Why May doesn't mean the surface is ready
May is when conditions in the UK start to allow exterior coatings to go on, but the month itself isn't the test. AJ McCormack and Son's pavingexpert, read on 2026-09-27, places the sealing season roughly across May to October and sets out the conditions the weather and the surface still have to meet within it.
- Three consecutive days above 10 degrees Celsius. One mild afternoon doesn't give a coating enough time to go off before the next shower reaches it.
- Six weeks of weathering for new paving. Freshly laid concrete and new jointing carry moisture and alkalinity that need that time to settle before a coating is applied over them.
Many buying guides quote a 24-hour drying window instead. That figure usually answers a different question, how soon the paving can take foot traffic.
Where a retailer's instructions and the weathering figure above point in different directions, the surface is the thing to check. A patio that still feels damp or cool to the touch after three warm days hasn't met the test yet, whatever the calendar says.
Know your surface before you open a tin
A patio or wall takes a coating well only when you know what it's made of and what, if anything, is already on it. Both of those are things you can check yourself in the weeks before you open a tin, and they decide which product and which preparation steps are right for your surface.
Identify what you're painting
Dense concrete, natural stone, cement render and lime render each take a coating differently, and a lime-rendered wall in particular can be damaged by the wrong choice. Working out which substrate you have, and the property that dominates it, is the first job before you think about products or weather. The guide to concrete, natural stone or lime render covers how to tell them apart.
Check what's already there
Many patios and paths have been sealed or painted before, often without the current owner knowing what was used. A sequence of simple tests on the surface itself, water, solvent and appearance, can tell you what you're dealing with before you commit to a product. Painting over an unidentified coating is one of the commonest causes of a job failing within its first season, so this check is worth doing even when the surface looks sound. Steps for running those tests are set out on painting over a surface that was sealed.
Decide whether you're painting or sealing
Substrate and existing coating both feed into the same decision: whether the fault you have calls for a paint or a sealant. A tired surface, a slippery one, a staining one and a breaking-up one each point toward a different answer, and it's worth settling that before you buy anything. The comparison on paint it or seal it sorts the choice by the fault.
Once you know the substrate, know what's on it already, and know whether you're painting or sealing, the only thing left to check is the weather window itself.
A checklist for the weekend you've set aside
A few checks before the tins come out decide whether the weekend's work holds, and each one is quick to do on its own.
Identify the surface you're working on
Dense concrete, natural stone, cement render and lime render don't take a coating the same way, and a lime render is the one where the wrong product can damage the wall. Working out which of these you have comes first. Concrete, Natural Stone or Lime Render sets out what to look for.
Check for anything already on it
A patio or wall that's been treated before can still be carrying something even where it looks bare underneath. A short sequence of tests on an unobtrusive patch, using water and then solvent, shows what's already there before anything new goes on top. The sequence is set out in Painting Over a Surface That Was Sealed.
Settle paint against sealant
A tired surface, a slippery one, a staining one and a surface that's breaking up each point to a different product, and not every one of them calls for paint. Paint It or Seal It sorts the choice by the fault in front of you.
Read the weather before you commit a weekend to it
Coatings of this kind need a run of dry, warm days to cure properly, and new paving needs time to weather before it will take a coating at all. Check the conditions your surface and the coating both need before you set the date.