French Drains for Stone Homes: Our In-Progress Installation

Every old granite house has its secret — ours just happened to be trapped water.

When I started leveling the floor inside our stone ruin, I dug nearly 85 cm (33 inches) down through compacted soil and veins of granite. What began as a quest for a few extra centimeters of ceiling height quickly turned into a lesson in geology, patience, and sweat equity. Underneath the rubble, I found what every off-grid renovator eventually faces: moisture paths leading straight into the walls.

Our house sits on the highest point of our land — the dream spot, or so I thought. Yet even at the top, rain finds a way. Each winter, runoff crept toward the granite foundations, slowly wicking up through the stone. To build a comfortable, durable home, I had to guide that water away before it could rise. No shortcuts, no guesswork — just honest work with an angle grinder, a jackhammer, and a five-month detour through rock.

Damp discovery — uncovering moisture-stained granite reminded us why proper drainage is non-negotiable.

This post isn’t a polished “how-to.” It’s a snapshot of where we are right now: halfway through the build, learning with each trench and each sore arm. Whether you’re restoring an old stone cottage or planning your first French drain, you’ll find practical details here — from slope math and tool choices to safety gear that actually matters.

By the end, you’ll know exactly how we’re keeping granite dry and breathable, and why that phrase has become our new renovation mantra.

If you’re tackling your own drainage or planning to renovate a rural stone house, follow along as our project unfolds. Join the Kraut Crew for behind-the-scenes updates, tool reviews, and the next stage of this series — where we finally connect the drain to our greywater line and put it to the test.

Why French Drains Matter for Granite Houses

Old granite houses age gracefully, but they don’t forgive neglect. For all their strength, those 50 cm (20 in) thick walls act like slow sponges — pulling moisture up from the ground and holding it for months. When I first stepped inside our ruin, the air felt heavy, the lower stones darker than the rest. That’s rising damp: moisture traveling upward through capillary action, leaving behind salts, crumbling mortar, and that familiar musty smell of time.

The problem isn’t the granite itself. Stone can handle moisture; it’s how we manage it that decides whether a wall stays solid or starts to fail. Decades ago, builders relied on natural balance — breathable lime mortar and gravity. Rainwater drained away through soil or gravel paths. But add modern concrete, compacted soil, or raised ground levels around the walls, and that balance breaks. Water has nowhere to go but in.

Discovering the base — every shovel stroke reveals more of the story our stone home’s foundation tells.

That’s where French drains earn their keep. A properly sloped gravel trench doesn’t stop water from existing — it simply gives it a better place to go. By redirecting runoff away from the wall base, you keep hydrostatic pressure low and allow the granite to stay dry enough to breathe. When combined with lime mortar (never cement), the system works both ways: the drain carries water out, and the wall can release any moisture trapped within.

In short, it’s about prevention, not repair. Once damp rises into granite, drying out takes seasons, not weeks. Installing a French drain while the ground is open saves you years of patching, repainting, and wondering why the wall keeps sweating. It’s a small, unglamorous task that protects every other step of renovation — from your ring beam to your plaster finish.

On our land, the lesson came the hard way. The house sits high, but not high enough to ignore runoff. Each storm carved subtle channels downhill, guiding water straight toward the foundations. We could either fight the slope or design with it. The French drain became the line between erosion and equilibrium — the quiet infrastructure that lets the old granite stay dry, stay strong, and stay breathable.

Keeping Granite Dry and Breathable

If there’s one phrase I repeat like a broken record, it’s this: “dry and breathable.”

Those two words are the foundation of every decision we make with this old house.

Granite is nearly indestructible, but it isn’t waterproof. Moisture moves through the tiny joints between stones and the mortar that binds them. In the past, lime mortar handled that perfectly — it absorbed water during wet spells, then released it slowly as the wall warmed in the sun. It was a living, breathing system.

Then came the age of cement. Builders everywhere sealed stone houses with concrete renders and dense mortars in the name of “modernization.” The result? The walls stopped breathing. Water still entered from below or behind, but it could no longer escape. That trapped moisture expands and contracts with the seasons, pushing mortar apart and causing that familiar flaky white crust known as efflorescence.

Planning the slope — we measure twice, dig once, ensuring water will never linger against our wall again.

