Concrete Carbonation

Concrete Carbonation

 

By Kate Allen (Malone Associates Ltd) 

 

Blown concrete caused by carbonation

Blown concrete caused by carbonation

We’ve completed a number of projects lately to non-traditional properties and high rise blocks where we’ve had to consider the effects that concrete carbonation has had on the structure. This has included quantifying the number of defects to allow us to go out for tender on concrete repairs. Apart from the localised repairs, there is a further consideration with regards to how we limit the future effects of carbonation.

What is carbonation?

Concrete is a highly alkaline material and if un-carbonated it has a pH in the region of 12.6. Carbonation starts on the surface of the concrete and can ultimately reach the depth of the steel reinforcement within the concrete.  Reinforcement bars are required in most concrete structures as concrete is strong in compression but weak in tension, therefore reinforcement is added to provide tensile strength. The alkaline state of the concrete provides a passive resistive layer to the surface of the steel reinforcement that prevents corrosion.

Rebar corrosion & spalling caused by carbonation

Rebar corrosion & spalling caused by carbonation

Once concrete comes into contact with carbon dioxide and other pollutants within the air, then a reaction may occur. Carbon dioxide can form carbonic acid with the water in the cement that then neutralizes the alkaline state of the concrete. If this happens, then carbonation moves through the concrete as a front that  gradually reduces the pH value to 8pH; neutral is 7pH. However, corrosion to the reinforcement can occur if the pH value falls below 11pH.

Different factors determine the timeframe of carbonation, such as the quality of the concrete. For example, if the cement is very porous or has low cement content then the timeframe will be significantly quicker than if the concrete is not very porous and has high cement content.

The Importance of Concrete Cover

The term concrete cover relates to the distance from the embedded reinforcement to the outer surface of the concrete. This distance is significant for structural integrity, durability, protecting the reinforcement from corrosion and fire.  Ordinarily we wouldn’t want to see less than 50mm of concrete cover, yet many non-traditional buildings built in the 50s and 60’s had less than 10mm of cover in places.

The concrete cover can be accurately measured using a cover meter which is a non-invasive device.  The cover meter uses electromagnetic pulses to determine the location of the reinforcement bar. ‘BS 1881-204: Testing concrete’ should be referred to for information when using electromagnetic cover meters. We use a Kolectric MC8020 micro cover meter.

Rebar corrosion process

Rebar corrosion process

If the concrete cover surrounding the reinforced bar is insufficient then the bar will be susceptible to corrosion as the carbonation front does not have far to travel. Once the passive resistive layer is lost then the embedded steel will start to corrode. Corrosion is an expansive reaction and it is this expansive reaction that causes cracking and  spalling of the concrete. Cracks allow direct water ingress which can further accelerate the deterioration of the concrete . In particular, concrete framed buildings built from 1950s to the late 1960s had insufficient depth of concrete cover. It was not unusual for the reinforcement bars to corrode causing the covers to crack and detach over a period of time. It was particularly common in the 1950-1960s due to architects striving for an aesthetically pleasing property.

West Midlands Projects

Recently we worked on a project in the West Midlands, a concrete framed block of flats. There were many defects throughout the property including concrete carbonation and we were required to write a concrete repair specification after completing the initial survey work.

Cracked concrete due to corroded embedded steel

Cracked concrete due to corroded embedded steel

The adjacent photograph shows a reinforced concrete lintel suffering from carbonation. This is most likely due to an insufficient concrete cover which over time results in the reinforcement bar corroding when carbon dioxide and water affect the concrete. Subsequently, the alkaline value lowers in the concrete therefore increasing the risk of corrosion to the reinforcement.

Assessing the Depth of Carbonation

As previously mentioned, the rate in which carbonation spreads to greater depths depends on the factors of the concrete and the environment.  However, concluding the depth of carbonation is important and it can be determined by using a Phenolphthalein indicator solution. The solution consists of 1g Phenolphthalein dissolved in 50ml of alcohol and further diluted with 100ml de-ionized water.

This solution is applied to newly broken concrete; if a purple stain occurs on the concrete then the pH value is above 9 which means carbonation has not taken place. However, if the solution applied to the concrete remains colourless then there is a value of below 9pH – this means that carbonation has occurred.

The depth in which the coloured solution travels depends on how deep the carbonation has reached. It is important to leave the tested concrete for a period of 24 hours until measuring the depth.

