Lime Plaster and Lime Mortar: Types, Uses and How to Choose
Lime plaster is a trowel-applied wall finish made from lime, fine mineral aggregate and water that hardens as it absorbs CO₂ from the air. Lime mortar is the coarser, structural version: the mix laid between bricks and stones, or built up as a base coat. Below: the types, lime plaster vs drywall and Venetian plaster, and which Origen product goes on which layer.
What is lime plaster?
Lime plaster is a mineral coating, not a paint film. Lime binds the aggregate, and the finished layer stays porous, so water vapor passes through the wall. It is the traditional finish of masonry and old plaster walls, and today it also goes over drywall.
It hardens by carbonation: the calcium hydroxide in the lime reacts with carbon dioxide in the air and turns back into calcium carbonate, the mineral of limestone. That is why it cures slowly (about 30 days in our products). The same chemistry is behind limewash, which is lime in paint form.
Lime plaster vs lime mortar
The difference is thickness and job. In the U.S., lime mortar usually means masonry mortar: the bedding and pointing mortar between bricks and stones, including the mortar used to repoint old masonry. Lime plaster is the coating on the face of the wall, from a base coat to a thin finish coat.
On older buildings one rule applies to both, and it is the core of the National Park Service guidance on repointing (Preservation Brief 2): new mortar or plaster should be softer and more vapor-permeable than the masonry it touches, so moisture and salts leave through the joint or coating, not through the brick. Hard cement mortar can hold moisture in an old wall and lead to spalling.
Origen makes lime and mineral plasters; we do not sell a repointing mortar in the U.S.
Non-hydraulic and hydraulic lime
The difference is how they harden. Non-hydraulic lime (also called air lime or aerial lime, sold as lime putty or hydrated lime) sets only by carbonation in air. Natural hydraulic lime (NHL) also contains calcium silicates and aluminates that react with water: it sets faster and harder, even in damp conditions, but is stiffer and less vapor-open.
| Non-hydraulic lime | Natural hydraulic lime (NHL) | |
|---|---|---|
| How it hardens | Carbonation with CO₂ from the air | Reaction with water, then carbonation |
| Speed | Slow: weeks | Faster: days |
| Strength | Moderate and flexible | Higher and more rigid |
| Vapor permeability | Very high | High, somewhat lower |
| Typical use | Interior plaster, decorative finishes, restoration | Exposed masonry, base courses, work that needs early strength |
The lime products in our U.S. range, TerraGen™ Extra Fine, TerraGen™ Adhesive and EnluGen™, are all based on non-hydraulic lime.
Lime plaster vs drywall
They are different layers, not rivals: drywall is a substrate, lime plaster is a finish, and lime plaster can go over drywall. Drywall is gypsum panels with taped joints, usually finished with latex paint, which leaves a plastic film. A lime or mineral plaster gives a seamless, matte surface with depth, stays vapor-open and has no paint film to peel.
The trade-offs are skill and time: trowel finishes need an experienced applicator, and the wall reaches full hardness after 30 days. TerraGen™ Gratti and Marmolino go over drywall, gypsum plaster, stucco or skim coats, and over well-adhered latex paint they need no dedicated primer under normal conditions. On smooth, non-porous surfaces, use Primer Contac as an adhesion bridge.
Which product for which layer
Each layer has its own product. This is the Origen range from substrate to protection, with data from our Technical Data Sheets.
| Layer or need | Product | What it is | Thickness | Coverage |
|---|---|---|---|---|
| Consolidate a weak, dusty or very absorbent mineral surface | MinerGen | Potassium silicate consolidating primer; penetrates without forming a film | 2–3 coats, 1 hr recoat | 530–650 sq ft/gal per coat |
| Bond to smooth or non-porous surfaces | Primer Contac | Bio-based adhesion bridge for plasters and adhesives | 1 coat; 24 hr before plastering | 325–365 sq ft/gal |
| Repair, base coat, tile and board adhesive | TerraGen™ Adhesive | Non-hydraulic lime adhesive and repair mortar in paste form | 0.04–0.20 in (1–5 mm) | Approx. 37–244 sq ft per 37.5-lb pail |
| Superfine, marble-like lime finish | TerraGen™ Extra Fine | Non-hydraulic lime coating in paste form, ready to use | 0.04–0.08 in (1–2 mm); max. 0.12 in per day | Approx. 90–245 sq ft per 37.5-lb pail |
| Fine mineral texture | TerraGen™ Gratti (50 µm) | Mineral coating of aggregates, bio-based resins and CaCO₃™ Technology (Graphene Technology); not a pure lime plaster | 0.08–0.12 in per coat; 0.12–0.20 in in total | Approx. 17–48 sq ft per 44-lb pail |
| Richer texture, eight hand finishes | TerraGen™ Marmolino (100 µm) | The same mineral formula with a coarser aggregate; not a pure lime plaster | 0.08–0.12 in per coat; 0.12–0.20 in in total | Approx. 17–48 sq ft per 44-lb pail |
| Matte or polished lime stucco | EnluGen™ | Ready-to-use lime-based stucco | 0.012 in per coat, usually 3 coats | 73–92 sq ft/gal per coat |
| Protection in bathrooms and kitchens | TerraGen™ PU Water-Repellent | One-component polyurethane sealer that repels liquid water and resists bleach and degreasers | 2 coats, 12–24 mils in total | 0.7–1.0 oz/sq ft per coat |
Extra Fine, Gratti, Marmolino and Adhesive are rated A1 for reaction to fire, and EnluGen™ A2 (EN 13501-1, European classification). All the plasters and primers above are Trace VOC (< 1 g/L, ISO 11890-2). Trowel finishes: experienced applicator recommended. Full data on our specifications page.