The goal of a French drain isn’t to make your house watertight. It’s to give the water somewhere better to go so the wall can do its natural job. When the base of a granite wall stays drier, lime mortar can breathe again. Together, they create balance — the drain relieves external pressure, and the mortar handles internal moisture movement.

Before I even started adding gravel or pipe, I spent days cleaning the wall base and repointing the joints. Every gap where soil touched stone became a highway for damp. Repointing with a natural hydraulic lime (NHL 3.5) mortar seals those cracks without suffocating the wall. Think of it as repairing lungs, not wrapping them in plastic.

It’s tempting to rush this step, but nothing pays off more. Once the French drain is in place, that line of lime-repointed stone will act as a clear boundary: above it, breathable wall; below it, managed drainage. No waterproof coatings, no magic membranes — just physics and patience working together.

On a dry day, the contrast is already visible. The granite that used to stay dark after rain now dries evenly within hours. That’s the difference between “sealed” and “safe.” Breathable systems don’t trap water — they guide it, slowly and predictably, back to the soil where it belongs.

Planning the System — Slope, Depth & Design Logic

Planning a French drain sounds straightforward—until you meet granite.When I first grabbed the shovel, I thought I’d be done in a few weekends. Five months later, I’m still at it. Granted, the summer pause helped; no point digging drains when there’s no rain. But the rest of that time was spent figuring out how to make the system work with the land instead of fighting it.

Our granite house sits almost at the highest point of the property. That means water wants to run away, but not always in the direction you’d expect. The ground dips slightly from the south-west corner down toward the north-east—perfect for a gravity-fed layout. Using that natural fall, I planned a 2 % slope for the entire drain run. That’s roughly 2 cm drop per meter (¼ inch per foot). It’s enough to move water steadily without eroding the trench base.

Early excavation stage — this is where our French drain journey begins, balancing precision with pickaxe power.

Depth was the next challenge. Inside, we’d already poured a new concrete slab over compacted gravel. To protect that edge, I needed the drain to sit below the slab’s bottom line, plus the height of the pipe itself. That meant cutting through the outer rock shelf until the trench base sat about 15 cm lower than the interior floor. On paper it’s simple; in practice it meant hours behind a 250 mm corded angle grinder fitted with diamond discs and a very patient jackhammer.

I started by marking the perimeter, then removed about 80 cm of topsoil and loose rubble around the exterior walls. After that came the slow, noisy part: cutting a 40 cm-wide channel through solid granite. Five diamond discs later, the trench finally followed the slope I wanted.

Every decision came back to one principle: drainage equals direction.A French drain doesn’t work by storage—it works by slope. Even a few flat spots can trap water and turn the system into a bathtub. I kept rechecking my string lines with a spirit level and laser, adjusting the gravel base until the numbers were right.

The lowest point—the north-east corner—will become the outlet. From there, the drain will connect into our existing greywater line, protected by a boxed maintenance hatch so I can flush the pipe with a garden hose whenever sediment builds up. It’s a simple safeguard that saves a lot of digging later.

This stage isn’t glamorous. It’s dusty, loud, and hard on your shoulders. But once you see the trench take shape, the logic clicks: every centimeter of fall is one step closer to a dry, breathable wall. Planning before backfilling is what turns a trench into a lifetime fix instead of a seasonal experiment.

A DIY Guide from the Trench Up

Once the layout and slope were locked in, the real work began — and let me say this up front: cutting granite is not a weekend hobby. It’s a patience game powered by caffeine, a corded grinder, and the occasional reality check.

This is the stage where ideas become infrastructure. Every layer in the drain serves a purpose, and skipping one will only invite damp back in. Here’s how I tackled it, step by step.

1. Clear the Perimeter and Set the Base

After carving the trench, I cleaned out loose dust and small rock fragments. Then I measured again — laser, string, level — because once you start filling, there’s no easy way to fix the slope. The target remained steady: 2 % fall from southwest to northeast.

At the bottom of the trench, I spread a 5–10 cm (2–4 in) layer of sharp, washed gravel (20–40 mm stones). This creates a firm but permeable base that lets water flow freely beneath the pipe. A quick tap with a hand tamper helped settle it without compacting the flow channels.

