gravel with fabric for soft spots is the best combination. Proper drainage and stability is crucial!

Gravel Drainage Tips

To maximize water drainage, here are some key things to remember:

• Maintain a 1/4 inch per foot slope away from the house or structure.

• Set the gravel base lower than the surrounding ground level. This prevents water running under the deck.

• Keep the gravel clear of fallen leaves, dirt, and other debris that can block drainage.

• Make sure roof runoff is directed away from the deck area. Use downspout extenders as needed.

• On hillsides, you may need to build a retaining wall and extra backfill to create a flat platform.

• In persistently wet spots, install perforated pipe in a gravel trench to divert water away from the blocks.

Proper drainage and moisture management will save you from a ton of headaches down the road! Don‘t take shortcuts here.

Preventing Erosion Around the Gravel

In addition to good drainage, it‘s important to contain the gravel base and control erosion:

• Use edging secured around the gravel perimeter. Try commercial plastic lawn edging or landscape timbers.

• On sloped ground, make small retaining walls from stones or blocks to secure the platform for your deck blocks.

• Plant grass or mulch bare areas right away so soil doesn‘t wash away. Consider erosion control blankets for steep slopes.

• Add mulch rings around the deck blocks to cover exposed gravel. This limits erosion while improving aesthetics!

Proper gravel containment and erosion control ensures your solid base stays put. Don‘t forget this step!

Do Deck Blocks Need Local Permits?

Most areas require permits for any detached deck over a certain size – make sure to check with your local building department!

Important considerations per code include:

• Height restrictions – decks higher than 2 feet usually need anchored posts.

• Maximum decking span between the blocks – typically 6-8 feet.

• Required sizing and spacing for the deck blocks themselves.

• Specific rules if attached to the house.

• Electrical requirements like ground wires if installing lights.

I‘d hate to see you go through the work only to have the city red flag it! Taking the time to pull local permits is worth it for the peace of mind that your DIY deck is up to code.

Safety Tips

Make sure your gravel base and blocks are prepped and installed correctly – but also remain vigilant about safety:

• Periodically check for shifting or settling blocks and re-level as needed.

• Do not exceed the weight limits. Add blocks under heavy items like hot tubs.

• Use the manufacturer‘s recommended joist sizing and spacing between blocks. No shortcuts!

• Keep the gravel contained and carefully monitor drainage over time. Address any persistent wet spots.

• Never cover blocks or gravel completely with deck boards – leave them open.

• Watch for signs of erosion, vegetation, or debris buildup around the gravel base and correct it.

Adhering to building codes and these common sense practices ensures your DIY floating deck stays structurally sound for decades of use. Have fun with your project!

The Bottom Line

Well there you have it – everything you need to know about putting gravel under your deck blocks.

While it involves a little more prep work upfront, a proper crushed stone base really is worth the effort. You‘ll avoid so many issues down the road by taking the time to do it right.

The end result will be a super stable, level deck that drains freely, stands the test of time, and provides your family years of enjoyment.

Let me know if any other questions come up! I‘m always happy to share my experience. You‘ve got this!