Outdoor stairs: natural stone or sintered stone
Outdoor stairs need a dense stone with low water absorption, most often granite with a brushed or flamed finish. Sintered stone is also frost-resistant and non-absorbent, but it can be slippery and is harder to repair. In both cases durability also depends on the base, the fall and drainage.
Winter is the hardest test
Water gets into the pores of the stone, freezes and breaks it apart from the inside. Freeze-thaw cycles destroy absorbent materials faster.1 That is why low water absorption matters outdoors.
Natural stone
Granite is dense and absorbs little water, so it copes well with frost. It also has the advantage that the pattern and colour go through the whole thickness: a chip does not reveal a different material underneath, and the steps can be restored by grinding years later.
Sintered stone
Sintered stone is practically non-absorbent and frost-resistant. Its weak point on stairs is the edge, which is more brittle than granite, and the fact that the pattern is only on the surface. It also needs a very flat base.
Slipperiness
Wet, icy stone can be slippery, and research shows that freeze cycles change the slip resistance of the surface.2 For outdoor stairs choose a brushed or flamed finish, or one with milled grooves at the nosing.
Salt and de-icers
Road salt and chlorides damage stone and joints. Use sand or products made for natural stone, and sweep them away after winter.3
Base and fall
The best stone will not last on a badly prepared base. The steps need a slight fall so water does not stand, and the base must not get soaked through. We check this when we measure.
(Sources)
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Use Natural Stone, Natural Stone vs. Manmade Materials for Exteriors
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MDPI Engineering Proceedings, Investigation of the Freezing-Thawing Effect on the Slip Resistance of Natural Stone
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Landscape Solutions, Safely De-icing Natural Stone, Pavers, and Concrete
(Questions)
Can I put salt on granite stairs?
Better not. Salt and chlorides can damage the stone and the joints. Sand or products made for stone are safer.
Which finish for outdoor stairs?
Brushed or flamed. A polished surface is slippery in rain and on ice.
