Hornbeam
Established Member
There have been quite a few questions over the years about the suitability of profiled metal sheeting for small domestic size workshop buildings.
As I have worked with coated steels for cladding for the last 20+ years, I thought I would pull together a couple of guidance notes for people on this forum to refer to. I will try and cover the following areas but not all at once
Which coating to choose
Different profiles/products
All the bits and bobs to make a good system
Putting it all together.
Coatings
Selecting the right coating is really important as this is one of the main factor which will dictate teh durability of teh building. There can be quite a cost difference between a high spec coating and a cheap one, but after that the rest of teh build costs are the same so saving a couple of pounds at the start is false economy
All profiled cladding will have a steel substrate which provides the structural strength for the product. As steel corrodes quite quickly, this will then be coated on both sides with a zinc or zinc alloy. Better quality products generally use a zinc/aluminium alloy, which has a much better corrosion resistance, particularly at the cut ends of teh sheets where the steel is exposed. One of the ways manufacturers cut costs is by putting less zinc/zinc alloy coating on. The amount of coating is quoted as grams zinc/square metre, Better products will have 250 to 275g/m2 but some of the cheapest will have less than 100g/m2. More coating gives more protection. Note some plain galvanised products may have higher coating weights but these are generally not used for cladding
Virtually all steel for profiled cladding will have a paint system applied to the zinc alloy coated steel..
Polyester coatings. These are generally the cheapest coating system and are only about 18 to 25 microns thick. They tend to scratch very easily, which as well as not looking great gives an easy starting point for corrosion on the zinc. Polyester coatings can also suffer from blister failure, where very limited corrosion starts under the coating which then blisters away from teh substrate. Manufacturers guarantees on polyester coated steel are very limited. In a non coastal environment, I would expect this type of coating to need some form of maintenance within 10 years
PVDF, These are very high specification coatings, with outstanding surface appearance and extremely good colour fade resistance which is why they are often used on buildings like car show rooms etc. They are generally applied at between 25 and 40 microns. While they have a good appearance, they tend to scratch extremely easily and so are often provided with a thin plastic strippable film which is removed after installation. Again these coatings can suffer from blistering but much less than polyesters. In a non coastal location, I would expect this type of coating to need some form of maintenance after about 15 years As they are an expensive/aesthetic coatings I would generally not recommend this type of coating for this type of application
Polyurethane coatings. These coatings are what I would term a medium build, generally between 50 and 80 microns thick. They tend to strike a balance between aesthetics and durability. They have much better scratch resistance than polyesters or PVDF and the scratches have to be quite significant to go all the way through the coating. There is quite a variation in the quality of these systems and so the durability/ life expectancy is quite varied. I would expect this type of coating to need some form of maintenance within 20 to 30 years depending on quality
Plastisols. These are thick robust coatings usually 200 microns with either a leathergrain or dimpled emboss pattern. They are very scratch/scuff resistant and are the only coating I would recommend for areas which might get scratched of for roofs. A big word of warning is that the performance of these coatings is very variable from different manufacturers as it is the small (expensive) additives in the paint formulation which give it high resistance to sunlight , colour fade and cracking. The best product will last over 40 years, the poorest will need maintenance within 15 years, The problem is that the ones with the leather grain emboss all look the same on day 1 and you cannot tell by looking. The product with the dimples is unique to one manufacturer and this is an outstanding product
Reverse side coating. Most material is sold as single sided, which means that it will have one of the above coatings on the exposed side. The reverse side will usually have a very thin polyester coating (~10 microns thick) which is generally adequate
Colours. Be aware that brighter and darker colours tend to absorb more UV and so tend to fade quicker and are also slightly less durable
Guarantees. Most manufacturers do not offers guarantees for domestic customers, however if you look at what they offer to commercial and industrial applications it will give you a good indication. These range from nothing to some limited liability through to full repairs for the duration of the guarantee (up to 40 years in 1 case)
The best starting point is a good quality plastisol from a reputable manufacturer
If people are still interested I will do another bit in the next day or so
As I have worked with coated steels for cladding for the last 20+ years, I thought I would pull together a couple of guidance notes for people on this forum to refer to. I will try and cover the following areas but not all at once
Which coating to choose
Different profiles/products
All the bits and bobs to make a good system
Putting it all together.
