I had not thought much about the topic of lath before moving into this house and working on the beat up walls. Now I think about it everyday. It is a sickness. I love talking about and thinking about lath now and I try to figure out what kind of lath is under the plaster in old houses I go into.

Hand-riven lath.
I certainly don't know all there is to know about it, but I will outline what I have learned. Lath are the long strips of wood that plaster is applied to when finishing a wall. They were nailed up on the underlying framing with small gaps, called keys, that the plaster would be pushed into, helping the plaster to adhere. There are three types of lath that were primarily used prior to metal mesh lath being invented. The type of lath used on a particular wall helps to date at least that wall, if not the building.

The earliest type of colonial wall covering is wattle and daub which is an ancient building material consisting of interwoven laths or twigs plastered with a mixture of mud or clay. Replacing that in the late 17th century was riven lath. Each piece was hand split, or riven, from a piece of chestnut, oak, or other hardwood. As far as I know, riven lath was not generally used after 1800. Our house doesn't seem to have any riven lath.
Accordion lath and timber beam from our house.
Folsom Tavern, Exeter, NH
What we do have is accordion lath. It was used in at least one case in Exeter as early as 1775 in the construction of the Folsom Tavern. According to James Garvin's, A Building history of Northern New England, "it enjoyed almost universal popularity until the mid-1800's when the introduction of the circular saw made made possible the production of individually sawn laths."

The use of this lath varied from region to region because it required access to a saw mill, which riven lath didn't. This type of lath was created by splitting mill-sawn boards on each end with a lath-splitter or hatchet and then pulling the board open like an accordion. Then it was nailed up onto the framing to be plastered. This was apparently the least effective kind of early lath because it didn't have adequate "keys," or open spaces, to hold the plaster and keep it from sagging over time. We have had to remove large chunks of sagging plaster from our ceilings where the plaster came loose from the accordion lath. 

Below is a late 18th C lath splitter that Otis Caroll and Nate Clark of Pownalborough Restoration found sealed up in the cavity above a ceiling in an early house in Dresden, Maine. I had never seen one of these before. I'm so glad that there are people out there who take the time to share what they have found and learned. Here is their description of it from their blog,
The splitting wedge is made of white oak and very nicely fashioned. Oval in cross section and lightly chamfered on the strike end, it appears to have seen little use.

Lath splitter
Lath splitter
This is a bedroom ceiling where I took down the sagging plaster from the original accordion lath.
On the left, above, there are mill-sawn laths in between the two "new" windows where a window had been removed and lath and plastered over. On the right you can see the original center window from this exterior photo of The Stovers.
After accordion lath came mill-sawn lath, which we have as well. Mill-sawn laths are usually 3 ft. long by 2 inch wide strips of refuse quality wood. It's easy to tell these from riven lath because, unlike riven lath, they are sawn to regular dimensions. The mill-sawn lath in our house is in places where the old lath was taken off and replaced, where windows used to be and on walls that were added later, probably after the house was moved. This type of lath was not available until circa 1825-1835, after the circular saw came into more general use (Henry C. Mercer's 1923 article "The Dating of Old Houses")

Written by Kerry Baldridge

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