Lath and plaster work is a means of finishing the internal surfaces of a house and was very common up to the introduction of plasterboards (sheetrock in the USA) in the 1950’s.
This method of internal finishing consists of thin strips of timber, called laths that were either sawn or riven (split along the grain),which are nailed cross-ways onto the timber framework of the house approximately 1/4″ or 6mm apart. The lath was then covered with a plaster, usually a two coat haired lime mortar mix and levelled off. A further thin coat of fine plaster was applied shortly afterwards and trowelled smooth to provide a good and durable finish.
Many lath and plasterwork walls and ceilings lasted well over one hundred years before requiring repairs apart for normal decorating, some lath and plaster ceilings have been in place for several hundred years, especially in the UK.
A crucial element of this construction is the 6mm gap between the laths, as this provides a ‘key’ for the plaster as it pushes through and bulges out the back of the lath slightly. This crucial keying of the plasterwork is also the source of most plasterwork failures; as the keys gradually break away due to normal movement of houses over extended periods of time.
Once a significant amount of the plasterwork keys have broken away, the plasterwork starts to crack and can separate from the laths, dropping down or sagging.
There are many ways of repairing sagging lath and plasterwork, but due to financial reasons, it is often removed and replaced with modern materials such as sheetrock (plasterboard). This method does at least allow for much better insulation material to be used, thus saving energy and heating costs in the future life of the house.
My Top Ten Ways to Repair Lath and Plaster
This is a short summary of all the ways that you can repair the lath and plaster in your home, depending upon the look you want to achieve, the time you want to spend on it and of course, your budget.
- Re-decorate as it is. Vacuum to remove dust, (wash down, if required) and then re-decorate with suitable water based paint. Not a good repair if the plasterwork has gone beyond the cracking stage, i.e. sagging badly. Depends on original plasterwork condition.
- Cost: Very economical and quick.
- Pros: Period charm in abundance. Ideal for very old cottages that don’t have a straight edge or surface in them. Shows imperfections.
- Cons: Potentially dangerous and possibly very short term solution for damaged plasterwork. Not a ‘flat’ finish. Shows imperfections!
- Fill the cracks and blemishes. Scrape out all cracks and vacuum out loose material. Fill cracks and small blemishes with decorators’ filler using a suitably sized scraper or drywall spreader. Gently sand the filler flat and vacuum all dust away. Wash down if required and re-decorate.
- Cost: Economical repair.
- Pros: Retains period feel. Looks good initially. Easy and quick repair.
- Cons: Might only last a few years depending on plasterworks original condition.
- Use thick lining paper. Scrape out and fill cracks as No.2. Glue a thick grade of decorating lining paper to the plasterwork. Re-decorate.
- Cost: Reasonably economical repair.
- Pros: Retains period feel. Could gain many more years out of reasonable plasterwork.
- Cons: Relatively difficult on uneven surfaces. Won’t stop further cracking over time if surface is still moving.
- Glue sagging plasterwork back into place. Plasterwork can be ‘glued’ back into place by drilling holes in the plasterwork, vacuuming out the dust and injecting a suitable adhesive. The plasterwork is then gently pushed back into place and supported until the adhesive dries.
- Cost: Medium to high cost, depending on time taken and plasterwork condition.
- Pros: Medium term effectiveness. Retains period feel.
- Cons: Arguably a specialised job and may be too difficult for an effective DIY repair.
- Expose the beams. Completely remove the lath and plaster, de-nail and clear away. Wire brush all plaster marks off the joists. Re-route any wiring, if required and repair any damage, holes in the timberwork etc. Clean up and vacuum all surfaces. Leave as is or decorate with varnish, wood stain, or paint. Usually just used on ceilings.
- Cost: Economical to medium depending on timberwork condition.
- Pros: All the old plasterwork is removed and finished with newly decorated surfaces.
- Cons: Different look and feel, arguably only suited to certain properties and owners. Difficult electrical wiring and limited choice of light fittings.
- Over board with plasterboard or sheetrock. Find the frame or ceiling joists, mark their position on the wall and then over-board with plasterboard / sheetrock using long (60mm to 75mm) drywall screws into the original timberwork. Board joints are then taped and filled if tapered edge drywall is used or skimmed with finish plaster if square edges boards are used. One of the most common methods to ‘repair’ a lath and plasterwork.
- Cost: Medium to high.
- Pros: Effectively a brand new surface is created out of plasterboard/sheetrock.
- Cons: Potential problems with adding additional weight or levels if there is a cornice. Loses that period feel.
This one is not strictly a lath and plaster repair as it removes it! But I include it, as this is a VERY common solution to lath and plaster ceilings that have badly failed and sagged.
- Remove the plasterwork and lath entirely.Replace with plasterboards / sheetrock. Mark positions of all joists and timbers then fix 12.5mm plasterboards to the underside of the original joists using 38mm drywall screws. Board joints are then taped and filled if tapered edge boards are used, or skimmed with finish plaster if square edged boards are used.
- Cost: High. Removal of old material, new boards and finishing makes this one of the most expensive options.
- Pros: Plasterboards/sheetrock are stable and very flat. A permanent repair.
- Cons: Loses the period feel.
- Re plastering keeping the original laths. Removing the existing plasterwork entirely and if the lathwork is sound, re-apply the three coat plasterwork, two base coats and a thin finish coat.
- Cost: High, due to special skills and materials needed.
- Pros: Good as new finish, that also matches the surrounding period work. Long term repair.
- Cons: Arguably not a DIY proposition due to work involving lime plasterwork.
Heritage quality. Fully support the plasterwork from underneath on blanket covered timber on props or staging. Working from above, gently remove all loose debris, old keys or nibs and dust. Employ one of the various systems available, for example fixing a wire mesh to the inside edges of the joists just above the plasterwork and then applying adhesive to the plasterwork embedding it into the mesh.
- Cost: Expensive due to extreme care needed and labour involved.
- Pros: Retains all original period features. Usually only used on plasterwork of significant historical interest.
- Cons: Arguably not a DIY proposition due to care needed to preserve original features without damage.
- Buy a newer house. Sorry, I couldn’t make ten and nine ways to repair your lath and plaster just didn’t sound right. Any ideas for number ten are most welcome…
- Cost: Horribly expensive, removal companies, estate agents, lawyers etc.
- Pros: No lath and plaster to repair.
- Cons: Everything is very, very flat, smooth and arguably…boring.
The above list is roughly in order of cost to carry out, although some aspects are moving into specialist craftsmanship where costs could escalate. It could be argued that the two most common solutions are, either to over-board the ceiling or remove it entirely and replace it with sheetrock or plasterboard.
It should be noted that complete removal of a lath and plaster ceiling involves a significant amount of mess, notably large amounts of dust and debris that requires extensive time and effort to contain and clear away.
Suitable safety equipment should be used when working on old lath and plaster.