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Wooden laths: how should we use them, and should we even be using them at all? Laths were widely used until the mid 20th century, but they have now been largely replaced by modern solutions such as plasterboard. However, many owners of period properties will encounter laths when renovating or restoring.
In their most basic form, laths (or lathes) are traditionally timber strips attached to a stud frame. This studwork frame is usually comprised of panels. These are fixed onto the floor and ceiling. The wooden strips, or laths, have gaps between them that allow plaster to settle behind and bond more strongly to the lath itself. Once the plaster has oozed through the laths and adhered to the backside of the lath, this forms a 'key'.
Lath and plaster ultimately derives from an earlier technique, wattle and daub, which has been in use for at least 6,000 years. From around the 18th century, lime plaster was used on brick, stone, or laths. Metal laths can also be used. These date from around the late 19th century, and they have increased strength and rigidity in comparison to wood. Conversely, the angular edges of metal laths mean that working with non-hydraulic lime plasters is more difficult. Both metal and wooden laths serve a similar function.
Before you begin work on your laths, ensure that they are clean. This includes being free from any greasy substances, dirt, or plant matter. Similarly, if the laths are damaged in any way, they should be replaced prior to plastering. At Best of Lime, our Douglas Fir laths are sawn 'green', so have a raised grain texture that also acts as a key for the plaster. Before applying a scratch coat to the laths, spray them with water.
At Best of Lime, we find the easiest way to illustrate the correct spacing of wooden laths is through 'Goldilocks'. Use your little finger as good guide - the gap between the laths should be around 1/4 of an inch, or the width of the average little finger. The first set of photos show laths that are too close, and the plaster won't push through to form the key. However, too widely spaced, and the key is likely to fall off the back. The final image shows laths that have been spaced just right!
The following photos show how lime plaster on laths should look from behind.
There are two key benefits to wooden laths: their sound-proofing properties, and their role in delaying the spread of fires. In comparison to modern plasterboard, lime plaster and laths play a role in absorbing sounds, particularly low frequencies. Due to the non-uniform keys, echoes can also be deflected. It is also proven that lath and plaster can limit the spread of fires, as a result of the density of lath and plaster construction limiting the oxygen supply needed to fuel the fire.
The question is not how we use timber (or metal) laths, but should we be using them at all? At Best of Lime, we develop and manufacture low carbon lime plasters for use internally and externally. We like to think that the longevity of our plaster is measured in generations. The use of timber lath ticks the conservation box, but the thermal efficiency of lath as a background is poor, so from an energy conservation perspective we should be looking at alternatives.
Do you have questions about using our products with wooden laths? Get in touch with Best of Lime today.
"Thanks,, I'm fully converted now 👍 won't be using lime putty for a while that's for sure, much better finish compared to what I've been using for the past 8 years or so, and peace of mind that it doesn't crack, lighter, less mess, no binding in needed.
I was also pleasantly surprised about how far it goes per bag 👍 definitely a game changer for me, will be back next week sometime for some more."
"Used their product Patchcote on my timber framed house for some repairs.
Really easy to mix, apply and finish.
Left-over product was just as pliable 3 days later, it can be left sealed inside the container supplied, after mixing, for up to a year!
Best product I’ve worked with!!"
"Limecote and Warmcote are ideal products for use on timber framed buildings and low strength substrates with their excellent flexibility, bond, and light weight compared to sanded plasters. Being dry bagged makes it easy to transport and store, with the added advantage of being able to adjust the mix to suit thin or very thick coats without compromising the product, or the quality of the finished work."
