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Porcelain paving joint mortar for 20–30 mm slabs

Updated: October 2026

Porcelain paving joint mortar is a narrower question than which cement is cheapest. You are jointing slabs about 20–30 mm thick, often with a gap of only a few millimetres, and the unit barely absorbs water. A bricklaying bag that never mentions porcelain is the wrong default. Every pack is on the [paving joint mortar comparison](/hub/flooring-tools-and-accessories/paving-joint-mortar). How the families split is the [buying guide](/hub/flooring-tools-and-accessories/paving-joint-mortar/sub/paving-joint-mortar-buying-guide). The lead listing for ordinary flags is [best paving joint mortar](/hub/flooring-tools-and-accessories/paving-joint-mortar/sub/paving-joint-mortar-best). The damp method for concrete flags is [how to point patio slabs](/hub/flooring-tools-and-accessories/paving-joint-mortar/sub/paving-joint-mortar-how-to-point), and it is not the method to copy here.

Porcelain paving joint mortar is a narrower question than which cement is cheapest. You are jointing slabs about 20–30 mm thick, often with a gap of only a few millimetres, and the unit barely absorbs water.

Our top picks

Bostik Bostik All Weather jointing compound, 15 kg

Best overall

Bostik Bostik All Weather jointing compound, 15 kg
8.8/10about £39.35
View offer
Joint-It Joint-it Simple, 12.5 kg dark grey

Alternative

Joint-It Joint-it Simple, 12.5 kg dark grey
6.8/10about £155.58
View offer
Dansand Dansand Kerama patio grout, 15 kg

Alternative

Dansand Dansand Kerama patio grout, 15 kg
0.0/10about £39.99
View offer
On this page
  1. 1.Why a cement bag is a poor default on porcelain
  2. 2.What Dansand Kerama actually allows
  3. 3.Joint-it and Bostik on ceramic or porcelain
  4. 4.If the joint is narrower than the product

Why a cement bag is a poor default on porcelain

Porcelain and outdoor ceramic at this thickness are dense. Pavestone's notes make the practical point: the slab will not draw water out of a mortar bed the way a concrete flag does, so the back needs a primer if you are laying on mortar. That primer is about the bed, not the joint. Do not point until the slabs are down the way the paving maker describes. Marshalls' porcelain guide sets joints at about 3–5 mm. A slurry grout sold from 2 mm exists in the trade and is not one of the listings kept here. The bag that states 20–30 mm ceramic and porcelain is Dansand Kerama.

What Dansand Kerama actually allows

Kerama is a grey sweep-in bag. There is no mixing step, and a brush is not confirmed in the box. The captured page has no Customer Reviews line, so you are buying the stated window. The maker also says it is not for the joint against a plinth. A 20 mm slab only gives you 20 mm of depth if the joint is open through the edge and not choked with bedding.
Bostik Bostik All Weather jointing compound, 15 kg

Testsieger

Bostik Bostik All Weather jointing compound, 15 kg
8.8/10about £39.35
View offer

Joint-it and Bostik on ceramic or porcelain

The material field on Joint-it Simple says silicone. A 20 mm slab cannot offer the maker's 25 mm of joint depth unless you cut the bedding back. Bostik All Weather lists ceramic tiles and states 5–30 mm. A porcelain joint at the 3–5 mm Marshalls describes is under that 5 mm floor, so the Basalt tub is not a substitute for Kerama on a 3 mm gap.

If the joint is narrower than the product

Forcing a 3 mm grout into a 2 mm line leaves voids. If the paving was laid butted, relay with a joint the product allows, or use a grout that states 2 mm, which this set does not contain. Do not jet-wash the joint on day one to clear a haze. Nothing here claims that Kerama meets BS 7533, or that any joint stays free of weeds for the life of the patio.

Common questions

What joint width does Kerama allow?
The listing says joints up to 10 mm on ceramic and porcelain 20–30 mm thick. The maker sets 3–10 mm and at least 20 mm deep. Use the tighter window. A joint under 3 mm, including a butt near 2 mm, is outside it. The listing claims 5–10 m² per 15 kg bag and has no UK star line on the captured page.
Can you use Kerama on a mortar bed?
Kerama is specified for an unbound, permeable sand-and-gravel base. Dansand's tips say a bound base stops the binder hardening properly. Porcelain on a solid mortar bed is the case the bag is not written for, even at 20 mm thick. Bed the slabs as the paving maker requires, then choose a joint product that allows that bed.
Is a 2 mm joint close enough?
No. Two millimetres is below Kerama's 3 mm floor, Bostik's 5 mm floor and the 3 mm the Joint-it maker asks for. A tight butt joint needs a grout that states that width. This set does not include that slurry. Leaving the gap short of the wrong product is a better result than packing in a grout that cannot enter it.
Does Joint-it Simple state a porcelain joint size on amazon.co.uk?
It names porcelain and does not print a width. The price is £155.58 and the file shows 3.4 from 9 reviews, with the saved texts marked United States. The maker's minimum of at least 3 mm by 25 mm on a permeable base is the maker's figure, not a line on that listing. A 20 mm slab cannot supply 25 mm of depth unless the bed is cut back.
Will Bostik All Weather fill a 3 mm porcelain joint?
The stated minimum is 5 mm, with at least 25 mm depth on the UK sheet. A 3 mm porcelain joint is under 5 mm, so this tub is not the stand-in for Kerama. Ceramic tiles on the listing help a wider ceramic joint and do not lower the floor. The amazon bullets also mention driveways, which the same sheet excludes.
Can you point porcelain with Cementone or Laeto?
Neither listing states a porcelain joint width. Cementone is a 10 kg pointing mortar with a large review file on general repairs. Laeto is a 20 kg blend that names bedding and pointing without millimetres. They suit the jobs they state. They are the wrong assumption on 20–30 mm porcelain. The same refusal covers Jetcem, the Home Packs and the SX cartridge.
What weather does Kerama require?
The maker wants dry tiles and temperatures above 5°C, on an unbound draining base. Sweeping into damp porcelain, or into a joint still holding rain, sits outside the cure. The listing's no-mixing line does not mean any weather. Wait for a dry spell, and do not pressure-wash the haze off the same day.

Related pages

Paving joint mortar vs sand and cement

Paving joint mortar

Best paving joint mortar for the job in front of you

Paving joint mortar buying guide: width, depth and base

How to point patio slabs with damp mortar in batches

Sources

Public sources used for this comparison, with the amazon.co.uk listings read on 20 October 2026.

  1. Bostik UK TDS02249, All Weather jointing compound (retrieved 20 October 2026)
  2. Joint-it Simple (retrieved 20 October 2026)
  3. Dansand Kerama (retrieved 20 October 2026)
  4. Marshalls concrete paving installation guidelines (retrieved 20 October 2026)
  5. England: permitted development technical guidance (retrieved 20 October 2026)
  6. BSI on BS 7533-101 (retrieved 20 October 2026)
  7. HSE: cement (retrieved 20 October 2026)
  8. HSE: chasing concrete and raking mortar (retrieved 20 October 2026)