What is magnesite floor screed?
Magnesite floor screed is a flooring material made from magnesium oxychloride cement, a mixture of magnesium oxide (MgO) and magnesium chloride (MgCl2), combined with fillers such as sawdust or wood flour. A screed is the smooth layer laid over a floor base. Once poured, magnesite screed sets into a strong, smooth surface.
It was often used as a subfloor or screed layer beneath tiles, linoleum or carpet. The organic fillers lightened the mix and improved its insulating properties, but they also made the screed more vulnerable to moisture, which can lead to significant problems over time.
When was magnesite screed used?
Magnesite screed flourished in the early to mid-20th century. It became a go-to flooring solution for many buildings, driven by the need for sturdy, efficient flooring suited to the construction demands of that era. It has since fallen out of favour because of its susceptibility to moisture damage and its potential to cause structural issues.
Why was magnesite screed popular?
Builders favoured it because it insulated well, was easy to install and was light. Like many vintage building materials, it was once hailed as revolutionary, yet some of its flaws only emerged over time.
- Insulation: it improved the thermal efficiency of buildings.
- Ease of installation: it was relatively easy to mix and apply.
- Rapid setting: it sets and hardens relatively quickly, allowing faster progress on site.
- Lightweight: the organic fillers reduced its weight, making it suitable for multi-storey buildings and where loads were a concern.
- Smooth finish: it can give a smooth, hard surface suited to certain decorative finishes.
- Fire resistance: magnesite has good fire resistance properties.
- Sound insulation: some formulations offer good acoustic properties.
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What are the problems with magnesite floor screed?
The main problem is moisture sensitivity: prolonged exposure to moisture can degrade the screed. It may not be suitable for wet areas unless adequately sealed.
- Salt efflorescence: over time, soluble salts can come to the surface, causing aesthetic concerns.
- Asbestos: deteriorating screeds that contain asbestos can release harmful fibres.
How can deteriorating magnesite screed affect the rest of a building?
- Walls: moisture from the screed can cause discolouration and weakening.
- Mould: moist screed can lead to mould growth, affecting health.
- Decoration: peeling paint and wallpaper increase maintenance costs.
- Electrics: moisture might interfere with electrical systems, risking short circuits.
How do you identify magnesite floor screed?
Look at its colour, texture and thickness, and check it for moisture. Identification can be challenging for those unfamiliar with the material.
| Feature | What to look for |
|---|---|
| Colour | Often a reddish-brown or pinkish hue |
| Texture | Usually smooth, perhaps slightly glossy; can become pitted or cracked over time, especially after exposure to moisture |
| Thickness | Often laid in layers 10-20mm thick; measurable at an exposed edge, such as a doorway or under a removed section of flooring |
| Moisture | Elevated readings on a moisture meter, especially where the floor has been exposed to damp |
What to look for when viewing a property
- A reddish-brown or pink, smooth floor surface, or one that is pitted or cracked.
- Discolouration, swelling or crumbling of the screed, often worst around room edges or near windows and doors where water may get in.
- Discoloured or weakened walls, peeling paint and wallpaper.
- Mould growth.
- An exposed edge at a doorway where the screed thickness can be seen.
When should magnesite floor screed be removed?
Removal is advisable where the screed shows significant deterioration. While magnesite screed can remain stable and functional for many years, cracking or crumbling screed has likely lost its structural integrity and removal is likely to be advised.
Often, replacing damaged screed entirely is the best approach. Where asbestos is suspected, seek professional guidance immediately.
What to do next
- If the property dates from the early to mid-20th century, ask whether the floors contain magnesite screed.
- Have the screed professionally examined to identify damage or potential issues.
- If asbestos is suspected, seek professional guidance immediately.
- Where the screed is cracking or crumbling, plan for replacement.
- Keep inspecting the floor regularly and consult experts if signs of moisture appear.
What a survey can — and cannot — tell you
A building survey provides an informed assessment of the visible condition of a property. Inspections are non-intrusive and limited to areas that are accessible at the time of inspection.
A qualified surveyor has the expertise and equipment to identify magnesite screed and assess its condition, which is useful where a buyer is unsure whether a property contains it.
- The colour, texture and visible condition of exposed screed.
- Moisture readings taken with a moisture meter.
- Discolouration, swelling, cracking or crumbling, especially at room edges and near doors and windows.
- Related signs in walls and decoration, and mould growth.
However, there are limitations to what a survey can determine without intrusive investigation.
- Screed beneath tiles, linoleum or carpet may not be visible, and its thickness can only be measured at an exposed edge.
- Whether a screed contains asbestos cannot be confirmed by sight and needs professional guidance.
Where higher-risk indicators are identified, further specialist or intrusive investigation may be recommended.
Frequently asked questions
What colour is magnesite floor screed?
It often has a reddish-brown or pinkish hue, and is usually smooth, perhaps slightly glossy.
When was magnesite screed used in the UK?
It was popular in the early to mid-20th century and has since fallen out of favour because of its susceptibility to moisture damage.
Why is moisture a problem for magnesite screed?
Its organic fillers, such as sawdust and wood flour, make it vulnerable to moisture. Prolonged exposure can degrade it, causing discolouration, swelling and crumbling.
Does magnesite screed contain asbestos?
Some may. Deteriorating screeds that contain asbestos can release harmful fibres, so seek professional guidance immediately if asbestos is suspected.
Should magnesite screed always be removed?
No. It can remain stable and functional for many years, but removal is advisable where it is cracking or crumbling, and replacing damaged screed entirely is often the best approach.