Prevention and Repair Methods

Precast panel having rebar descaled ready for concrete repairs.

Precast panel having rebar descaled ready for concrete repairs.

Preventing and slowing down carbonation in concrete is a simple method.  Anti-carbonation coatings can be applied to the cleaned surface of the concrete to prevent the ingress of carbon dioxide and other pollutants. This method should prevent carbonation for approximately 10 years.

Rebar prepared for repair mortar.

Rebar prepared for repair mortar.

However, if carbonation has already taken place , then the repair methods are not as straight forward. To repair carbonated concrete with exposed reinforced bar the following steps are required. Firstly, the works should comply with EN 1504: Principle 11 – Preventing Corrosion of the Steel Reinforcement.

 

The reinforced bar must be descaled and cleaned ready for an anti-corrosion coat to be applied. This coat isolates the bar and protects it from water and chemicals that could cause further corrosion. Next the missing concrete needs to replaced; if a higher cement to water ratio is used then carbonation will be a slower process. Furthermore, once the repair mortar is set then an anti-carbonation coating can be applied to prevent carbonation of the concrete.

Completed concrete repairs with anti-carbonation coating

Completed concrete repairs with anti-carbonation coating

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Investigating Leaking Drains & Other Subterranean Leaks

Subterranean Leaks are almost always responsible for damp as well as structural issues

Sink hole or something less serious?

Sink hole or something less serious?

 

We recently attended an old property in Nottingham where minor structural cracking was evident and in these cases we always suspect a problem with leaking drains, but what initially prompted the call was the  fact that a small sink hole appeared to have developed under the clients rear patio; we understand that the clients foot had simply fallen through the joint in a slab as it gave way due to lack of adequate sub base.

 

Drainage Excavation Underway

Drainage Excavation Underway

On attending we lifted paving slabs and noted that a void had appeared beneath the slabs. We read a lot in the press these days about sink holes appearing but I was confident that this was something far less severe, a subterranean leak.

Leaking drains are often the Cause of Structural Cracking

The building itself was starting to show some evidence of structural cracking to the rear corner of the building, which supported our initial view that there was a localised leak to the foul drains, the storm drains or the incoming water main, which was washing the fines away from the foundation bearing strata.

Minor structural cracking evident

Minor structural cracking evident

Testing the water main

Whilst the labourer was excavating the patio, we carried out a back siphon test on the incoming water main, which proved we had a leak on the incoming main. Locating the exact position of that leak could prove challenging but excavation continued in the location of the ‘sink’ hole that had appeared until we eventually uncovered that salt glazed clay drainage pipework. It was immediately clear there was a problem when looking in the inspection chamber, as a hole had been smashed into the top of the drain to allow the storm drain pipework to discharge into the top of the smashed drain; all signs pointed to poorly installed and poorly designed drainage.

Crudely installed drainage

Crudely installed drainage

Fluorescein dye test

Fluorescein dye highlights badly leaking joints

Fluorescein dye highlights badly leaking joints

We excavated further to locate the joints in the foul drain and tested the system for leaks using fluorescein dye, which showed the drainage and joints to be leaking badly. It was becoming clear that the drainage system and the inspection chamber to the rear of the property was a mess so we advised the client to replace both the drainage and the inspection chamber; the client agreed and further excavation to dig out both the drainage and the inspection chamber continued, and this is where we got lucky… as excavation continued we uncovered the leaking water main, which essentially was a leaking joint between old lead pipework and the section of polyethylene piping entering the building. The water was escaping at a fair rate of knots once uncovered so in essence we had two substantial subterranean leaks in the same location.

Excavating old inspection chamber. Note lack of connection to main foul drain!

Excavating old inspection chamber. Note lack of connection to main foul drain!

 

Drainage Repairs

We advised the client that the lead main should be replaced but this couldn’t be done at this time and the leaking joint was repaired, followed by installation of a new preformed plastic inspection chamber and associated pipework. The clay collar was cut off existing salt glazed pipework to allow a connection to be made to the new plastic drainage with a flexible rubber connector, which was secured with stainless steel hose clips.

 

Completed drainage repairs

Completed drainage repairs

As a business we’ve invested heavily in diagnostic equipment, even purchasing our own CCTV drain inspection camera, because wherever we deal with structural cracking or indeed dampness in buildings, we almost always find subterranean leaks to be the cause of the problem and we like to give our clients answers rather than deferring that work to others.

