Soudal SoudaGum Hydro is a single-component, solvent-free waterproof roof coating suitable for roofs, gutters, joints and flashings. Ready to use straight from the tub, rain resistant in 2 hours, and permanently flexible once cured.
Soudal SoudaGum Hydro is a ready-to-use waterproof roof coating based on hybrid polymer technology. It comes in a 5kg tub, ready to apply with no mixing required. As a waterproof roof coating, it handles the kind of jobs that catch out lesser products: ageing felt roofs, leaking gutters, cracked flashings, and exposed joints where water finds a way in if you give it half a chance.
The formula is solvent-free and isocyanate-free, which matters both for safety during application and for compatibility with a wide range of substrates. You get excellent adhesion on most common roofing materials without needing a primer on the majority of surfaces. It bonds to bitumen felt, metal, concrete, masonry, fibre cement, EPDM, and more.
One of the most useful properties on site is the 2-hour rain resistance. Apply SoudaGum Hydro and if the weather turns, you are not left hoping the job survives a shower. That short window before rain can ruin a freshly applied coating is one of the more frustrating aspects of flat roof work, and this product genuinely reduces that risk.
Where Soudal SoudaGum Hydro Earns Its Keep
SoudaGum Hydro is applied in two layers for full waterproofing performance. The first coat seals and penetrates, the second builds the protective membrane. The coating remains permanently flexible after curing, so it moves with the substrate through thermal expansion and contraction without cracking. This is particularly important on flat roofs and metal gutters where movement is constant over a year of temperature swings.
Once cured, the surface is paintable, which is useful where the finished appearance matters or where you need to apply a reflective topcoat. UV and weather resistance is good, so the coating holds up to prolonged sun exposure without degrading quickly.
WT1-Comparable Performance
SoudaGum Hydro is considered a practical alternative to liquid waterproofing systems classified under the WT1 category. It provides the kind of waterproof roof coating performance that works for repair and maintenance applications on existing substrates, without the cost or complexity of a full liquid-applied system. For roofers maintaining domestic and light commercial properties, that makes it a sensible option to keep on the van.
The 5kg tub gives you enough material for a meaningful area of repair work or a section of guttering, and the single-component format means no waste from unmixed components going off in the bucket. Clean tools with water before the product cures.
SoudaGum Hydro is produced by Soudal, one of the more established names in sealant and coating chemistry. The hybrid polymer base gives it a profile that sits between traditional bitumen coatings and higher-end polyurethane systems: better flexibility and adhesion than standard bitumen, without the solvent content or mixing requirements of a two-part PU.
Pro Tip: Apply SoudaGum Hydro to a clean, dry surface and allow the first coat to become touch dry before applying the second coat, overlapping the edges by at least 50mm to avoid thin spots at the lap lines.
Soudal SoudaGum Hydro is used on flat and low-pitch roofs, gutters, parapet walls, flashings, and roof penetrations such as pipe collars and upstands. It is suited to repair and maintenance work on domestic and light commercial properties where an existing substrate needs waterproofing or where joints and cracks need sealing against water ingress.
Roofers use it for patching worn felt, sealing metal gutters and downpipe joints, and treating areas around rooflights and skylights. It also works well on concrete and masonry surfaces where damp is penetrating through fine cracks or porous material.
Best For
Flat and low-pitch roof repairs
Gutter sealing and waterproofing
Flashings and roof upstands
Pipe collars and roof penetrations
Cracked or porous masonry and concrete
Joint sealing on internal and external surfaces
Compatible Surfaces
Bitumen roofing felt
Metal (steel, aluminium, zinc)
Concrete and masonry
Fibre cement
EPDM rubber
Most common roofing substrates
Key Properties
Single-component, ready to use
Solvent-free and isocyanate-free
Rain resistant in 2 hours
Permanently flexible when cured
Paintable surface finish
Good UV and weather resistance
Applied in 2 layers for full performance
Not suitable for: SoudaGum Hydro is not intended as a primary waterproofing membrane on new-build flat roofs where a full system specification is required. It is not suitable for use on surfaces that are actively wet or where standing water is present at the time of application.
Clean the substrate thoroughly before application, removing loose material, dirt, grease, moss, and any standing water. Dry surfaces give the best adhesion. Apply the first coat of SoudaGum Hydro using a brush, roller, or trowel, working the material into cracks and joints. Allow this coat to become touch dry before applying the second coat in the same direction or cross-direction for even coverage.
For joints, cracks, and areas of movement, embedding a reinforcement fleece into the first wet coat before it skins will significantly extend the service life of the repair. This is standard practice on any joint that is likely to move.
Clean the surface thoroughly, removing loose material, moss, grease, and standing water
Allow the surface to dry completely before starting application
For cracks wider than 2mm, fill with a suitable filler or press SoudaGum Hydro into the gap and allow to skin
Apply the first coat using a brush, roller, or trowel at an even thickness across the full repair area
Embed reinforcement fleece into the wet first coat over joints, cracks, or areas likely to move
Allow the first coat to become touch dry before applying the second coat
Apply the second coat at a consistent thickness, overlapping edges by at least 50mm
Clean tools with water immediately after use before the product cures
How long does SoudaGum Hydro take to become rain resistant after application?
SoudaGum Hydro becomes rain resistant approximately 2 hours after application under normal conditions (around 20°C). Full cure takes longer and depends on temperature, humidity, and coat thickness. Cold or damp conditions will extend both the rain resistance window and the full cure time.
Does SoudaGum Hydro need a primer before application?
On most common roofing substrates, no primer is required. The product has good adhesion directly to bitumen felt, metal, concrete, masonry, and fibre cement. On very porous or dusty surfaces, a light primer or diluted first coat can improve adhesion and coverage, but this is not a standard requirement.
How much area will a 5kg tub cover?
Coverage depends on the surface texture, the number of coats, and the application method. As a general guide, 5kg applied in two coats over a smooth or moderately textured surface will typically cover around 2 to 3 square metres. Rough or porous surfaces will consume more material, so factor that in when estimating for larger jobs.
Soudal SoudaGum Hydro is a hybrid polymer-based waterproof coating formulated without solvents or isocyanates. The hybrid polymer chemistry delivers a balance of adhesion, flexibility, and weather resistance that bitumen-based coatings do not match, while remaining simpler to apply than two-part polyurethane systems. The cured membrane is permanently elastic, UV stable, and compatible with a broad range of common construction substrates.
Reviews
There are no reviews yet.