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My Blog


Keeping a roof clean

Posted on 13 May, 2013 at 13:00 Comments comments (107)
Keeping a roof clean 
By F. Moal 

When looking at an ageing building, few people cast a critical eye at the state of the roof. The windows are clean, the garden tidy and the interior spotless, but the roof is almost invariably unkempt. Black moulds hide it's colour and moss slowly mats itself in the bonds, so slowly that few take notice. 

The encroachment of grime and moss has it's effects :  Beyond the architectural downgrade the fabric of the building is at risk. Doing nothing is ultimately the expensive option. The risk varies with the nature of the roofing material : Thatch and wood shingles are at a more immediate risk of decay. 
Metals erode under the acidic releases of lichen and moss. Lead and zinc used in soakers and rainwater disposal will thin down to eventually leak. Clay tiles need to dry between rainfalls to fulfill the promise of durability - if not premature shaling or frost damage may occur. 
On all material the permanent presence of a bio film is deleterious by increasing capillary creep in laps and interstices. This in turn leads to undetectable moisture ingress. Generally materials retaining moistures are prone to contamination and combined with a shady winter exposure porous materials such as concrete tiles will become a good host for moulds such as A. Niger, then algae, followed by moss and lichen. As the bio film becomes established, the moistures are more permanent, and the cycle accelerates. 
Architects do not seem to enter this constrain in their choice of roof material : 
This was of no consequence in the days of acidic rain, but  cleaner air results in nature reclaiming it's place in unforeseen ways. There is no easy answer to the return of nature :  
Excessive moss has to be removed by hand. Mechanical means used on the ground are ill adapted to a pitch roof.  
Jetting causes irremediable erosion to the surface. As a result the un-wanted host returns with a vengeance, only to hide the uneven, permanent discolorations of the roofing tiles. After clearing the roof from the bulky growth the next and final step is to spray the area with a dedicated anti algal wash. The right product, such as Mossgo-Pro will kill the remaining biological life at the surface and, most importantly, in laps and interstices. The dead bio film will soon loosen under diurnal cycles, helped by the wind, rain, heat and frost. 
Self cleansing is a lengthy affair - months in most cases with latent effects stretching over a period of two or three years. The roof will become cleaner with the change of seasons and reveal it's original colour and texture. 
There is no known preventative measure of any durability. 
Clear hydrophobic  resins degrade under UV in a matter of months. The same causes - substrate porosity and sun exposure - will have the same effects, at the same rate. This however is slow and a roof treatment is to be regarded as decennial maintenance. 
Further maintenance will not be as heavy as the first clean, if carried out as or before the surface contamination triggers the condition for accelerated growth. 
On the continent, antiseptic roof shampoo has been standard practice for decades. Roofing firms offer it as a standard way of finishing remedial work and as preparation to fitting out solar panels. In Britain the practice is expending quickly :  The process has been adapted to the northern more demanding climate of the British Isles. 
The website hosts a wealth of information on roof maintenance treatment. 

HD Roofing Services in Ireland, are among the most experienced contractors to use the Mossgo pro roof cleaning system. For more info or advice call Andrew on 087 9323863 or mail him at [email protected]  

Walls, rough cast render and pebble dash cleaning.

Posted on 15 April, 2013 at 13:28 Comments comments (9)
Hi Folks,

Just a quick one on something that we are coming across a fair bit lately.

Wall Cleaning 

Walls, roughcast renders and pebble dash treatment. 

The extensive use of rough cast renders and pebble dash on walls has led to the development of appropriate cleaning techniques. 
Coloured renders or Monochouche as it’s also known was particularly popular during the most recent building boom here in Ireland.  
Although the new build industry has all but gone these types of plastering are appearing more and more as services such as External Insulation continue to grow. 
There’s nothing wrong with these wall coverings, done right they actually look really well and versus a traditionally plastered then painted wall I’d choose a coloured render all day long. 
Like all external surfaces though it’s only a matter of time before they become dull, discoloured and stained from growths such as red and green algae or lichen.  Trouble is, due to the granular type finish to render or the easily loosened pebbles on pebble dashing the very last thing you would want near these surfaces is PRESSURE WASHERS! 

 I recently done a roof repair for a girl whose house was finished in a bright yellow render, the place was immaculate, you could tell she spent many hours in the garden and cleaning her home. A little too much as it happened. I asked what happened to the gable wall where I noticed a section where there was streaks going in all sorts of directions. Putting her hand to her forehead she told me that after noticing a red colour appearing on the wall she decided to try and rinse it off with her little electric pressure washer, big mistake!   
Like our Roof Cleaning technique, our treatment of Moss, Algae and Lichen is soft and safe enough to use on any type of external surface without any risk of damage to the substrate, and without the use of PRESSURE WASHERS!