 

 

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Structurally Unsound Composite Floor Joists

Floor Fails to Take the Load in Bovis New Build

 

Typical composite I Beam

Typical composite I Beam

We carried out an inspection of a Bovis new build last week that was less than 2 years old and in buildings of this age you don’t expect to find structurally unsound composite floor joists in the floor but that is precisely what we did find.

Visual Defects

We noted a number of defects to the first floor all centred on the landing area between three bedroom access doors and the airing cupboard.

We noted a large run out to the base of a bedroom door but checking the door showed it to be square, whereas the floor to the landing area was sloped significantly.

Significant slope to floor

Significant slope to floor

Moreover, we noted large gaps to the base of the bedroom door frames, which were so large that we could see where the nails in the sole plate had pulled from the floor as the floor had sank.

We then found that the dividing wall between the bedroom and airing cupboard could actually be rocked from side to side, and of course this movement explained why a number of cracks had opened up to skirting boards and door architraves.

 

Floor defects point to simple conclusion

We’ve inspected properties on this site before so we are intimately familiar with the construction and poor build quality so we know that the floors are constructed using composite I beams, which are then overlaid with tongue and grooved chipboard.

Floor separating from stud wall

Floor separating from stud wall

 

 

 

 

 

 

 

 

 

 

 

 

Insecure stud walling

Insecure stud walling

Failure of Composite Floor Joists

In this particular case  the range of defects led to one very obvious and significant conclusion, the floor was failing under the weight of the Megaflo hot water cylinder in the airing cupboard. The cylinder was not sat on a plinth and we are of the opinion that the floor was not strengthened in any way to take the significant  weight of this live load, which could be in the region of 350Kg’s.

 

As expected we also noted that the kitchen ceiling below was showing evidence of bowing under the live load and we have to wonder how many more properties on this new development will suffer from the same problem?

Floor sinking under the load of the Megaflo cylinder

Floor sinking under the load of the Megaflo cylinder

 

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Investigating Sulphate Attack in Floor Slabs

1960's bungalow. Sulphate attack in floorslab?

1960’s bungalow. Sulphate attack in floorslab?

We were asked if we could carry out another investigation into potential sulphate attack in a floor slab this week. The scenario was that the property, a 1960’s bungalow in a Nottinghamshire village, had recently been subject to a homebuyers survey report, which raised concerns with regard to potential sulphate attack in the solid concrete floors. The Chartered Surveyors report contained the usual caveats, “Inspection of the floor was limited due to existing floor coverings” etc. However, the report contained the following statement… “It is noted that some floors to the property are uneven and require further investigation. This type of unevenness felt within the floor is an indication there may be a problem with sulphites in the base to the floors.” Unusual I thought, since sulphites are more usually found in food and wine rather than floor slabs. However, we got the crux of the problem and explained the potential implications to our client when we received the call.

Straight edge highlights degree of heave in floorslab.

Straight edge highlights degree of heave in floorslab.

Sulphate attack is caused when sulphates contained within the concrete aggregate contain sulphates or the hardcore sub-base below the concrete contains sulphates. These sulphates react with the Tricalcium Aluminate in ordinary portland cement (OPC) to form Ettringite, a crystal that expands as it grows, in the process often causing  substantial damage to the concrete floor slab. Moreover there can be consequential structural damage as heave within the floor can displace internal walls built off the floor or indeed displace brickwork in the outer perimeter walls.

In terms of the investigation process we are looking to establish a number of things.

  1. How significant is the heave or cracking in the floor slab?
  2. Is there consequential structural damage?
  3. Is there a damp proof membrane installed between the floorslab and the hardcore?
  4. Sampling of both concrete and hardcore for laboratory analysis.
  5. Measurements to aid providing the client with a budget figure for floor replacement should sulphate attack be confirmed.
Verdigris to copper radiator pipes and localised cracking

Verdigris to copper radiator pipes and localised cracking

On internal visual inspection it was immediately obviously that there was substantial heave to the floorslab in a number of rooms and we pulled up two carpets for a closer inspection. It was obvious to us that there was high probability that the floorslab had failed due to sulphate attack. Sulphate attack is expedited by the present of moisture and we also noted that there were copper central heating pipes running through the concrete floorslab and also the the central heating boiler pressure was low. This raised alarms that a central heating system leak may well be contributing to floor moisture levels. Verdigris on the copper pipes indicated copper corrosion caused by being in direct contact with the highly alkaline concrete.

