“My dad told me about them!”: Lath and plaster ceilings

17.02.2017
Blog Post
Picture of roofs to illustrate lath and plaster ceilings article

Lath and plaster ceiling
Most pre-1930s houses will have traditional lath and plaster ceilings. Picture courtesy of Malone Associates Ltd

What is lath and plaster?

Laths are thin strips of wood (around 25-38mm wide and 3-8mm thick) spaced around 5mm apart and nailed to the ceiling joists above. Plaster was then applied to the underside of the laths, held in place by being squeezed through the gaps to create a ‘key’ or lug.

The plaster was usually made from lime mixed with sand and cement and included horse hair to act as a natural reinforcement and effective bonding key. The lime improves workability and breathability of the plaster. It was usually applied in two or three layers to a thickness of around 25mm. 

Interested? Browse our "My dad told me about them!" articles

How to check for lath and plaster

In older properties you can check the type of ceiling by looking under the loft insulation, or lifting a bedroom floorboard. If there are lots of small timber laths with creamy lugs of plaster in between, the ceiling is original.

The pros and cons

Plaster is brittle by nature and will crack at its weakest point under vibration or through water ingress. This weak point is usually at the lugs that wrap around the laths.  If this spreads across the ceiling even the horsehair can’t support the weight and the ceiling, or sections of it, will sag and then may collapse. Where sagging is evident the ceiling will move if gently pushed or make a hollow sound if tapped. Sometimes this failure can be disastrous, the collapse at the Apollo theatre in 2014 injuring 88 people during a performance was caused by water ingress weakening the lath and plaster ceiling.

However there are some good reasons for keeping an original lath and plaster ceiling. Aside from the features of an historic interior it has better soundproofing and insulating qualities than modern plasterboard. The mess associated with their removal, particularly over bedrooms with the debris found if loft spaces above will also make many think twice. Despite some being quick to condemn cracks or bulges they can usually be repaired for a fraction of the cost of replacement.

Irregular-shaped cracking, significant bulging or unevenness are more serious signs. Unless you can address the cause of the cracking there’s little point replastering because it may just crack again. Today's plasterboards have removed this problem although it’s still possible to get hairline cracking along board edges and blistering where screws haven’t been screwed in deep enough. 

There is also a tendency to take a short cut and overboard, leaving the existing ceiling in place. 

If this is being considered then you may need to check with an engineer to ensure the floor or ceiling joists are capable of carrying the additional load. Lath and plaster ceilings weigh around 0.5kN/m2 and plasterboard 0.15kN/m2. The screws used also need to be suitable and in sufficient number to take the additional weight.

Comments

(No subject)

Submitted 1 month 3 weeks ago

I find it unusual to find any lath and plaster ceilings with the addition of cement. The original mix would have been lime putty and well graded local sand and hair of some description this may not necessarily be horse. In areas of East Anglia there was a plaster made from lime putty, Chalk and hair that is much lighter than a sand lime plaster and a lot more flexible. This has been recreated by The Anglia Lime Company in Suffolk. I feel this article is not necessarily indicative of the true lime plaster that may be encountered.

(No subject)

Submitted 1 month 3 weeks ago

Thanks for the interest. We have tried to raise awareness of a different type of construction that some may not have come across or understood how it works. We do recognise that there is so much more to this particular topic and indeed several books have been written just on this area. Hopefully it might spark interest for readers to research further.

(No subject)

Submitted 1 month 3 weeks ago

What about mentioning the issue of anthrax testing?

Reply

Submitted 1 month 3 weeks ago

There have been no cases of anthrax in construction workers reported to the HSE in the last 20 years and so the risk of acquiring the disease is therefore very low. It is, however, better to adopt a precautionary approach if redeveloping industrial sites, and assume that anthrax spores are likely to be present although probably at low numbers which would not put the worker at significant risk (HSE guide HSG174).
More information can be found at:
http://www.hse.gov.uk/construction/healthrisks/hazardous-substances/harmful-micro-organisms/anthrax.htm
and http://www.hse.gov.uk/pubns/priced/hsg174.pdf

Thanks,
Julie, LABC

(No subject)

Submitted 1 month 3 weeks ago

COULD NOT RESIST THE TEMPTATION TO PASS ON THIS OLD SURVEYORS SURVEY TRICK. FIND A BROOM IN A CUPBOARD WITH A SOFT HEAD AND GENTLY PUSH AGAINST THE CEILING TO IDENTIFY LOOSE AREAS.
FROM DAD

(No subject)

Submitted 1 month 3 weeks ago

I used to do this until a ceiling fell on me! Now suggest further investigation from scaffold or trestles.

(No subject)

Submitted 1 month 3 weeks ago

Anlother useful indication that there may be loose plaster is where there is a significant amount of uneveness to the ceiling and it has been papered. It is difficult to conceal hairline cracks effectively and permanently and a papered ceiling is a useful starting point to investigatge further as suggested in your article. Hairline haphazard cracks in an artexed ceiling can also suggest the need to look further

(No subject)

Submitted 1 month 3 weeks ago

My son who is 49 has put up a large punch bag, he has drilled a hole through the iron girder that goes across the garage.
Is this safe enough, as I do not want my house having cracks or falling down. Thank you

Reply

Submitted 1 month 3 weeks ago

Hello there - I'm afraid you would really need a private surveyor to come out and have a look at that for you. Sorry!

Webmaster note

Submitted 1 month 3 weeks ago

All comments posted at an earlier date to this one have been transferred from our old website.

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