Filler Sealant

About Filler Sealant

Filler sealants represent a versatile category of building materials that combine the gap-filling properties of traditional fillers with the waterproofing and adhesive qualities of sealants. These hybrid products have become essential for both professional tradespeople and DIY enthusiasts tackling a wide range of interior and exterior projects. Whether you're sealing expansion joints, filling cracks in masonry, or creating watertight seals around windows and doors, the right filler sealant can deliver long-lasting, professional results that withstand the demanding British climate.

Modern filler sealants are formulated to address specific challenges that traditional products cannot. They typically offer excellent adhesion to multiple substrates including wood, metal, concrete, brick, and uPVC, whilst remaining flexible enough to accommodate structural movement. Many are paintable once cured, making them ideal for decorative applications where a seamless finish is required. The best products also resist mould growth and remain elastic in both hot and cold temperatures, crucial considerations for external applications in the UK's variable weather conditions.

Available in cartridges for use with standard skeleton guns or in squeeze tubes for smaller applications, filler sealants come in various colours to match common building materials. Professional-grade options often feature rapid curing times, low shrinkage, and compliance with relevant British Standards, ensuring they meet the demanding requirements of commercial construction and renovation projects whilst remaining accessible for home improvement tasks.

Jargon Buster

MS Polymer

A modified silane polymer technology that offers the flexibility of silicone combined with the paintability of acrylic. These sealants can be used on virtually any surface and are particularly popular for both internal and external applications.

Elasticity/Elastic Movement

The ability of a cured sealant to stretch and compress without cracking or losing adhesion. Typically expressed as a percentage, with higher values indicating greater flexibility to accommodate structural movement in joints.

Paintable/Overpaintable

Refers to filler sealants that accept paint once fully cured, allowing for a seamless finish that matches surrounding surfaces. Essential for decorative applications where the sealant line needs to be disguised.

Thixotropic

A property that prevents the product from sagging or slumping when applied to vertical surfaces. Thixotropic sealants maintain their position during curing, ensuring neat joints without drooping.

Shore Hardness

A measurement of the sealant's hardness once cured, with lower values indicating a softer, more flexible product. Different applications require different hardness levels depending on the degree of movement expected.

COSHH Compliance

Indicates the product meets Control of Substances Hazardous to Health regulations. COSHH-compliant filler sealants have reduced solvent content and lower VOC emissions, making them safer for use in confined spaces.

Who Uses Filler Sealant?

Filler sealants are invaluable across numerous trades and applications:

• General Builders – for sealing expansion joints, filling gaps in blockwork, and weatherproofing external structures
• Plasterers and Renderers – for filling cracks and joints where flexibility is needed to prevent future cracking
• Painters and Decorators – for filling gaps around architraves, skirting boards, and coving before painting
• Window Fitters – for sealing around window and door frames whilst allowing for thermal expansion
• Roofers – for weatherproofing roof penetrations, flashings, and joints exposed to the elements
• Bathroom Fitters – for creating water-resistant seals around baths, shower trays, and sanitaryware
• Maintenance Contractors – for quick repairs to buildings, preventing water ingress and improving thermal efficiency
• DIY Enthusiasts – for home improvement projects requiring durable, flexible gap-filling solutions

How to Choose the Right Filler Sealant

Application Location: Consider whether you need the product for internal or external use. External applications require UV resistance, enhanced weatherproofing, and the ability to withstand temperature extremes common in the UK climate. Internal products can focus more on low odour and fast decoration times.

Substrate Compatibility: Identify all surfaces the sealant will contact. MS polymer formulations offer the broadest compatibility, adhering reliably to porous surfaces like brick and concrete, as well as non-porous materials such as uPVC, metal, and glazed tiles without requiring primers.

Joint Movement: Assess how much expansion and contraction the joint will experience. High-movement areas such as expansion joints in brickwork or connections between different materials require sealants with higher elasticity ratings (typically 25% movement accommodation or more).

Paintability Requirements: If you plan to paint over the sealant, ensure it explicitly states paintable or overpaintable on the specification. Some sealants can be painted within hours, whilst others require 24 hours or more to cure sufficiently.