Bitumin oversite removed and coring through concrete slab for sampling.

Bitumin oversite removed and coring through concrete slab for sampling.

We set about sampling both the concrete and the hardcore because in our experience, the hardcore is often the prime culprit and the source of sulphates. Obviously, if there was a DPM installed then this barrier between the hardcore and the concrete slab significantly reduces the risk of sulphates coming into contact with the concrete. However, the concrete itself could contain aggregate with a high sulphate content, hence why both the concrete and hardcore are sampled and analysed for sulphates. Additionally we have a cement content analysis carried out on the concrete because this helps us determine the ratio of sulphate to cement, an important factor in determining the severity of failure.

Hardcore material on left and concrete on right.

Hardcore material on left and concrete on right.

We cored through the floor, initially cutting through an oversite of poured bitumen, which of course acts as a surface applied damp proofing barrier, this in itself told us that we would not find a polyethylene DPM installed. DPM’s started to be installed in floors around 1965 so this property would have been at the very front end of installations had one been installed.

The concrete itself was of very low quality and only circa two inches thick  so it didn’t take long to  cut through. We packed both a sample of concrete and retrieved a sample of hardcore material before making good the hole with a quick setting concrete mix; we did note that the hardcore material was extremely damp, adding to our concerns regarding a potential subfloor leak. Carpets were replaced and stretched with a knee kicker and we dropped the samples off at our laboratory. We’ve not actually obtained the results yet but we have warned of the very strong possibility that the heave found within these floor slabs is caused by sulphates. The reason for our pessimism, is the obvious visual damage seen to the floors and the poor quality of the hardcore material, which appeared to be crushed builders rubble rather than the usual fly ash or blast furnace waste that can cause this problem. Crushed builders rubble is a low quality hardcore fill material that often contains sulphates.

Cored hole made good prior to refitting carpets.

Cored hole made good prior to refitting carpets.

Our report will contain commentary on any structural implications found and of course will confirm or disprove whether the heave and cracking was caused by sulphates. We will of course also provide additional commentary relating to supplementary factors, such as the leaking central heating  system. A budget figure to replace internal floor slabs came in at around £15k, so this is a costly problem to remedy  when found.

 

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Rare Timber Framed House

Timber Framed and Technically Obsolete.

Rare 1940’s Timber Framed Building

I was asked to carry out a survey on a fascinating building this week, a very rare 8 bedroomed timber framed building. I’m told that there are only two of these buildings remaining in the whole of the UK so its highly likely that I won’t see another one and most  of us won’t see one of these buildings in our whole career. The building remains largely unchanged from the day it was built.

The building currently has a wall U-Value of around 2.1 W/m2K which is as bad as you’re likely to find and well below the current UK building regulations requirement for 0.16 W/m2K. There is no functional central heating system installed and residents gain what little warmth they have from an AGA in the kitchen, which is where they spend most of their time. It’s fair to say that they are built of sterner stuff than most of us, myself included.

Failed Hip Shingles

You won’t find any reference to this particular building in BR282, ‘Timber frame housing 1920–1975: inspection and assessment.’ The building was constructed in 1941 when masonry construction was the norm but I think there was a need for rapid construction and anecdotally I’m told that the building was used as accommodation for land girls during WWII.

Most timber buldings constructed at this time were platform framed but we’d need a more invasive inspection to confirm the exact method of construction.  We think that this is post and beam construction, or a structural frame of widely spaced timber posts with infill studwork set between the sole plate and wall plate. Joisted  and planked flooring and  4″ x 2″ rafters fixed to the wall plates at 400mm centres. Roof battens are 3″ x 1″ and closely centred to allow for a large headlap to the cedar shingles, because the roof has no sarking membrane installed. The internal walls are clad with plasterboard, which came into common use during the 1930’s.

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Closely centred roof battens allow for a large shingle headlap

 The building’s timber frame is built off traditional brick footings, to which a timber sole plate is attached, the timber frame is then built off the sole plate. There should be a physical damp proof course between the brick footings and the sole plate and indeed, the timber sole plate can be weak spot in these buildings as they are subject to timber decay. For a full assessment of these buildings the sole plate and the base of the timber posts should be opened up for inspection. However, for a timber framed building approaching 75 years old this in in remarkably good condition and serves as an interesting historical marker with regard to the need for rapid construction in the 1940’s.

