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Crack Sealer Plus is a pure injection filler designed to bond those hard to fill narrow cracks in bricks, blocks, render and concrete. Small flexible nozzles enables masonry cracks as. The render on your house has cracked due to a number of reasons, it could of been done in poor weather, or not enough mechanical key. In my experience you can take of the damaged parts and patch in, but personally I would take it all off and start again, making sure that a good key is achieved in the scratch coat (1st coat of render).
We recently had a conservatory built (during very wet and cold weather), last week I noticed a vertical hairline crack running from top to bottom on one wall (wall is 4.5M wide). when the render was tapped it sounded hollow or live. Working with a small screwdriver of part of the crack a 2.5M x 1.5M section of render simply fell off and the whole of this wall sounds live although the other two walls seem sound. It can now be seen that the uniform hairline crack goes the entire height of the wall and there appears to be another starting about a meter further down. I called the company back and they are sending the builder to have a look before they have it re-rendered. I understand that thermalite can shrink and crack as the blocks were saturated when laid. Question is what is the correct procedure now?
There are three hairline cracks running the entire height of the wall from damp-course to the leaded top of the wall, nothing below the damp-course which is concrete block. The cracks are even top to bottom and are less than a millimetre in width. The was just one crack visible before the render came off then two more are revealed but the render over these was not effected.
The wall was built and rendered in February when the weather was both wet and cold but not at frost conditions, the blocks were saturated and since the wall faces South the unusually hot sun this year has pitched on the wall for about ten hours each day.
Thermalite Lightweight Building Blocks
The builder has said he will do whatever is necessary to remedy it but doesn’t seem too sure as to how to proceed. I have suggested that he angle grinds a half inch gap along the crack and then fill with a expanding joint mastic of some sort – not sure if this is the right way to go, then finally PVA the wall and re-render.
44 Answers from MyBuilder Bricklayers
Best Answer
72434is a thermal shock
due to warm and cold water you must use elastic and heat resistant material
2018-08-12T10:25:01+01:00due to warm and cold water you must use elastic and heat resistant material
Answered 12th Aug 2018
72444Yes blocks do crack in extreme weather.i would take off render.put mesh on then render.never crack again.even if blockwork cracked.
2018-08-12T19:30:02+01:00 Answered 12th Aug 2018
72495Hack it all off and dot and dab. Thermalite and hardwall dont mix
2018-08-13T21:50:02+01:00 Answered 13th Aug 2018
72770Hi.
If the render appeared ‘live’ before falling off, it is the bond between block and render that is at fault. Possibly caused by a combination of excessively wet block (although rendering wet blocks can be ok) and an overly weak mix. If it was cold during the build and the render was affected you frost, this could also account for problems.
I would take issue with ‘...blocks do crack in extreme weather..’ speak to any block manufacturer for clarification of this.
Occasionally a block WALL may crack in extremely dry conditions if it’s foundation bears on highly plastic soil, and this shrinks due to reduced moisture content (dry summers/demand from proximal vegetation). I have never known a single BLOCK to crack -50<T<50 degrees C.
I would advise against simply meshing and rendering if there is a prob with the blockwork. You do not state wether the crack is in the block as well as the render. If the blocks are cracked, there could be an issue with the footing. Crack wider at the top?
If you give me a bit more info. I’d be happy to advise how you should deal with the installer
2018-08-23T19:00:02+01:00 Answered 23rd Aug 2018
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If you see cracks in your external walls then you may well be worried that the structural integrity of your home is at risk. There is no need to panic, however, as only a small amount of cracks are symptomatic of a more serious underlying structural problem. The majority of the time these cracks can be easily repaired. This guide provides information around determining the type of crack you have, what course of action to take in particular how to repair your walls using crack stitching.
Repairing Cracks in Walls: What Do I Do?
