The Best Patio Grout: Choosing, Installing & Maintaining Guide

For most patios, a polymer-modified cementitious jointing mortar (sometimes called a slurry grout or pointing mortar) is the best all-round choice: it bonds well to natural stone and paving slabs, cures hard enough to resist foot traffic and freeze-thaw cycles, and costs roughly £15–£30 per 25 kg bag, enough to joint around 5–8 m² depending on joint width. For porcelain tiles, a flowable jointing compound such as SikaCeram FlowFix is the specialist pick. For block paving or anywhere you need permeable drainage, single-sized kiln-dried aggregate or a resin-stabilised jointing compound is the right call. The 'best' grout is always substrate-specific, and using the wrong type is one of the most common and costly mistakes I see on DIY patios. For a concise, substrate-by-substrate recommendation, see what to use for patio grout.

What this guide covers and who it's for

This guide is written for homeowners tackling a new patio, re-pointing an existing one, or trying to figure out why their joints keep failing. Whether you're laying porcelain tiles, natural slate, flagstone, concrete paving slabs, or block paving, the jointing material you choose, and how you apply it, has a bigger effect on the finished result than most people expect. A poorly jointed patio looks bad within a season; a well-jointed one can last 15–25 years with light maintenance.

I'll walk through every major grout and jointing product category, compare their real-world performance across the key attributes that matter outdoors (strength, flexibility, permeability, freeze-thaw resistance, colour stability), then give substrate-specific recommendations with named products, approximate costs, step-by-step DIY installation notes, and a maintenance schedule. There's also a section covering UK-specific considerations, relevant standards, planning rules around permeable surfaces, and where to source materials.

Patio grout, mortar, and jointing compounds: what's actually different

These three terms get used interchangeably at garden centres and that causes real confusion at the buying stage. Bedding mortar (or bed mortar) is what goes underneath the paving unit to fix it to the sub-base. Jointing mortar or grout is what fills the gaps between paving units once they're laid. For a concise definition and distinctions between jointing mortar and bedding mortar, see what is patio grout. Jointing compound is a broader catch-all that covers everything from brush-in polymeric sand to two-part epoxy systems. BSI's BS 7533 series treats bedding and jointing as entirely separate operations with separate performance specifications, which is the correct way to think about it.

For external paving specifically, BS 7533 sets performance thresholds for proprietary jointing mortars: compressive strength above 40 N/mm², adhesive strength above 1.5 N/mm², and flexural strength above 6 N/mm². Those numbers are worth knowing because they tell you exactly why the cheap bag of brush-in sand from a discount store fails, it simply doesn't achieve those thresholds. When you see a product labelled 'BS 7533 compliant' on the bag, it's a meaningful claim, not just marketing.

The main grout and jointing options available to homeowners

Polymer-modified cementitious jointing mortars (slurry grouts)

These are the workhorses of patio jointing in the UK. Products like Instarmac UltraScape Ultracem and similar proprietary mixes are pre-blended dry powders that you mix with water to form a slurry, which is then worked across the whole paved surface so it flows down into the joints. They cure to a hard, semi-permeable finish with good compressive strength (the better products exceed the BS 7533 thresholds above). They suit natural stone, concrete slabs, and brick paving. Cost: roughly £15–£30 per 25 kg bag. Coverage depends heavily on joint width and depth, but expect around 4–8 m² per bag for standard 10 mm joints.

Flowable porcelain jointing compounds

Products like SikaCeram-621 FlowFix are purpose-designed for rectified porcelain and ceramic paving tiles. They're water-mixed to a self-levelling consistency, poured and squeegeed across the surface, and they cure to a non-permeable finish in around 60 minutes under normal conditions. The manufacturer specifies joint widths of 3–10 mm and joint depths up to approximately 20 mm. They work well on the smooth, low-absorption surface of porcelain where a standard cementitious mortar can struggle to bond and where residue is notoriously difficult to clean off. Cost: approximately £20–£35 per 5 kg pack.

Epoxy grouts

Two-part epoxy systems (the LATICRETE SPECTRALOCK PRO range is the most widely specified in the UK) consist of a resin and a hardener mixed together on site. Once cured, they are extremely dense, absorption figures below 0.05% are quoted by LATICRETE, highly resistant to staining, chemicals, and efflorescence, and they don't require sealing. The downsides are cost (roughly £60–£120 for a unit covering 8–12 m² at narrow joint widths), a shorter working window (particularly in warm weather), and the need for careful, timely haze removal because cured epoxy residue on the tile face is very difficult to shift. These are genuinely worth it for high-traffic or high-stain-risk installations, or for food-prep and pool-surround environments.

