Sealing joints for: Movement and connection joints, Facade elements, Balconies, Window and door frames, Pre-cast elements, Infill panels. (TDS p.1)
- Temperature stated in TDS
- −40 °C to +70 °C (TDS p.2)
- Pack
- 300 ml cartridges
Step-by-step solution
Damp external walls (rain penetration)
Rain soaking through brick walls, cracked plaster or open joints around windows causes seelan and peeling paint inside. This guide covers walls above ground. For damp rising from the floor, see the rising-damp guide.
- 6 steps
- 7 products
- 4 answers
You need this when…
- Damp patches inside an outside wall after rain, worst on the wall facing driving rain
- Peeling or blistering paint and powdery plaster
- Cracks in the outside plaster or around window frames
- Water getting in around window and door frames
- Algae or dark streaks on the outside face
The work, step by step
General guidance based on the manufacturer data sheets. Site conditions differ: confirm the system with MCT before you start. Where we do not name a product, ask us and we will confirm the right one.
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Step 1: Find the real source
Rule out rising damp (a band at floor level), leaking pipes, roof or parapet leaks and condensation. Map the cracks, open joints and frame gaps on the outside face.
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Step 2: Seal frames and joints
Rake out old sealant, insert a backer rod and seal window and door frames and facade joints with an elastic sealant (Sikaflex AT Connection p.1; Sikaflex Construction AP p.1, p.3).
Sikaflex AT Connection Sika Request a quotation Other options for this stepAsk us The right product here depends on your site. We confirm it before naming it.
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Step 3: Re-render hollow or cracked plaster
Cut out hollow render. Lay a bonding bridge of SikaLatex PK mixed with cement and sand, never neat (SikaLatex PK p.2). Re-render with waterproofed mortar: Sikalite-101 PK at 2 % of the cement weight (Sikalite-101 PK p.1, p.2) or Sika-1 PK (Sika-1 PK p.1).
SikaLatex PK Sika SikaLatex® PK is used as bonding agent and sitemix mortar admixture for the following applications: Grouts and screeds, Patch repair mortars, Mansonry mortars, Renders, Tile adhesives. (TDS p.1)
- Pack
- 05 ltr jerry can 20 ltr plastic can 200 ltr drum 1000 ltr IBC Bulk supply in tanker is…
Sikalite-101 PK Sika Sikalite®-101 PK is used to waterproof cement/sand mortars, screeds and renders for walls, facades, floor toppings and jointing mortars. (TDS p.1)
Sika-1 PK Sika Request a quotation Sika®-1 PK is used for waterproofing of mortars and concrete, in particular for: Renders, masonry mortars and screeds, Reinforced and unreinforced concrete, Brick, concrete and stone substrates, Indoor and outdoor applications, such as basements, swimming pools, tunnels, water tanks, manholes, cu… (TDS p.1)
- Pack
- 05 ltr jerry can 20 ltr plastic can 200 ltr drum 1000 ltr IBC Bulk supply in tanker is…
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Step 4: Option A: cement-based waterproof coating
Coat walls exposed to driving rain with a polymer-modified cement coating. Use 1.07 kg/m² for the first coat and 0.54 kg/m² for the second on a dampened wall (Sika Thoroseal Plus p.2, p.3). Run a small adhesion trial first and let it cure for 7 days (Sika Thoroseal Plus p.2).
Sika Thoroseal Plus Sika Request a quotation Diverse building substrates Walls Foundations Tunnels Basements Blocks, bricks, stone and concrete Concrete High tanks Interior and exterior (TDS p.1)
- Pack
- 35 lb (15.9 kg) pail
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Step 5: Option B: clear water repellent
Where you want to keep the look of exposed brick, fair-faced concrete or render, apply a clear silane/siloxane impregnation from the bottom up, wet-on-wet (Sikagard-700 S PK p.1, p.2). The surface must be free of paint and look dry (Sikagard-700 S PK p.2).
