Problem Solving Black Limestone

We are often contacted in particular about black limestone, the appearance of stains and mineral deposits is not uncommon and occurs with most types of limestone, however the appearance on black limestone or darker stone is more prevalent. This is why it is possible to notice some marks appearing even before sealing. As a naturally occurring chemical reaction it is often difficult to avoid. So this blog is all about some of the different things that can happen, what you can do to prevent it or what you can do to resolve the issues as best you can.

Mineral Stains

Mineral deposit stains on black limstone

Mineral stains are sometimes caused when rain water trickles through sand-cement mortar screeds, toppings and bedding under limestone paving can become moderately alkaline. As this rainwater evaporates, its alkalinity increases until the solution becomes saturated.
This solution then can travel to the surface within the limestone where it starts to deposit solids such as white and grey encrustations of calcium carbonate also known as lime plumes.
To remove the the mineral salts from the surface wash the surface with a mild solution of acid*. This will help disperse the mineral salt deposits from the surface.
LTP Grout Stain Remover is a product suitable for the task, dilute 1 part LTP Grout Stain remover in 4 parts warm water and apply to the surface of the stone. Agitate using an emulsifying pad or similar abrasive pad and then rinse thoroughly with plenty of clean water. Repeat process if necessary.
For more information about LTP Grout Stain Remover please see the Technical Data Sheet.

*N.B Grout stain remover may etch the surface and cause the stone to dry lighter.
If the Limestone is either Honed or Polished do not use LTP Grout Stain Remover and instead use LTP Powerstripper.

Mineral deposits causing a banding effect

Halo Stains & Bands Of Mineral Deposits.

This is caused by trace amounts of sodium and potassium oxides within the Limestone which can also be activated by rain water. Even where rain is slightly acidic, the solutions of these salts in rainwater will gradually become alkaline. Surface wetting and evaporation can produce recurrent patches and bands of dampness known as accumulation zones ( rainwater pooling on the surface where it cannot run off).

Evaporation concentrates the alkaline solutions until they become saturated at the  outer limits or edge of accumulation zones. Further evaporation then causes precipitation, crystallisation and immobilisation of the salt at the surface and in pores immediately below the surface. The resulting bands of distinct pigmentation are halo stains as seen in the image above of Limestone.

Grout & Adhesive Stains.

img_0122

Adhesive Stains On Limestone

Grout and adhesive stains like this appear often, if the stone has been sealed beforehand then the process of removing the residues is easier.
After grouting most of the residues should be taken off with water before it fully dries on the surface. For the removal of most grout residues on Limestone we would recommend using LTP Powerstripper. However on more severe cases as shown in the picture above, using a mild solution of LTP Grout Stain Remover may be more effective.
Grout Stain Remover is an acid based cleaner and will etch any acid sensitive surfaces (Limestone, marble, some sandstones, chrome etc).
We would always recommend to test on a small inconspicuous area first.
LTP Grout Stain Remover Tech Data Sheet.

General Dirt & Grime

If your limestone has been outside for a couple of years, it may have seen better days.
General dirt and grime can be easily removed with LTP Grimex.
Dilute in a bucket of water as per instructions on the back of the bottle, then apply and leave for 10 minutes. Give it a scrub with a deck brush or an emulsifying pad and then rinse with plenty of clean water.
After cleaning allow to dry for 24 hours and then the stone will be ready for resealing.

Protect your Limestone with the correct sealing product.

Sealers used to enhance the appearance and help prevent limestone pavers staining from organic matter outside need to be breathable. LTP Mattstone H20 & LTP Stone Oil are examples of breathable sealers suitable for external use. As well as protecting the stone from staining, breathable sealers will allow the microscopic transition of moisture assisting any trapped moisture to escape through the stone from the mortar and sub surfaces. However, moisture permeating through the stone and sealer to the surface can still dry to leave a calciferous deposit.

Once the stone is thoroughly dry and mineral salt deposits are greatly reduced, general dirt and grime has been cleaned off, reseal the stone with an appropriate limestone sealer. LTP Mattstone H20 is highly effective natural stone sealing solution and is suitable for exterior use. However many of our customers have used LTP Stone Oil after acid washing their stone as it helps to re-enhance and deepen the colour.