Polymeric sand (brush-in jointing sand)

Polymeric sand is a fine aggregate pre-blended with a polymer binder that activates when wetted. You brush it dry into the joints, compact it, then activate with a light spray of water and it sets semi-rigid. It's widely available at DIY sheds and is suited to block paving and flag paving with wide joints (typically 8–20 mm). The catch: product quality varies enormously. Many cheap one-part versions sold in garden centres have limited freeze-thaw durability and cohesive strength well below BS 7533 thresholds. Buy named specification-grade products and follow the TDS precisely, undermixing or over-watering both cause failures. Cost: roughly £8–£18 per 20 kg bag.

Resin-stabilised and resin-bound jointing

Products in this category (Resiblock is the best-known UK trade name) use a liquid resin binder applied to existing jointing sand or mixed into aggregate to consolidate joints. Resiblock's block-paving sealers bind the jointing sand, reduce permeability to hydrocarbons and water penetration, and the manufacturer quotes service lives up to around 5 years for certain products. They're particularly common on driveways and heavily trafficked block-paved areas, but some homeowners use them on patio areas where oil staining from outdoor cooking is a concern. Note that sealing joints this way effectively eliminates permeability, relevant if you're in a front-garden SuDS zone.

Mortar pointing (traditional sand-and-cement)

Traditional pointing with a sand-and-cement mix (typically 3:1 or 4:1 sharp sand to Portland cement) is still used for natural stone and brick, particularly on heritage or conservation projects where a traditional aesthetic is required. It's low cost in materials (£5–£10 to mix a batch) but labour-intensive, requires good skill to finish neatly, and a poorly mixed batch can crack, stain, or blow (spall) under freeze-thaw cycles. For most residential patio projects, a proprietary polymer-modified mortar is more reliable and not much more expensive.

Flexible sealant and expansion-joint products

Silicone-based flexible sealants are not structural jointing products, they're used in movement/expansion joints at perimeter edges, transitions between surfaces, or against fixed structures like walls and steps. They accommodate thermal movement that rigid grouts cannot. For a patio, plan movement joints at a maximum 3–4 m spacing and wherever the paving meets a fixed structure. Cost is low (£5–£15 per cartridge), but the right colour match to your jointing mortar matters aesthetically.

How to compare patio grout options: the attributes that actually matter

A few of these attributes deserve more explanation. Permeability is increasingly important in UK planning contexts: if your patio is in a front garden or includes a driveway element, local council SuDS guidance (informed by CIRIA's SuDS Manual C753) may require a permeable surface. Local authority SuDS operation and maintenance guidance (blank" rel="noopener noreferrer">Technical Note referencing CIRIA C753 operation & maintenance (example local authority drainage document)) cites CIRIA C753 for permeable paving maintenance tasks, annual removal of debris/leaf fall, occasional flushing of silt, mechanical sweeping and periodic re‑top‑up of jointing aggregate (typically every 3–5 years depending on clogging signs). Using an impermeable jointing product across the full surface technically makes that surface non-permeable, regardless of how permeable the paving units themselves are. If SuDS compliance matters for your project, single-sized aggregate joints (2–6.3 mm or 6 mm nominal) are the CIRIA-recommended approach, and avoid fine kiln-dried sand, which migrates into the sub-base and clogs the drainage structure. The SuDS Manual (C753), CIRIA recommends single-sized aggregates (typically 2–6.3 mm or 6 mm nominal), warns against fine kiln‑dried sand that clogs sub‑bases, and sets maintenance regimes of annual sweeping with joint top‑ups on a multi‑year cycle The SuDS Manual (C753) — CIRIA.

Freeze-thaw durability deserves equal weight if you're in a colder part of the UK or anywhere that sees regular sub-zero winters. The failure mechanism is straightforward: water trapped in a porous joint expands on freezing and forces the joint apart. Specification-grade proprietary mortars are tested for this; many cheap brush-in products are not. Never apply any jointing product below approximately +3 °C, and allow the correct cure time before the first frost hits. I've seen perfectly laid patios ruined by joints done in October that weren't given the full 48–72 hour cure before a cold snap.

Choosing grout for slate patios

Slate is one of the trickier substrates to joint correctly because of two competing problems: its surface can stain easily from cement residue, and its natural cleft face means surface texture varies dramatically between pieces, making consistent joint finishing difficult. The priority is a jointing product that flows into the joint under light working rather than one that needs forceful tooling, which risks scratching the slate face.