2. Repoint the Wall Base

Before backfilling anything, I turned my attention to the granite itself. Any open joint where soil met stone became a direct path for moisture. I raked out loose mortar and repointed the lower wall with natural hydraulic lime (NHL 3.5) — breathable, strong, and flexible enough to move with the seasons.

Cement mortar might be faster, but it traps moisture. Lime lets the wall exhale, even when the drain is taking most of the load.

3. Add the Dimpled Drainage Mat

Next came the dimple sheet — a tough, textured plastic membrane that sits against the wall side of the trench. It creates a vertical drainage channel and shields the stone from direct soil contact. I ran the sheet so it rose a few centimeters above the future soil line, then fastened it gently to stay in place. That small overlap ensures that splash water drains behind, not into, the wall.

4. Line with Filter Fabric

I rolled out non-woven geotextile filter fabric, letting it drape across the trench and up both sides, like a loose burrito wrapper. This fabric keeps soil fines out of the gravel, preventing clogs years down the line. If you’ve ever opened an old, muddy drain, you’ll know why this layer matters.

5. Add the First Gravel Lift

With the fabric in place, I poured another 10–15 cm (4–6 in) of washed gravel. The idea is to give the drainage pipe a clean, supportive bed that maintains flow even during heavy rain.

6. Lay the Drainage Pipe

The heart of the system: a 100 mm (4 in) perforated pipe, laid holes-down, following that same 2 % slope.Every few meters — and at corners — I added inspection tees so I can flush the line later. At the high corner, I’ll install a small boxed hatch where a garden hose can be inserted to clean the entire run.

Tough Tip: Don’t rely on “eyeballing” the slope. Use a level on the pipe itself. Even small humps can hold water.

7. Backfill in Layers

Once the pipe sat perfectly, I filled the trench with more washed gravel, stopping about 10 cm (4 in) below the final grade. Then I folded the filter fabric back over the top and added one last thin layer of gravel to complete the “burrito.” That wrap keeps the system clean and breathable — exactly how the granite prefers to live.

8. Finish and Forget (Almost)

The final trench layer depends on your landscaping plan. I’ll top mine with decorative gravel near paths and soil where future plants will go. Whatever you choose, keep the top breathable — no concrete caps or dense clay. The system needs air just as much as the wall does.

9. Safety and Sanity Notes

This job will test both. Here’s what saved me (and my lungs):

• Corded tools only: Battery grinders can’t keep up with granite. I use a 250 mm (10 in) angle grinder and a heavy corded jackhammer from earlier demolition work.

• PPE that earns its keep:

  • Good goggles and hearing protection

  • Heavy gloves and long sleeves (granite chips burn skin fast)

  • Safety boots with steel toes

  • A 3M 6000 Series half-mask respirator — worth every cent in dust control

• Work slowly, rest often, and treat the grinder like a scalpel, not a sword.

Dust, stone, and focus — this is the hands-on stage where power meets heritage at Tough Kraut.

Tough Tip: When fatigue sets in, stop. Cutting granite isn’t about power; it’s about control. The moment you rush, the tool will remind you who’s boss.

Each meter of this trench represents a small victory. Progress feels slow because it’s supposed to. French drains don’t just move water — they move you toward understanding how your house and land really breathe together.

Tools & Materials Checklist

There’s no shortcut through granite, and cheap gear only teaches expensive lessons.Here’s the exact setup that’s gotten me this far — tested in dust, noise, and stubborn rock.

Power Tools (Corded — Always)

When it comes to cutting or breaking granite, corded tools are non-negotiable. Battery models fade fast under heavy load and can overheat your inverter if you’re off-grid.

• 250 mm (10 in) Angle Grinder — your main cutter for trenching rock.

  • Used with five diamond discs so far; expect to swap often.

• Large Jackhammer (corded) — essential for loosening the granite shelf once cut.

  • Bought earlier for interior excavation; still earning its keep.

Tough Tip: Keep both tools cool between passes. Granite dulls discs faster than you think; overheating them costs time and money.

Hand Tools

Even with power on your side, hand work makes or breaks the job.

• Shovels and trenching spades

• Mattock or pickaxe for roots and compacted soil

• Pry bar or crowbar for levering out larger stones

• Measuring tape, string line, spirit level, and laser level for slope checks

• Hand tamper for settling gravel base

• Buckets or wheelbarrow for hauling spoil and gravel

Drainage Components

The skeleton of the system — everything here serves one function: move water away.

