Stone Veneer and Natural Stone Exterior Cleaning Guide

Quick Answer

Clean stone veneer and natural stone siding using low to moderate pressure (1,500-2,000 PSI for manufactured stone, 1,200-1,800 PSI for natural stone), white or green nozzle, and pH-neutral cleaners (6-8 oz sodium percarbonate/gallon). NEVER use acids on limestone, marble, or travertine—test all chemicals on inconspicuous area first, as many stones are acid-sensitive.

Key Takeaways

• Mortar is the weak point - Softer than stone and easily damaged by pressure
• Many stones are acid-sensitive - Limestone, marble, travertine dissolve with acids
• Test everything first - You can’t tell stone type or sensitivity by looking
• Sealer matters - Sealed stone cleans differently than unsealed
• Manufactured vs natural - Different durability and cleaning approaches

---

Understanding Stone Veneer and Natural Stone

Stone veneer siding comes in two forms: manufactured (cultured) stone and natural stone. They look similar from a distance but have very different characteristics, vulnerabilities, and cleaning requirements.

Manufactured stone veneer is concrete poured into molds textured to look like natural stone. It’s lightweight, consistent, and attached to walls with mortar and metal lath. The stone itself is durable (it’s concrete), but the mortar joints and the attachment system are vulnerable. High pressure can dislodge stones entirely—I’ve seen homeowners lose dozens of stones in one afternoon of overly aggressive washing.

Natural stone veneer is real stone cut thin enough to use as siding. Common types: limestone, sandstone, slate, quartzite, marble, travertine, granite. Each has different characteristics:

• Limestone and marble: Soft, acid-sensitive, easily etched
• Sandstone and quartzite: Harder, more durable, still vulnerable to pressure
• Slate: Durable but can delaminate with aggressive washing
• Travertine: Porous, acid-sensitive, easily stained
• Granite: Hardest, most durable, but still has vulnerabilities

The mortar joints are the weak point in ALL stone veneer—manufactured and natural. Mortar is softer than stone and erodes under pressure. Once mortar is damaged, water penetrates behind the veneer, causing structural issues you can’t see until they’re extensive and expensive.

I’ve cleaned hundreds of stone veneer installations. The most common mistake? Treating it like concrete. Homeowners crank up the pressure, blast away, and damage mortar or dislodge stones. Stone veneer requires patience and lower pressure than you’d expect.

---

The Damage You Can Do

Damaging Mortar Joints

This is the most common and most visible damage. Mortar is softer than stone and erodes under pressure. Once mortar is recessed or missing, the wall looks terrible and water penetrates behind the veneer.

Re-pointing mortar is expensive and labor-intensive—$3-6 per sq ft for professional work. And color-matching new mortar to old is nearly impossible—repairs are visible.

Dislodging Stones (Manufactured Veneer)

Manufactured stone is attached with mortar and metal lath. High pressure or aggressive angles can break the mortar bond and dislodge stones entirely. I’ve seen homeowners lose 20-30 stones in one afternoon of overly aggressive washing.

Re-attaching stones is possible but tedious and expensive. And you’ll never get the perfect match the original installation had.

Etching Acid-Sensitive Stones

Limestone, marble, and travertine dissolve with acid exposure. Even mild acids (vinegar, citric acid cleaners) can permanently etch these stones. Once etched, the damage is irreversible—you’re replacing stones or living with it.

This is tricky because you can’t always tell stone type by looking. I’ve seen homeowners etch expensive limestone siding with cleaner that was perfectly safe for sandstone.

Damaging Sealers

Many stone veneers have sealers applied for protection. Harsh chemicals or high pressure can strip these sealers, leaving raw stone exposed. Once sealer is gone, the stone is vulnerable to stains and weathering. Re-applying sealer to existing installation is expensive and sometimes impossible to match.

Forcing Water Behind Veneer

High pressure forces water deep into mortar joints and behind the veneer. This leads to:

• Mold growth inside the wall cavity
• Rot in the wood sheathing behind the veneer
• Structural damage from freeze-thaw cycles
• Efflorescence (mineral deposits) as water migrates out

You won’t see this damage for months or years, but by then it’s extensive and expensive.

---

Identifying Your Stone Type

Manufactured (Cultured) Stone

• Consistent shapes and sizes (molded)
• Hollow back side (you can see this if a stone falls off)
• Light weight for the size
• Colors are uniform and repeated
• Often installed in regular patterns

Manufactured stone is concrete—durable but the mortar and attachment are vulnerable.

