How to mix mortar

Based on a thorough demonstration by DIY Doctor. This guide draws on "Mixing sand and cement mortar using a plasticiser admix" from DIY Doctor (diydoctor.org.uk), one of the UK’s longest-running DIY advice sites. Their video covers the plasticiser technique in detail, which is well worth understanding before you start mixing for any pointing or bricklaying job.

1. Choose the right ratio for the job

Mortar isn’t one fixed recipe - the right mix depends on what you’re doing. A general-purpose mix for bricklaying and pointing is four parts building sand to one part cement (4:1). That’s the one you’ll use most of the time.

For repointing exposed or older brickwork, where you need something slightly softer to move with the masonry and not trap moisture, a 5:1 or even 6:1 mix is better. Pointing that’s harder than the brick itself can cause the brick face to spall over time, especially in UK winters. For patio bedding and garden walls you’re back to 4:1 or even 3:1 if it’s exposed to heavy loads.

2. Gather your materials and equipment

You’ll need: building sand (not sharp sand, which is too coarse for mortar), ordinary Portland cement, a bucket or gauge box for measuring, a plasticiser admixture if you’re using one, a mixing board or spot board, a gauging trowel, and water. For anything more than a couple of buckets’ worth, a cement mixer saves a lot of effort.

Wear gloves and safety glasses. Wet cement is strongly alkaline and causes serious skin burns if left in contact - it doesn’t feel dangerous until the damage is already done, which is a good reason not to work barehanded.

3. Measure out the dry ingredients

Use the same container to measure both the sand and cement. Consistency matters - if every batch has the same ratio, the colour and strength will be uniform throughout the job. Mixing by eye produces patches that dry at different rates and crack.

For a 4:1 mix, measure four buckets of building sand and one bucket of cement. Tip them onto the mixing board and spread them out. Work in small batches when mixing by hand; roughly half a barrowful at a time is manageable.

4. Mix the dry ingredients thoroughly first

Turn the dry sand and cement over repeatedly with a spade until the colour looks uniform throughout - no streaks of pure grey cement or pockets of plain sand. This dry mixing stage is worth doing properly: it ensures the cement is evenly distributed before water goes in, and an uneven mix leads to weak spots that crack early.

If you’re using a mixer, load the sand first, then the cement, and let it rotate dry for a minute before adding water. The tumbling action mixes the dry ingredients well.

5. Add a plasticiser if you’re using one

A liquid plasticiser admixture makes mortar smoother and more workable without adding extra water. It gives that almost buttery consistency that professional bricklayers look for. Add it to a small amount of water first, following the manufacturer’s dilution rate - usually a small capful per bucket of water - then introduce this to the mix rather than adding it neat.

Plasticiser also slows the set slightly, giving you more working time. In warm or dry weather that can be a real help. Mind you, in cold weather it’s less relevant since mortar sets slowly anyway.

6. Add water gradually and mix to the right consistency

Make a well in the centre of the dry mix and add a little water. Pull the dry material from the sides into the water and keep turning. Add more water in small amounts - you want to reach a consistency similar to thick peanut butter. It should hold its shape when you slice through it with a trowel, and not slump or run.

Too wet and it’ll squeeze out from under bricks and be weak when it hardens. Too dry and it won’t key properly. Getting the feel for the right consistency takes a batch or two, but once you know it, you know it.

7. Use it before it goes off

Mortar has a working life of roughly one to two hours depending on temperature and the amount of plasticiser used. Once it starts to stiffen, don’t add water and re-temper it - that weakens the mix significantly. If it’s going off in the bucket, scrape it out and start fresh.

Keep any unused dry bags of cement sealed and stored somewhere dry. Building sand can sit outside in a heap, but cement absorbs moisture from the air and will go lumpy in a wet environment. Lumpy cement makes lumpy mortar.

When to call a handyman

Mixing a small batch of mortar for pointing a few joints or bedding a post is well within most people’s capabilities. Where it makes sense to bring Richard in is when there’s a larger area of repointing to do, structural brickwork is involved, or the job also needs cutting, grinding, and making good. Masonry repairs across Sandwich and East Kent are a regular part of the work.