For most slate patios, a polymer-modified cementitious slurry mortar applied using the slurry grouting technique (described in the installation section below) is the most reliable choice. Pre-wet the slate surface before applying the slurry, this slows absorption, prevents the cement from bonding to the face, and makes the subsequent clean-up far easier. Use a colour-matched jointing mortar (grey or charcoal tones suit most slate) and don't attempt to joint slate with a standard unsanded wall grout or a flowable porcelain compound: neither has the body and strength for an outdoor joint.

For very porous or textured slate (particularly rougher Indian or Brazilian varieties), some professionals prefer a hand-pointed approach with a stiffer mortar mix rather than a slurry, precisely because porous slate can absorb slurry staining aggressively. In that case, use a pointing trowel or grout bag to place mortar directly into the joint rather than spreading it across the whole surface. Either way, a penetrating stone sealer applied to the slate before jointing acts as an excellent insurance policy against surface staining. You'll find more substrate-specific detail in the related guide on the best grout for slate patios.

Choosing grout for flagstone and irregular natural stone

Flagstone patios, whether you're using sandstone, limestone, granite setts, or reclaimed York stone, present a wide range of joint widths and depths, often irregular, which is part of the aesthetic appeal but a genuine jointing challenge. Joint widths on an informal flagstone layout might vary from 8 mm to 30 mm or more on the same patio, which means you need a product with sufficient body to fill wider joints without shrinking or cracking, while still working into narrower ones.

Polymer-modified cementitious jointing mortar remains the standard recommendation here. For wider joints (15 mm+), look for a product with a coarser aggregate or use a pointing mortar (stiffer consistency) rather than a pourable slurry. BS 7533 guidance reinforces that joint depth is proportional to shear resistance under load: deeper is better, and you want joints filled to within 3–5 mm of the surface rather than half-filled. Limestones and lighter sandstones are particularly vulnerable to cement staining, so pre-wetting and careful timing of the surface clean-up are critical.

Avoid using polymeric sand on flagstone with irregular joints: it performs poorly in joints wider than about 20 mm and the fine aggregate looks out of place against the texture of natural stone. Epoxy grout is overkill for most flagstone applications and the high cost isn't justified unless there's a specific staining risk (poolside, outdoor kitchen area, etc.). For the most naturalistic look on reclaimed stone, a warm grey or buff pointing mortar typically suits better than a stark white or silver-grey finish.

Choosing grout for concrete paving slabs and block paving

Concrete paving slabs and block paving are the most forgiving substrates to joint because the surfaces are generally non-porous and dimensionally consistent, giving you regular, predictable joint widths. The jointing choice here depends heavily on whether permeability matters for your installation.

For a standard patio application where drainage flows to an edge or a lawn, a specification-grade polymeric sand or a polymer-modified cementitious slurry mortar both work well. Polymeric sand is faster to apply on block paving (brush in, compact, wet to activate) and is the more DIY-accessible option. For a more detailed product comparison and recommendations specifically for paving slabs, see the guide on the best patio grout for paving slabs. For driveways or areas subject to vehicle loads, move up to a two-component resin-stabilised product or a specification-grade jointing mortar that meets BS 7533 compressive strength requirements.

If your front garden or driveway falls under UK SuDS requirements (which many do, London borough guidance and CIRIA C753 make this increasingly the default for new and re-laid hardstandings), the joint must remain permeable. Use a single-sized aggregate (6 mm nominal is typical) in the joints rather than fine kiln-dried sand or any polymeric product that cures impermeable. The CIRIA SuDS Manual C753 is explicit that fine sand will clog the sub-base structure over time and destroy infiltration performance.

One product worth mentioning here is Resiblock: it's used primarily as a surface sealer on block paving that also consolidates the existing jointing sand. It's not a primary jointing product but it's useful for stabilising joints that are loose or starting to blow. Manufacturer-quoted service life is up to about 5 years, after which re-application or joint refilling is typically needed.

Choosing grout for porcelain and large-format outdoor tiles

Porcelain paving has become the dominant mid-to-premium patio surface in the UK, and it's also the substrate where I see the most jointing mistakes. The combination of near-zero porosity (which means standard cementitious mortars don't bond well to the tile face and leave haze), very tight specified joint widths (often 3–8 mm), and the large format sizes (600x600 mm, 900x600 mm, and larger) creates a set of requirements that most generic grout products don't meet.

The correct product category for rectified porcelain paving outdoors is either a flowable porcelain jointing compound (SikaCeram-621 FlowFix is the most commonly specified in the UK residential market) or a two-part epoxy grout for higher-specification or commercial installations. SikaCeram FlowFix is water-mixed, applied by squeegee across the surface, flows into joints 3–10 mm wide and up to around 20 mm deep, and reaches a workable surface in roughly 60 minutes. The squeegee application method suits large porcelain surfaces well because it minimises residue left on the tile face.

