As I mentioned on a recent post regarding roof maintenance, this is the time of year that I see contractors come out of the wood work with their pressure washers unleashing havoc on unsuspecting home owners.
Many contractors offer services to pressure wash the exterior walls on homes. This is especially prevalent on stucco homes. In the worst case scenario, the contractor will even add a soap dispenser to the gun.
Pressure washing any building component is usually a bad idea. You are blowing water at high pressure at surfaces that are not water proof. This water often migrates below the cladding's surface where it can become trapped for weeks or even months in the wall assembly. The water will often migrate to large areas behind the cladding utilizing capillary action (water can travel in all directions when a small gap/crack is present). This trapped moisture can then start to deteriorate the building paper or wrap, change the properties of the paper or wrap (once these materials are wet for over an hour, they loose most of their ability to shed water - no protection during next rain storm). These actions then can lead to the underlying structure (Plywood/OSB sheathing) getting wet and starting to deteriorate. A secondary problem is that any part of the wall assembly that has been previously saturated tends to attract water in the future (even if it has completely dried out) lowering its defence during subsequent rain events. Finally, just the pressure itself can lead to mechanical damage of the wall components.
Adding soap to the mix really escalates the problems. Soap contains surfactants. These surfactants change the molecular makeup of building papers and wraps substantially reducing their effectiveness to shed water (on a permanent basis). You have now compromised the buildings sole defence against water ingress (the cladding is only considered a water shedding surface not a water resistant surface).
Most wall cladding can be cleaned with a simple brush and low pressure garden hose. For stucco, you might want to try specific cleaners formulated for this application. They are sprayed on, allowed to soak for minutes/hours and then rinsed off. You may also benefit from one of those car washing wands that attach to a garden hose and have a spinning head. Just stay away from the pressure washer. This includes trying to remove loose paint prior to re-painting. You will often create the problems mentioned above and the wood surfaces are often still wet (on the underside surface) when the cladding is re-painted leading to a paint job that will not last as blister form as the trapped moisture evaporates in the sun and causes a vapour bubble to form below the paint's surface.
Do not be duped by these contractors. Do your research and get informed. Say no thanks to any contractor who offers to pressure wash any part of your home's exterior.
Thursday, June 23, 2011
Cedar Roof Maintenance - Pressure wash services
It is about this time every year that my blood starts to boil, not because it is so hot (like that is going to happen this year), but because I see the vast deluge of contractors out offering pressure washing services to unsuspecting home owners who want a better 'looking' home.
In the last week alone, just in my neighborhood, I have seen two contractors pressure washing roofs (one shake and one asphalt shingle). If you talk to any knowledgeable building envelope professional, they will cringe when you discuss this subject because this cleaning method often leaves behind a trail of destruction long after the contractor has left.
Lets look at each of these in detail. Bare in mind that most pressure washer contractors are like Tim Taylor from the popular TV show Home Improvement, it always makes sense to buy the biggest & baddest monster machine you can get your hands on. Translation - Lots of Pressure!
First the wood shake roof. Wood shakes are usually split. This results in the wood pieces separating from each other along the cell wall boundaries. The wood cell walls are much harder than the cell interior so this process leaves each shake with a hardened surface. This surface provides better water shedding capabilities and stands up better to UV degradation. Most pressure washers have more than enough pressure to strip away the cell wall leaving the softer cell interior. This cell interior absorbs water much easier and breaks down quicker under the sun's rays. The process also saturates the shake (often on both sides of the shake). The shake would not get this wet under normal rain conditions. As this work is normally done in sunny seasons, the top exposed side of the shake often dries quite quickly in the sun and wind, usually much faster than the bottom-hidden side of the shake. This results in stresses to the shake which often lead to cupping and eventually cracking. Now you need to call a roofer to flash all of these new cracks so that you have a properly lapped system again (do not have a cracked shake lining up over a shake seam in the row below). Now you also have a shake surface that is not as durable as the surface that was blasted off with the pressure washer.
The wood shingles fair even worse. These are almost always cut (not split) so the soft cell interiors are already exposed. It takes very little pressure to etch the wood material away. I have often seen roofs during inspections that have up to 1/4" blasted from their surface. They are also much more susceptible to cupping and cracking after a pressure washing incident.
There is also a secondary source of damage created by these contractors. Most wear some form of cleats while on the roof. Think of these cleats as two meat tenderizers on the bottom of their feet as they are producing the exact same effect. In both wood shingle and shakes, the contractor is peppering the surface full of holes that now lets the rain water penetrate to a much deeper depth which in turn accelerates the rate of deterioration of the roof.