Cracks appear in a wall for a number of reasons. They can occur as a new house ‘settles’ or when the construction materials expand and contract overtime with environmental changes. They can also be caused when the foundations of the house move. It is important to establish the root cause and then to take professional advice before making a judgement as to what action to take. Some minor cracking occurs naturally and there is no need for concern or action although it is always worth monitoring them closely for any change. There are other cracks that will need some form of repair work and others that will need more immediate and drastic attention.
Categorising Cracks
The BRE (Building Research Establishment), who offer expert advice for the built environment sector, produced the BRE Digest 251 Assessment of Cracks in Houses. In this document, they identified six categories for cracks, which they describe along with the recommended crack repair method. You can see the categorisations below:
![Lowe Lowe](/uploads/1/2/6/6/126617567/297063132.jpg)
Usefully, the BRE link the width and number of cracks to the appropriate type of repair. The first three types of crack - 0, 1, 2 – only require redecoration and no major work. Those cracks described in 3 and 4 require more major work but it is only the fifth type of crack that indicates severe structural damage and needs urgent attention from a professional surveyor.
It is important to point out that even with smaller cracks, you should monitor them over time in case they increase in width. Any increase could be indicative of a more serious underlying issue. Those cracks that emerge over a short space of time, even small ones, are also potential causes of concern when compared to those that have been there for years.
Consult a professional structural engineer to confirm any diagnosis as well as an appropriate course of action.
Important Questions
If you consult a structural engineer or building professional they will want to know the following:
- How long have the cracks been there?
- Are they getting wider?
- Are they increasing in number?
It is worth making notes as to when any new cracks appear and take measurements. A pencil line can be drawn across the crack to monitor its movement.
Identifying Cracks in External Walls
There are two main types of crack that can appear in your masonry walls – vertical and stepped.
Vertical Cracks
Vertical cracks usually occur in foundation walls when there is insufficient support below. The main reason for this lack of support is when the soil beneath the foundation has not been properly compacted and compresses or even washes away.
The following is an example of a vertical crack:
Stepped Cracks
Stepped cracks usually follow mortar joints and are most common near the corners of buildings. They usually occur through wall movement related to foundation movement including subsidence.
The following is an example of a stepped crack:
Why Are My Walls Cracked?
![Thermalite blocks lowe Thermalite blocks lowe](/uploads/1/2/6/6/126617567/634791013.jpg)
Cracks in walls can occur for a number of reasons. With new build houses, cracks can appear as the house ‘settles’ (settlement of soil due to the weight of the building). In older properties small cracks can be fairly common as building materials shrink overtime. We have divided the main causes of cracked walls into structural and environmental factors:
Structural
- Subsidence – Subsidence is the downward movement/sinking of the ground that supports a building. These changes in ground conditions under and around a building can cause walls to move and cracks to appear. Subsidence is more common in areas with clay soil (mainly in the South of England), which can shrink in dry weather. Sandy and silty soils in the foundations can experience leaching when minerals get washed away. For more on Subsidence, read this guide from the ABI.
- The shrinking, drying out and degradation of construction materials like timber, plaster, and concrete.
- Structural failure – if an element of your house has been built incorrectly and subsequently fails then this can cause cracks to appear in your home.
- Corrosion of wall ties.
- Failure or damage of timber lintels over windows and doors.
- Mining – in former coal mining areas subsidence can occur.
- Heave - refers to upward ground movement as soil expands due to an increase in moisture content. When older trees and shrubs are removed, the ground can swell up as the moisture the tree had previously removed builds up.
Environmental
- Thermal expansion – this usually affects long or tall brick walls and the overall superstructure of the building. Cracks occur when the brick work is exposed to summer heat and there is a lack of sufficient control joints or expansion joints.
- Leaks – over time leaks can cause water to get into the render and for walls to crack.
- Freezing – ice can affect the render.
- Decay of materials.
- Moisture and temperature changes – significant changes in temperature and moisture like driving rain.
- Vibration from heavy traffic.
