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.

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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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Common Problems when Fixing Stone Outside

Stone patios and white blooms- Efflorescence

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olive-limestone You’ve seen the magazine pictures: Designer patio’s decked out with stylish garden furniture, blue skies and a perfect sandstone/limestone  floor tiles… Yes all this is perfectly feasible but for a flawless floor you rely on that blue sky..infact from our experience at least 3 days of blue sky.     The most important factor when deciding  to seal any stone outside is the British Weather.. unless 3 dry days and nights (no rain…no dew) can be guaranteed then there is a strong chance your floor will not look like the one in the picture.

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Kotah Black Limestone

A much more common scenario is a phone call to the supplier of the stone asking why the tiles and or grouting  have gone white overnight. salts on patio2photo 1

This is not a insurmountable problem as the bloom can easily be removed and in all the cases we have seen the tiles settle down over a period of time.

However, to save unnecessary worry it might be useful to learn why this issue can arise and how to resolve it.

All stones located outdoors can be susceptible to a condition known as efflorescence. It is caused by water moving through the substrate of a material collecting and carrying minerals and salts found in the mortar bed, grout, soil or the stone itself.

When the impure water reaches the surface  and evaporates, the minerals and salts will be left behind., these form those white marks or efflorescence, seen on the surface. Whilst this phenonemom is more common on unsealed surfaces it can also occur on sealed surfaces especially if the stone becomes wet before the sealer has fully cured, which can take up to three dry days.

Ironically once the stone is sealed this efflorescence can seem enhanced as the sealed surface traps the rain water on the surface which also evaporates leaving a white residue especially in hard water areas..  However no pain no gain.

It is important to go through this scenario and run the risk of a white bloom on the surface as it is only by fully sealing stone that will prevent water percolating through the stone and triggering the efflorescence cycle once again.

How to remove efflorescence:

If the surface is not a Limestone or a Sandstone containing high iron content then wash the surface with an acid based cleaner such as LTP Grout Stain Remover On acid sensitive surfaces then simply use water or a very mild solution of Grout stain remover (trial in a small area first). The efflorescence will fade and can be removed over time and provided the surface is properly sealed it will cease over a period of a few months.

What is the best sealer to use:

It is vital to use a breathable sealer that allows the transition of moisture from underneath, examples include

LTP Stone Oil (offers colour enhancement for Dark Stones)

LTP Mattstone H20.

LTP External Stone Sealer

One final bit of advice:

Do not over apply the sealer as the second cause of efflorescence , after the British weather , is too much sealer on the surface. As a rule of thumb it is best to apply roughly half as much sealer as would be appropriate for interior use.

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.

How to remove staining from Black Limestone before sealing.

Visible stains on Black Limetone

Visible stains on Black Limetone

After quarrying, milling and then packing a black limestone it is possible for residues of moisture and sediment to remain on the surface. If left over a period of months these deposits of mineral and sediment absorb into the pores of the stone. This type of staining can be very difficult to remove using conventional cleaning materials. The following is a guide to help restore the                                                                                     appearance of the stone using a strong                                                                                   cleaner and then sealing to restore and                                                                                   enhance the colour.

DIRECTIONS FOR CLEANING AND SEALING

1. LTP Grout Stain Remover is applied and 2. GSR scrub immediatelythen immediately scrubbed into the surface using a black emulsifying pad. This should be done for 1 – 2 minutes making sure to cover the whole surface of the stone. This cleaner will slightly etch the surface of the stone to release the stains from within.

 

3. Rinse well with plenty of water2. Do not leave the cleaner to dwell on the surface. Rinse with water immediately after scrubbing. Change the rinsing water every 5 M².
After cleaning leave surfaces to dry for 24 hours.

 

4. Leave to dry
3. Once dry, surfaces will appear grey rather than black. The stains should no longer be visible. The surface of the stone has been conditioned ready for sealing.

 

5. Apply Stoneoil4. Apply a small amount of LTP Stone Oil to the surface of the Limestone and spread out evenly. Leave to absorb into the surface of the stone for 1 hour. Any visible excess after this time work should be worked off using a soft absorbent towel.

6. Spread out evenly

5. The sealer should be left to dry for a minimum of 24 hours with light traffic only.
It will take a further 3 days to reach full hardness, so surfaces should be kept as dry as possible during this time.

INTERIORS
Finishing the stone with a light coat of LTP Mattstone should be considered if the stone is to be used in kitchen areas.

INITIAL CLEANING:                LTP GROUT STAIN REMOVER                   1ltr & 5ltr

This should be done after fixing and before sealing LTP-GroutStainRemover5L&1L_2011_Weband grouting to remove calcium carbonate and mineral deposits including dust and dirt that has accumulated during the production and fixing process. Apply undiluted solution to the surface of the stone and agitate immediately with an emulsifying pad. Rinse thoroughly with a separate pot of clean fresh water. Wipe away the released calcium dirt and grime with a mop or sponge and water and leave to dry for 24 hrs.

TDS – http://www.ltp-online.co.uk/images/tds-Grout_Stain_Remover.pdf

MSDS – http://www.ltp-online.co.uk/images/msds-Grout_stain_remover_clp_GHS.pdf

SEALING:                                      LTP STONEOIL                                        1ltr & 5ltr

Before grouting apply a light coat of LTP Stone Oil, LTP-StoneOil5LTin_1L_Grp_Webcheck that all of the sealer has been
fully absorbed within 1 hour, any excess that remains on the surface after 1 hour should be worked in with a soft cloth or buffing machine. Leave for a further 4 hours or overnight before grouting the joints. Once all residual grout has been removed and the surface and joints are thoroughly dry; apply a final light coat of StoneOil covering the joints as well. Buff to remove any excess within 1 hour and then leave for a minimum of 3 days to fully harden before making excessively wet.

TDS – http://www.ltp-online.co.uk/images/tds-Stone_Oil.pdf
MSDS – http://www.ltp-online.co.uk/images/msds-Stone_oil_clp_GHS.pdf

IMPORTANT NOTES:
When cleaning or sealing vertical surfaces always start at the top and work down.
Provided that the surfaces are correctly sealed and maintained protection should last 3 – 4 years before considering applying a top up coat. Sealing will not prevent wear from abrasion.Used externally sealers will last between 1 & 2 Years before light cleaning and topping up.
After Intensive cleaning to remove any ingrained dirt or other staining and once dry, always test for moisture ingress. If evident cleaned areas should be re-sealed.
When using LTP Grout Stain Remover, gloves should be worn.
For detailed application instructions please see Technical Data Sheets.
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

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.