Why preparation decides the result
An impregnation works when it has somewhere to penetrate and something to bond with. If dirt, grease or moisture stay on the surface, the product either does not reach where it should or seals the dirt underneath. The result is weaker, uneven and less durable.
That is why surface preparation is not a step you can shorten. It is the foundation of the whole job. Three conditions repeat regardless of the surface, namely clean, dry and absorbent.
Clean
The surface must be free of dirt, dust, deposits and loose parts. On pavers and facade you remove green growth and dirt with a cleaner, wood you wash and sand if needed. Every bit of dirt that stays will end up under the product and stay there.
Dry
Water in the structure of the base blocks the product from penetrating and leads to streaks. The surface must be dry not only on top but just below it. After rain or washing you have to give the material time to dry, and when in doubt wait longer.
Tip
A simple sign of moisture is darker joints and hollows. If the joints are still dark after the top has dried, there is still water in the material and you have to wait with the impregnation.
Grease free and absorbent
Grease stains, remains of old coatings and dirt reduce absorbency. On the driveway you remove oil stains, on wood you sand off the grey, dead layer, and on previously painted surfaces you check whether the product can penetrate at all. An absorbent surface is one that takes in water, not one off which water runs without a trace.
The absorption test and the moisture test
Two simple tests save you a lot of trouble later.
- Absorption test. Put a little water on the surface. If it soaks in and darkens, the base is absorbent and ready for the product. If the water beads and sits on top, the material is low absorbing or carries the remains of an old protection.
- Moisture test. After rain or washing, watch the joints and hollows. A darker colour means there is still water inside.
- Product test. Regardless of the above, apply the product to a small, inconspicuous area to judge the effect and consumption.
Preparing the surface step by step
- 1Remove loose dirt and growth. Sweep the surface, remove weeds from the joints and collect loose dirt.
- 2Wash and remove deposits and stains. Use a product matched to the surface. Difficult stains such as oil or rust you treat separately.
- 3Sand or repair if needed. On wood you sand off the grey layer, on other surfaces you fill gaps and joints.
- 4Let the surface dry thoroughly. Wait until the material is dry just below the surface too. This is the condition for effective impregnation.
- 5Do the tests. Check absorbency and moisture, then do a product test before applying it to the whole surface.
The most common mistakes in surface preparation
- Haste and a shortened drying time.
- Impregnating a dirty or greasy surface.
- Skipping the absorption test, so the product reaches where it cannot penetrate.
- Applying a penetrating impregnation over an old, sealed coating.
- Giving up the test and being surprised by the result on the whole surface. See also the guide on common impregnation mistakes.
Frequently asked questions
How do I check whether the surface is absorbent enough?
Put a little water on the surface. If it soaks in and darkens, the base is absorbent and ready for the product. If the water beads and sits on top, the material is low absorbing or carries the remains of an earlier protection.
How long should the surface dry after washing?
Long enough for the surface to be dry just below it too. The time depends on the weather and the material, so when in doubt wait longer rather than too short.
Does every surface need sanding?
No. Sanding mainly concerns wood, which greys and roughens. On pavers and facade what matters most is thorough cleaning and drying.
Can I impregnate a previously painted surface?
A penetrating impregnation needs an absorbent base, and a sealed paint layer may not let it in. Check whether the chosen product is suitable for such a surface, or remove the old layer.