On asphalt roofs, the damage created by pressure washers is obvious. A big pile of granules in the gutters at the bottom of the roof. Granules that are needed to protect the waterproofing asphalt substrate from being damaged by the Sun's UV rays. By removing these granules (and even a low pressure pressure-washer will), you are accelerating the deterioration of the roofing system.
Many of these contractors advise their unsuspecting clients that there services will extend the roof and some even offer a 'guarantee' (good luck trying to collect on it). In all of my experiences, the act of pressure washing a roof has significantly diminished the lifespan of the roof not extended it. I consider these contractors as incompetent at best and fraud artists at worst. It is time for the public to demand better. One step would be to require any contractor, who works on any part of your roof system, to be trained and certified by the Roofing Contractors Association of BC. That way, they would be required to follow the RCABC best practices guide even when it comes to maintaining a roof's surface. Homeowners can check out the RCABC Consumer Guide for instructions on how to properly maintain a cedar roof (pg 117).
Do not be duped by these contractors. Do your research and get informed. Say no thanks to any contractor who offers to pressure wash any part of your homes exterior.
In the last week alone, just in my neighborhood, I have seen two contractors pressure washing roofs (one shake and one asphalt shingle). If you talk to any knowledgeable building envelope professional, they will cringe when you discuss this subject because this cleaning method often leaves behind a trail of destruction long after the contractor has left.
Lets look at each of these in detail. Bare in mind that most pressure washer contractors are like Tim Taylor from the popular TV show Home Improvement, it always makes sense to buy the biggest & baddest monster machine you can get your hands on. Translation - Lots of Pressure!
First the wood shake roof. Wood shakes are usually split. This results in the wood pieces separating from each other along the cell wall boundaries. The wood cell walls are much harder than the cell interior so this process leaves each shake with a hardened surface. This surface provides better water shedding capabilities and stands up better to UV degradation. Most pressure washers have more than enough pressure to strip away the cell wall leaving the softer cell interior. This cell interior absorbs water much easier and breaks down quicker under the sun's rays. The process also saturates the shake (often on both sides of the shake). The shake would not get this wet under normal rain conditions. As this work is normally done in sunny seasons, the top exposed side of the shake often dries quite quickly in the sun and wind, usually much faster than the bottom-hidden side of the shake. This results in stresses to the shake which often lead to cupping and eventually cracking. Now you need to call a roofer to flash all of these new cracks so that you have a properly lapped system again (do not have a cracked shake lining up over a shake seam in the row below). Now you also have a shake surface that is not as durable as the surface that was blasted off with the pressure washer.
The wood shingles fair even worse. These are almost always cut (not split) so the soft cell interiors are already exposed. It takes very little pressure to etch the wood material away. I have often seen roofs during inspections that have up to 1/4" blasted from their surface. They are also much more susceptible to cupping and cracking after a pressure washing incident.
There is also a secondary source of damage created by these contractors. Most wear some form of cleats while on the roof. Think of these cleats as two meat tenderizers on the bottom of their feet as they are producing the exact same effect. In both wood shingle and shakes, the contractor is peppering the surface full of holes that now lets the rain water penetrate to a much deeper depth which in turn accelerates the rate of deterioration of the roof.
On asphalt roofs, the damage created by pressure washers is obvious. A big pile of granules in the gutters at the bottom of the roof. Granules that are needed to protect the waterproofing asphalt substrate from being damaged by the Sun's UV rays. By removing these granules (and even a low pressure pressure-washer will), you are accelerating the deterioration of the roofing system.
Many of these contractors advise their unsuspecting clients that there services will extend the roof and some even offer a 'guarantee' (good luck trying to collect on it). In all of my experiences, the act of pressure washing a roof has significantly diminished the lifespan of the roof not extended it. I consider these contractors as incompetent at best and fraud artists at worst. It is time for the public to demand better. One step would be to require any contractor, who works on any part of your roof system, to be trained and certified by the Roofing Contractors Association of BC. That way, they would be required to follow the RCABC best practices guide even when it comes to maintaining a roof's surface. Homeowners can check out the RCABC Consumer Guide for instructions on how to properly maintain a cedar roof (pg 117).
Do not be duped by these contractors. Do your research and get informed. Say no thanks to any contractor who offers to pressure wash any part of your homes exterior.
Subscribe to:
Posts (Atom)