Apply LTP Stone Oil to the surface of the stone using a paint brush. Allow it to absorb into the stone and then remove any visible excess from the surface after 45 minutes using an absorbent dry towel. The aim is to completely saturate the stone with as many coats of the sealer as necessary, but do not allow the sealer to dry and leave a film on the surface. Do not apply in direct sunlight.
For more information on how to apply please see the Technical Data Sheet.

LTP Mattstone H20 is applied to the surface with a paint brush, allow to absorb for 15 minutes and then apply a second coat. Remove any visible excess on the surface after 45 minutes.
For more information on how to apply please see the Technical Data Sheet.

 

Please note that this information is offered as general guidance only and without guarantee. Your specific circumstances may need an alternative approach. In case of doubt, any process should be tried out in an inconspicous area before general application. 
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Sealing Stone Outside.

Limestone, Sandstone, Travertine, Marble, Slate, Granite, concrete:
Regardless of what type of flooring you choose, the likelihood is it will require some form of sealing.

This is because natural stone is porous, and therefore if left unsealed, any moisture will be soaked up by the stone making it very difficult to remove, and potentially leaving the surface permanently stained (sometimes even fallen leaves can cause stains).

The best way to prevent all this is to seal the stone.

When you seal a stone, you are essentially filling any voids or pores of the stone with the sealer. This prevents any further liquid to absorb in to the tile, as demonstrated here with this close up shot of a water droplet on a tile sealed with LTP Mattstone.

When sealing natural stone outside it is important to use a breathable impregnating sealer, this will allow the transition of moisture from underneath.
Examples include LTP Mattstone H20 & LTP External Stone Sealer both are water based breathable sealers and ideal for use outside.

It is important to note that all stones located outdoors are susceptible to a condition known as efflorescence.
This blooming is caused by water moving through the substrate of a material and carrying minerals and salts found in the mortar bed, grout, soil or the stone itself.
We have a blog here all about efflorescence.

Its also very important when laying Natural stone to make sure that its fixed on a full bed of adhesive and not spot fixed.
The end result could look like this if its spot fixed.
Spot fixing issue Sandstone

If this has already happened to your patio, we have a blog here.

When sealing different natural stones, what will vary the most will be how many coats the stone will need before it is fully sealed.
Each stone exhibits different levels of porosity. A tumbled Limestone may have a higher porosity level than a Honed and filled Limestone.

Sealing natural stone with Mattstone H20

Shake bottle before use.

Test the porosity of your stone with water and a teaspoon, using the LTP porosity test.

Once surfaces are clean and dry, apply the product to the surface evenly using a sealant applicator pad, brush or soft cloth.

When sealing its important not to over apply the sealer and redistribute excess, avoid letting the sealer pool on the surface, as this can cause white marks to appear on the stone when it dries.
On highly absorbent surfaces apply several coats wet-in-wet.
After 15 minutes, remove any excess sealer with an absorbent cloth. Do not allow residues to dry on the surface.
Do not walk on the surface for 3 hours.

Sealing natural stone with External stone sealer.
Apply evenly to the surface using a foam roller or paint brush. On more absorbent surfaces apply further coats at hourly intervals until the surface is completely saturated. Remove any residual sealer if still visible after one hour.

Cleaning Tiles Outside

Before you start sealing your stone it is important to make sure your stone is clean and dry, other wise you will just seal in dirt and grime.

Old layers of sealer, dirt residues and light deposits of organic matter and algae must be removed from the surface and pores of the stone.

This can be done by either using LTP Grimex which is a intensive cleaner or LTP Mouldex Paving Cleaner.

To Clean with LTP Grimex, dilute 1:3 with water, apply to the surface with a sponge or water brush and leave to sit on the surface of the tiles for as long as it takes for the dirt to release. (5-30 minutes depending upon the level of dirt). If areas look as if they are drying out just add a little more solution to keep the area wet.

Agitate the surface with a stiff deck brush after approx 10 minutes (scrubber machines can be used).

Continue to scrub while adding clean water. Remove residues from the surface with water or scrubber machine.