 

 

Typical Directly Clad Stud Timber Frame

 

The walls of our building have  4″ timber studding at 400mm centres  that is externally sheathed with timber, however where the technical detail differs from the image is that this building has no insulation installed and rather than external timber boarding, this buildings is clad with cedar shingles. The roof is also clad with timber shingles. Whilst the technical details are interesting, the very obvious problem is that this building is technically obsolete and can not provide the level of thermal comfort required for modern living.  In fact, there is an oil fired central heating system installed but heat losses were so great in the building that once the system failed, the occupants had no interest in getting it repaired due to the high cost of heating the building. Unsurprisingly, the occupants tell us that the building is incredibly hot in the summer and incredibly cold in the winter.

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Shingle clad chimneystack

We understand the need to retain the external appearance of this building and we see no reason why this building should not provide accommodation for another 75 years, however, to achieve that aim, a substantial upgrade in thermal insulation is required, either internal wall insulation (IWI) or external wall insulation (EWI). Installing IWI, using something like 93mm Gyproc Thermaline would future proof this property without affecting the external aesthetic appearance but there would be a loss of internal floorspace, not a particular concern in a property of this size, however, this would involve major upheaval for the occupants and would also not deal with another concern relating to poor security. You’d gain entry into this property within two minutes with a decent battery powered circular saw.

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Cedar shingles can be retained.

Our preference would be to remove and store the cedar shingles and clad externally with a structural external wall insulation (SEWI) system, Structherm or similar,  the building lends itself very well to this approach since it has a wide soffit detail. The SEWI could then be over clad with the existing cedar shingles and the aesthetic appearance would be retained bar the fact that windows would be noticeably set back, a feature that would afford better weather protection. Whatever approach is adopted, this is a fascinating building that thoroughly deserves a new lease of life.

 

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Structural Assessment of Freestanding Walls

Sliding into Danger

Freestanding Wall & Zip Slide

We’ve had to assess structural integrity of two freestanding walls recently, the first was relatively straightforward and involved a resident who reversed their car into the boundary wall surrounding his apartment block. The client wanted to know whether the wall was safe in its damaged condition. Since it was also a retaining wall and damage fell outside of acceptable limits, we recommended that it was taken down and rebuilt. It was a very easy & objective decision based on information outlined in BRE Good Building Guide GBG 13.

The second was a little more unusual and called for a more urgent and subjective opinion. As a surveyor, there are often grey areas that call for professional opinion. In this particular case we noted damage to a 2m high rendered free standing wall, it had failed at its junction with the corner of the main building and also had a long horizontal crack at a bed joint. Both the leaning wall and the degree of cracking are easy issues to assess but what made this assessment unusual was the installation of a large zip slide to the rear garden that ended at the garden wall. The steel support post was installed just beyond the garden wall. In fact the damaged render tended to indicate that that users of this feature were hitting the wall hard with the base of their feet as the zip slide came to a stop. Now you might expect that hitting the wall would cause it to lean away from the zip slide but in fact it had the opposite effect. Impacting against the wall caused failure along a slip plane near the wall base, 4 courses up from the floor. Essentially, there was almost  a complete horizontal fracture of the mortar bed joint.  Impacting against the wall appears to have caused counter rotation at the top of the wall so that it leaned towards the zip slide button seat rather than away from it.

Extract from BRE GBG13

You’ll see by the extract taken from BRE GBG13 that a decision to take down and rebuild was fairly straightforward since the wall in question had a full width horizontal crack exceeding 600mm in length. The lean was within acceptable limits.

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Horizontal failure across the mortar bed joint.

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Fracture at Junction with Main Building

Where the matter becomes complicated is when assessing whether the wall presents any immediate danger to the occupants or general public that facilitates the requirement for immediate taking down to make safe. Had the zip slide not been present then we were satisfied that this wall presented no immediate danger but  the structurally unsound wall and a zip slide installation were a dangerous combination and we advised the occupants to not use the zip slide and further advised our client that the wall needed immediately taking down and rebuilding. Digging up and re-siting the steel support post for the zip slide so it is planted in front of, rather than behind, the rebuilt garden wall may prevent re-occurrence of future impact damage.

