Intermediate

Mortar Types Explained: Adhesive, Pointing, Anchor & More

17/04/2026 13 min read

On your self-build site you’ll encounter around fifteen different mortars: bedding mortar for concrete blocks, tile adhesive for tiling, anchor mortar for fixing frames, plasterboard adhesive (MAP) for drylining, refractory mortar for the fireplace… Each has a precise formulation for a precise use. Using an anchor mortar instead of a tile adhesive is a recipe for disaster (tiles coming off, cracked walls). This guide gives you the right mortar for each task, with mix ratios, set times and prices.

Mortar vs concrete: the essential difference

Before anything else, let’s clear up the most common confusion:

Criterion	Mortar	Concrete
Composition	Cement + sand + water (+ admixtures)	Cement + sand + aggregate + water
Max aggregate	0/4 mm (sand only)	4/22 mm (gravel)
Use	Bedding, render, anchoring	Load-bearing structure, mass
Typical strength	5–15 MPa	20–50 MPa
Application	Trowel, float, hawk	Skip, pump, vibration

Mortar is a binder: it bonds, points, anchors. Concrete is a structural mass: it carries loads. To understand concrete strength classes, see our guide on concrete resistance classes.

The 6 main mortar families in self-build

1. Bedding mortar (cement or bastard mortar)

This is the mortar you use to lay your concrete blocks, bricks and stones. It bonds the elements together and transfers vertical loads.

Typical mix for 1 m³:

Pure cement mortar: 350 kg CEM II 32.5 cement + 1 m³ 0/4 sand + 175 L water
Bastard mortar (recommended): 200 kg cement + 200 kg NHL 3.5 hydraulic lime + 1 m³ sand + 200 L water

Mixer batch (130 L drum): 1 × 35 kg bag cement + 1 × 35 kg bag lime + 7 buckets sand + 30 L water.

Property	Value
Strength at 28 days	8–12 MPa
Set time (initial → final)	1 h → 6 h
Working open time	1 h 30 max after mixing
Cost per m² of wall laid	£2–4

Tip — Bastard mortar (half cement, half lime) is more workable, easier to spread and limits joint cracking. It is the professional choice for blockwork and general masonry. Pure cement mortar (without lime) is reserved for below-ground or heavily stressed applications.

2. Tile adhesive (tiles and brick slips)

Tile adhesive is a cement mortar modified with polymers (resins) to bond to smooth substrates and accommodate dimensional movement of tiles.

Classification	Typical use	Common brands
C1	Standard internal dry-area tiling	Webercol Flex, Mapei Adesilex
C2	External tiling, large format, underfloor heating	Weber.col HP, Mapei Keraflex
C2 ET S1	Flexible substrates, OSB, tile-on-tile	Weber.col Flex, PCI Nanolight
C2 ET S2	Very large format, extreme exposure	Mapei Ultraflex S2

Codes: C = cementitious adhesive, F = fast set, E = extended open time, T = non-slip (vertical), S1/S2 = deformability (movement absorbed).

Mix: 25 kg powder + 6 to 7 L water (always read the bag — varies by brand).

Warning — For bathroom, wet-room or pool tiling, class C2 is mandatory. Class C1 does not hold long-term in wet conditions. For external terrace tiling, always use C2 ET (outdoor, variable temperatures).

3. Tile grout / pointing mortar

Once tiles are laid, you fill the gaps with grout. There are two families:

Type	Use	Joint width
Cement grout CG1	Internal dry-area joints	2–15 mm
Waterproof cement grout CG2	Bathroom, kitchen, floor	2–15 mm
Epoxy grout RG	Worktops, pools, food industry	1–12 mm
Silicone sealant	Internal angles, sanitary/tile junctions	3–10 mm

Cement grout mix: 5 kg powder + 1.3 L water — enough for ~3 m² of 30×30 tiles with 3 mm joints.

Best practice — Tile joints are the first to get dirty and go black. For the bathroom, choose a mould-resistant waterproof grout (e.g. Weber.joint hydrofuge, Mapei Ultracolor Plus) and apply a pore sealer once dry. You’ll gain 5 years before the joints need replacing.

4. Anchor mortar (and chemical anchor)

To fix a steel post, bed a window sill, or secure a stair handrail, you use either a fast-set anchor mortar (to keep the site moving) or a chemical anchor (for heavy loads in fragile substrates).