Coatings
Selecting the right coating is really important as this is one of the main factor which will dictate teh durability of teh building. There can be quite a cost difference between a high spec coating and a cheap one, but after that the rest of teh build costs are the same so saving a couple of pounds at the start is false economy
All profiled cladding will have a steel substrate which provides the structural strength for the product. As steel corrodes quite quickly, this will then be coated on both sides with a zinc or zinc alloy. Better quality products generally use a zinc/aluminium alloy, which has a much better corrosion resistance, particularly at the cut ends of teh sheets where the steel is exposed. One of the ways manufacturers cut costs is by putting less zinc/zinc alloy coating on. The amount of coating is quoted as grams zinc/square metre, Better products will have 250 to 275g/m2 but some of the cheapest will have less than 100g/m2. More coating gives more protection. Note some plain galvanised products may have higher coating weights but these are generally not used for cladding
Virtually all steel for profiled cladding will have a paint system applied to the zinc alloy coated steel..
Polyester coatings. These are generally the cheapest coating system and are only about 18 to 25 microns thick. They tend to scratch very easily, which as well as not looking great gives an easy starting point for corrosion on the zinc. Polyester coatings can also suffer from blister failure, where very limited corrosion starts under the coating which then blisters away from teh substrate. Manufacturers guarantees on polyester coated steel are very limited. In a non coastal environment, I would expect this type of coating to need some form of maintenance within 10 years
PVDF, These are very high specification coatings, with outstanding surface appearance and extremely good colour fade resistance which is why they are often used on buildings like car show rooms etc. They are generally applied at between 25 and 40 microns. While they have a good appearance, they tend to scratch extremely easily and so are often provided with a thin plastic strippable film which is removed after installation. Again these coatings can suffer from blistering but much less than polyesters. In a non coastal location, I would expect this type of coating to need some form of maintenance after about 15 years As they are an expensive/aesthetic coatings I would generally not recommend this type of coating for this type of application
Polyurethane coatings. These coatings are what I would term a medium build, generally between 50 and 80 microns thick. They tend to strike a balance between aesthetics and durability. They have much better scratch resistance than polyesters or PVDF and the scratches have to be quite significant to go all the way through the coating. There is quite a variation in the quality of these systems and so the durability/ life expectancy is quite varied. I would expect this type of coating to need some form of maintenance within 20 to 30 years depending on quality
Plastisols. These are thick robust coatings usually 200 microns with either a leathergrain or dimpled emboss pattern. They are very scratch/scuff resistant and are the only coating I would recommend for areas which might get scratched of for roofs. A big word of warning is that the performance of these coatings is very variable from different manufacturers as it is the small (expensive) additives in the paint formulation which give it high resistance to sunlight , colour fade and cracking. The best product will last over 40 years, the poorest will need maintenance within 15 years, The problem is that the ones with the leather grain emboss all look the same on day 1 and you cannot tell by looking. The product with the dimples is unique to one manufacturer and this is an outstanding product
Reverse side coating. Most material is sold as single sided, which means that it will have one of the above coatings on the exposed side. The reverse side will usually have a very thin polyester coating (~10 microns thick) which is generally adequate
Colours. Be aware that brighter and darker colours tend to absorb more UV and so tend to fade quicker and are also slightly less durable
Guarantees. Most manufacturers do not offers guarantees for domestic customers, however if you look at what they offer to commercial and industrial applications it will give you a good indication. These range from nothing to some limited liability through to full repairs for the duration of the guarantee (up to 40 years in 1 case)
The best starting point is a good quality plastisol from a reputable manufacturer
If people are still interested I will do another bit in the next day or so
