Why Lime Asks Different Things of Your Tools

Lime plaster is not gypsum skim. It sets by carbonation rather than chemical hydration, it stays softer and more porous, and it moves with the building as moisture and temperature change. That has two practical consequences for your tool kit. First, lime needs to be worked with tools that compress and consolidate without sealing the surface. Second, because you will often be matching old work on a listed or historic building, the finish you are chasing is usually a gently textured, slightly irregular one rather than a mirror-smooth modern wall. The tools below are the traditional set that lime plasterers have relied on for centuries, and they remain the right choice today.

Hawks and Mixing Boards

The hawk is the flat board you carry in your left hand, holding a manageable pile of mortar while your right hand works the trowel. A good hawk is typically 350–450 mm square, made from well-seasoned ply or a hardwood board, with a handle set slightly off-centre so it sits level on your palm. Look for a lipped or raised edge on at least two sides; it stops runny lime putty sliding off as you turn. For larger jobs, a spot board on a stand keeps a bigger batch within reach and saves endless trips to the tub.

Mixing is its own small chapter. Lime putty and sharp sand are best combined on a clean board or in a tub with a gauging trowel and a hoe, and a mixing board with a shallow rim makes it far easier to fold the sand through the putty evenly. If you are knocking up coarse stuff with hair, mix it stiff enough that it holds a ridge on the hawk without slumping.

Trowels: Laying On, Not Polishing

The laying trowel is the workhorse. For lime, a 280–300 mm steel trowel with a little flex in the blade is ideal: stiff enough to push mortar into a wall, springy enough not to fight you on a soft substrate. Keep the blade clean and slightly damp, because a rusty or dry trowel drags at lime and pulls the coat about.

• Laying trowel — for applying scratch, float and finish coats.
• Pointing trowel — 100–150 mm, for filling cracks, repairing edges and working mortar into joints in brick and stone.
• Gauging trowel — a smaller, round-nosed trowel for measuring and mixing small batches of putty, sand and any additives.
• Bucket trowel — for scooping plaster from tub to hawk without mucking up the rim.

The golden rule with lime is restraint. Press the mortar in, then leave it alone. Over-trowelling with a steel blade draws the lime to the surface, closes the pores and leaves you with a hard, brittle skin that will craze and shell off. The trowel lays on; the float does the rest.

Floats: Where the Finish Is Really Made

If you buy one tool after the trowel, make it a wooden float. Wood compresses lime gently, closes the surface just enough and leaves the subtle texture that reads as traditionally plastered.

• Wood float — the staple for consolidating float coats and rubbing up. Keep it dry-ish and free of dried mortar.
• Devil float (nail float) — a wood float with nails or screws driven through, used to scratch the surface of a scratch or float coat so the next layer keys in. Make your own: 25 mm nails, driven through and cut off, protruding about 5 mm.
• Sponge float — for closing and smoothing a finish coat, and excellent when working with fine stuff. Damp, not wet.
• Plastic or Dutch float — useful on very soft or friable backgrounds, and gentler on delicate historic surfaces than steel.

Work in circular passes first, then straight ones, and never float a coat that has already begun to set. You will only pull it apart.

Brushes: Damping, Cleaning and Finishing

Lime needs water, but it needs it carefully. A wide water brush or soft bristle brush is used to damp down a wall before a coat goes on, so the suction does not steal the moisture the lime needs to cure. The same brush, flicked or sprayed onto the surface, helps you close a sponged finish.

A churn brush or stiff bristle brush, on the other hand, is for cleaning: sweeping dust and loose material from old walls, scrubbing back dried mortar, and texturing a finish if a coarser look is wanted. Keep one brush for water and one for cleaning, and never use the cleaning brush on fresh work.

Pulling Your Kit Together

A sensible starter set for lime repair work is: a 400 mm hawk, a 300 mm laying trowel, a pointing trowel, a gauging trowel, a wood float, a sponge float, a devil float you have made yourself, a water brush and a churn brush. Add a clean bucket, a mixing board, a hoe and a spray bottle, and you can tackle most patch repairs and small areas of re-plastering.

Look after them. Wash lime off steel tools at the end of every session, as lime is alkaline and will pit a blade if left. Wooden floats and hawks should be wiped, not soaked, and allowed to dry slowly so they do not split. A trowel worn smooth by years of use is a pleasure; one left crusted over is a liability. Treat your tools well and they will pay you back on every wall you touch.