Grout and Jointing for Porcelain Patios: Widths, Colours and The Best Products To Use

A great porcelain patio deserves a neat, durable finish that stays looking sharp for years. The secret lies in the joints. In this guide we cover recommended joint widths for 20 mm outdoor porcelain, the main grout and jointing options, how to choose colours that flatter your slabs, and the right way to install. We also flag common mistakes and how to avoid them, so your project ends with crisp lines and confident performance.

Why Jointing Matters With Porcelain

Porcelain’s dense, low-porosity body makes it strong and stain resistant, but it also means joints need to be well planned. Good jointing helps control movement, keeps water out of the bed, prevents edge chipping and ties the whole surface together. For larger areas, you or your installer should also plan movement joints in line with the latest update to BS 5385-3 so the system can handle thermal changes outdoors.

What Joint Width Should You Use?

For rectified 20 mm outdoor porcelain, a typical joint width is 3 to 5 mm. This keeps lines clean, allows for small dimensional tolerances and gives enough space for grout to bond properly. If the tiles are not rectified, allow a little more.

Quick rule of thumb:

• Rectified edges: 3–5 mm
• Non-rectified edges: usually 6 mm or more for a consistent look

Jointing Options For Porcelain: Which Is Best?

Best choice for porcelain patios: ProJoint RapidFlow Brush In Porcelain Grout

RapidFlow is formulated for porcelain, works from 3 mm joints, and is designed for use on a permeable bed. It delivers a neat, stain-free finish and is ideal for pedestrian areas like UK patios and paths. Available in neutral, light grey, mid grey, basalt and black, so you can match or contrast with your slabs.

When RapidFlow is the right call

• Your slabs are 20 mm outdoor porcelain and joints are 3–5 mm
  
• The paving is laid on a full bed and the build-up allows for a permeable bedding mix
  
• You want a quick, clean brush-in application with colours that suit popular porcelain shades 

What About Other Jointing Products?

ProJoint Fusion (brush-in, all-weather)

Great for natural stone and concrete setts or flags around your porcelain area, but it is not positioned as a porcelain product. Use it on adjoining stone paths, edging bands or mixed-material projects, not in porcelain joints.

ProJoint Titan (two-part epoxy, heavy duty)

A high-strength grout for stone or concrete, including vehicular areas up to 10 tonnes. Not suitable for porcelain, keep Titan for driveways or heavy-use stone zones and stick with RapidFlow for porcelain.

Colour: How To Choose A Shade That Flatters Your Slabs

Colour can make or break the finish.

• Match for a seamless, contemporary look. Kandla-style greys suit mid-grey grout, creams benefit from warm light beige.
• Contrast to frame each slab. Dark grout against light tiles sharpens lines and hides day-to-day dust.
• Blend for low maintenance. Mid tones hide minor dirt better than very light colours.
• Lay a few tiles outside and view sample grout colours in daylight before deciding.

Explore our porcelain paving range to help you decide. 

How To Grout and Joint A Porcelain Patio

It may be necessary to  tailor the method to your chosen products, but these steps reflect current best practice:

1. Confirm joint width and movement joints - Mark the layout, joint width and movement joint positions at perimeters and intermediate bays for larger terraces in line with BS 5385-3 guidance. 
2. Prepare clean, dry joints - Clear out spacers and debris. Slightly dampen edges if the product instructions call for it.
3. Mix Correctly - Follow the manufacturer’s water ratios and pot life. For flowable slurries, mix to the stated viscosity. For tile grouts, mix to a creamy paste that can be packed into 3–5 mm joints.
4. Apply:
   • Flowable slurry: pour and squeegee diagonally across joints so they’re fully filled, then begin the wash-off cycle as specified.
   • External tile grout: work diagonally with a rubber float, fully compact each joint.
   • Brush-in: thoroughly wet the surface where required, brush in, compact, top up, and rinse carefully to avoid haze. Trial first and keep the surface clean.
5. Wash Off - Wash in stages using clean water and sponges or washboys, refreshing water often. Do not leave residue to dry.
6. Protect during cure - Keep foot traffic off for the recommended time and shield from rain or direct sun if specified by the product.

Common Mistakes To Avoid

• Joints too tight. Joints under 3 mm are hard to fill and more likely to crack or debond. Stick with 3–5 mm on rectified porcelain. 
• Using an unsuitable brush-in compound. Not all are designed for porcelain or narrow joints. Always check the data sheet. 
• Skipping movement joints on big areas. External porcelain expands and contracts with temperature. Planned movement joints reduce stress. 
• Poor wash-off technique. Leaving a film can spoil the finish. Follow the product’s wash-off time scales.

Recommended Products from KPT Timber

You can find our current jointing range here: KPT Timber Jointing Compounds.

Choose by joint width, application method and colour to match your paving. For porcelain set on a full bed, consider a porcelain-specific flowable grout or an external tile grout approved for outdoor use and 3–5 mm joints.

Within this range you’ll also find a selection of other products such as jointing squeegees, porcelain paving cleaner and paving tile spacers to help you with all of your patio laying tasks.

Conclusion

Neat, durable joints are what make porcelain patios look expertly finished. Select the right joint width, pick a product designed for outdoor porcelain, and follow a careful application and wash-off routine. Explore the range here: Jointing Compounds and don’t forget to browse our Porcelain Paving for matching slabs.