Breaking the Mould

Posted on 10 January, 2013 at 5:14 Comments comments (5)
Breaking the Mould   

      Mould is easier to clean than the soot of old, but with the return of clean air, nature has reclaimed ground in a way not always foreseen. Problems sometimes arise when a building does not receive its full share of sun. In other places there are not enough sunny days in a year to stop deleterious growth. The issue does not affect all materials in the same way. Most roofing materials will someday need cleaning, but not all, and not at the same intervals. Choosing a roofing material with regard to its susceptibility to mould and moss encroachment is good design practice in shady locations. Below is a brief summary of material behaviours towards biological growth and reactivity to a non-aggressive biocide treatment.
Natural slates are not porous and display a smooth surface. As a result the material dries rapidly and is not naturally prone to roof growth with the notable exception of yellow lichen in coastal environments. The material cleanses readily upon treatment. It is a product of choice for shady locations. 

Manmade slates offer some of the advantages of natural slates, but not always to the same degree.
Fired clayof good quality is not porous. The surface dries rapidly and sheds the bio film satisfactorily when treated. The roof surface is however more textured than slates offering intersects where growth can take a foothold. 
Old clay tile roofs are fragile and are best treated from the eaves.   

Concrete tilesare not indicated in the vicinity of tall trees. The high porosity combined with a rough surface provides a natural host surface. Removing mated moss from concrete tiles is labour intensive. The material cleanses well, but more slowly than other materials. The alkalinity of the surface seems to benefit black blanket moulds. In recent years smooth and less absorbent concrete tiles have arrived on the market. They are a better choice for higher humidity regions.
Zincis not a natural host to live contaminants. It is however susceptible to organic acid releases from rotting leaves, moss and lichen and should be avoided on lower draining slopes and box gutters. 

Leadis also not a natural substrate for life. It is vulnerable to mild organic acids but paradoxically resistant to harsher mineral ones. Mossy tiled roofs draining into lead gutters will eventually jeopardise its integrity. 

Copperhas biocide properties. Water running over copper will acquire some of its cathodic properties by contact and hampering further downstream growth. The protection may not be sufficient to maintain the tiles in pristine condition along the whole rafter length. On canal tiles the protection is limited to the trough, where it is still the most needed. 

Aluminiumis not particularly affected by acid releases. Water running over it will become anodic and display the reverse effect to that observed on copper. The illustration of this is seen in the splash area of TV aerials.   

Flat roof feltsof bituminous kinds are not unduly prone to moss, but ponding, cluttered designs and raised walkways will host them. PVC felts become very slippery, but as is usual with algae, the treatment is rapid.   

Organic materialsare best used in full light where they can dry rapidly. Durable presence of moulds and algae will eventually jeopardise their integrity as roof covering. As the lining of wood shingles washes away, the grey cellulose needles are exposed and offer a slightly abrasive surface hosting algae. The treatment will reinstate the silver grey appearance for some time. Thatch, if badly affected will need combing beforehand.   
 For the existing stock, periodical maintenance is the solution. The general wisdom is to opt for the milder cleaning processes before considering harsher ones. Blanket moss has to be removed by hand, bagged and disposed of in all cases. The tiles can then be treated by the appropriate biocide. After the treatment, the dead bio-film will begin to loosen under diurnal and seasonal cycles, until the roof has regained the true original colour of its material. The rate of cleansing will vary greatly with the type of material, and the exposure to wind and driving rain. Not all chemicals are appropriate, and a few only authorised by the Health and Safety Executive (HSE). All formaldehydes, caustic soda or bleach based chemical are proscribed. 
The application method and knowledge is as important as the biocide itself. Jet cleaning is seldom appropriate to roof cleaning. The pressure removes surface aggregates, creating a moisture retaining surface favourable to the return of the contaminants. Tile impregnation and coatings are ways of mitigating the damage done by jetting, but at a cost sometimes higher than simply replacing the tiles by new ones. In conclusion, the return of clean air means new parameters for the choice of roofing materials by the Architectural Technology professional, and the specification of a nonaggressive maintenance procedure for existing roofs. This is easily searched for on the Internet. A comprehensive approach to roof cleaning and the provision of specification support is a sign of an experienced specifier.   

The author is Managing Director of TVSPLtd, which specialises in a roof cleaning process known as the Mossgo Roof System, supplier to HD Roofing Services Ireland.