Rinse thoroughly with clean fresh water to remove all remaining residues. Use a power washer if necessary.

Allow the surface at least 24 hours to dry before sealing.

To clean with LTP Mouldex Paving Cleaner, Shake well before use.
Surfaces to be treated should be completely dry before application.
Pour solution undiluted directly onto the pavers and spread out evenly using a sponge or paint brush, Garden sprayers can also be used and leave for a minimum of 1 hour.

Apply a little water and agitate with a stiff Deck brush or emulsifying pad to release the dirt and grime, and then rinse thoroughly using a hose or jet wash.
Some stubborn stains and black spot may require a longer treatment, in which case apply and leave on surfaces overnight. If some black spot remains after treatment, It should fade and disappear after a few days following the treatment. If not: re-apply. Keep pets off at all times during treatment. In case of contact with metals, fabrics and painted surfaces rinse with water immediately. Do not use on warm surfaces. Do not apply if rain is imminent. Avoid contact with ponds & plant life: if contact is made rinse well with plenty of water.

General Maintenance.
Weekly or daily depending on conditions, use a hose and a brush to remove any debris that may be lying on the stone.
Then annually if required use LTP Grimex, this will remove surface dirt and grime, possibly every 6-12 months depending on condition.
Dilute Grimex 1:3 parts water and apply the solution on to the surface and agitate.
Leave for 10 minutes before agitating again and then rinse with water.
Allow 24 hours to dry and then if necessary re-apply a light coat of sealer.

PLEASE NOTE: Always follow the detailed instructions on the product labels. Protect stone surfaces from contact with acidic substances. Do not use abrasive materials on honed or polished stones. Avoid using normal detergents or strong bleach cleaners on sealed surfaces as they will gradually remove the protective seal.

Please note that this information is offered as general guidance only and without guarantee. Your specific circumstances may need an alternative approach. In case of doubt, any process should be tried out in an inconspicuous area before general application.

 

PROBLEMS WITH STEAM CLEANING LIMESTONE

The simplicity of water-based steam cleaning can be appealing, but repeated use of too much super heated water can lead to risks of residual staining, mobilisation of salts and corrosion of hidden particles of Iron within some limestone surfaces.

 

Mud vein in limestone magnified 120 Microns

Surface of a Limestone magnified by 120 microns

Steam can penetrate the small cracks and fissures on the surface of the limestone.
This does clean the limestone, but will also embed water into the surface.
Repeated cleaning using a steam cleaner can activate salts and weaken the stone over time. This can also lead to spalling or fragmentation of the surface.

Cleaning to expose new fissuresCOMPROMISED SEALER?
Surfaces that have been treated with an impregnating sealers can also be compromised. Steam cleaning does not normally remove the impregnating sealer, however repeated use can expose new fissures and capillaries within the stone. The newly exposed and unsealed surface takes in more dirt and becomes harder to clean, which then requires more frequent cleaning. This increase in cleaning can exacerbate the problem.

 

SURFACE SEALER DAMAGE?Damage to stone surface

Sealers used to finish the surface of stone can also be damaged. Steam is often used to remove paints, wall papers and other
coatings from surfaces. If a film forming
sealer has been used then contact by a
steam cleaner can cause a partial separation of the seal from the surface of the stone causing it to turn white or opaque.

 

                                                                        Rust stains in Limestone after spalling
RUST STAINS ON THE SURFACE?                                  
Rust stains:  These stains are reddish-orange and are caused by the oxidation (rusting) of iron. The source of iron staining is normally from within the stone, as most of the iron on the surface is normally
removed or discarded at the point of fabrication by the quarry. Therefore most Iron remains hidden and within the stone rather than on it; however, water from steam cleaning penetrating through natural fissures in the  stone can activate or accelerate rusting.
CRUMBLING OF THE SURFACE?
Moisture from repeated steam cleaning can in someSpalling Limestone
cases cause spalling or fragmentation of the surface.
The migration of salts from moisture in the limestone can promote crumbling of the surface causing larger fissures and craters to appear. This is more
common in Limestone’s and marbles that contain naturally occurring mud or calcite veins which are more vulnerable to this issue.

