Patio Sealing: When to Do It, When Not To

Which surfaces should be sealed

Indian sandstone and limestone: yes, worth doing. Both are porous, both stain, and both grow algae readily in our climate. A breathable impregnating sealer makes a real difference.

Concrete slabs and block paving: optional. Sealing slows colour fade and makes cleaning easier, but it is cosmetic and it commits you to reapplying every three to five years.

Porcelain: no. It absorbs almost nothing, there is nothing for the sealer to soak into, and residue on the surface can leave a haze.

Slate and granite: generally no, other than a colour enhancing sealer if you want the wet look permanently.

Resin bound: no. Sealing traps moisture in the matrix and can cause cloudiness.

The three types of sealer

Choose by the finish you want and by how much maintenance you are prepared to accept.

When to apply it

Timing is where most DIY sealing goes wrong. The patio must be genuinely dry all the way through, not just dry on top, so you want at least three or four dry days beforehand and ideally a settled spell.

In the UK that means late spring through early autumn, at air temperatures between about 10 and 25 degrees, out of direct hot sun. Sealing a hot slab in full July sun flashes the solvent off before it can penetrate and leaves a patchy finish.

A new patio needs to cure first. Wait a minimum of four to six weeks after laying, longer in a cold spell, so that construction moisture and any efflorescence has worked its way out.

How to do it properly

Clean first, and be patient about it. Remove moss and algae with a proper treatment rather than pressure alone, wash, rinse and let it dry fully. Any dirt you seal in is there for four years.

Test on a spare slab or a hidden corner. Colour enhancing sealers can darken sandstone dramatically and it is not reversible.

Apply thin and even with a low pressure sprayer or a lambswool applicator, working in one direction, and back roll any pooling. Two thin coats beat one thick coat every time. Keep off it for 24 hours and keep it dry for 48.

What sealing will not fix

It will not stop weeds in joints, because those grow in the joint material not the slab. It will not stop moss returning in permanent deep shade, only slow it. It will not lift existing stains, which need treating first. And it will not repair a patio that is moving, because sealer has no structural function whatsoever.

If your patio is rocking, holding water or lifting at the edges, sealing is money spent on the wrong problem. Fix the base or the pointing first.

Sealing versus just cleaning

For a lot of patios in this area the honest recommendation is a proper clean and rejoint every few years rather than a sealing programme. A rejoint with a resin compound at £18 to £35 per square metre solves weeds, loose pointing and water ingress in one go and lasts far longer than a sealer coat.

We do both, and we will tell you which one your patio actually needs. Call 07538 218723 or request a quote and we will look at it before selling you a product.