Type	Set time	Admissible load	Use
Express anchor mortar (Sika MonoTop, Sikadur, Lankoplomb)	30 min	Medium	Sills, thresholds, decorative fixing
R4 repair/anchor concrete	24 h	High	Posts, guardrails, roof structure on concrete
Resin chemical anchor (Spit Maxima, Hilti HIT)	30 min – 2 h	Very high	Ties, heavy fixings in hollow masonry

Warning — Fixing a balcony or mezzanine guardrail is subject to a mandatory 60 daN/m linear resistance requirement (NF P01-012 (FR) / BS 6180 (UK)). Standard anchor mortar is not sufficient. You must use a certified chemical anchor (ETA approval for structural use) or R4 concrete cast at the post base.

5. Plasterboard adhesive (MAP)

MAP (Mortier Adhésif pour Plaques) is a plasterboard adhesive specifically formulated for bonding plasterboard and insulated composite panels (EPS + plasterboard, mineral wool + plasterboard). It is the alternative to the metal rail and stud system for straight walls.

Property	Value
Standard bag	25 kg
Coverage	~3 m² of bonded plasterboard
Open time	30 minutes
Price per bag	€8–12
Brands	Weber.MAP, Knauf MP75, Placo Pregylis

Method: apply dabs of MAP the size of a fist every 30–40 cm (3 vertical lines per board), press and straighten with a straight edge. Much faster than metal stud framing — but reserve this technique for truly flat walls (shuttered concrete, regular stonework).

Tip — For bonding plasterboard to concrete block walls, MAP saves around 50 % of the time compared with metal stud installation. However, on irregular walls (old house, rough stone), keep the rail/stud system: MAP cannot compensate for more than 20 mm of deviation.

6. Specialist mortars (refractory, waterproof, fibre-reinforced)

For specific applications there are technical mortars formulated to order:

Mortar	Use	Price per 25 kg bag
Refractory	Fireplace firebox, pizza oven, barbecue	€15–25
Bulk waterproof	Cellar tanking, pits, pools	€20–35
Fibre-reinforced (polypropylene)	Screed, levelling in trafficked areas	€10–18
Lightweight (perlite/vermiculite)	Light screed on old timber floor	€15–25
R4 repair	Concrete repair, structural anchoring	€25–50
Injection grout	Filling voids/structural cracks	€30–60

Summary table: which mortar for which use?

Question

Use	Recommended mortar	Mix / class
Lay concrete blocks, bricks	Bastard mortar	200 kg cement + 200 kg lime + 1 m³ sand
Lay facing stonework	Pure NHL 3.5 lime mortar	350 kg lime + 1 m³ sand
Bond internal floor tiles	Tile adhesive C1	25 kg + 6 L water
Bond bathroom tiles	Tile adhesive C2 ET	25 kg + 6.5 L water
Bond external tiles	Tile adhesive C2 ET S1	25 kg + 6.5 L water
Grout kitchen/bathroom tiles	Waterproof grout CG2	5 kg + 1.3 L water
Grout pool, worktop	Epoxy grout RG	See product data sheet
Bond plasterboard to shuttered wall	MAP	Dabs every 30–40 cm
Bed window sill	Express anchor mortar	25 kg + 4–5 L water
Fix guardrail post	R4 concrete or chemical anchor	Cast into pocket
Build fireplace firebox	Refractory mortar	25 kg + 5–6 L water
Tank a damp cellar	Bulk waterproof mortar	25 kg + 4 L water
Repair a structural crack	R4 mortar	See product data sheet
Pour a screed	Screed mortar (or liquid screed)	350 kg cement + 1 m³ sand

Reading a bagged mortar label: decoding the codes

When you buy a bag of mortar, the label carries standardised codes (standard EN 998 for render/bedding mortars, EN 12004 for tile adhesives). Here are the main ones to know:

Render and bedding mortars (EN 998)

GP: General Purpose — general-purpose render mortar
LW: Lightweight — lightweight mortar
CR: Coloured Render — coloured render
R: Renovation — renovation mortar
T: Thermal — insulating mortar
CS I to IV: compressive strength class (CS I = ≥ 0.4 MPa; CS IV = ≥ 6 MPa)
W0/W1/W2: water absorption (W2 = mortar for highly exposed locations)

Tile adhesives (EN 12004)

C1 / C2: bond strength after immersion (C2 ≥ 1 N/mm²)
F: fast set (hardened within 6 h)
T: thixotropic — non-slip on vertical surfaces
E: extended open time (≥ 30 min)
S1 / S2: deformability (S2 ≥ 5 mm deflection without failure)

A tile adhesive for large-format external use would typically be marked C2 TE S1: enhanced bond, non-slip, long open time, deformable.