Natural Stone

• Irregular shapes and sizes (except cut stone)
• Solid throughout the piece
• Heavier for the size
• Colors vary naturally
• Individual stones are unique

Natural stone varies in hardness and acid sensitivity based on type.

Common Natural Stone Types

• Limestone: Gray, tan, often has fossils. Soft, acid-sensitive.
• Sandstone: Various colors, grainy texture. Medium hardness.
• Slate: Dark gray, black, purple. Distinctive layered appearance. Hard.
• Quartzite: Similar to sandstone but harder and more durable.
• Marble: Veined appearance, often white or colored. Soft, acid-sensitive.
• Travertine: Pitted surface, often tan or cream. Very porous, acid-sensitive.
• Granite: Speckled appearance, various colors. Hardest, most durable.

When in Doubt, Test

You can’t always identify stone type visually. And you can’t determine acid sensitivity by looking. TEST your chemicals on a small, inconspicuous area before applying to the whole wall.

---

Equipment for Stone Veneer

Pressure Washer

Manufactured stone: 1,500-2,000 PSI maximum. The stone itself is durable (concrete), but the mortar and attachment system are vulnerable.

Natural stone: 1,200-1,800 PSI maximum. Natural stone varies in hardness—start lower and increase only if needed.

For both types, lower pressure is better. Let chemicals do the work.

Nozzles

White (40°) nozzle for most work. Green (25°) only for stubborn stains on durable stones (granite, quartzite, slate). Never yellow (15°) or red (0°)—these will damage mortar and dislodge stones.

Chemical Application

Pump sprayer (2-3 gallon) gives you control over where cleaner goes and how much. Downstream injector works but makes protecting vulnerable areas more difficult.

Brushes

Stiff synthetic bristle brush for agitating cleaner. NO wire brushes—wire damages both stone and mortar. A handheld scrub brush for detail work around mortar joints.

---

Chemical Selection

General Cleaning: Sodium Percarbonate (Oxygen Bleach)

Mix 6-8 ounces per gallon of water. Safe for ALL stone types when used properly. Won’t damage mortar. Won’t etch acid-sensitive stones.

Apply with pump sprayer. Let dwell 20-30 minutes. Agitate with stiff brush for stubborn stains. Rinse thoroughly.

Commercial products: Wood Cleaner, Simple Cherry, or any sodium percarbonate-based cleaner.

Efflorescence Removal: Masonry Detergents

Efflorescence (white mineral deposits) appears on stone and mortar as water migrates through and evaporates, leaving minerals behind.

For light efflorescence, scrub with stiff brush and water. For heavier deposits, use dedicated masonry detergent or efflorescence remover following manufacturer’s instructions.

Rust Removal: Oxalic Acid (Use Caution)

Mix 4-6 ounces per gallon of water. Oxalic acid removes rust stains BUT:

• TEST FIRST on acid-sensitive stones (limestone, marble, travertine)
• Use minimal concentration and dwell time
• Rinse thoroughly
• Consider professional help for valuable stone

Oxalic acid will etch limestone and marble—use only if you’ve confirmed stone type and know it’s safe.

Mold/Mildew: Sodium Hypochlorite (Use Caution)

Bleach solutions kill mold but:

• Can discolor some stones (especially porous varieties)
• Can damage mortar with repeated use
• Use minimal concentration (1:1 with water max)
• Rinse thoroughly
• Sodium percarbonate is safer for most situations

What to Avoid

NO muriatic acid or hydrochloric acid—these will dissolve limestone and marble, damage other stones, and destroy mortar.

NO vinegar, citric acid, or other mild acids on acid-sensitive stones (limestone, marble, travertine).

NO abrasive cleaners or scouring powders—these scratch stone surfaces.

NO wire brushes or abrasive pads—these damage both stone and mortar.

---

Preparation

Identify Stone Type

Before ANY cleaning, identify stone type:

• Manufactured vs natural
• If natural, determine specific type (limestone, sandstone, slate, etc.)
• Check if sealer has been applied (water beads up = sealer present)

If you can’t identify with confidence, ASSUME it’s acid-sensitive and avoid all acids.

Test Chemicals

Find a small, inconspicuous area (behind a bush, low corner, near ground). Apply your intended cleaner at full strength. Let dwell full recommended time. Rinse thoroughly. Let dry completely.