• 100 mm (4 in) perforated pipe, rigid or flexible

• Inspection tees and end caps for maintenance access

• Non-woven geotextile filter fabric — prevents soil fines from clogging gravel

• Sharp washed gravel (20–40 mm / ¾–1½ in)

• Dimpled drainage mat — protects the wall face and channels vertical flow

• Boxed flush hatch or silt trap — lets you clean the line with a hose

Masonry & Wall Work

Before any backfill, secure the wall base.

• Natural Hydraulic Lime (NHL 3.5) mortar for repointing

• Pointing trowel and small brush for cleaning joints

• Spray bottle or gentle hose mist to pre-dampen before repointing

Lime breathes. Cement traps. Choose accordingly.

Personal Protective Equipment (PPE)

No badge of honour comes from granite dust in your lungs. Suit up right.

• 3M 6000 Series Half-Mask Respirator with P100 or A1P2 filters

• Impact-rated goggles

• Hearing protection (muffs or plugs)

• Heavy gloves for vibration and abrasion

• Long-sleeved work shirt to deflect hot chips

• Steel-toe boots for the rocks that always aim at your feet

Consumables & Support Gear

• Diamond discs (buy in multi-packs; granite eats them)

• Extension cords rated for outdoor heavy-load use

• Dust sheets or tarps for spoil piles

• Buckets of patience — because nothing about granite is quick

Smooth-cut granite drainage trench — our careful groundwork for a hidden but crucial water-management system.

This list isn’t about brand loyalty; it’s about survival. Good tools and good protection turn a brutal task into a manageable one — and let you finish the day without coughing up a dust storm.

Common Mistakes and Simple Fixes

French drains are simple in principle, but they don’t forgive shortcuts.I’ve learned most of these the hard way — the rest from patient masons who’ve been at this longer than I’ve been alive. Here’s what to avoid (and how to fix it) before the rain teaches you instead.

Mistake 1: Forgetting the Slope

Water doesn’t guess which way to go — you have to tell it.

Even a short section of flat pipe can hold water like a bathtub.

Fix:

Keep that 2 % slope consistent from start to finish.

Recheck with a spirit level or laser every few meters before backfilling.

If the pipe dips, pull it up slightly and re-bed it in gravel. The few extra minutes now save you from digging up a soggy mystery later.

Mistake 2: Skipping the Filter Fabric

It’s tempting to save time and skip the fabric.

Without it, fine soil particles slowly clog the gravel until your drain becomes nothing more than a buried puddle.

Fix:

Always line the trench with non-woven geotextile, folding it over the top like a loose wrap.Think of it as the drain’s lungs filter — it keeps the system breathing.

Mistake 3: Wrong Mortar for the Job

One size doesn’t fit all, especially when it comes to stone walls.

Lime is brilliant above ground, but below the soil line, it never fully dries.

Fix:

Use natural hydraulic lime (NHL 3.5) for all repointing above the French drain line — it breathes and flexes naturally.

For the lowest joints that sit below soil level, switch to cement-based mortar for durability.

Since those sections will be covered by the dimpled drainage mat, they don’t need to breathe — they just need to hold. The mat provides a protective gap, channeling any moisture straight down to the drain.

Finishing touches — we restore the wall’s lower courses to pair perfectly with the new French drain system.

Tough Tip: A stone mason taught me this hybrid trick — cement below, lime above, drainage mat between. It’s the sweet spot between tradition and practicality. You keep the wall strong where it’s buried, and breathable where it lives.

Mistake 4: Using Dirty or Crushed Gravel

Not all gravel is equal. The wrong kind compacts, traps silt, or blocks water flow.

Fix:

Use washed, angular gravel between 20–40 mm (¾–1½ in). Avoid crushed concrete or sand-heavy mixes. The sharper edges help water move freely and prevent the pipe from sinking over time.

Mistake 5: No Access for Maintenance

Out of sight shouldn’t mean out of mind. Without an access point, any future blockage means full excavation.

Fix:

Install inspection tees at corners and a flush hatch at the highest point. Once a year, give it a quick flush with a garden hose. You’ll sleep better when the next downpour hits.

