In the shop, three products look as if they do the same job: the water repellent (hidrofugante), the waterproofer (impermeabilizante) and the elastic “membrane” paint. They do not. One lets the wall breathe, one forms a film, and the third is a paint that copes with fine cracks. Picking the wrong one can trap water inside the wall. This guide explains the difference, when each one fits and the conditions for applying it, based on data sheets we read.
Updated on 4 November 2026. General information, not a substitute for an assessment by a technician.
The essentials
- A water repellent forms no film. The weberhydrofuge sheet describes silanes and siloxanes in water and says it “does not change the look of the finish”. It is for porous materials that are not cracked.
- An elastic paint (“membrana” in the name) is a paint. Barbot 1316 Membrana Elástica is V2 (medium vapour permeability) and W3 (low water absorption), and resists shrinkage cracks.
- Neither one treats damp coming from inside (from the ground, a leak, condensation). The Topeca Acrilpaint Repel sheet forbids use on walls with rising damp.
- Application is always on a dry surface, with no rain, within temperature limits that differ from product to product.
- Find where the water comes from first. Choose the product after.
The three families side by side
| Water repellent | Elastic paint (“membrana”) | Waterproofing membrane | |
|---|---|---|---|
| Forms a film? | No (weber sheet: original look kept) | Yes, thin | Yes, thick |
| Example read | weberhydrofuge (sheet of 06-11-2024) | Barbot 1316 (sheet of 10-12-2024) | Sikalastic-560 (roofs) |
| Cracks | Only uncracked surfaces | Shrinkage cracks | Depends on the system |
| Can it be painted over? | “Do not coat” (weber) | It is the finish | See sheet |
| Typical use | Render, exposed brick, stone | Exterior render | Roofs, balconies |
The third column needs a note. We looked for Portuguese sheets for facade “membranes” and found only roof membranes. The Portuguese Sikalastic-560 sheet (version of November 2021, read through a search summary, not directly) describes it as a liquid membrane for waterproofing roofs. On a house facade, what is sold as a “membrane” is usually an elastic paint such as Barbot 1316.
Water repellent: when it fits
A water repellent goes into the pores and makes rainwater run off instead of soaking in. The wall looks the same. It is the logical choice when the facade is good-looking and you want to keep it visible: exposed brick, natural stone, unpainted render, roof tiles.
The weberhydrofuge sheet (Saint-Gobain Portugal, 06-11-2024) says:
- substrates: cement or lime render, concrete, exposed brick, tiles, roof tiles, natural stone
- do not apply on gypsum, on wet surfaces, or on weberdecor betão
- working temperature 5 to 30 °C, no frozen surface or frost risk within 24 hours, no strong sun, strong wind or rain
- surface “perfectly clean, dry”, cracks treated
- two coats, the second while the first is still damp
- consumption 0.3 to 2.0 l/m², depending on porosity
- drying 24 hours, best effect after 7 days
- after cleaning with anionic detergents, wait 2 to 3 weeks
One practical consequence: a water repellent does not fill cracks. If the facade has cracks, repair them first (see cracks in render before painting).
Sikagard-705 L (Sika Portugal, sheet of August 2025) is another example, but it is for concrete. The sheet describes it as a hydrophobic impregnation for reinforced concrete, “open to water vapour diffusion”. It asks for a base below 5 to 6% moisture and 5 to 35 °C air. It also says it cannot be coated with lime or cement paint. It is a product for structures, not for painting a house.
Elastic paint: when it fits
This is the option when the facade will be painted and has fine shrinkage cracks. Barbot 1316 Membrana Elástica (sheet of 10-12-2024) gives:
- classes G2 E2 S1 V2 W3 A0 C0 (EN 1062-1)
- crack resistance above 600 µm dry film (NP 4505, annex B)
- air above 5 °C, relative humidity below 80%, surface moisture below 5%, surface 2 to 3 °C above dew point
- 2 coats, 6 to 24 hours between coats, up to 10% dilution on the first
- coverage of 1 to 1.5 m² per litre per coat
Coverage is low, so expect many litres for a facade. Use the paint calculator for the area, then adjust to the sheet’s coverage. The choice between elastic and ordinary acrylic is in exterior facade paint.
The same sheet tells you to treat problem surfaces first: fungi and algae with a cleaning solution, efflorescence brushed off, cracks up to 2 mm opened and filled. A film does not fix the cause.
When it is the wrong choice
A film, even a “breathable” one, does not solve damp that comes from below or from inside. The Topeca Acrilpaint Repel sheet (02-01-2023) lists among its limits: do not apply on walls with rising damp or in contact with very damp ground.
What can go wrong:
- Damp from the ground. Water rises through the wall. If the outer face dries badly, the water rises higher or comes out inside, with salts. See rising damp.
- A leak through a defect (gutter, window, large crack). Seal the entry. Paint on top only hides it.
- Condensation inside. It is an indoor air problem and paint outside does not touch it. See the types of damp.
- A wall that is still wet. The sheets we read ask for a dry surface: Barbot below 5%, Sika below 5 to 6%, weber “dry”.
We found no Portuguese rule with a number (“the wall must be at X% before sealing”). What exists are the limits in each product’s sheet. A moisture meter measures it: see measuring wall damp.
A checklist before you buy
- Mark where the water shows (stain, efflorescence, blistering paint) and when (after rain, or always).
- Check for cracks. Repair them with a filler made for exterior use.
- Measure the surface moisture and wait for dry weather.
- Visible facade (brick, stone, unpainted render): water repellent, if the sheet allows your surface.
- Painted facade with fine cracks: elastic paint, two coats, with a primer if the sheet asks for one.
- Facade of a block of flats: the decision belongs to the owners’ association. See painting the facade: licence and condominium.
- Keep the data sheet and the batch number. They prove what you used.
- Test a small area first: the sheets advise preliminary trials.
What we could not confirm
- We did not read the EN 1062-1 or EN 1504-2 standards (paid): we use what the sheets print.
- We found no Portuguese sheet for a liquid membrane designed for house facades. The Sikalastic-560 sheet is for roofs and was read through a summary.
- We found no independent study on water repellents on Portuguese facades. Performance claims come from manufacturers.
- We have no reliable dated prices for these products.
- The effect of paint vapour permeability on wall drying was studied by LNEC (2009), but we could not open the document. It remains unread.
Sources (read on 4 November 2026)
- Saint-Gobain Portugal, “weberhydrofuge, Hidrofugante para fachadas”, data sheet MOD.FTW.142, 06-11-2024: PDF. All 3 pages read.
- Barbot, “1316 Membrana Elástica”, data sheet Rev.01, 10-12-2024: PDF. Read in full.
- Topeca, “Acrilpaint Repel, 100% acrylic water-repellent paint”, data sheet, 02-01-2023: PDF. Field of use, limits and application data read (copy hosted by a reseller).
- Sika Portugal, “Sikagard-705 L”, product data sheet, August 2025: PDF. Read in full.
- Sika Portugal, “Sikalastic-560”, product data sheet, November 2021: cited through a search result, not read directly.
- LNEC (2009), dissertation on vapour permeability of exterior paints and wall drying: cited through a search result, not read directly.