Check for:

• Color change or staining
• Surface etching or dulling
• Sealer damage
• Mortar damage

If ANY damage occurs, stop and reconsider your approach.

Inspect Mortar Condition

Walk the entire wall and check mortar joints:

• Cracks or gaps
• Missing mortar
• Recessed mortar (eroded)
• Loose stones

Make repairs before cleaning. Damaged mortar makes cleaning risky—water penetrates behind veneer more easily.

Protect Landscaping

Cover plants within 10 feet with tarps. Pre-saturate with water before covering. Stone veneer cleaning produces lots of runoff that can damage plants.

Close and Protect

Close windows and doors. Cover vents and exhaust fans. Remove or cover light fixtures.

Plan Your Approach

Work systematically: one section at a time, bottom to top (so runoff doesn’t stain already-cleaned areas). Plan where you’ll start and how you’ll move around the house.

---

The Cleaning Process

Step 1: Pre-Rinse

Light rinse with garden hose or white nozzle on pressure washer (stay 18+ inches back). Remove loose dirt and debris. Pay special attention to mortar joints—debris collects here.

Step 2: Apply Cleaner

Mix sodium percarbonate cleaner (6-8 ounces per gallon). Apply with pump sprayer, working in sections.

Let dwell 20-30 minutes. Stone veneer is porous—cleaner penetrates deeply. Keep surfaces wet—mist occasionally if drying.

Step 3: Agitate

For stubborn stains or heavy organic growth, agitate with stiff synthetic brush. Focus on mortar joints where dirt accumulates. Scrub individual stones if needed.

This is tedious work but necessary for good results on stone.

Step 4: Rinse

Rinse with white nozzle, staying 12-18 inches from surface. Move constantly—never hold still. Overlap passes by 50%.

Start at the bottom and work up (unusual, but this prevents dirty water from staining already-cleaned areas below). Rinse thoroughly—no foam, no suds, cleaner smell completely gone.

Step 5: Treat Stubborn Stains

For remaining stains:

• Efflorescence: Scrub with stiff brush and water. Heavy deposits need masonry detergent.
• Rust: Oxalic acid solution (4-6 ounces per gallon) ONLY if stone type confirmed safe. Test first.
• Organic stains: Re-apply sodium percarbonate at stronger concentration (8 ounces per gallon) or use enzyme-based cleaner.

Step 6: Final Rinse

Final thorough rinse with garden hose. Ensure no cleaner residue remains.

Step 7: Re-Seal (Optional but Recommended)

If the stone previously had sealer or if you want added protection, apply penetrating stone sealer after cleaning and complete drying (48-72 hours). Follow manufacturer’s instructions.

---

Special Considerations

Manufactured vs Natural Stone

Manufactured Stone:

• Can handle slightly higher pressure (up to 2,000 PSI)
• Watch for loose or dislodged stones
• Mortar and attachment system are the vulnerability
• More uniform cleaning results expected

Natural Stone:

• Use lower pressure (1,200-1,800 PSI)
• Stone type determines chemical sensitivity
• Natural color variations mean cleaning results vary by stone
• More likely to have sealers that need protection

Acid-Sensitive Stones

For limestone, marble, and travertine:

• NO acids of any kind
• Use pH-neutral cleaners only (sodium percarbonate)
• Test EVERYTHING first
• Consider professional cleaning for valuable installations

Sealed Stone

If sealer is present (water beads up on surface):

• Use milder cleaners (sodium percarbonate at 6 ounces per gallon)
• Lower pressure (1,200-1,500 PSI)
• Re-apply sealer after cleaning if it was stripped

Old vs New Installations

Old Stone Veneer (10+ years):

• Mortar may be soft or eroded
• Stones may be loose
• Sealer may be worn or gone
• Use extra care—lower pressure, test everything

New Stone Veneer (less than 2 years):

• Mortar still curing (may be lighter color)
• Sealer likely present
• Stones firmly attached
• Clean gently to protect curing mortar and fresh sealer

---

After Cleaning

Inspect for Damage

Check carefully for:

• Mortar damage—eroded, recessed, missing
• Loose stones—especially manufactured veneer
• Sealer damage—uneven water absorption
• Surface etching or staining (from using wrong chemicals)

Repair any damage promptly. Re-point damaged mortar. Re-attach loose stones. Re-seal if sealer was stripped.

