Lath and plaster is old school; you won’t find it in newer homes. It was used until around the middle of the 20th century, when it was superseded by plasterboard. So, if you own an older home, there’s a distinct possibility that your property will have lath and plaster walls and ceilings.
Unlike modern methods of plastering walls, lath and plaster takes a different direction. This is more time-consuming to repair for DIYers, and for larger fixes, you’ll need a specialist. In this guide, we look at how they were constructed and how they can be repaired if they are, as many will be, showing signs of wear and tear.
Matt Clare is the owner of Gower Plastering Services, a plastering contractor with over 15 years' experience in all aspects of internal and external plastering across South Wales.
What is lath and plaster?
Matt Clare, owner of Gower Plastering Services, offers a quick overview of lath and plaster, "Lath and plaster is a traditional wall and ceiling construction method common in British buildings built before the 1950s.” He adds, “It consists of narrow timber strips (laths) fixed horizontally across timber studs or joists, onto which multiple layers of plaster are applied to form the finished surface."
Article continues belowThree coats of plaster were given. The first was a 6mm thick render layer designed to stick to the lath and fill the gaps between each one. Next was a 'floating' layer, again of around 6mm thick. This provided a smoother surface for the final 'setting' layer to be applied. The setting layer was usually 3mm thick and provided a smooth surface for decoration.
Shop these to help fix or repair lath and plaster
This lime-based plaster is breathable and lightweight and is suitable for use with traditional plasters and substrates like lath and plaster.
This metal mesh provides reliable, durable reinforcement for larger areas requiring repair and replastering. Simply cut to size, nail into place, and add new plaster.
This elongated trowel is perfect for finishing the last coat of plaster. The blade is made out of a flexible, 0.3 mm thick stainless steel and has rounder corners for a smooth finish.
What type of plaster was used for lath and plaster?
“Typically, lime-based plaster was used for lath and plaster,” shares Mark Irving, building specialist at Build & Plumb. He continues, “Lime-based plaster was made by mixing lime putty with sand, usually at a 1:3 ratio. Some lime plasters also previously included animal hair, which acted as reinforcement to reduce cracking and improve the plaster's strength.”
To finish the third layer was commonly made up of lime putty and a fine sand in a 3:1 mixture – or sometimes just lime putty.
Later on, it became common to add gypsum or, sometimes, cement to speed up the setting time between layers. These mixtures usually use a 1:1:6 combination of gypsum or cement, lime putty and sharp sand for the initial two coats, then equal parts of lime putty and gypsum for the final layer.
Mark has over 20 years of experience in the building sector, leading to a wealth of knowledge surrounding building and renovating that he enjoys sharing with others who are looking to complete their own building projects.
How to repair lath and plaster walls
Of course, if your walls are still in good condition, there is no need to touch them. Simply check them regularly and keep an eye on any new cracks that appear. If you do see any minor issues, Clare says, "For minor surface cracks and areas of delamination where the laths are still intact and sound, a skim of suitable lime plaster is usually the most straightforward repair. I'd recommend a fine lime putty plaster or a pre-mixed lime finishing plaster, applied in thin coats and worked back to match the original surface level.”
If tackling the job yourself hew offers some must-follow advice: “It's important to dampen the existing plaster before applying - lime doesn't bond well to a dry surface.”
For larger areas of damage, a different approach is needed, shares Clare, “For larger areas of damage or where the laths themselves have broken or detached, those sections will need to be cut back to a clean edge before any new plaster can be applied."
There are several ways in which to repair lath and plaster – using modern or traditional techniques, or by learning how to patch plaster.
Irving adds a note of caution, "I would always avoid using gypsum based plaster for any repairs, as it can trap moisture and lead to further issues down the line." He adds, "Lime plaster is specifically designed for breathable walls, so it is important to ensure that breathability remains when dealing with fixtures.”
Modern methods for repairing lath and plaster
The two most commonly used modern methods mean cutting back the laths and plaster to the nearest studs either side of the damage. You can then cover the hole in one of two ways.
The first way (and the one which is usually preferred by conservation and heritage groups) is to galvanised mesh called Expanded Metal Lathing (EML). This mesh is nailed between studs before being plastered over. This method results in an aesthetically pleasing uneven finish similar to that of lath and plaster walls.
The second method is to use sheet plasterboard to fill the hole once the damaged area has been cut back, fixing it in place with plasterboard nails.
In both cases, using a lime-based plaster, similar in texture and density to the original is always advisable.
Repairing lath and plaster the traditional way
There are companies that specialise in lath and plaster repair, and if you want to remain true to the original construction of your home, it is well worth considering this route.
Clare says, "For a sympathetic repair that preserves the original character - particularly important in period properties – the traditional approach is to replace any broken laths like for like using thin timber strips, then re-plaster in three coats using a lime-based mix."
He says, "Start with a scratch coat first with hair reinforcement, then a float coat, then a lime putty finishing coat."
However, this isn't a job for the average DIYer, continues Clare, "It will require the right skills." He adds, "It takes longer and requires more skill, but the result sits seamlessly alongside the existing plaster and allows the wall to breathe in the same way the original construction intended. In older or listed buildings, this is nearly always the better option."
After repairing any old lath and plaster you'll probably want to decorate. Check our guide to painting over lime plaster to ensure you do it right. For inspiration, check out the latest paint trends and our rustic living room ideas.