Mistake 6: Ignoring Safety

Cutting granite without protection is a quick way to ruin your day (and your hearing).

Fix:

• Corded tools only — battery grinders aren’t built for granite.

• Wear full PPE: goggles, hearing protection, long sleeves, safety boots, and your 3M 6000 Series respirator.

• Work in short bursts and step back often to clear dust. The wall should breathe, but so should you.

Mistake 7: Sealing the Top with Concrete

This one’s surprisingly common.

A solid concrete cap traps water instead of shedding it, turning your careful drain into a permanent puddle.

Fix:

Finish with breathable materials — gravel, mulch, or soil with plants that tolerate dry feet.

Let air and water move freely through the top layer.

Each of these fixes comes down to one rule: respect water, but don’t fear it.If you give it direction and space, it’ll quietly leave you alone.

Technical and Off-Grid Notes

Every drain is a small engineering project, even if it’s just you, a grinder, and a lot of granite dust.These are the details that keep the system working year after year — the kind you won’t find printed on a bag of gravel.

Pipe Size and Flow

For a small rural house, 100 mm (4 in) perforated pipe is ideal.

It carries plenty of runoff without needing deep excavation.If your roof area is large or you’re tying in multiple downspouts, you can bump up to 125 mm (5 in), but the key isn’t pipe diameter — it’s unbroken slope.

Tough Tip: Bigger pipe won’t fix a flat trench. Water needs direction more than capacity.

Slope Math

A 2 % slope equals 2 cm per metre (¼ in per foot).That means over a 10 m run, your outlet should sit 20 cm lower than the start.I checked mine with a laser and string line every few metres.It sounds obsessive, but precision here saves digging later.

Gravel Gradation

Stick with 20–40 mm (¾–1½ in) washed, angular gravel.

Round river stone looks pretty but compacts too easily.

Angular pieces interlock and create permanent voids for drainage.

Anything smaller collects silt; anything larger lets the pipe shift under weight.

The Dimpled Drainage Mat

This mat does more than protect the wall — it also acts as a pressure-relief zone.

By creating a narrow air gap, it allows the wall base to drain vertically without direct soil contact.

Where the mat overlaps the cement-pointed joints, it forms a waterproof-yet-drainable barrier that shields the foundation from constant splash and soil movement.

Managing Power Off-Grid

Granite doesn’t care if it’s sunny.Your tools, however, do — at least in the early days of off-grid living.

When I worked on the French drain, I didn’t have to think twice about power. From April through mid-October, our solar system easily carried everything — grinder, jackhammer, and radio included. Long days and strong sun hours meant I could cut, grind, and hammer without checking the inverter screen every five minutes.

But if you’re still at the start of your setup or running on a small battery bank, heavy tools will drain your reserves fast. Running a 250 mm corded grinder or jackhammer pulls continuous load that early solar systems often can’t sustain on cloudy days.

Tough Tip: If you’re still building your solar confidence, plan major cutting or demolition during the bright months and run high-draw tools through a solar generator or backup line. You’ll find detailed comparisons and setup tips in our guide: Choosing the Best Solar Generator for Off-Grid Living: 2025 Buyer’s Guide & Setup Tips

Once your panels and batteries scale up, you’ll reach the same point we’re at now — where power is no longer the bottleneck, and you can focus on dust, slope, and sanity instead.

Seasonal Workflow

I paused the trench work through summer.

With no rain expected and the ground like concrete, there’s no sense burning discs and energy.

Instead, I used that time to prepare tools, order materials, and let the walls fully cure from interior work.

French drains are best tackled in shoulder seasons — cool enough to dig, dry enough to keep the trench stable.

Testing and Maintenance

Before backfilling, always test.

I poured a few buckets of water into the high end of the trench.

Watching it flow smoothly to the outlet confirmed the slope and peace of mind.

Once a year, a quick flush through the inspection hatch keeps everything clear.

These aren’t glamorous steps, but they’re what make the system last. A French drain done right is one you never have to think about again — and that’s the highest compliment you can pay to any piece of infrastructure.

Cost & Time Breakdown

Every renovation task looks cheap on paper until granite enters the chat.French drains don’t just cost money — they cost time, patience, and a few worn-out tools along the way.

