Choose by the joint and the exact product specification. A construction PU sealant and a sanitary silicone are not automatic substitutes. Check the substrates, movement requirement, exposure and finish before selecting a grade.
Two product examples from the Buildcare catalogue
The images below identify the catalogue products discussed in this guide. They are examples of different sealant types, rather than a claim that either product suits every joint.
FIXX PU SEAL
Listed as a single-component, moisture-curing polyurethane joint sealant. Check its current technical sheet for the intended joint and substrate. [1]
View FIXX PU SEAL ↗
Sikasil 117 Sanitary
An acetoxy silicone intended for specified sanitary sealing uses. Manufacturer-listed surfaces include glass and glazed ceramics; exclusions also apply. [2]
View Sikasil 117 ↗Catalogue images illustrate the listed packs. Confirm the exact variant, colour, pack size and availability with the quotation.
What is the practical difference?
PU describes polyurethane chemistry
Polyurethane sealants include grades developed for construction joints. FIXX PU SEAL is one catalogue example. Another manufacturer example, Sikaflex Construction Purform, is specified for concrete and masonry façade joints. Its requirements and limitations belong to that exact grade. [1] [3]
Silicone also includes different product types
Sikasil 117 is a sanitary acetoxy silicone, with mildew resistance for its listed wet-room uses. Its technical sheet excludes alkaline substrates and identifies other restrictions. A sanitary product should therefore not be treated as a general solution for every construction joint. [2]
Start with “What must this joint do?” Then check which exact product meets the requirement.
A comparison checklist for the buyer
| Check | Construction PU enquiry | Sanitary silicone enquiry |
|---|---|---|
| Application | Name the construction joint and approved product grade. | Identify the sanitary joint and specified silicone type. |
| Substrate | Confirm both surfaces, preparation and any required primer. | Check permitted surfaces and cure-type compatibility. |
| Movement | Match the joint design to the exact grade’s performance. | Check the stated movement capability and joint detail. |
| Paint or finish | Confirm paintability for the chosen product and coating. | Confirm finish requirements; do not assume overpaintability. |
| Exposure | State traffic, weather, chemicals or water contact. | Distinguish splashes from immersion or specialist uses. |
Read the full current technical sheet for the selected product. A broad chemistry comparison cannot establish project suitability.
Choose by application, not by packaging
Concrete or masonry construction joints
Begin with the approved joint schedule. Ask about substrate preparation, backing, movement and finishing. Where a PU grade is named, enquire about that grade and its required supporting materials. Do not substitute a sanitary silicone solely because it is available in a convenient cartridge.
Glass or glazed ceramic sanitary joints
Check that the chosen sanitary silicone lists both surfaces and the intended use. For Sikasil 117, Sika identifies glass and glazed ceramic applications, while its data sheet restricts submerged joints and certain other uses. [2]
Painted joints, natural stone or specialist work
Flag these requirements in the enquiry. Paint compatibility, staining risk, fire rating and structural glazing need product-specific checks. The catalogue photograph or a similar product name does not establish suitability.
Explore our joint sealants catalogue or read the waterproofing materials overview for related planning questions.
What to include in your sealant enquiry
- Application and both adjoining substrates.
- Approved manufacturer, product name and grade.
- Joint width, depth, total length and movement requirement.
- Exposure to weather, traffic, chemicals or water.
- Colour, finish and any painting requirement.
- Specified backer rod, primer and application accessories.
- Pack quantity, delivery location and required date.
If you are still comparing options, say so when enquiring. This lets the team distinguish a request for product information from an order against an approved specification.
Common questions
Is PU sealant always better than silicone?
No. The application and exact product matter more than a general ranking. Compare substrates, joint movement, exposure, finish and the approved specification. A sanitary silicone and a construction PU sealant can serve different purposes.
Can I use Sikasil 117 on concrete or natural stone?
Sika’s data sheet excludes alkaline surfaces such as concrete, plaster and brick, and does not recommend this product for porous materials such as stone, marble and granite. Ask for a suitable product for the specific substrate rather than substituting it. [2]
Can I paint over a PU sealant?
Check the exact grade. Sika allows overpainting of Sikaflex Construction Purform with many conventional coatings after full cure and compatibility trials, while warning that paint can crack over moving joints. This is not a paintability claim for every PU sealant or for FIXX PU SEAL. [3]
Does sanitary silicone replace bathroom waterproofing?
A sealant joint and an under-tile waterproofing layer perform different roles. Follow the complete wet-area detail. Do not leave out the specified waterproofing system because the perimeter joints have been sealed.
What should I send to get a sealant price?
Send the product or approved specification, both substrates, joint width and depth, total length or pack quantity, colour, pack size, site location and required date. Include any specified backer rod or primer.
Need to check a product or get a price?
Send the joint detail, approved product, colour and quantity to Buildcare for availability, documents and a quotation.
Call 02 448 1915 · info@buildcareint.com
Sources & product-specific guidance
This guide supports product enquiries. Check current manufacturer documents and the approved joint design before final selection. Product-specific statements should not be transferred to other grades.
- Buildcare: FIXX PU SEAL catalogue listing.
- Sika GCC: Sikasil 117 Sanitary and its product data sheet.
- Sika GCC: Sikaflex Construction Purform, including painting and application requirements.
References checked on 20 October 2026.