 

 

 

 

 

 

 

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Cutting Corners – Builder Short Cuts

A Number of Builder Short Cuts Adopted by Builders

Builder Short Cuts – We come across so many short cuts adopted by builders that I thought I’d start a regular post highlighting some of the strange decisions made by site trades people to save on time or money. As you’ll see, some of the decisions taken make no sense whatsoever. See for yourself.

Short Cuts 1

New consumer unit

New consumer unit

Why not use the circuit labels supplied?

New Ground Spike

New Ground Spike

Laid directly over the patio as a trip hazard.

Need a matching slate?

Need a matching slate?

This will do fine!

Need to remove downpipe?

Need to remove downpipe?

No need, just render around it.

Use of plumbers mate to stop leak

Use of plumbers mate to stop leak

Quicker to tighten unions on valve?

Need a roof vent?

Need a roof vent?

Just hide duct behind rafter.

Need another roof vent?

Need another roof vent?

Just hide duct behind rafter.

Double glazing in timber frame

Double glazing in timber frame

Needs installing on glazing bars.

Installed drains in wrong place?

Installed drains in wrong place?

Just grind a hole in your Aco channel.

Not maximising access costs

Not maximising access costs

Ignoring other defects is not smart.

No frost protection on condensate

No frost protection on condensate

A critical omission

Need a newel post fixing kit?

Need a newel post fixing kit?

Just nail them on!

 

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A Case of Pillowing or Mattressing? – EWI Failure

A Brief Explanation of Failure Modes in External Wall Insulation Systems

Screen Shot 2015-10-11 at 20.05.42We were recently asked to look at an EWI failure for a potential client. This was a homeowner who had spent £15k on having their home externally refurbished with an EWI system. At circa £100 per square meter this was an expensive system but they’d done their homework and were happy to pay a little extra because they believed that they were buying the best. I was more than a little alarmed when they explained that the system had been installed in 4.5 days and indeed, this did not align with  the 3 week programme that had been described by the installer.

Thankfully the  homeowner had taken photo’s throughout each stage of the installation and this made it easier to understand exactly what had gone wrong, even ahead of doing any invasive site investigation work. Our understanding is that within days of the installation being completed the homeowner noticed that the underlying EPS insulation boards could be seen through the finished coat of decorative render. This was initially noticed at night when the external uplighters shone against the render but as the days went by the boards also became clearly visible during the daytime.

The system designer looked at the problem and described ‘pillowing’ in the EWI system though no explanation for this phenomena was presented. Their proposed remedy was to strip off the render back to the EPS boards and to re-apply the base coat, mesh and finished render; a proposal that we do not feel will go close to addressing the problems on this installation.

In fact, we didn’t agree that this was pillowing but we can understand why the term was used since the insulation boards can also be seen under the finished render when either pillowing or mattressing occurs.  Both effects are generally linked to poor adhesion when the board is bonded to the substrate unevenly across its surface,  for mechanically insulation fixed boards the same effect could also occur where the recommended fixing pattern has not been followed.  We recently encountered an installer who fully bonded phenolic boards to counteract board shrinkage but we’re not aware of any evidence proving this proposition and our view is that it will have little or no effect on the problems caused by board shrinkage, our solution to this problem is not to specify Phenolic boards.

Whether you see pillowing or mattressing can depend on external temperatures and pillowing is linked to warm temperatures, whilst mattressing is linked to cooler temperatures.  The amount of adhesive recommended varies from system to system and for this system a minimum coverage of 40% was recommended.  There is a slight anomaly here since generally you should avoid voids between the insulation and substrate to prevent a stack or chimney effect, this is a naturally induced vertical flow of air that is to be avoided in these systems.

