Popular: Sikaflex · waterproofing · grout · data sheets
Hairline and map cracks in plaster, renders and concrete surfaces, mostly from shrinkage and heat, which let rain in and spoil paint. This guide covers telling them apart from structural cracks, filling them with the right sealant, and preventing them in new plaster.
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.
Cracks that are wide, growing, diagonal from window or door corners, or running through the wall or a beam need an engineer: see the structural-cracks guide. This guide is for non-structural surface cracks only (Sikadur-20 Crack Seal p.1).
Groove the crack and clean it free of dust and water (Sikadur-20 Crack Seal p.2). The surface must be clean, dry and sound for acrylic sealants (Sikacryl S p.3). On porous plaster, Sikacryl can be diluted with water 1:1 to 1:5 as a primer (Sikacryl-110 p.3).
Sikacryl-110 is an interior acrylic sealant for low-movement cracks and joints, ±7.5 % movement, over-paintable after a paint trial (Sikacryl-110 p.1, p.3).
Sikacryl®-110 is designed for interior crack and joint filling with low movement. Sikacryl®-110 is also suitable for duct sealing in HVAC applications. Main applications: Head of wall joints, Wall joints, Interior joints around windows and doors, Around the penetrations, As a gap filling in the c… (TDS p.1)
Sikacryl S fills internal and external cracks that are not constantly under water, ±7.5 % movement, and can be over-painted with most facade paints after a trial (Sikacryl S p.1, p.2).
Sealing joints for: Interior joints on many types of substrate with a limited amount of movement, Connections around window and door frames, Around wall and ceiling penetrations Crack filling:, Internal and external cracks not exposed to permanent water immersion. (TDS p.1)
For non-structural cracks in slabs, chhajjas and balconies, pour Sikadur-20 Crack Seal into the vee-notched crack until full; maximum width 10 mm, concrete at least 28 days old (Sikadur-20 Crack Seal p.1, p.2).
To fill and seal non-structural crack and cavities in structural concrete such as concrete decks, balconies, concrete roof structures, wet room, swimming pool and especially before waterproofing works. (TDS p.1)
Hack off loose plaster. Use SikaLatex PK as a bonding bridge with cement and sand, applying the plaster wet on wet; it also reduces shrinkage and cracking in the mix (SikaLatex PK p.1, p.2). Sika Crackstop Fiber 6 mm reduces plastic and drying shrinkage cracking in renders and plasters (Crackstop Fiber p.1). Cure well in heat with polythene or wet hessian (SikaLatex-200 SBR PK p.2).
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)
For most types of non-structural concrete and cementitious mortars which need to reduce the incidence of shrinkage cracking: Ground bearing slabs, Screeds and overlays, Renders and plasters, Precast concrete elements, Sprayed applications, Extruded concrete. (TDS p.1)
SikaLatex®-200 SBR PK is used as bonding agent and site-mix mortar admixture for the following applications: Thin layer patching mortars, Renders, Floor screeds, Concrete repair mortars, Abrasion resistant linings, Tile fixing mortars. (TDS p.1,2)
Over repaired walls, Sikagard-550 W Elastic (G) is a crack-bridging, vapour-permeable facade coating for concrete, brick, block and masonry (Sikagard-550 W Elastic (G) p.1). For a colourless finish, Sikagard-700 S PK water repellent; repair cracks over 200 µm first (Sikagard-700 S PK p.1, p.2).
Sikagard®-550 W Elastic (G) 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)
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)
A starting point for a site proposal. Quantities, prices and the final specification follow a site visit or photos.
| Step | Product | Pack | Source |
|---|---|---|---|
| 3. Fill interior plaster cracks | Sikacryl-110 | — | TDS p.1 · May 2025, Version 04.01 |
| 4. Fill exterior plaster and render cracks | Sikacryl S | 300 ml cartridge: 12 cartridges per box. | TDS p.1 · May 2021, Version 01.01 |
| 5. Seal concrete surface cracks | Sikadur-20 Crack Seal | 160 mL and 850 mL set | TDS p.1 · March 2025, Version 03.02 |
| 6. Re-plaster badly cracked areas | 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 |
| 6. Re-plaster badly cracked areas | Sika Crackstop Fiber 6 mm | — | TDS p.1 · November 2025, Version 02.02 |
| 6. Re-plaster badly cracked areas | SikaLatex-200 SBR PK | — | TDS p.1,2 · February 2026, Version 03.01 |
| 7. Weatherproof the facade | Sikagard-550 W Elastic (G) | — | TDS p.1 · May 2025, Version 04.01 |
| 7. Weatherproof the facade | Sikagard-700 S PK | 1000 ltr IBC | TDS p.1,2 · August 2026, Version 01.01 |
Ask us: it depends on site conditions. Wide, growing or diagonal cracks, or cracks through beams and columns, need an engineer (see the structural-cracks guide).
Sikacryl-110 is made for interior crack and joint filling with low movement and can be painted over after a compatibility trial (Sikacryl-110 p.1, p.3).
Sikacryl S fills internal and external cracks that are not constantly under water (Sikacryl S p.1, p.2).
Sika Crackstop Fiber 6 mm reduces plastic and drying shrinkage cracking in renders and plasters (Crackstop Fiber p.1). Cure fresh mortar well, especially in heat (SikaLatex-200 SBR PK p.2).
No. Sikagard-700 S PK is not intended to seal visible cracks, and cracks over 200 µm must be repaired first (Sikagard-700 S PK p.2).
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.