Interior and finishes · Wall Finishes & Linings
Reed Board and Reed Mat Plaster Base
Explains what a reed plaster base is, why it belongs with lime and clay plaster work as a background rather than a finish, and what to ask before it is used on timber or straw construction.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What reed board is
Reed board is made from cut reed stems laid parallel, compressed into a mat or a thicker board, and bound together with galvanised wire run across the stems at intervals. Nothing is added as a binder: the mat holds together because the wire holds the stems, and the stems keep their natural hollow structure through the whole thickness of the board.
Its purpose is to give plaster something to grip. When a wet plaster is pressed onto the mat it squeezes between and behind the stems and forms a mechanical key, in much the same way that plaster keys behind riven timber lath or through metal lath. The reed is a background rather than a finish, and none of it is seen once the plaster is on.
What separates it from those other laths is the material and the company it keeps. Timber lath is sawn or riven wood fixed with gaps between the strips, and metal lath is an expanded or woven steel sheet. Reed is a natural plant stem, used chiefly where lime and clay plasters are applied over timber or straw construction, on backgrounds where a rigid or metallic lath would sit awkwardly with the rest of the fabric.
Terminology
Common names and aliases
These names describe the same thing. The library keeps one entry per material so that an acronym, a trade name or a regional spelling never becomes a second, thinner page.
- reed mat plaster base
- reed lath
- reed board backing
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Providing a plaster key over timber framing in traditional and natural building work.
- Forming a plaster background over straw bale construction where a key is needed.
- Lining ceilings between joists in buildings being plastered in lime or in clay.
- Bridging junctions between dissimilar backgrounds so that plaster runs across them with a consistent key.
- Repair work where an original reed or lath background is being matched.
Consideration
Where it is commonly considered
- Where lime or clay plaster is being used and the background needs a key rather than a suction face.
- Where the surrounding construction is timber or plant based and a matching background is wanted.
- Where a natural material background suits the wider approach the design team has taken.
- Where existing reed work is being repaired and continuity of material matters to the result.
- Where a background has to run over dissimilar materials and a common key is useful.
Professional review
Where additional professional review is especially important
These are the situations where the answer depends on the specific building, and where a qualified professional should be involved before anything is decided.
- Where a gypsum plaster or a modern board system is being used, since this background belongs to different plasters.
- Where the position could get wet or stay damp, because a plant material in damp conditions is a question for others.
- Where the background must carry any load, since a plaster base carries plaster and nothing else at all.
- Where the fixing background is unknown, because reed has to be fixed back to something sound.
- Where a specific tested assembly is required, since only its documented components may be used.
Properties
Key properties to discuss
Qualitative topics worth raising. Measured values, classes and grades come from the manufacturer's technical documentation for the specific product, not from a reference page.
- Substrate dependency
- The reed exists to give plaster a mechanical key. It is fixed to a background that must itself be sound, and it carries nothing beyond the plaster applied over it.
- Installation dependency
- The reed and the plaster system are chosen together, and both need trades practised in lime or clay work rather than in board and skim finishing.
- Moisture behaviour
- It is a plant material bound with wire, so how the wider fabric handles and releases moisture is the governing question and one for others to assess.
- Appearance
- Nothing of the reed shows. The finished look comes from the plaster, though a keyed background can give a slightly softer plane than a flat board does.
- Repairability
- Repair means cutting plaster back carefully to sound reed and splicing new material in, which is skilled work rather than a straightforward filler job.
- Maintenance
- Once plastered, later occupants have no way of knowing what sits behind the surface, which is why a handover record is worth insisting on.
- Documentation
- There is little documentation to be had for a natural background, so what matters is a clear written record of the reed, the wire and the plaster used over it.
Exposure
Exposure and environmental conditions
- Is the position interior and protected, and will it stay dry in normal use?
- How does the surrounding construction handle moisture, and does the plaster choice suit it?
- Is the building ventilated in a way that lets the fabric dry out?
- Will the reed be left exposed on site for long before plastering begins?
- Are there any leaks or damp sources that must be resolved before work begins?
Assembly
Substrate and system dependencies
What this material sits on, is fixed to or depends on. This is usually where performance is won or lost.