Poorly Installed EWIS

IMAG1882

Poorly jointed EPS

20150708_172146

Insufficient base coat application

20150708_173127

Exposed edge bead

20150708_172320

Poor coverage to reinforcing mesh

20150708_173526

Bead prior to decorative coat application

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Mesh prior to decorative coat application

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Poorly trowelled base coat

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Poorly trowelled base coat

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Poorly trowelled base coat

Screen Shot 2015-10-11 at 21.27.28

EPS boards visible under decorative coat

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EPS boards visible under decorative coat

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EPS boards visible under decorative coat

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EPS boards visible under decorative coat

IMAG1878

Poorly installed EPS

IMAG1870

Poorly installed EPS

IMAG1877

Poorly installed EPS

IMAG1835

Uninsulated reveals

IMAG1876

Poorly applied corner bead

IMAG1841

Poorly jointed EPS

IMAG1885

Timber pattressing and poorly jointed EPS

IMAG1888

Timber pattressing and poorly jointed EPS

IMAG2046-2

Failed sealant 8 weeks after installation

Interestingly, in this particular case, the system designer ordered some 20mm thick insulation boards that we understand were to be used to level off the substrate but they were never used by the installer. Once the EPS boards were installed they should present a  ‘smooth in-plane finished surface’, any high spots should be rasped or sanded to achieve this if required. The installers mentioned to the homeowner that they were short of base coat but when questioned as to why they hadn’t ordered more, said that they’d ‘managed’ with what they had.  Clearly they didn’t because the the mesh should be free of wrinkles and fully embedded in the base coat with the mesh pattern just visible on the finished surface. The system  logo should not be visible through the cured reinforcing coat and yet it was clearly visible. The manufacturer of this system also states that supplementary mechanical fixings are used with the adhesive insulation systems, especially during the strength development phase of the adhesive curing and yet supplementary fixings were only partially used for reasons we cannot fully understand. You will see from the image slider that the insulation boards are clearly visible in the finished EWI system and it is our belief that the reason for this is simply down to the fact that the base coat was too thinly applied to fully cover the underlying EPS boards. The effect got progressively worse in the days following installation due to shrinkage in the  base coat and decorative coat as it fully dried after the installer left site. They may have applied the term ‘pillowing’ as a generalised term to describe a situation where the underlying boards could be seen but as we said, we do not believe this is the technically correct description. The standard of installation is so bad on this particular property that we don’t believe that the three foreign sub-contractors who installed this system were certified installers, site communication was very poor due to language issues and they certainly weren’t managed during the process. However, we don’t want to mention the particular system that was used because we think this is probably irrelevant at this point. It is yet another perfectly good EWI system that has very poor site specific design and installation.

We have an update to this particular tale… 2 weeks after writing this blog and approximately 6 weeks after installation the system has developed its first moisture blister, we expect this to be the first of many but we’ll continue to monitor whilst the system designer provides a second technical report into the alleged reasons for failure. For some reason the first technical report was never made available and will never see the light of day though I suspect that may be due to our involvement.  We’ve inserted two images, one of the area where failure has occurred prior to application of the reinforcing mesh and topcoat and another of the finished render showing the moisture blister.

IMAG2081

Moisture blister near base of downpipe. Note terrible edge detailing on render.

Note poor detailing at base supporting rail

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Alternative Support – Timber Decay Case Study

An Unusual Approach to Providing Support for Replacement Floor Timbers

IMG_0103

New tannelised timbers at risk of further decay.

I thought this item worth posting purely because of the unusual approach adopted to dealing with the problem… The problem found is fairly typical; a cellar that would have originally been incredibly well ventilated due to an open coal chute had at some point seen the chute bricked up. This drastic reduction in air flow resulted in high relative humidity levels in the cellar, which is subsequently absorbed by the timbers, thereby placing them at risk of timber decay.

In this case the floor joists had all been recently renewed and ordinarily, the method adopted to replace the floor joists would be to build them back into the wall, ensuring that a ‘boot’ is formed around the end of the joist using a DPC material to ensure that the timber is not in direct with wet brickwork, or you could install joist hangers and sit the floor joist ends  on those.

What was clear is that the the high humidity levels that caused the original timbers to rot were still present because on testing the timber moisture content we found  moisture content to be above the 20% danger limit for ongoing risk of timber rot.

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Bespoke steel supporting framework

What is unusual about this particular case is that once the new floor joists were installed someone saw fit to specify a bespoke steel frame around the perimeter walls to support the joist ends. This must have been a very costly and to my mind completely unnecessary installation.  The joist ends appeared to be built into the masonry though I can’t say if they had the required bearing surface and perhaps the specifier was concerned about further rot to the joist ends and adopted this belt and braces approach.  They would have been far better to deal with the root cause of original timber rot by reinstating the volume of air flow that previously existed with the open coal chute.

 

 

 

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Bricked up coal chute significantly reduces air flow to cellar.

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