Marshalls, Brett, and other major UK porcelain paving suppliers explicitly specify compatible jointing systems in their installation guides and typically void any warranty on the paving if off-spec products are used. This is not just legal cover: porcelain's thermal movement characteristics are different from concrete, and a jointing mortar without sufficient flexibility to accommodate that movement will crack within a couple of freeze-thaw cycles. Always check the paving manufacturer's installation guide before selecting a jointing product.

One thing I always tell people buying porcelain paving: budget for the jointing product at the same time as the tiles. It's easy to spend £40–£60 per m² on premium porcelain and then try to save money by using a £10 bag of generic grout from the shed. The saving is false, the joint failure costs far more to put right than the proper product would have cost upfront.

Joint width and depth rules worth knowing

Joint size directly affects which products are suitable and how well the joints perform under load. BS 7533 and trade guidance are consistent on the principle that joint depth provides shear resistance: a shallow joint (less than 15 mm deep) is significantly weaker under edge loading than a properly filled joint at 40–50 mm depth. For paved patios in domestic settings, aim to fill joints to within 3–5 mm of the paving surface, don't leave the bottom two thirds of a joint void.

How to apply patio grout: step-by-step for slurry grouting

Slurry grouting is the standard application method for polymer-modified cementitious jointing mortars and flowable compounds on most patio surfaces. It's faster than hand pointing and gives more consistent joint fill on irregular surfaces. Here's the method I use, based on trade guidance from Paving Expert and manufacturer TDS documentation.

1. Check the weather forecast: do not apply jointing products below +3 °C or in forecast rain within the cure window (typically 24–48 hours). Avoid direct strong sunlight on hot days, which accelerates drying and can cause cracking or surface haze.
2. Clear all joints of loose debris, weeds, and standing water. If re-pointing, rake out old joint material to a minimum depth of 25 mm and brush clean.
3. Pre-wet the entire paving surface thoroughly with a watering can or hose. The paving should be damp but not puddling. This is critical on porous stone: it slows absorption, prevents the slurry bonding to the face, and makes cleanup easier.
4. Mix the jointing mortar per the manufacturer's instructions — typically a powder-to-water ratio by weight, mixed to a thick, lump-free slurry consistency (similar to thin cream). Don't over-water.
5. Pour the slurry onto the surface in manageable sections (2–3 m² at a time). Use a soft brush or squeegee to work it across the paving and into the joints. Chase the slurry back and forth along each joint to ensure it fully penetrates to the base.
6. Allow the slurry to settle for 5–10 minutes, then top up any joints where the mix has dropped below the surface level.
7. At the manufacturer-specified timing (check the TDS — typically 20–45 minutes after application depending on temperature and porosity), begin cleaning. Keep the surface damp while washing: use a soft brush and clean water to remove surface residue. Do not allow the mortar to dry on the surface before washing or it will bond permanently.
8. Repeat the wash with clean water until the surface is clear of haze. Change the wash water frequently — using dirty water redeposits residue.
9. Allow to cure fully before foot traffic (typically 24 hours minimum, 48–72 hours in cold weather). Protect from rain and frost during the cure window.
10. Check joint levels after 24 hours — some products shrink slightly on cure. Top up any low joints with a second application before the surface is returned to full use.

Hand pointing: when to use it and how

Hand pointing (placing mortar directly into joints using a pointing trowel, grout bag, or squeegee bottle) is the better method for porous or heavily textured stone where slurry spreading carries a staining risk, for wide irregular joints that a slurry would be too thin to fill correctly, and for small repair patches where you don't want to disturb a large area of existing jointing. Mix the mortar to a stiffer, pressed-into consistency (not pourable), press firmly into the joint to eliminate voids, and finish flush with or 2–3 mm below the paving surface. Clean the stone face with a damp sponge as you go rather than waiting until you've done the whole area.

Repairing failed or damaged patio grout

Failed jointing, cracked, loose, or missing grout, is one of the most common patio maintenance issues and also one of the easiest to fix if caught early. Left unattended, water gets under the paving units, erodes the bed, and eventually causes the paving to rock, settle unevenly, or crack. The repair process is straightforward but the prep work is 80% of the job.