Reasons why you should not pressure wash a roof

Posted on 21 June, 2012 at 9:02 Comments comments (196)
I have been asked recently about some of the posts and comments I have been making on things like Facebook and Twitter regarding why you should never pressure wash your roof. 
A power washing company recently sent me an e-mail asking for reasons why I think this. So here you go...
The three most commonly used roofing materials in Ireland are probably concrete tiles, fibre cement (man-made) slates and natural slates. I can give you a few examples for each as to why they shouldn't be pressure washed, and anyone experienced in fitting these products will tell you the same.

Concrete Tiles
I feel like I've beaten this one to death over the last few months but it is the most common cause of leaks that we come across. On a concrete tile you have a lip either side, one high one low, so side by side they interlock. If the lower lip of the tile breaks, and the break is higher than the headlap (the coverage you have with one tile over another) then you have hole in your roof. This is a weak point on most tiles, and some so much so that a tap of a knuckle will break it easily not to mention a pressure washer. 
Leak sourcing and repair.These holes may be already present on the roof before a pressure washer gets there and becuase they are covered by the higer lip, would not be seen without inspection of every individual tile. Then follows the increased flow of water into the hole, with only in some cases an underlay to keep it from some very expensive damage. 

Fibre Cement Slates
These man-made slates were definitely the favoured choice of most  building contactors during the now distant construction boom in Ireland. They offered a cheaper alternative with the same sleek finish as the more expensive natural slate, but unfortunately have no where near the life expectancy or colour durability of the natural stone alternative. 
Over a short period of time weathering takes its tole on this type of material, on installation these slates can withstand a certain amount of bending before they break, after a couple of years on the roof they become almost as brittle as a thin sheet of glass and again a tap of a knuckle is enough to break them.
Effects of moss growth. Damaging moss growth. With only a thin protective layer on these slates, moss and lichen can eat through them very easily and expose the the inner layers rendering the slate next to useless. Also a with moss's ability to hold water like a sponge, expansion between the joints and ends of the slates can cause the now brittle slate to snap. The slates are fixed at three points, two nails either side and a copper crampon at the bottom, because of this even broken slates often stay in place and to the eye all looks as it should do without close inspection.
Add a couple of thousand p.s.i. to these weaknesses and you will only shave years of the already short lifespan of fibre cement slates.

Natural Slate
If well maintained and cared for correctly, natural slates will last a number of lifetimes and in most cases will only give problems when they've outlived the man made fixing they were fitted with.
Like all natural products no two are the same, gradient, texture and shape differ with every slate. Because of this each slate has its own level of durability. When laid out on a roof it is next to impossible to tell which slates are strong, which are weak, or if they may be cupped slightly. For this reason, not matter how careful, foot traffic should be kept off natural slates completely so not to run the risk of any damage. 
The very same has to be said for pressure washers. 
Before pic natural slate roof kildare village. Dark algae and lichen.after image of natural slate roof cleaned by HD Roofing Services Ireland 
With each of these materials, moss and algae can grow in and under joints and completely out of reach of the spray of any pressure washer.
The reason the person is having the roof cleaned in the first place is so that these growths are removed. Leaving bits behind to continue the organisms reproductive cycle is pointless and at best will only keep the roof looking clean for a few months, before things start heading back to square one.

These are only an example of reasons not pressure wash a roof, and i'd be here all day if I was to go on.
We, at the same time, do highly recommend keeping a roof cleaned and well maintained for reasons I will touch on more next time. Just know your options, you really do get what you pay for.

Behaviour of Algae, Lichen and mosses

Posted on 6 June, 2012 at 9:34 Comments comments (353)
Algae are a diverse group of simple, plant like organisms. Like plants, most algae use the energy of sunlight to make their own food, a process called photosynthesis. However, algae lack the roots, leaves, and other structures typical of true plants. Algae are the most important photosynthesising organisms on Earth. They capture more of the sun’s energy and produce more oxygen (a by-product of photosynthesis) than all plants combined. Algae vary greatly in size and grow in many diverse habitats. Microscopic algae, called phytoplankton, float or swim in lakes and oceans. Although most algae grow in fresh water or seawater, they also grow on soil, trees, and animals, and even under or inside porous rocks, such as sandstone and limestone. 