Let Dry Completely

Stone veneer is thick and holds moisture. Wait 48-72 hours for complete drying before re-sealing. Test with moisture meter if unsure—should be below 15%.

Re-Seal if Needed

If sealer was present and stripped, or if you want added protection:

• Choose penetrating stone sealer appropriate for your stone type
• Follow manufacturer’s instructions carefully
• Two coats better than one for even coverage
• Re-seal every 3-5 years for ongoing protection

---

Common Problems and Solutions

Efflorescence Returning

Water still penetrating behind veneer. Check for:

• Damaged or missing mortar—repair immediately
• Missing or damaged flashing—repair
• Water from sprinklers hitting the wall—redirect
• Poor drainage around foundation—improve grading

Treat efflorescence with masonry detergent. Address water source to prevent recurrence.

Stones Falling Off (Manufactured Veneer)

High pressure or poor installation dislodged stones. Re-attach with mortar appropriate for manufactured stone. For extensive loss, consider professional help—re-attachment is tricky and needs to match original appearance.

Stone Discoloration

Used wrong chemical or stone was acid-sensitive. Discoloration from acid is permanent—stones must be replaced. Discoloration from other causes might be cleanable with specialized stone cleaners.

Mortar Discoloration

Bleach or harsh chemicals stained mortar. Some discoloration can be cleaned with specialized masonry cleaners. Severe discoloration requires re-pointing (replacing mortar).

Mold Returning Quickly

Shady area, poor drainage, or vegetation too close. Trim vegetation. Improve drainage. Consider applying mold-resistant sealer. Clean more frequently (annually).

---

Pro Tips

Test Everything

I can’t emphasize this enough. Test chemicals. Test pressure. Test your technique on a small area first. Stone is expensive and permanent damage is, well, permanent. Better to spend 30 minutes testing than thousands repairing.

Work Bottom to Top

Unlike most siding, clean stone veneer from bottom to top. Dirty runoff stains cleaned areas below. Working bottom to top minimizes this problem.

Keep Your Distance

Stay 12-18 inches from the surface. Stay extra distance from mortar joints and loose or vulnerable areas. The temptation to get closer for better cleaning is strong—resist it.

Hand-Clean Vulnerable Areas

For areas with soft mortar, loose stones, or unknown condition, hand-clean with sponge, mild detergent, and stiff brush. Slower but safer.

Know When to Call a Pro

For valuable stone installations (marble, limestone, slate), extensive damage, or situations you’re uncertain about, professional help is cheaper than damaging expensive stone.

---

DIY vs. Hiring a Pro

Hire a professional for:

• Valuable natural stone (marble, limestone, slate)
• Extensive damage or mortar issues
• Large installations (2,000+ sq ft)
• Situations where stone type is uncertain

Professional stone cleaning: $1.50-4.00 per sq ft for manufactured stone, $2.50-6.00 per sq ft for natural stone. A 500 sq ft wall runs $750-3,000 depending on stone type and condition.

DIY materials: $40-60 for sodium percarbonate cleaner, $30-50 for masonry detergent if needed, $100-200 for stone sealer. Total: $170-310. Time: 10-20 hours for typical 500 sq ft installation.

Risk: High. Stone is expensive and permanent. Mistakes are visible and costly to fix. Mortar damage is expensive to repair. Acid damage to acid-sensitive stones is irreversible.

---

Maintenance

Inspect stone veneer annually for:

• Mortar condition—cracks, gaps, erosion
• Loose stones (especially manufactured veneer)
• Efflorescence or mineral deposits
• Mold or algae growth
• Sealer condition

Clean every 2-3 years with sodium percarbonate cleaner. Homes in humid or shaded areas may need annual cleaning.

Re-seal every 3-5 years with penetrating stone sealer appropriate for your stone type.

Trim vegetation away from stone veneer. Ensure sprinklers don’t spray directly on stone. Maintain good drainage around the foundation.

Address water issues promptly—water penetration behind veneer causes extensive damage that’s expensive to repair.

---

Next Steps

• Cleaning Retaining Walls: Block, Stone, and Timber
• Brick Exterior Washing: Mortar-Safe Techniques
• Sodium Percarbonate: Oxygen Bleach for Wood Cleaning
• Oxalic Acid: Wood Brightening and Rust Removal