Mixing mortar: the golden rules

The water/powder ratio is CRITICAL

As with concrete, too much water = loss of strength. For a bag of tile adhesive or grout, the manufacturer gives a precise water volume (e.g. 6.5 L ± 0.2 L per 25 kg). Follow it to the letter.

Water/powder ratio	Consequence
Under-watered	Mortar stiff, hard to spread, sets too fast
Correct	Optimum workability, maximum strength
Over-watered	Mortar flows, excessive shrinkage, cracks, 30 % strength loss

The mixing sequence

Pour the water first into the drum or mixing tub
Add half the powder gradually while mixing
Mix for 1 minute
Add the remaining powder progressively
Mix for 2 to 3 minutes until fully homogeneous
Leave to slake for 5 minutes (maturation)
Briefly re-mix and use

Warning — Never use mortar that has started to set. If your mortar hardens before you have finished laying, discard it and make a smaller batch. Adding water to “soften” it is the fatal mistake: the mortar loses 50 to 70 % of its final strength.

Weather and temperature

Condition	Action
T° < +5 °C	Do not lay mortar (or use a winter mortar with antifreeze admixture)
T° > +30 °C	Mist the substrate, mix small batches, work in the shade
Heavy rain	Stop work (fresh mortar is washed out)
Strong wind + sun	Mist repeatedly to slow drying

Common (and costly) mistakes

1. Confusing tile adhesive with anchor mortar. Tile adhesive cannot carry structural loads. Anchoring a post with tile adhesive is virtually guaranteed to end in collapse.

2. Mixing two brands of tile adhesive. Formulations differ. You end up with a blend of unpredictable performance.

3. Tiling without combing the adhesive. The regular ridges from a notched trowel are essential for bond and air evacuation. Without combing, tiles sound hollow and come loose.

4. Using lime mortar below ground. Lime dislikes rising damp. Use waterproof cement mortar for anything in permanent contact with the ground.

5. Storing opened bags. A part-used bag absorbs atmospheric moisture and sets within 2–3 weeks. Buy just enough or reseal tightly (polythene bag + wide tape).

6. Not checking the use-by date. Mortars have a best-before of 6 to 12 months. Beyond that, the chemistry degrades and bond strength falls. Check the date printed on the bag before buying — especially at DIY stores (Wickes, B&Q) where stock can sit for months.

Tip

How much to buy: quick calculation rules

Use	Standard quantity
200 mm concrete block bedding	~25 kg ready-mix mortar per m² of wall
30×30 floor tiles	~4 kg tile adhesive per m² (8 mm notch)
20×20 wall tiles	~3 kg tile adhesive per m² (6 mm notch)
Grouting 30×30 (3 mm joint)	~0.5 kg grout per m²
15 mm cement render	~25 kg per m²
MAP plasterboard bonding	~5 kg per m² (3 lines of dabs)

Always add 10 to 15 % waste allowance (residual mix, off-cuts, top-ups). Unused cement and lime can be stored dry for a maximum of 3 months.

Where to buy: builders’ merchants vs DIY stores

Supplier	Advantages	Disadvantages
Builder’s merchant (Travis Perkins, Jewson, Buildbase)	Trade pricing, pallet delivery, technical advice	Trade account sometimes required (but not always)
DIY store (Wickes, B&Q, Screwfix)	Immediate availability, clear labelling	Prices 15–30 % higher, stock sometimes old
Tile specialist (Topps Tiles, CTD)	Wide C2/epoxy range	Higher retail prices
Online (ManoMano, builder merchant websites)	Easy price comparison	Pallet delivery charges = €80–150

Tip — For orders of more than 10 bags, go directly to a builder’s merchant. Even without a trade account, you can request a quote by email: most accept private self-builders and prices are 15 to 25 % cheaper than DIY stores. See also our article on essential tools for self-build for a supplier list.