 

WHAT TO DO?

COMPROMISED SEALER: Intensively clean the surface of the stone with LTP Grimex. Leave overnight to dry. Re-apply impregnating sealer – LTP Mattstone or LTP Colour Intensifier. For routine aftercare use LTP Waxwash. This is a PH neutral cleaner that will not damage the stone or compromise the seal.

SURFACE SEALER DAMAGE: Remove the Film forming sealer using LTP Grimex or LTP Solvex. Leave overnight to dry. Re-apply the film forming sealer – LTP Ironwax Satin or LTP Ironwax Gloss. For routine aftercare use LTP Floorshine. This gentle cleaner will clean the surface and repair the seal where it has worn from abraision every time the floor is washed.

RUST STAINS ON THE SURFACE: Intensively clean the surface of the stone with LTP Power Stripper. Leave overnight to dry.Re-apply impregnating sealer – LTP Mattstone or LTP Colour Intensifier. For routine aftercare use LTP Waxwash. This is a PH neutral cleaner that will not damage the stone or compromise the seal.

CRUMBLING OF THE SURFACE: Intensively clean the surface of the stone with LTP Grimex. Leave overnight to dry. Use a suitable resin stone filler of the correct colour to fill in the voids. Re- hone the surface of the stone using a twister pad and sponge down with a little water to remove any dust or sediment. Leave to dry. Re-apply impregnating sealer – LTP Mattstone or LTP Colour Intensifier. For routine aftercare use LTP Waxwash. This is a PH neutral cleaner that will not damage the stone or compromise the seal.

This information is offered without guarantee.  The material should be used so as to take account of the local conditions and the surfaces to be treated.  In case of doubt, the product should be tried out in an inconspicuous area.

Natural Stone – Internal Cleaning, Sealing and Maintaining

Cleaning, Sealing and Maintaining Stone Surfaces – Part One

Natural stone has been used on floors and walls for centuries. As with all natural materials, it does need a certain level of care.

This is the first in a 16 part series of posts that will offer a comprehensive guide to cleaning, sealing and maintaining all types of stone, porcelain, quarry, terracotta and glazed ceramic tiles and surfaces. This first post explains the LTP three-step approach to cleaning, protecting and maintaining natural stone surfaces used in internal situations. 

Natural Stone Surfaces – Internal Application

The following instructions are appropriate for Travertine, Limestone, Marble, Sandstone, Terrazzo and some Granite.

Step one: Initial cleaning 

Before sealing natural stone must be thoroughly cleaned to make sure that sealing of the surface can be achieved effectively. This is true of newly installed surfaces, as well as existing, due to the contamination that can occur during fitting. Equipment recommended for this step is a bucket, mop, scrubber or scrubber dryer machine.

Newly installed surfaces

LTP recommends LTP Grimex as the solution for cleaning newly installed natural stone surfaces before sealing. LTP Grimex removes grease, dirt and grime from the surface ensuring the natural stone surface is best prepared for application of a sealing product.

Cleaning newly installed stone surfaces

  1. Dilute LTP Grimex 1:10 with water.
  2. Apply solution to the surface with a mop or sponge. Under floor heating must be off.
  3. Agitate to release the residual dirt and grime from the surface.
  4. Do not use acidic cleaners, such as LTP Grout Stain Remover.
  5. Allow the surface to dry (preferably for 24 hours).

Cleaning natural stone with LTP Grimex

Refurbishing used and heavily soiled stone surfaces

  • Before sealing the stone must be thoroughly cleaned. Old layers of sealer, residues from aftercare products and deposits must be removed from the surface and pores of the stone. Film forming layers of sealer (such as boiled linseed oil) should be removed with LTP Solvex before washing with LTP Grimex.
  • Depending upon the levels of dirt, dilute LTP Grimex 1:3 with water. Apply with a sponge or cloth and leave to sit on the surface of the tiles for 5-10 minutes.
  • Agitate the surface with a nylon pad or scrubbing-brush and leave for a further 5 minutes (scrubber machines can be used).
  • Continue to scrub while adding clean water. Remove residues from the surface using a cloth or scrubber dryer machine.
  • Rinse thoroughly with clean fresh water to remove all remaining residues.
  • Allow the surface to dry for a minimum of 24 hours before applying the protective seal.
  • For the removal of other types of dirt: Do not use acid based cleaners on limestone or marble. If you are unsure please call our helpline on +44 (0) 01823 666213 for advice.

