Interior and finishes · Wall Finishes & Linings
Magnesium Oxide Board for Wall and Ceiling Linings
Describes how magnesium oxide board is made, why its salt-based binder distinguishes it from cement-bound and calcium silicate boards, and what an owner should establish before it is used.
Educational reference entry. Suitability depends on the complete assembly, substrate, exposure, installation method, manufacturer documentation, local requirements and qualified professional review.
Overview
What mgo board is
Magnesium oxide board is made by mixing calcined magnesium oxide with a magnesium salt solution, usually a chloride or a sulphate, together with fillers such as perlite or wood flour and a reinforcing mesh laid in near each face. The mix sets through a chemical reaction between the oxide and the salt rather than by the hydration of a cement, and the sheets are cured rather than autoclaved.
That binder is the whole story of the material. Magnesium oxychloride and oxysulphate cements set quickly and give a hard, dense sheet that can be cut and drilled, but the salts that formed them remain in the finished board. Products vary widely between makers, because the ratio of oxide to salt, the fillers and the curing all differ, so two sheets that look identical can behave quite differently.
This is what separates it from the boards it is sold alongside. Fibre cement is bound with Portland cement and calcium silicate board is autoclaved into calcium silicate hydrate, and neither carries residual salt. Where a magnesium board is kept damp, salts can migrate to the surface, and salt in contact with steel fixings raises corrosion questions that simply do not arise with the other two.
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.
- mgo board
- magnesium oxide panel
- magnesia lining board
Applications
Common applications
Where this material is typically encountered. A typical application is not a statement that it suits your project.
- Interior wall and ceiling lining where a mineral board is specified and conditions are reliably dry.
- Sheathing and lining in dry, protected positions within an interior build-up.
- Substrate boarding beneath other finishes where the design team has confirmed the choice.
- Boarding in workshops, stores and back-of-house spaces where a hard mineral face is wanted.
- Lining components in modular and offsite construction where the maker has specified the board.
Consideration
Where it is commonly considered
- Where a mineral board has been specified by the design team with knowledge of this product's chemistry.
- Where conditions are reliably dry and are expected to remain so throughout the life of the assembly.
- Where the maker's documentation is available and names the conditions the board is intended for.
- Where a hard, dense mineral face is wanted and the professionals involved have weighed the alternatives.
- Where the board forms part of a system supplied and documented by a single maker.
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 the board could become damp or see high humidity, because residual salts and moisture interact.
- Where steel fixings, framing or fasteners are in contact with the board in anything but dry conditions.
- Anywhere external or weather-exposed, since this is not a weatherboard whatever a supplier may suggest.
- Where provenance and documentation are unclear, because formulations vary a great deal between makers.
- Where a specific tested assembly is required, since substitution changes what that assembly actually is.
- Where a wet area is involved, because that is a designed waterproofing strategy rather than a board choice.
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.
- Moisture behaviour
- The binder is formed from magnesium salts that remain in the sheet, so moisture behaviour is the defining question and dry service conditions have to be established first.
- Substrate dependency
- What the board is fixed to, and what those fixings are made of, matters unusually much here, because salt and steel together in damp conditions raise corrosion questions.
- Documentation
- Formulations vary widely between makers, so the maker's documentation and clear provenance are the only reliable basis for using this board at all.
- Installation dependency
- Boards must be stored dry, cut with dust control, and fixed and jointed by the maker's documented method rather than by transferred plasterboard habit.
- Appearance
- The face is a hard, fine, flat mineral surface with reinforcing mesh close beneath it, so sanding is limited and priming follows the maker's guidance.
- Surface wear
- The set sheet is hard and dense, which helps at a wall face, though impact behaviour in a specific position is not something a reference page can quantify.
- Fire-related questions
- Fire performance is a property of a tested assembly rather than of a board, and any requirement is settled from the maker's documentation with the relevant authority.
- Repairability
- Replacing a panel means sourcing a matching board from the same maker, which is only possible if the provenance was properly recorded at the time.
Exposure
Exposure and environmental conditions
- Will this board ever be damp, either in use or during the construction period?
- What humidity does the space reach, and for how long at a time?
- Are the boards to be stored under cover and kept dry before they are fixed?
- Is there any risk of water reaching the board from services or from the building fabric?