Timeframe

From start to the point where we are now, the drainage project has taken me nearly five months.That includes trenching, cutting, repointing, slope testing, and pausing during the summer months when digging made no sense.With no rain expected from June through mid-October, I focused on other work and let the site rest. Realistically, active tool time adds up to about six to eight solid weeks of labor spread across that period.

If you’re planning something similar, aim to schedule drainage work for late autumn through spring, when the soil is soft and the temperature is on your side.

Material Costs (approximate for DIY builds)

Exchange rate used: €1 ≈ $1.09 USD (October 2025)

Item	Estimated Cost	Notes
100 mm (4 in) perforated pipe + fittings	€2.5 – €4 per m	Add tees & caps for maintenance
Non-woven geotextile fabric	€1 – €2 per m²	Prevents silt buildup
Dimpled drainage mat	€6 – €12 per m²	Shields wall, channels runoff
Washed sharp gravel (20–40 mm / ¾–1½ in)	€25 – €45 per m³	Delivered, washed only
Lime mortar (NHL 3.5)	€12 – €18 per 25 kg (55 lb) bag	For above-grade joints
Cement mortar	€6 – €9 per 25 kg (55 lb) bag	For joints below soil level
Flush hatch / inspection box	€35 – €90	Optional but worth it
PPE (filters, gloves, discs, earplugs)	€50 – €120	Reusable gear with replaceables
Total (materials only)	~€400 – €800 (≈ $435 – $875 USD)	Depending on trench length & site conditions

Tool Costs and Hidden Consumables

Most of the expense hides in tool wear.

If you’re cutting through granite, expect to burn through several diamond discs — they’re not cheap, but they’re worth it.

Tool / Consumable	Typical Cost (€)	Notes
Angle Grinder (250 mm / 10 in)	€100 – €150	Corded, continuous-duty model
Jackhammer (corded)	€200 – €350	Reliable for granite
Diamond Cutting Discs	€30 – €35 each	Buy several — granite eats them
Replacement Carbon Brushes	€10 – €25 per set	Keep spares on hand

Both my grinder and jackhammer use carbon brushes, not brushless motors.Brushes wear faster under continuous load, especially in dust.Buy at least one spare set ahead of time — the day a brush burns out mid-cut is the day you learn patience the hard way.

Tough Tip: Brushless motors are great for light tools, but for stonework, corded models with replaceable brushes still win on torque and service life.Keep vents clear and let them cool between passes; granite dust eats everything it touches.

Realistic Expectation

If you already own the tools, your main costs are materials, discs, and sweat equity.Starting from scratch, expect your first trench to total around €700 – €1,200 (≈ $760 – $1,300 USD) including tools.

It’s slow work by design — each meter (3 ft) of trench is a mini-project: cut, clean, check slope, breathe, repeat.

Five months might sound long until you realize that every day spent doing it right buys decades of dryness inside your walls.

From Trench to Trust

Every stone house teaches patience.You think you’re just digging a drain, but what you’re really doing is learning how water thinks.

When I first started this French drain, it felt endless — just rock, dust, and noise. But step by step, meter by meter, the system began to take shape. Now, seeing the slope carved, the gravel set, and the wall breathing again, it’s clear that this isn’t just about keeping granite dry. It’s about building trust — between the land, the materials, and the hands that shape them.

There’s no quick way through a project like this. Each day behind the grinder or the trowel is a quiet investment in the next decade of comfort. The drain won’t be visible once it’s buried, but that’s the point. The best work on a homestead is often the kind no one ever sees — the kind that quietly keeps everything else standing.

So if you’re knee-deep in dust and wondering whether your trench will ever end, take it from me: you’re closer than you think. Every clean cut, every slope check, every bag of gravel brings your home one step closer to breathing on its own again.

And when the first heavy rain hits, you’ll know exactly where that water’s going — away from the walls and into the earth where it belongs.

Long-term resilience — our French drain now wraps the granite wall like a hidden moat of protection.

If you’re building, renovating, or simply planning your off-grid dream, join the Kraut Crew for updates from the field. You’ll get early access to future guides — from connecting this French drain to our greywater system.

We share every success and every mistake so you don’t have to learn them the hard way.

