Lath and plaster walls explained

Learn to spot a genuine lath and plaster wall before you drill, screw or hang anything on it.

LP-01Understand what lath and plaster actually isLath and plaster is an old wall-building method used in most UK homes before plasterboard took over from the 1930s onwards. Thin wooden strips called laths are nailed horizontally across the wall studs (the vertical timber frame), with small gaps left between each strip. Wet plaster was pushed into these gaps by hand, forming little ridges called 'keys' on the back that lock the plaster onto the laths once it dries.

LP-02Do the knuckle tap testKnock gently on the wall with your knuckle in a few different spots. Lath and plaster tends to sound hollow and slightly bouncy, because there's an air gap behind the laths. Plasterboard sounds flatter and more even, and solid brick or block sounds dull and dead. The beginner mistake is expecting one clear answer everywhere - the sound changes depending on whether you're tapping over a solid stud or over the gap between laths.

LP-03Press the wall to feel for givePress firmly on the wall with a flat hand, away from any visible crack. If it flexes very slightly and springs back, that's a sign of lath and plaster, because the thin wooden laths behind can move a little. On its own this isn't proof - some plasterboard on wooden battens flexes too - so treat it as one clue, not the answer.

LP-04Check the age and features of the houseHouses built before around 1930 often have lath and plaster walls as standard. Look for clues that suggest original walls: high ceilings, ornate coving, or a picture rail (a thin timber strip running round the room about 30cm below the ceiling), all commonly fitted onto lath and plaster. The mistake beginners make is assuming an old house always has original walls - many have been stripped and replaced with plasterboard during past renovations, so don't rely on age alone.

LP-05Drill a small test hole to confirmChoose a spot low down and out of sight, such as behind where furniture will sit. Before you drill, always expect a cable or pipe could be there and prove otherwise - a cable and pipe detector helps, but it can miss cables that run deep, sit in metal conduit, hide behind metal-backed plasterboard, or simply don't follow the usual safe zones, which is common in older houses with amateur wiring. If you have any doubt at all, isolate the circuit at the consumer unit (the fuse box) before drilling, and turn the water off at the stopcock before cutting into anything that could carry water. Drill slowly with a small bit, no more than about 20mm deep to start, and stop the moment you feel a change in resistance.

LP-06Check what's inside the hole to know you're rightShine a torch into the hole and look closely. Lath and plaster shows thin wooden strips with small dark gaps between them, and you may see little plaster nibs poking through those gaps. Plasterboard behind the top coat looks like flat grey card with a paper-like surface, and solid masonry looks like brick or block with no wood at all. Seeing wooden laths is the clear confirmation - anything else means it isn't lath and plaster.

LP-07Patch the test holeOnce you've confirmed the wall type, fill the small hole with a bit of filler using a flexible filling knife, pressing it in so there are no air gaps. Let it dry fully, then give it a light sand once hard. This stops the hole weakening the plaster further or catching on clothing and furniture later.

1 small tub · Multi-purpose filler

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