Cure Time: Professional tradespeople often require rapid-curing formulations that allow same-day decoration or exposure to the elements. DIY users may prioritise ease of application over speed of cure, particularly for non-urgent repairs.

Colour Matching: Select a colour that matches your substrate or can be easily painted over. Common options include white, grey, brown, and clear/translucent for applications where the sealant line should be inconspicuous.

Environmental Conditions: For damp environments or areas prone to condensation, choose products with anti-fungal additives. For food preparation areas or enclosed spaces, look for low-VOC, low-odour formulations that comply with current COSHH regulations.

Popular Accessories

• Skeleton Guns and Applicators – manual and battery-powered options from brands like Makita, DeWalt, and Milwaukee for dispensing cartridge-based filler sealants with precision
• Finishing Tools and Smoothers – shaped profiles for creating neat, professional joints in various configurations
• Nozzles and Extension Tips – for reaching awkward areas and controlling bead size
• Surface Preparation Products – primers, cleaners, and degreasers to ensure optimal adhesion
• Masking Tape – for protecting adjacent surfaces and creating straight, clean sealant lines
• Spirit Levels and Measuring Tools – from manufacturers like Stanley and Bahco for accurate joint preparation
• Joint Backing Materials – foam backer rods for deep joints to control sealant depth and improve efficiency
• Dispensing Cartridges and Refills – replacement cartridges and bulk packs for frequent users

Safety Information

When working with filler sealants, always read the manufacturer's safety data sheet and product labels before use. Ensure adequate ventilation when applying products indoors, particularly when working with solvent-based formulations, though most modern products are low-odour and low-VOC compliant.

Wear appropriate PPE including safety glasses to protect against splashes and nitrile gloves to prevent skin contact, as some formulations may cause irritation. Brands like Portwest, Scruffs, and DeWalt offer suitable protective equipment for sealant application work.

Store cartridges upright in cool, dry conditions away from direct sunlight and heat sources. Keep products out of reach of children and pets. If working at height when sealing external joints, ensure proper scaffolding or access equipment is used in accordance with HSE guidelines.

Dispose of empty cartridges and contaminated materials responsibly according to local authority guidelines. Partially used cartridges can typically be resealed and stored for future use if the nozzle is cleaned and capped properly.

Frequently Asked Questions

What's the difference between filler sealant and standard decorator's caulk?

Filler sealants offer greater elasticity and movement accommodation than standard acrylic caulks, making them suitable for joints that experience expansion and contraction. They typically provide superior adhesion to a wider range of materials and better weatherproofing for external applications, whilst decorator's caulk is primarily designed for internal, low-movement joints before painting.

Can I use filler sealant in wet conditions or on damp surfaces?

Many modern MS polymer filler sealants can be applied to damp (though not wet) surfaces and will cure in humid conditions, making them ideal for the British climate. However, always check the manufacturer's specifications, as some products require dry substrates for optimal adhesion. For permanently wet areas like underwater applications, specialist products are required.

How long before I can paint over filler sealant?

This varies by product, but most paintable filler sealants available from Tooled-Up.com can be overcoated within 1-4 hours for water-based paints. Solvent-based paints may require longer cure times. Always verify the specific product's technical data sheet, and note that thicker applications and lower temperatures will extend curing times. The sealant surface should be touch-dry and have formed a skin before painting.

Will filler sealant work on all materials including uPVC and metal?

MS polymer and hybrid filler sealants offer excellent multi-surface adhesion without primers, including uPVC, aluminium, powder-coated metal, wood, masonry, and many plastics. However, some materials like polypropylene, PTFE, and silicone surfaces require specialist primers or are unsuitable for standard sealants. Always ensure surfaces are clean, dry, and free from loose material, oil, or previous silicone residue.

What joint size can filler sealants accommodate?

Most filler sealants work best on joints between 5mm and 25mm wide. For deeper joints, use foam backer rod to support the sealant and control depth—the ideal sealant depth-to-width ratio is approximately 1:2. Joints wider than 25mm may require specialist expansion joint sealants or alternative detailing methods to ensure long-term performance and accommodate movement effectively.