Herman’s Tough Kraut Fixes: Common Challenges Installing French Drains for Stone Homes

No project goes exactly as planned. Granite shifts, pipes tilt, and even the best-laid gravel has a mind of its own. Here are a few lessons and real-world fixes gathered along the way — practical, proven, and free of guesswork.

Q: My trench is holding water instead of draining. What did I do wrong?

A: This usually means your slope isn’t consistent or the pipe has settled into a small dip.Use a laser or spirit level to recheck your fall — you’re aiming for 2 cm per meter (¼ inch per foot). If the pipe has sagged, scoop out the section, refill with gravel, and reset it. Even a slight belly can trap water for weeks.

Q: Should the perforated pipe holes face up or down?

A: For French drains beside foundations, point the holes down.Water enters from the bottom and flows through the pipe’s voids, not across the top. Facing the holes up can collect silt faster and reduce efficiency over time.

Q: My gravel keeps clogging — how can I fix or prevent this?

A: Clogging means fine soil has migrated into your trench.If it’s localized, open a small section, remove the muddy gravel, and replace it with washed sharp gravel. Then make sure your filter fabric fully wraps the gravel bed, with generous overlaps. A simple burrito-style fold can extend your drain’s lifespan by decades.

Q: Can I use cement mortar near the foundation, or will it trap moisture?

A: Both — depending on where. Use cement-based mortar for joints below the soil line, especially where the dimpled drainage mat covers the wall. That zone needs durability, not breathability. Above the mat, return to lime mortar (NHL 3.5) to keep the rest of the wall vapor-open.

Q: How deep should the drain be compared to the interior floor?

Always below the lowest point of your interior slab. That ensures water outside never reaches the same level as the inside floor. Add the pipe diameter (about 100 mm / 4 in) below that line, plus gravel clearance, to guarantee the path of least resistance leads away from your home.

Q: Can I connect my French drain to my greywater line?

A: Yes — carefully. If your greywater pipe already handles kitchen or shower runoff, install a silt box or inspection chamber between the systems to catch debris and balance flow. Never tie directly into a sealed tank or soakaway without pretreatment. When in doubt, keep the French drain outlet separate, or daylight it to a gravel pit within your land boundary.

Q: What’s the best way to test if it’s working before backfilling?

A: Before you close the trench, pour several buckets of water into the high end and watch it flow to the outlet. If it moves freely without pooling, you’re ready to backfill. A yearly flush with a garden hose keeps it that way — that’s why inspection points matter.

Q: How often should I inspect or maintain it?

A: Once a year is plenty. After the first heavy rain of the season, check your flush box. If water flows clear and freely, you’re good. If it burps or backs up, flush the line for a minute or two. The simpler the system, the easier it is to keep alive.

Recommended Books & Resources

Books

• Building with Lime: A Practical Introduction by Stafford Holmes & Michael Wingate

  The clearest starter on lime mortars and plasters for old masonry. Perfect for understanding why lime above grade + drainage below grade keeps granite healthy.

• Water in Buildings: An Architect’s Guide to Moisture and Mold by William B. Rose

  Definitive building-science read on how water moves, condenses, and causes trouble. Great for anyone designing drains, ventilation, and breathable wall systems.

• Old House Handbook: A Practical Guide to Care and Repair (2nd ed.) by Roger Hunt & Marianne Suhr

  Conservation-minded guidance for traditional materials and details. It pairs beautifully with our lime + drainage approach on heritage stone.

• Renovating Old Houses: Bringing New Life to Vintage Homes by George Nash

  A practical classic that covers foundations, site drainage, and the “do it once, do it right” mindset that saves years.

Resources

• Catch-Basin Filter Insert for 12" Basins (NDS 1200 series)

  Drop-in geotextile filter for 12 in catch basins that traps silt and organics before they reach your French drains for stone homes outlets or greywater interface. Maintenance takes minutes, not days.

• 30 m (100 ft) Sewer/Drain Inspection Camera (reel + LED head)

  An affordable push-rod camera that lets you diagnose clogs, bellies, or silt pockets without digging. Game-changer for yearly checkups via your flush box.

• Tough Kraut Resources

  Our living library of field-tested tools, lime mortars, work lights, and drainage gear we trust on our own land. If it can survive Portuguese granite, it earns its place there.