Venetian plaster, marmorino and lime plaster: the differences
All three are trowel-applied lime finishes; they differ in grain, number of coats and sheen.
- Lime plaster is the general term: lime and fine aggregate, left matte, floated or burnished.
- Venetian plaster is a very fine lime plaster in several thin coats, burnished with a steel trowel to a deep sheen. Many products sold under that name are acrylic: check the binder.
- Marmorino is a lime plaster with marble dust and a slightly coarser grain, with a matte to satin, stone-like finish.
In our range, EnluGen™ is the lime stucco for smooth work: 2–3 coats of 0.012 in, sanded for matte or burnished for polish (30–40 minutes by hand, or after 90 minutes with an electric polisher). TerraGen™ Extra Fine gives a superfine, marble-like lime surface. TerraGen™ Marmolino takes its name from marmorino, but it is not a traditional Venetian marmorino of lime and marble dust: it is a mineral coating with a 100 µm aggregate, applied by roller or trowel and finished by hand in eight textures.
Smooth and textured plaster finishes
For a smooth plaster finish, choose EnluGen™ or TerraGen™ Extra Fine; for texture, TerraGen™ Gratti or Marmolino.
- Smooth: EnluGen™, sanded matte or polished; Extra Fine, troweled smooth or pressed; Marmolino in its Smooth Trowel finish.
- Fine texture: Gratti, scraped, floated, burnished or smooth.
- Bolder texture: Marmolino in Hammered, Dragged, Broomed, Wood-Float Swirl, Wet Sponge Swirl, Sand Float or Fine Brush.
The texture comes from the applicator's hand, so no two walls are identical: see a sample before you decide.
Tadelakt and lime plaster in bathrooms
Tadelakt is a traditional Moroccan lime plaster, compacted and polished with a stone and then treated with black soap; the soap reacts with the lime and makes the surface water-repellent.
EnluGen™ is not tadelakt and is not a substitute for it. It is a polished lime stucco that gives bathroom walls a surface with no grout lines, sealed after at least 7 days with two coats of TerraGen™ PU Water-Repellent. Two limits from the Technical Data Sheets: the seal reduces breathability, and EnluGen™ is not suitable for surfaces in permanent contact with water. Before plastering a wet zone, email support@origenpaints.com with the details. Step by step: bathroom without grout lines.
How lime plaster is applied
Always in the same order: sound substrate, coats at the right thickness, finish, slow cure. Times at 77 °F and 60% relative humidity.
- Prepare the substrate. Dry, clean, free of dust and salts. Consolidate friable surfaces with MinerGen; use Primer Contac on non-porous ones. Dampen only if very dry. Use mesh where different substrates meet.
- Choose the conditions. 46–86 °F for most products (EnluGen™ 41–90 °F), out of direct sun. In heat or wind, mist the coat for 48 hours.
- Mix. All come ready to use; stir until even. Gratti and Marmolino accept up to 10% water.
- Apply in coats. A keying or leveling coat, then an even second coat. Recoat after 24–48 hours for Extra Fine, Gratti and Marmolino, 4–6 hours for Adhesive and 1 hour for EnluGen™.
- Finish. As the material begins to firm up: scraped, floated, burnished, troweled or polished.
- Cure and protect. Do not water it; lime hardens with CO₂ from the air. Protect from rain for 4 days and do not scrub before 30 days. PU Water-Repellent after 7 days.
Wet lime is strongly alkaline: wear gloves and eye protection, and read the label and SDS.
Lime plaster on old walls
On an old wall, the new coat has to let out what the wall holds, so use a soft, vapor-open lime coat.
If old plaster is crumbling or white salt stains keep coming back, the plaster is rarely the cause: there is usually moisture behind it. No plaster or paint fixes the moisture that causes it, so find and fix the source first. Then consolidate with MinerGen, repair with TerraGen™ Adhesive and finish with Extra Fine, EnluGen™ or limewash. More in crumbling plaster on old walls.
Frequently asked questions
What is the difference between lime plaster and lime mortar?
Thickness and job. Lime mortar is the masonry mix laid and pointed between bricks and stones; lime plaster is the coating on the wall face, from a base coat to a finish coat of 0.012 in, like EnluGen™.
Is lime plaster better than drywall?
They do different jobs: drywall is a substrate, lime plaster a finish that can go over it. It gives a seamless, matte, vapor-open surface, but needs a skilled applicator and a 30-day cure.
Is TerraGen™ Marmolino a Venetian plaster?
No. It takes its name from marmorino, but it is not a traditional marmorino of lime and marble dust. It is a mineral coating with a 100 µm aggregate, finished by hand in eight textures.
Can lime plaster go over drywall or painted walls?
Yes, with the right preparation. Gratti and Marmolino go over drywall, gypsum plaster and well-adhered latex paint with no dedicated primer under normal conditions. For EnluGen™, remove poorly bonded or vapor-blocking paints; on non-porous surfaces, use Primer Contac.
How long does lime plaster take to cure?
About 30 days to full hardness. You can paint over Extra Fine, Gratti and Marmolino after 4 days, but do not scrub before the month is up.
Can I use lime plaster in a bathroom?
On walls, yes: EnluGen™ sealed with TerraGen™ PU Water-Repellent after at least 7 days. The seal reduces breathability, EnluGen™ is not suitable for surfaces in permanent contact with water, and it is not tadelakt.
How much lime plaster do I need?
It depends on thickness: Gratti and Marmolino cover approx. 17–48 sq ft per 44-lb pail; Extra Fine approx. 90–245 sq ft per 37.5-lb pail; EnluGen™ 73–92 sq ft/gal per coat. Test on site.
See all our decorative finishes, choose a shade on the Harmony color card and inquire for a sample kit. Not sure about your substrate? Email support@origenpaints.com with a photo.