1. Rake or grind out all loose and failed jointing to a minimum depth of 25 mm (use a plugging chisel, oscillating multi-tool, or angle grinder with a mortar-raking disc). Don't just apply new product over loose old material — it won't bond and will fail again quickly.
2. Brush out the joints thoroughly and vacuum or blow out dust and debris.
3. Check whether any paving units have lifted, rocked, or lost their bedding. If so, re-bed them before re-jointing — grouting over a rocking slab is a waste of time and material.
4. Pre-wet the joints as described in the installation steps above.
5. Apply new jointing mortar using the slurry or hand-pointing method as appropriate for your surface.
6. Cure and protect as for a new installation.

For small localised repairs (a few joints rather than a whole area), hand pointing with a matching mortar colour is the practical approach. The colour match won't be perfect immediately, new mortar is always slightly lighter when fresh, but it weathers in over a season. If you're patching a large area, re-doing the whole patio in one session gives a far more consistent finish than patching in sections over time.

For guidance on more complex repair scenarios, including re-pointing crumbling natural stone joints, dealing with efflorescence, or repairing failed epoxy grout, the dedicated guide on the best patio grout repair covers those situations in more depth. See the dedicated guide on best patio grout repair for detailed step-by-step instructions and product-specific advice. For more detailed product comparisons and buying guidance, see the best outdoor patio grout guide.

Cleaning and maintenance: how often and what to do

Properly jointed patios need relatively little maintenance, but ignoring the joints entirely is what causes the most premature failures. The basic annual routine is straightforward.

• Every autumn: clear leaf fall and organic debris from joints. Decomposing leaf matter generates acids that attack cementitious mortars and stain light-coloured stone. A stiff brush or blower is sufficient — avoid high-pressure jetting directly along joint lines.
• Every autumn: check joint levels visually. Any joints that have dropped, cracked, or lost material should be topped up before winter. A failed joint that lets water in ahead of a freeze-thaw cycle is the most common cause of patio damage.
• Every 2–3 years: consider applying a penetrating sealant to natural stone surfaces and refreshing any sacrificial surface sealer on porous stone or block paving.
• Every 3–5 years for permeable block paving with aggregate joints: mechanical sweeping and joint top-up. CIRIA C753 maintenance tables set this interval for SuDS-compliant permeable surfaces — the actual frequency depends on how quickly the joints accumulate silt and debris.
• As needed: treat weed growth in joints promptly. A good specification-grade jointing mortar or polymeric sand significantly reduces weed establishment, but not completely. Spot-treat with a path weedkiller rather than pulling weeds, which opens up the joint.

Epoxy grout joints have their own cleaning regime. Cured epoxy is highly stain-resistant but it can develop a haze from calcium deposits or atmospheric soiling. Clean with a dilute proprietary epoxy haze remover (LATICRETE publish product-specific instructions), do not use acidic stone cleaners or abrasive pads, which can dull the surface finish.

UK-specific notes: standards, SuDS, and where to buy

In the UK, the BS 7533 series remains the relevant standard framework for external paving and jointing. Products labelled as BS 7533-compliant have been tested against the compressive, adhesive, and flexural strength thresholds described earlier. When specifying or buying jointing products, look for this labelling on the product TDS (Technical Data Sheet), always download the TDS before buying rather than relying on bag descriptions alone.

On permeability and planning: if you're laying or re-laying hardstanding in a front garden in England, planning policy under the Town and Country Planning (General Permitted Development) (England) Order means that impermeable hardstanding over 5 m² typically requires planning permission. Using a permeable jointing system (and the correct sub-base construction) keeps you in permitted development territory and avoids the need for a planning application. The specific requirements vary by borough, London local authority guidance, for example, explicitly addresses jointing aggregate specification in relation to SuDS compliance.

For sourcing: the major UK builder's merchants (Travis Perkins, Jewson, Buildbase) stock a reasonable range of specification jointing mortars including Instarmac UltraScape and Sika products. For specialist porcelain jointing compounds and epoxy grouts, tile and paving specialists (Tile Merchant, Walls and Floors, Stoneer) carry wider ranges with better technical support. For permeable aggregate jointing materials, a good local stone and aggregates merchant will supply single-sized 6 mm limestone or granite aggregate in bulk or bags. Prices fluctuate but a useful rule of thumb: if a jointing product at a general DIY shed seems cheap, it probably doesn't meet the BS 7533 thresholds, buy from a specialist or a merchant that can provide the TDS on request.

For readers in Scotland, Wales, or areas with particularly hard winters, the freeze-thaw notes above are especially relevant. Pay close attention to the temperature application limits on any product TDS and plan your jointing work for spring or early-to-mid autumn rather than late autumn. If you're specifically looking for UK market availability, product comparisons, and supplier recommendations in more detail, the guide on the best patio grout UK covers those angles further.

Quick-reference: recommended products by substrate