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.


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. 

Polished Marble Fixing and Sealing Guide

The following instructions are appropriate for Polished Marble.


Apply adhesive to primed concrete or timber surface.

Using a notched trowel spread out the adhesive evenly.

Butter the back of each piece of stone with adhesive.

Leave adhesive to dry naturally. DO NOT force dry.

DO NOT cover stone. Covering slows curing and prevents the stone breathing.


Useful tools: Notched trowel, mixing trowel,mixing drill, adhesive whisk, bucket, sponge, electric wet cutter with diamond disc, grout float, 2mm spacers.


Dilute LTP Grimex 1:10 with water.

Apply to the surface and gently agitate using a mildly abrasive pad.

Rinse well using a sponge and water.

Buff off any water marks that remain before they dry.

Leave the stone to dry.

Useful tools: LTP white emulsifying pad, LTP pad holder & 4 pc pole.


Apply sealer evenly to the polished stone surface using sealant applicator or similar.

After 20 minutes buff visible sealer into the polished surface.

2 hours after the final coat of sealer grout the joints.

Rinse well with plenty of water.

Dust of remaining residues and leave to dry for a minimum of 24 hours.

Useful tools: LTP sealant applicator, 4 pcc pole & buffing cloth.

The surface should be clean and dry.

Apply sealer making sure to cover the joints as well.

Buff off excess within 20 minutes. DO NOT allow sealer to dry on surface.

Leave to dry. Light traffic only for first 24 hours.

DO NOT COVER. Covering slows curing and prevents the stone from breathing.

Useful tools: LTP sealant applicator, 4 pc pole & buffing cloth
Polished-Marble-Fixing-4STEP 5: Aftercare and Routine Cleaning

1 capful of LTP Waxwash per litre of water.

Mop surfaces with the solution.

Buff using microfibre cloth or similar to finish.

Leave to dry.


Useful tools: LTP 4 pc pole & pad holder,buffing cloth,bucket.



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