- Is the position permanently interior, protected, heated and dry?
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 framing or backing the board is fixed to, and what that framing is itself made of.
- What fixings are documented for the board, including any protective treatment on them.
- Whether dissimilar metals will be in contact with the board anywhere in the assembly.
- How joints are treated, since this differs from paper-faced board practice.
- Whether the assembly specification names this board or names a different mineral sheet.
Appearance
Appearance and finish considerations
- The face is a hard, flat mineral surface, usually grey or off-white, with a fine texture.
- Reinforcing mesh sits close to the face, which affects sanding and how deeply the surface can be worked.
- Priming before decoration follows the maker's guidance, since a mineral face absorbs unlike paper.
- Any salt bloom on the surface is a signal to stop and ask questions rather than to paint over it.
- Cut edges expose the body of the board and may look different from factory edges.
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.
- What does the maker's documentation say about moisture and the intended service conditions?
- How are steel fixings and framing protected where they come into contact with the board?
- Has anyone seen documented evidence of how this particular product behaves over time?
- What is the plan if surface bloom or staining appears after installation?
- How does the board respond to impact in the position being considered?
Upkeep
Maintenance and repair considerations
- How is a damaged panel removed and replaced, and are matching boards still available?
- What should an owner do if a stain or a bloom appears on a decorated surface?
- Who holds the record of which board was used and which maker supplied it?
- What coatings are compatible with this board face for later redecoration?
- Is the fixing arrangement accessible if it ever has to be inspected?
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.
- Boards must be kept dry in transit and in storage, since dampness before fixing is a real problem.
- Cutting produces mineral dust and needs extraction and site protection arranged in advance.
- Fixings, patterns and jointing follow the maker's documentation rather than plasterboard habit.
- The framing behind should be confirmed as suitable for contact with this board type.
- Substitution on site for a similar looking board changes the material entirely and should not happen.
- The building should be closed and drying before the boards are installed.
Documentation
Documentation to request
Ask for these in writing, for the specific product being proposed, and keep them with the project record.
- The maker's product documentation naming the binder type used in this specific board.
- A clear statement of the service conditions and humidity the product is intended for.
- Fixing guidance, including the fixings and the framing the maker documents for use with it.
- Jointing and surface preparation guidance written for this board face.
- Provenance information identifying the actual manufacturer of the sheets being supplied.
- Any guidance the maker gives about storage and handling before fixing.
Conversations
Questions for qualified professionals
Bring these to the relevant qualified professional, manufacturer or authority. Requirements vary by project and location.
- Why is magnesium oxide board being proposed rather than a cement-bound or calcium silicate board?
- Which binder does this specific product use, and where is that stated in writing?
- Who actually manufactured the boards being delivered to this site?
- Can this position ever become damp, and who has confirmed that it cannot?
- What fixings and framing are documented for use with this board?
- Is the board named in any specified assembly, or is this a substitution?
- How will the boards be stored and protected on site before fixing?
- What happens if surface bloom appears after the boards are installed?
- What is the route to replacing boards if a problem emerges later?
Blind spots
Commonly overlooked points
- Formulations differ enormously between makers, so experience with one board says very little about another.
- The binder is a salt system, and salt plus moisture plus steel is a combination worth taking seriously.
- The board is often offered as a general substitute for other mineral sheets, which it is not.
- Provenance can be hard to establish once boards have passed through several hands.
- Bloom or damp staining on a finished wall is a signal about the board, not merely a decorating fault.
- Storage on site before fixing is where a good deal of the damage happens, out of anyone's sight.
What this page does not do
- No fire claim is made on this page. Fire performance belongs to a complete tested assembly, to the maker's documentation and to the relevant authority.
- The salt-based binder means moisture questions are central. Whether a position is reliably dry is a judgement for qualified professionals, not an assumption.
- Contact between the board and steel fixings or framing in damp conditions raises corrosion questions that must be resolved before specification.
- This board is not interchangeable with fibre cement or calcium silicate board, even where a supplier presents them as alternatives.
- Provenance and documentation matter more here than with most boards, because product formulations vary so widely between makers.
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
Reference entries for internal wall and ceiling materials — plasterboard, gypsum, lime and clay plasters, polished plaster, paints, primers, wallpaper, panelling and acoustic linings.
Browse all wall finishes & linings entries →