Internal Cracks
You may also experience the following types of internal crack in your home:
Internal Cracks in Plaster Walls
Cracks in plaster walls can occur if the plaster dried too quickly, if it was mixed incorrectly or as part of environmental change (like temperature/moisture) in your home over time. These types of cracks can be resolved with simple repairs. If the cracks return, are more than 5mm wide and/or there are corresponding cracks on the external wall then it could suggest wall movement and structural issues. These will need to be investigated.
Cracks around Windows and Doors
If you have cracks around a window or door, then these can be down to the failure of an old timber lintel or a shift in the foundations.
How to Repair Cracks in Walls
There is an inexpensive and highly effective way of repairing cracked walls called crack stitching. With a crack stitching kit you can repair vertical and stepped cracks to protect the structure of your home. You will need to follow instructions closely when repairing cracks in walls.
What is Crack Stitching?
Crack stitching is a permanent solution to cracks in masonry walls. It involves embedding stainless steel helical bars into horizontal slots into the mortar bed joints of your wall to restore structural integrity.
When do I need Crack Stitching?
If you have identified and resolved the underlying issue that is causing the cracks in the wall to appear, you are then a position to repair the cracks in your walls. Even if you have smaller cracks, it is worth repairing them sooner rather than later as water ingress from leaks or driving rain can make the problem worse. Only once the root cause of the cracks has been resolved you can progress with crack stitching.
How do I Use Crack Stitching
1. Cut a slot in the mortar bed just over 500mm either side of the vertical crack and to the correct depth, dependent on the wall thickness (see the chart below).
Wall Thickness | Depth of Slot | Depth of Bar |
102mm | 30mm | 20mm |
215mm | 40mm | 30mm |
2. Ensure the mortar is completely removed to reveal the top and bottom faces of the masonry. Remove all loose material (you can use a blow out pump) and then flush the joint with water. Normally vertical spacing is every 4 - 6 brick courses but check with a structural engineer if in doubt.
3. Mix the PermaCEM Anchor Grout thoroughly using the paddle mixer provided and load into the gun. Pump the grout to the back of the slot in a continuous even bead to approximately two thirds of the slot depth.
4. Push the helical bar firmly into the grout, making sure that the bar extends 500mm either side of the crack.
5. Apply a second bead of grout into the slot making sure that the bar is completely covered and with the trowel provided force the grout into the slot until it is approximately 10mm from the surface and ensuring that the bar and grout are firmly packed.
6. Finish by making good the bed joint and filling the vertical crack with an appropriate filler to match.
Read our full How to Guide on Crack Stitching.
Tips
If two or more cracks are close together then bars can be lapped (overlapped) ensuring that the bar extends 500mm either side of the outer cracks and that the laps are at least 500mm.
Helical bars should be bent and bonded at least 100mm around corners when cracks are within 500mm of the corner or a reveal etc. This system can be used for rendered or plastered walls.
Crack Stitching Products: What I Need to Repair Cracks in Walls
Thermalite Blocks
Permagard sell specialist crack stitching kits, which provide all you need to repair cracks in your wall. Our kits contain helical spiral bars, special grout, a mixing paddle, a mortar gun with nozzles as well as a trowel. Permagard offer both a standard crack-stitching kit and a heavy-duty kit for larger cracks.
Permacem Grout – grout the steel bars into place using Permacem Grout. This shrink compensated grout with added polymer additives which sets around the helical bar and develops compressive strength rapidly to prevent axial deflection of the helical bar under load conditions.
Repairing Cracks In Thermalite Blocks Prices
Products
1. Crack stitching kits
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2. Heavy duty Crack Stitching
Permagard – Over 30 years’ property maintenance experience
Permagard are proud of our technical team who are available to advise you on all aspects of crack stitching. Whether you are a specialist installer or want help with installation our technical advisors are here to help. Give us a call today on 0117 982 3282.
Further Reading