Step two: Protect your natural stone surface from stains

To protect stone surfaces and help prevent staining natural stone should be sealed. LTP recommends applying LTP Mattstone for a natural (invisible finish) or LTP Colour Intensifier & Stainblock for an enhanced appearance. LTP Colour Intensifier & Stainblock deepens the colour and enhances the appearance of the stone surface.

Sealing prepared natural stone surfaces

  1. Surfaces must be clean and dry. Ensure under floor heating is off.
  2. Apply the product to the surface evenly using a sponge, brush or soft cloth.
  3. Redistribute to remove excess product and avoid pooling on the surface.
  4. Allow to dry. Do not walk on the surface for at least one hour.
  5. Protect from water for 24 hours and do not wash surfaces for at least 3 days.

Sealing natural stone with LTP Mattstone, LTP Mattstone H20 or LTP Colour Intensifier.

  • LTP Mattstone H20, LTP Mattstone and LTP Colour Intensifier will make the surface water and oil repellent.
  • Prevents stains, aids cleaning and simplifies the removal of surface stains.
  • Provides an invisible barrier of protection that will not greatly alter the surface character.
  • There are no health concerns once the product has properly cured.
  • LTP Mattstone H20, LTP Mattstone and LTP Colour Intensifier are micro porous and so can be used on surfaces that have no damp proof course.
  • Suitable for internal and external use.
  • If surfaces are properly maintained we recommend touching up the protective treatment every 3-4 years.

NB. Always test the product on an inconspicuous area. Wet or non absorbent surfaces cannot be treated. LTP Mattstone H20, LTP Mattstone and Colour Intensifier are impregnating sealers which need to fully absorb. Do not allow the product to dry on the surface. Carefully buff with a soft cloth or machine to remove any excess. Remove unabsorbed impregnating sealer, if left to dry on the surface, by rubbing over with a little more sealer. Some stones may be darker after application. Acidic substances, if left on the surface, may damage stone.

Step three: Maintaining your natural stone wall or floor

Using the correct maintenance product will increase the life of your floor seal, provide additional protection against staining and make sure your floor looks great. Common household cleaning products often contain harsh substances that can breakdown sealing products applied to stone. For this reason LTP recommends using LTP Waxwash on floors and LTP Stonewash for surfaces.

LTP Waxwash (for floors): Formulated for use on unglazed tiles such as travertine, stone, limestone, slate, terracotta and quarry. Ideal for washing floors sealed with LTP Mattstone H20, LTP Mattstone or LTP Colour Intensifier. Use routinely in place of normal detergent.

LTP Stonewash (for walls): This gentle surface cleaner is formulated for use on limestone, marble, granite, slate and polished porcelain. Will clean without breaking down and removing protective seals.

Regular maintenance on stone floors

  1. Add one cap full of product per litre of water in a bucket.
  2. Wipe surface with the solution. Do not rinse.
  3. Allow to dry. Do not walk on the surface during drying time – 20 minutes.

Maintaining natural stone with LTP Waxwash

A one litre LTP Waxwash will wash a 20 sq.m floor 40 times.

PLEASE NOTE: Always follow the detailed instructions on the product labels. Protect stone surfaces from contact with acidic substances. Do not use abrasive materials on honed or polished stones. Avoid using normal detergents or strong bleach cleaners on sealed surfaces as they will gradually remove the protective seal.
At LTP we believe in helping to provide solutions and this is why we offer
a no obligation LTP TECHNICAL HELPLINE, so please give us a call on
+44 (0) 1823 666213 and we will be happy to help you. 
Visit www.ltp-online.co.uk to purchase from the LTP Range of products or find out more about us.

Limestone: White or grey deposits on black paving?

Why do mineral stains show up so prolifically on black limestone pavers laid outside?