Sikagard-700 S PK Sika Sikagard®-700 S PK is used as water repellent and colourless protective surface treatment on absorbent exposed materials such as concrete, cementitious rendering, concrete tiles, fibre cement, brickwork (clay and lime sand, non-vitrified), natural stone. (TDS p.1,2)
- Temperature stated in TDS
- +5 °C min. / +30 °C max (TDS p.2)
- Pack
- 1000 ltr IBC
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Step 6: Option C: elastic coat on cracked concrete
On concrete facades at risk of cracking, use a crack-bridging protective coating (Sikagard-550 W Elastic p.1). A third coat may be needed for full durability (Sikagard-550 W Elastic p.2).
Sikagard-550 W Elastic Sika Request a quotation Sikagard®-550 W Elastic is used for protection and enhancement of concrete structures (normal and lightweight concrete), especially exposed outdoor concrete surfaces with a risk of cracking. (TDS p.1)
- Temperature stated in TDS
- +8°C min. / +35°C max (TDS p.3)
- Pack
- 15 l oval plastic pail
Proposal brief
Damp external walls (rain penetration): scope and system
A starting point for a site proposal. Quantities, prices and the final specification follow a site visit or photos.
Scope of work
- Damp survey of x m² of external wall
- Resealing of window, door and facade joints
- Removal of hollow render and re-rendering with waterproofed mortar
- Waterproof coating or clear water-repellent treatment
- Making good inside, if agreed
System build-up
| Step | Product | Pack | Source |
|---|---|---|---|
| 2. Seal frames and joints | Sikaflex AT Connection | 300 ml cartridges | TDS p.1 · May 2021, Version 03.01 |
| 3. Re-render hollow or cracked plaster | SikaLatex PK | 05 ltr jerry can 20 ltr plastic can 200 ltr drum 1000 ltr IBC Bulk supply in tanker is… | TDS p.1 · June 2025, Version 02.01 |
| 3. Re-render hollow or cracked plaster | Sikalite-101 PK | — | TDS p.1 · October 2023, Version 01.02 |
| 3. Re-render hollow or cracked plaster | Sika-1 PK | 05 ltr jerry can 20 ltr plastic can 200 ltr drum 1000 ltr IBC Bulk supply in tanker is… | TDS p.1 · August 2026, Version 02.02 |
| 4. Option A: cement-based waterproof coating | Sika Thoroseal Plus | 35 lb (15.9 kg) pail | TDS p.1 · September 2024, Version 02.01 |
| 5. Option B: clear water repellent | Sikagard-700 S PK | 1000 ltr IBC | TDS p.1,2 · August 2026, Version 01.01 |
| 6. Option C: elastic coat on cracked concrete | Sikagard-550 W Elastic | 15 l oval plastic pail | TDS p.1 · May 2021, Version 01.01 |
What we need from you
- Which walls are damp, and photos inside and outside
- Wall type: brick, block or concrete; plastered or exposed
- Current outside finish: paint, plaster or exposed brick
- Building height and access
- Is the damp only after rain, or all year?
Site conditions
- Dry spell for impregnations, which need a dry-looking wall (Sikagard-700 S PK p.2)
- New render at least 4 weeks old before Sikagard-700 S PK (Sikagard-700 S PK p.2)
- Scaffolding or safe access
Not included
- Plumbing, roof and parapet leaks (separate guides)
- Internal re-plastering and painting, unless agreed
- Window or frame replacement
Questions customers ask
Will the clear treatment stop the wall from breathing?
No. Sikagard-700 S PK lets water vapour pass in both directions and does not act as a vapour barrier (Sikagard-700 S PK p.1).
Can we paint after the clear treatment?
Not with limewash or cement paint (Sikagard-700 S PK p.2). It can be used as a water-repellent primer under solvent-based or emulsion protective coatings (Sikagard-700 S PK p.1).
Does the cement coating work on brick and block walls?
Yes. Sika Thoroseal Plus lists blocks, bricks, stone and concrete, inside and outside (Sika Thoroseal Plus p.1).
Can I just apply a waterproof paint on the inside wall?
Ask us: it depends on site conditions. Stopping the water on the outside face is the aim of the systems in this guide.
Steps and product facts are taken from the manufacturer data sheets (page cited). Products are named only where the data sheet confirms the use; quantities follow a site visit or photos. General guidance: check the data sheet or ask us before you start.