Concrete Joint Sealant Types – What to Use and When
When working with precast concrete, selecting the right joint sealant is essential. An incorrect choice can lead to leaks, chemical damage, wasted time on site, and even structural issues in the future.
The challenging part? There’s a wide variety of sealants available, and not all are suitable for heavy-duty, external, or agricultural use. We typically recommend polyurethane-based elastic sealants rather than mortars or standard silicones. Unlike silicone sealants used around baths or windows, polyurethane provides the strength, flexibility, and chemical resistance necessary for precast walls, bunds, silage clamps, and other applications.
Below, you’ll find a guide to the types of sealants we most frequently use on our projects, along with tips on preparation, quantities, and the ideal applications for each sealant.
Choosing the Right Sealant for the Job
Different precast applications require varying performance qualities – from flexibility to chemical resistance. Here’s a quick guide showing which sealants we typically use for common wall types:
Concrete Sealant Applications
| Application | Sikaflex® PRO-3 | Sikaflex® TS Plus | Hybriflex FR | Sikadur® Combiflex |
|---|---|---|---|---|
| Indoor | X | X | X | X |
| Outdoor | X | X | X | X |
| Livestock Building | X | |||
| Grain Store Walls | X | |||
| Silage Clamp Walls | X | X | ||
| Slurry Store Walls | X | X | ||
| Slurry Channels | X | |||
| Bund Walls | X | X | ||
| Flood Defence Walls | X | |||
| Grit Salt Walls | X | |||
| Waste & Recycling Walls | X | X | ||
| Fire & Blast Wall | X | |||
| Temporary Oil/Fuel Storage | X | X | X | |
| Sewage Treatment Plants | X | X | X |
How to use this table
Start with the wall type, then cross-reference which sealants are suitable. For example, silage clamps usually need TS Plus because of its resistance to aggressive silage leachate. For grain stores or livestock housing, Pro-3 is the all-rounder.
Preparing Joints Properly
Even the best sealant won’t perform if the joint isn’t prepared correctly. Two essentials we always use before applying polyurethane sealant:
- Sika® Primer-3 N – improves adhesion between concrete and sealant. One litre covers around 40m of joint.
- Sika® Backer Rod (closed-cell foam) – controls sealant depth and reduces material waste. Supplied in 550m rolls, usually 15mm diameter.
Pro tip: depth of sealant should generally be half the joint width. Skipping the backer rod often leads to overfilling, wasted sealant, and reduced flexibility.
Mastic Sealant Calculator
Wondering how much sealant you’ll need? As a rule of thumb, one 600ml foil pack covers approximately 5m of a 10mm x 5mm joint. Here’s a more detailed guide:
Metres of mastic per 600ml foil pack
| Joint depth/width (mm) | 3 | 6 | 8 | 10 | 12 | 15 | 18 | 20 | 25 | 30 |
| 3 | 66 | 33 | 25 | 20 | 16.5 | 13 | 11 | 10 | 8 | 6.5 |
| 6 | 33 | 16.5 | 12.5 | 10 | 8 | 6.5 | 5.5 | 5 | 4 | 3 |
| 8 | 25 | 12.5 | 9 | 7.5 | 6 | 5 | 4 | 3.7 | 3 | 2 |
| 10 | 20 | 10 | 7.5 | 6 | 5 | 4 | 3 | 3 | 2.5 | 2 |
| 12 | 16.5 | 8 | 6 | 5 | 4 | 3 | 2.5 | 2.5 | 2 | 1.5 |
| 15 | 13 | 6.5 | 5 | 4 | 3 | 2.5 | 2 | 2 | 1.5 | 1 |
| 18 | 11 | 5.5 | 4 | 3 | 2.5 | 2 | 1.5 | 1.5 | 1 | 1 |
| 20 | 10 | 5 | 3.5 | 3 | 2.5 | 2 | 1.5 | 1.5 | 1 | 1 |
| 25 | 8 | 4 | 3 | 2.5 | 2 | 1.5 | 1 | 1 | 1 | 1 |
Sealant Profiles – When and Why We Use Them
Sikaflex® PRO-3
Description: Sikaflex® PRO-3 is a 1-component, moisture-curing, elastic joint sealant with high mechanical and chemical resistance.
Best for: indoor & outdoor wall joints, bunds, flood defences, waste storage.
Why we use it: the all-rounder. High movement capability (±35 %), excellent chemical resistance, solvent-free, and bubble-free curing. Perfect when you want one product to cover most joint sealing applications.
Sikaflex® TS Plus
Description: Sikaflex® TS Plus is a 1-part, moisture-curing, elastic sealant that is resistant to liquid manure and suitable for sealing domestic sewage systems.
Best for: slurry stores, silage clamps, sewage tanks.
Why we use it: designed for agricultural and wastewater environments. Resistant to silage effluent, sewage, and liquid manure. High tear strength and long-term durability in aggressive environments.
Everbuild Hybriflex FR
Description: Hybriflex FR is a one-part, chemically curing, solvent-free sealant and adhesive combining the best qualities of silicone and polyurethane technologies.
It has a fire rating of up to 4 hours in certain joint configurations (when tested to EN1366 Part 4 2006 – Warrington Fire Certificate 195854/A October 2010).
Best for: waste/recycling, fire and blast walls, where fire protection is required.
Why we use it: it combines the flexibility of silicone with the toughness of polyurethane. Fire rated up to 4 hours (EN1366 Part 4), abrasion and chemical resistant, works on damp surfaces, and can be overpainted.
FAQs About Concrete Joint Sealants
01. Do I need to use a primer before applying the sealant?
Yes, using a primer (such as Sika Primer-3 N) ensures the sealant bonds properly to the concrete surface. Skipping this step is one of the most common causes of failed seals.
02. Can sealant be applied in wet weather?
Polyurethane sealants can tolerate some surface dampness, but for the best results, joints should be clean and dry.
03. How long does sealant last?
It depends on the product and the environment. For example, Pro-3 has excellent durability in standard wall applications, while TS Plus is designed to withstand the aggressive conditions in silage and slurry environments. With proper preparation, sealants should last for many years.
04. What’s the difference between polyurethane and silicone sealants?
Silicone is suitable for domestic jobs, such as windows and bathrooms, but polyurethane is much more durable. It has a higher movement capacity, better adhesion to concrete, and greater chemical resistance, making it far more suitable for precast walls, bunds, and storage areas.
05. How much sealant do I need for my project?
Use our calculator above to estimate based on joint size. As a rule of thumb, one 600ml foil sausage covers approximately 5m of a 10mm-wide joint.
06. Can I remove or replace the sealant later?
Yes, most polyurethane sealants can be cut out and replaced if necessary. If you expect to move units or adjust walls frequently, consider alternative options such as interlocking precast units that do not require sealing.
Want a step-by-step guide?
If you’re new to sealing precast joints, check out our guide to sealing precast concrete joints for a simple walkthrough.
Need Advice on Joint Sealing?
Choosing the right concrete joint sealant is all about matching the product with the environment. For most general precast walls, Sikaflex® PRO-3 is our go-to. But for slurry, silage, bunding, or critical applications, you should opt for TS Plus.
Get the preparation right, size the joints properly, and use the calculator above to minimise wastage – this way, you’ll save time, money, and avoid rework.
If you’re not sure which sealant you need or want to order a product for your retaining walls, get in touch with our team. We’ll help you choose the right option for your project and arrange delivery alongside your precast units.
