Ultimate Guide to Shale Testing
Your One-Stop Source for Understanding Shale, Its Testing, and Remedies
Welcome to our comprehensive FAQ section, the definitive source for anyone looking to understand shale testing. Whether you are a homeowner, builder, engineer, or just curious about the subject, our guide covers everything you need to know.
From the necessity of testing to the intricate processes involved, the underlying causes of subsidence, and the potential solutions—our FAQ section is the number one go-to guide in the industry.
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FAQ
Everything you need to know about Shale testing.
Shale testing, also known as an in-fill test, floor test, or bore test, is an investigation undertaken to ascertain whether a property has any existing or potential future problems with its structural integrity due to the presence of deleterious materials like shale or other hardcore fill materials.
A shale test is often required by mortgage lenders to ensure the property doesn’t pose any risks due to the presence of deleterious materials. Such materials, often used in house construction from the 1940s to the 1980s, can cause damage to floor slabs and abutting walls. This damage is typically not covered by household insurance and can cost £10-20k to repair.
While the term “shale test” is common in our local area due to the prevalence of Cleveland shale, similar tests elsewhere in the UK are referred to as in-fill tests. Other variations include bore test, floor test, floor survey, sub-floor fill test and concrete test.
In accordance with local government guidelines regarding the green environment, in some circumstances, it may not be necessary to carry out a full removal. However, this depends on the specific situation of your property, and it’s best to discuss with us for a thorough understanding.
The number of boreholes varies depending on factors like flooring type and the presence of a garage. For properties without an attached garage and with specialized flooring, one borehole may suffice. If testing reveals varying materials, additional boreholes may be required, potentially incurring extra costs.
Efforts are made to minimize any visual impact on the flooring. For example, tiles are carefully removed and replaced whenever possible. In some cases, you may see a small round area of different coloured concrete, particularly in garages. This will be explained and permission sought beforehand.
The duration of the on-site testing generally takes about an hour and a half but can vary depending on several factors such as access, density, depth and hardness of concrete, and the density and depth of the in-fill.
Though over 95% of dust is removed, some clients prefer to cover their furniture with their own dust sheets prior to arrival. However, dust sheets are provided, and precautions are taken to minimize any mess.
The on-site test duration may vary from as little as 45 minutes to as much as 3.5 hours. The typical duration is approximately 1.5 hours.
Damage can occur due to various mechanisms. For example:
- Cleveland Shale: This mud-rock can expand due to chemicals reacting with water and growing crystals, forcing laminations apart. This expansion can push up floor slabs and shift supporting walls.
- Slags: A by-product of the steelworks industry, slags can expand and then collapse into a powder, leading to lack of support and concrete damage.
- Sulfate Attack: A common issue, particularly with substances like gypsum, epsomite, and Glauber’s salt, sulfates in the hardcore can migrate into the concrete and react with its constituents, causing a deleterious effect known as sulfate attack.
The testing process is designed to identify the presence of these materials, and any anomalies or unusual behaviors are carefully observed. If problematic materials are found, samples may be sent to the lab for further analysis. Understanding the in-fill composition helps in taking the necessary precautions to prevent or mitigate any potential damage.
- Shale Expansion: Caused by the growth of crystals, leading to volume expansion and structural damage.
- Slags Problems: Expansion and collapse, leading to voids and damaged concrete.
- Sulfate Attack: The most common factor affecting infill materials.
Symptoms include uneven floors, cracks in the screed, obvious heaving, difficulty with internal doors, horizontal cracks in external walls, efflorescence on wall faces, and more.
The availability of water is crucial as it plays a part in crystal growth in shale and the reaction between sulfate and concrete. Groundwater, surface water floods, or leaking drains and pipes can be sources.
The number of holes drilled for testing depends on several factors, but typically two to three are required. The process is designed to be minimally invasive and any mess created is tidied up as part of the service.
While some customers request us not to test the samples, this often leads to a delay or additional costs, as lenders usually insist on a full analysis before offering money. It’s advised to always proceed with testing the samples.
Each dwelling needs to be considered on its own merits. A successful test at one property doesn’t automatically guarantee a successful outcome at a neighbouring property.
The procedure differs slightly based on the type of floor construction – solid concrete slabs or suspended timber floors. For both types, holes of 4-5″ diameter are drilled to expose the underlying in-fill, and samples are taken. The in-fill is visually identified, its depth determined, and any anomalies recorded. The hole is then filled, and the flooring is reinstated.
Yes, the testing process can be noisy, lasting around 30 minutes, but this could be shorter or longer. It’s advisable to make arrangements for pets during this time. As for mess, over 95% of dust is removed at source using an industrial vacuum cleaner. Dust sheets are provided, and many people have been pleasantly surprised at the lack of mess caused.
If tiles are present, attempts are made to remove them without breaking so they can be glued back down. Spare tiles are carried in case of breakage, although matching may not be guaranteed. If screed is present, the hole will be concreted up to the finished floor level, and the area may be clearly seen, but it’s generally not an issue if the floor is covered, such as with carpet.
Yes, the same testing procedure can apply to an attached or integral garage. You will be consulted and given an explanation before proceeding with the test in these circumstances.
The need to send samples to a lab is determined through careful observation, including the way concrete behaves when drilled and the presence of any anomalies or unstable materials. Stable materials include Dolomite, Clean gravels, and natural clays. Others like Cleveland shale, colliery spoil, slag, certain sands and gravels, ash, and brick rubble are often sent for further analysis.
Sulfate attack is a reaction between sulfates in the hardcore and the concrete. The sulfates, which include salts like gypsum, epsomite, and Glauber’s salt, can be readily soluble in water, allowing them to react with the concrete. This problem has been associated with materials like burnt colliery spoil, furnace bottom ash, blast-furnace slag, oxidized pyritic shales, and demolition debris. The amount of soluble sulfates in the material is crucial in determining the potential for sulfate attack on concrete, making it a significant concern in the testing process.
- Conventional or Ettringite Form of Sulfate Attack: Sulfates react with tricalcium aluminate in Portland cement to form ettringite, causing expansive destruction.
- Thaumasite Form of Sulfate Attack (TSA): This weakens the concrete and can reduce it to a mushy mass, affecting the building’s structural integrity.
Materials include Cleveland shale, colliery spoil, slag, certain sands and gravels, ash, and brick rubble.
- “This house has stood for years without problems”: The reactions can be slow, and problems may not be apparent yet.
- “This house has a damp-proof membrane, so sulfate attack won’t occur”: Membranes can be perforated or ineffective.
Remedial works are repairs required to fix in-fill problems. Tips for choosing a builder:
- Ensure they are experienced and knowledgeable.
- Verify their approach (e.g., removing the kitchen, knowing the depth of fill, involving a local building inspector).
- Be cautious of quotes without seeing the report or knowing the depth of fill.
Materials that are accepted as stable include Dolomite, Clean gravels, and natural clays.
These FAQs provide a concise summary of the key points related to sulfate attacks and related concerns in building and construction. Feel free to ask for further details or clarification on any of these points!