- What the reed is fixed back to, since it needs a sound background to take the fixings.
- Which plaster is being used, because reed belongs with lime and clay work rather than with gypsum.
- How the reed spans between supports, which is a matter for the people specifying the work.
- How the background meets other materials, since plaster running across a junction needs a plan.
- Whether the wider fabric is intended to be breathable, which is usually what leads here in the first place.
Appearance
Appearance and finish considerations
- The reed is never seen, so the finished appearance is entirely that of the plaster laid over it.
- The keyed surface can give a slightly softer, less machine flat plane than a board background.
- Where reed meets another background, a change in suction or key can read through the finished plaster.
- The plaster finish itself, whether floated, sponged or burnished, decides the character of the wall.
- Setting out has to allow for the plaster thickness building out from the face of the reed.
Durability
Durability questions
Questions to raise rather than a service life to expect. No material has a universal lifespan — it depends on the assembly, the exposure and the upkeep.
- How is the wire binding protected, and what does the specifier say about it?
- What condition is the background behind the reed in, and has anyone checked it?
- How does the assembly behave if it is ever wetted, and who has considered that?
- Is the plaster chosen compatible with movement in the background behind it?
- How would a future repair be carried out without disturbing sound work nearby?
Upkeep
Maintenance and repair considerations
- How is a damaged area of plaster cut back without destroying the reed behind it?
- Can new reed be spliced into existing work, and who is able to do that?
- What plaster should be used for repairs so that it matches what is already there?
- Who will record that the background is reed rather than lath or board?
- Is any of the original background being retained, and in what condition is it?
Installation
Installation dependencies
What the installation depends on — not how to do it. Method belongs to the manufacturer's instructions and the trades carrying out the work.
- The background it is fixed to has to be sound, and its condition established before work starts.
- Fixings have to suit both the reed itself and the background behind it.
- The plaster and the background should be decided together rather than one after the other.
- Reed is bulky to handle and to store, and it should be kept dry before it is fixed.
- Plastering follows the practices of lime or clay work, which have their own rhythm and skills.
- Junctions with other backgrounds should be detailed before plastering rather than improvised.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- The supplier's information on the reed board or mat actually being supplied.
- Confirmation of the wire binding used and of any protective treatment on it.
- Guidance on fixing the reed to the background present in this building.
- The specifier's statement of which plaster system is intended over it.
- A record for the owner that the background is reed rather than lath or board.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Which plaster is going over this background, and why is reed the right key for it?
- What is the reed being fixed back to, and is that background sound?
- How are junctions with other backgrounds being detailed and handled?
- Is the wider approach to this building intended to be breathable?
- Who is carrying out the plastering, and are they experienced in this kind of work?
- Is any existing reed or lath being retained, and what condition is it in?
- How will the reed be kept dry between delivery and plastering?
- What record of the background will I be given at handover of the work?
Blind spots
Commonly overlooked points
- It is a background and not a finish, and it disappears entirely once the plaster has gone on.
- The plaster decision and the background decision are really one decision, taken together.
- Reed is bulky and takes up rather more site storage than the same area of board would.
- Later owners drill into the wall expecting a board and find something quite different behind the plaster.
- The wire binding is what holds the mat together, and its condition matters more than the reed itself.
What this page does not do
- This is a plaster background, not a finish and not a lining board, and it carries nothing whatever beyond the plaster laid on it.
- Reed belongs with lime and clay plaster work. Pairing it with an incompatible plaster is a decision for the professionals specifying the system.
- Damp reaching a plant-based background is a matter for a qualified professional to assess and resolve, and this page offers no diagnosis and no treatment.
- No fire claim is made here. Fire performance is a property of a complete tested assembly and belongs with the relevant authority.
Related entries
Related materials
Materials from the same family, an adjacent role in the assembly, or a shared application.
Inspiration
Related Ideas Library pages
Design directions where this material commonly appears.
Preparation
Related planning checklists
Owner-side preparation before the conversation where this material comes up.
Go deeper
Related Build Design Hub guides
Planning guidance and neutral comparisons behind the decisions on this page.
Wall Finishes & Linings
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