Algae also form mutually beneficial partnerships with other organisms notably with fungi to form lichens-plant-like or branching growths that form on boulders, cliffs, and tree trunks.The algae provide oxygen and complex nutrients to their partner, and in return they receive protection and simple nutrients. This arrangement enables both partners to survive in conditions that they could not endure alone.There are more than 15,000 kinds of lichen in the world. They can grow on any surfaces and anywhere in the world. The lichen is a symbiotic association between a fungus (mycobiont) and an alga (photobiont). The filaments of the fungus support cells of the algae.The fungus needs carbon and energy. Generally it finds it on dead organic material or on living organisms (parasitism) which cause disease to plants. The algae, capable of photosynthesis, provide the carbohydrates it needs. It also provides some vitamins (biotin, thiamine). The algae changes the structure of the fungus which can absorb a lot of water and a part of sunlight to protect the algae from certain strong wavelengths.The fungal component of lichens produces organic acids that disintegrate rock, giving the lichen a better hold and contributing to the weathering process, which eventually turns a rock into soil. Lichens can withstand great extremes of temperature and are found in all parts of the world. In the built environment, the organic acids are notoriously deleterious to zinc and lead used for flashing or gutter lining. 

Many small plants bearing the name moss are not mosses in that they do not belong to the Bryophyta family. The “moss” found on the north side of trees is the green alga Pleurococcus;Irish moss is a red alga. Beard lichen (beard moss), Iceland moss, oak moss, and reindeer moss are lichens. Spanish moss is also a term used for a lichen. The term moss used in connection with MossGo does not refer to Bryophytas, but to the vernacular use of the word.   

Keep power washers off your roof!

Posted on 17 May, 2012 at 11:37 Comments comments (0)
I was sat in my car outside a local super market a few months back and a guy was sticking leaflets under the wiper blades of other parked cars. After he noticed I was in my car he knocked on my window to hand me his leaflet, he was advertising his 'pressure washing service' that included roof cleaning. I asked him how much to have the roof cleaned? 
"It depends on the house boss, give me your number and i'll have a look" he says to me.
"But will that not damage the roof?" I asked,
"Not at all boss, sure have you seen the rain we're getting lately, its no different to that"
"Sure I have your number here, i'll think about it and give you a bell."
Yeah right! 
Seriously though, are people really paying for guys like this to get up on their roof (insured or not) and pressure wash years off the life of their roofs materials, and that's getting away lightly too!
Firstly, to put this fella into perspective, for argument sake his washer was a mere 3000psi. A very hard rain falls at around 2psi...
Secondly, every roof, whatever its material type is, has certain weak points. Take the concrete tile for example. 
Leak repair. Leak sourcing.Where the two tiles meet side by side, the underside lip is often a weak point and walking wrongly on these is enough to break them, never mind directing around 3000psi of water at it. 
If the lip breaks higher than the head lap of the tile below then you have a hole, like you can see in this pic from the water marks on the timber. 
Without having to go through all roofing materials on the market concrete tiles are one of the stronger more durable ones and it doesn't take a lot to damage them.

Premature aging and exposing weaknesses are just a couple off a long list of reasons why I believe you shouldn't let a pressure washer near your roof, but unfortunately I haven't got all day.
At the same time, I do recommend you have your roof cleaned and guttering kept clear in order for everything to function correctly and water to get away safely.
We began our low pressure roof cleaning service for these reasons, and being roofers, understand the do's and don'ts involved in having a roof cleaned correctly and safely.
So to the guy with his pressure washer and knowledge of his industry...
                                                     Jog on (boss)!


Where's all this moss coming from?

Posted on 27 April, 2012 at 14:39 Comments comments (388)
While looking through some old photos (late 80s to 90s), it caught my eye that in the background many of the roofs that were visible were all virtually spotless. You can drive to any housing estate more than a couple of years old, or to any house on its own in the countryside nowadays and you'll do well to find one that is not either green with moss and algae or covered in yellow lichens.
Remove unsightly growths safely with damage to the roof materials.
So why all of a sudden, in the space of a few years is there so much moss, algae, lichens and other growths present on not only roofs but other external surfaces like walls and paths?
My first thought was climate change, but surely there hadn't been that much of a change in such a short time. After looking into a bit more it slowly began to make sense.

Governments across the world, including ours here in Ireland, have been working for some time now on regulations and directives brought about by what they call 'the clean air act'. This is something that, especially in the last few years, has always been high on the agenda of these big 'summits' that seem to happen a lot lately.
Moss, algae and lichens are just a bit of proof that the measures these governments are taking to clean up the air we breathe, are actually working.

New Roof. Fibre cement slating. Moss prevention. 
Loais Its widely known in the roofing industry that copper strips placed under a ridge, can go a long way towards preventing these growths (an expensive, and not 100% effective method in my opinion), due to the sulphars that are released from the copper oxidizing when wet (not perfect wording, I'm no chemist, as you can tell) It was these sulphuric acids and other pollutants that have been present in the air and rain for many years that were keeping the roofs and other external surfaces all along...

Simple really when you think about it. The part I found hardest to get my head around was the fact that the government actually seem to be getting something right! Ah boy Enda!