Sandstone Flooring and Cladding: Laying Steps, Joints, Gradient and Efflorescence

Step 2: mortar bed or adhesive

For most outdoor sandstone and floors, the stone is laid on a full bed of cement and sand mortar. A common mix is 1 part cement to 4 parts sand, and a UK council detail uses about 60 mm of 1:5 mortar under flags. Indian practice varies with the mason, so confirm the bed thickness and mix with your mason rather than copying a figure.

Soak or wet the stone back before laying, so it does not pull water out of the mortar. Lay the slab on a fresh bed, tap it level with a rubber mallet, and check it before the mortar sets.

Thin cladding pieces are usually fixed with a bonding mortar, or with a suitable adhesive, and sometimes with mesh and anchors on large walls. Follow the adhesive label for the stone and the wall surface.

Step 3: joint width

Joint width depends on how the stone is cut and how it is filled. Cut, even-edged sandstone is often laid with a joint of about 3 to 5 mm. Irregular flags, or stone laid in mortar, can have wider joints, and a UK council detail shows 10 mm joints with 1:4 mortar on random flags. Pick one width and keep it the same across the floor, so it looks even.

As a rough rule, a sand-filled joint wider than about 5 mm is more likely to wash out in heavy rain. For wide or wet joints, mortar is the better fill.

Step 4: gradient on terraces and outdoor floors

Outdoor stone must fall away from the house or wall so rain does not sit against the masonry. A common working fall for paving is about 1:60 to 1:80, which is roughly 1.25 to 1.7 percent. On smooth stone aim for a fall of at least about 1:100, and keep walkways no steeper than about 1:40 on a walkway, because steep falls become slippery and hard to walk on.

Set the gradient in the bed, using a string line or a level from the high point to the drain. A terrace that falls the wrong way will hold water, and that is where moss, staining and white marks start.

Step 5: curing, sealing and efflorescence

Let the mortar cure before you walk on the floor, and keep it damp for the first few days so it gains strength. Clean off mortar smears while they are soft.

Efflorescence is the white, powdery or crusty deposit left by salts that come out of the mortar and the stone as water evaporates. It is common on new work, and it often weathers out over time. A UK council guide for natural stone advises waiting 12 to 18 months before sealing, so the salts can come out first. Sealing too early can trap them under the sealer.

For removal, first brush the surface dry, then wash it with clean water and a soft brush. Test any cleaner on a small corner before you use it, and avoid acid on sandstone unless your supplier has approved it, because acid can etch the surface.

Apply a penetrating sealer only when the stone is fully dry and the efflorescence has settled. Follow the sealer label for the number of coats and the drying time.

Step 6: cleaning and everyday care

• Sweep regularly and mop with plain water or a mild soap.
• Remove oil and paint spills quickly, before they soak in.
• Reseal outdoor stone when water stops beading on the surface, usually every few years.
• Keep a few spare pieces for repairs. Stone matches are hard to find later.

Before you order

Look at the slabs in daylight and ask for the thickness, the finish and the quarry lot. Order 5 to 10 percent extra for cutting and breakage. Tell us the area, whether it is indoor, outdoor or a steps job, and we will suggest the right stone and a practical order quantity. Rates change by lot and size, so call or WhatsApp the store for the current quote.