How to Seal Indian Sandstone Properly — Step-by-Step UK Guide

Sealing Indian sandstone is one of those tasks that's easy to put off — the stone looks fine, it's already been laid, why bother? The problem is that an unsealed sandstone patio will stain, absorb oil and organic material, and develop moss and algae more readily than a sealed one. Getting the sealing right when the stone is new makes maintenance much easier for the lifetime of the patio.

Here's exactly how to do it properly.

Do You Have to Seal Indian Sandstone?

No, sealing isn't mandatory. Plenty of sandstone patios are left unsealed and survive perfectly well, particularly in gardens where the stone gets good sunlight and the owners are diligent about cleaning.

However, sealing is strongly recommended because:

• It reduces staining from oil, food, wine, and organic material
• It slows moss and algae growth in shaded or damp areas
• It helps maintain the stone's colour over time
• It makes routine cleaning much easier

The main reason people skip sealing is cost or not knowing how — this guide addresses the second reason completely.

When to Seal

New sandstone: Ideally seal after the mortar has fully cured (28 days for standard OPC mortar) and after you've done an initial clean. Don't seal before the mortar is cured — efflorescence (white salt bloom from the mortar) needs to be able to escape, and sealing too early can trap it under the stone.

Existing unsealed sandstone: Seal after a thorough deep clean. Don't seal over dirty stone; you'll lock the dirt in.

Resealing: Every 3–5 years, or when you notice water no longer beading on the surface.

What Type of Sealer to Use

There are two main types of stone sealer:

Impregnating (penetrating) sealer: Soaks into the stone's pores and creates a barrier below the surface. The stone looks natural — no sheen or colour change. This is the recommended type for most patios.

Topical (film-forming) sealer: Creates a coating on the stone's surface. Can give a wet look or slight sheen. More prone to peeling over time, particularly outdoors. Generally not recommended for outdoor sandstone; stick to impregnating sealers for exterior use.

For Indian sandstone, choose a solvent-based impregnating sealer specifically formulated for natural stone. Water-based sealers are easier to apply but generally less durable outdoors. Our Technical guide from Paving and Slabs Ltd. has more on product selection

Step-by-Step Sealing Process

Step 1: Clean the stone thoroughly

For new stone, a basic clean with clean water and a stiff brush is usually sufficient to remove installation dust and debris. For existing stone, a full deep clean is needed:

• Sweep the surface completely
• Apply a dedicated patio cleaner or Indian sandstone cleaner
• Scrub with a stiff deck brush
• Pressure wash thoroughly
• Allow to dry completely (ideally 48 hours in warm weather; longer in cool, damp conditions)

For moss and algae, use a biocide treatment and allow to dwell as directed before washing off. See our maintenance guide for cleaning product recommendations.

Step 2: Check for efflorescence

White salt bloom (efflorescence) on the surface must be dealt with before sealing. Use a dedicated efflorescence remover or diluted hydrochloric acid wash (follow the product instructions carefully and neutralise with water afterwards). Never seal over active efflorescence.

Step 3: Apply the sealer

Work on a dry day when temperatures are above 10°C and no rain is forecast for 24 hours.

• Pour sealer into a paint tray
• Apply with a lamb's wool applicator, a clean paint roller, or a low-pressure garden sprayer
• Work methodically in small sections, keeping a wet edge
• Apply evenly and avoid puddles — pooled sealer can leave white marks
• Allow the first coat to absorb for the time specified by the manufacturer (typically 10–20 minutes)
• Apply a second coat before the first is fully dry — this ensures thorough penetration

Step 4: Remove excess sealer

Any sealer that hasn't absorbed within 30 minutes should be buffed off with a clean cloth. Sealer left on the surface can dry as a sticky, white residue.

Step 5: Allow to cure

Keep foot traffic off for at least 24 hours. Keep the surface dry for this period. Full cure typically takes 48–72 hours.

How Often to Reseal

The water bead test: periodically sprinkle water on the sealed surface. If it beads, the sealer is still working. When water starts to absorb rather than bead, it's time to reseal — typically every 3–5 years.

For all your sandstone care needs, browse our Indian sandstone collection or Flagstonesand refer to our Maintenance Guides and Indian sandstone technical guide