When sealing goes wrong - patchy, uneven, or gone after one season - the cause almost always lies before the preparation went on, not in the preparation. The substrate was dirty, wet, too fresh or too cold. Here are five things to check, in the order in which they matter.
Five conditions, in order
Clean
A sealer soaks in together with whatever it finds. Efflorescence, cement laitance and grease have to go first.
Dry
Not 'dry on the surface' but dry in the pores. Every sealer has a set maximum substrate moisture.
Cured
Fresh concrete and paving have to give up their mixing water - for some products that takes up to 28 days.
Within the temperature window
Every product has its temperature range - outside it the result can be weaker.
Tested on a patch
One slab somewhere out of sight settles what no description can.
1. Clean - because a sealer fixes what it finds
This is the condition that costs the most when skipped. The preparation soaks into the pores together with bloom, grease and dust, and then shuts them in underneath. Removing a stain from under a sealed layer means stripping that layer.
Each kind of soiling has its own preparation: lime efflorescence is dissolved with an acid, greasy stains with a degreaser, and cement laitance from the build needs a preparation of its own. If you have several problems at once: grease first, mineral deposits second, then rinse.
2. Dry - deeper than it looks
A surface can look dry while the pores are still full of water after washing or rain. A sealer that meets wet pores does not penetrate as it should - hence patches and an uneven finish.
When in doubt, wait longer - rushing usually shows in the result.
How long to wait before you start
| Situation | What you are waiting for | Where to check |
|---|---|---|
| Freshly laid paving or poured concrete | Substrate curing | The sealer's technical data - 'substrate curing' |
| After washing with a chemical preparation | Rinsing and full drying | The cleaner's instructions - dwell time and how to rinse |
| After rain | The pores drying, not just the surface | The sealer's technical data - maximum substrate humidity |
| A second coat of sealer | The interval between coats | The sealer's technical data - interval between coats |
3. Cured - fresh concrete is still working
For many weeks after laying, concrete and concrete paving give up their mixing water. A sealer applied too early closes that route, and the result is sometimes efflorescence trapped under the layer.
The curing time depends on the preparation - for some sealers it is 28 days. Do not cut it short by feel.
Preparations for getting the substrate ready
Cleaners and degreasers that get the surface ready for sealing.
StandardAnti-slip treatment for granite and gneiss tiles R-9G CTS Chemistry
59,90 zł
59,90 zł/L≈ 9,22 zł/m²
StandardAnti-slip treatment for ceramic and porcelain tiles R-9C CTS Chemistry
59,90 zł
59,90 zł/L≈ 11,98 zł/m²
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StandardOil stain remover for concrete and paving OL-1 CTS Chemistry
55,20 zł
55,20 zł/L
StandardHeavy-duty mineral soiling cleaner D-4 CTS Chemistry
40,16 zł
37,64 zł/L
StandardLime efflorescence remover D-2W CTS Chemistry
35,67 zł
30,50 zł/L≈ 7,63 zł/m²
StandardPost-construction residue cleaner D-2B CTS Chemistry
49,20 zł
40,59 zł/L≈ 10,15 zł/m²
5. The test patch - fifteen minutes that save a weekend
Only a test will show how your paving reacts to a particular preparation - material varies by batch, by age and by what has been on it already. Put the preparation on one slab somewhere not visible from the street and judge it once fully dry - not before, because a wet substrate looks different.
With wet-look sealers the test is not optional, because the effect cannot be undone.
Common questions
Does paving that looks clean still need washing?
Not if it is new and carries no bloom or building residue. Do sweep off sand and dust, though - that is usually what decides whether the preparation soaks in evenly.
How do I check the substrate is dry enough?
A simple test is taping a sheet of plastic down for a few hours: condensation underneath means the pores are still damp. That is a rough method - where a maximum substrate humidity is given as a percentage for the preparation, a moisture meter gives you a reliable reading.
Can I seal in full sun?
Better not. On a hot surface the preparation evaporates before it can penetrate. Seal in the morning or evening, when the substrate is cooler, and keep within the upper temperature limit given for the preparation.
Is a second coat necessary?
On an absorbent substrate, often yes - the next coat then goes on wet on wet. The number of coats depends on the preparation and on how much the material drinks.
What should I do if the sealer came out patchy?
Establish the cause first, because it decides whether another coat will even it out or whether the preparation has to come off. Uneven absorbency, damp pores and leftover soiling each look different. Write to us with a description and a photograph - we answer within 24 hours.