We are often contacted about mineral stains on black limestone paving. This is often perceived as an issue with the supplied paving stones, laying process or sealing method. Below we explained how a combination of naturally occurring elements can cause this phenomenon. It is in fact not uncommon and occurs with most types of limestone; however the appearance of mineral salt deposits on a black or darker coloured stone is more prevalent. This is why it is possible to notice some marks appearing even before sealing. As a naturally occurring chemical reaction it is often difficult to avoid. However, if fully understood and considered when laying and protecting black limestone this potential issue can be effectively managed.

What causes white and grey mineral stains on black limestone pavers?

When rain water trickles through mortar it can dissolve and transport soluble alkaline compounds. Rain water percolating through sand-cement mortar screed, toppings and bedding under limestone paving can become moderately alkaline. As this rainwater evaporates, its alkalinity increases until the solution becomes saturated. This solution can then travel via natural capillaries within the limestone to the surface where it starts to deposit solids such as white and grey encrustations of calcium carbonate commonly known as lime plumes and efflorescence as seen in the image of the black limestone pavers shown below.

Mineral deposit stains on black limstone

Halo stains and bands of mineral deposits

Trace amounts of sodium and potassium oxides within limestone can also be activated by rain water. Even where rain is mildly acidic, the solutions of these salts in rainwater will gradually become alkaline. Surface wetting and evaporation can produce recurrent patches and bands of dampness known as accumulation zones (rainwater pooling on the surface where it cannot run off). Evaporation concentrates the alkaline solutions until they become saturated at the outer limits or edge of accumulation zones. Further evaporation then causes precipitation, crystallisation and immobilisation of the salts at the surface and in pores immediately below the surface. The resulting bands of distinct pigmentation are halo stains as seen in the image of limestone pavers shown below.

Mineral deposits causing a banding effect

Reducing the impact

Protect your paving with the correct sealing product

Sealers used to enhance the appearance and prevent limestone pavers staining from organic matter outside should be breathable. LTP Mattstone, LTP Stone Oil and LTP Colour Intensifier are examples of breathable sealers suitable for external use. As well as protecting the stone from staining, breathable sealers will allow the microscopic transition of moisture assisting any trapped moisture to escape through the stone from the mortar and sub surfaces. However, moisture permeating through the stone and sealer to the surface can still dry to leave a calciferous deposit.

How do I remove mineral salt stains from the surface of limestone

Wash the surface with a mild solution of acid. This will help disperse the mineral salt deposits from the surface. The downside of this approach is that the acid solution can have a slight etching effect on the surface of the stone causing it to dry much lighter.

LTP Grout Stain Remover is a product suitable for this task. Dilute 1 part LTP Grout Stain remover in 4 parts warm water and apply to the surface of the stone. Agitate using an emulsifying pad or similar abrasive and then rinse thoroughly with plenty of clean water. Repeat this process to remove all mineral deposits.

Ensure you protect your paving by resealing

Once the surface is thoroughly dry and  mineral salt deposits on the surface are greatly reduced, re-seal the stone with an appropriate limestone sealer. LTP Mattstone is our most popular and highly effective natural stone sealing solution and is suitable for external use. However, many of our customers have successfully used LTP Stone Oil after acid washing their stone as it helps to re-enhance and deepen the colour.

Apply LTP Mattstone or Stone Oil impregnating sealer to the surface of the stone using a paint brush. Allow it to absorb into the stone and then remove any visible excess from the surface after 45 minutes using an absorbent dry towel. The aim is to completely saturate the stone with as many coats of sealer as necessary, but do not allow the sealer to dry and leave a film on the surface. Do not apply in direct sunlight.

Please note that this information is offered as general guidance only and without guarantee. Your specific circumstances may need an alternative approach. In case of doubt, any process should be tried out in an inconspicuous area before general application.

Resolving stain issues on natural stone can prove difficult. At LTP we believe in helping to offer solutions and this is why we offer a no obligation LTP TECHNICAL HELPLINE, so please give us a call on +44 (0) 1823 666213 and we will be happy to help you.

Alternatively visit our main site to view our full range of cleaning, sealing and maintenance products for all types of artificial and natural stone.