Insulation with polyurethane foam: pros, cons, technology

Energy prices have been on the rise lately, and efficient home insulation is one of the main tasks that homeowners have to solve. One of the latest materials that appeared on the market a few years ago is polyurethane foam. This is a coating that is applied in a continuous layer on any (practically) surface. Insulation with polyurethane foam is the most effective. 

Types of sprayed polyurethane foam and application technologies

Polyurethane foam is obtained by mixing two components – a diisocyanate and a polyol. Both components individually are toxic, therefore, work is carried out with respirators. Mixing two toxic substances form a safe polymer – polyurethane – absolutely neutral, which does not react with any substances. Polyurethane foam after hardening is absolutely harmless and is often used in the food industry.

When mixing the two components, active gas formation occurs – mainly carbon dioxide is released. It turns out to be enclosed in the thinnest polyurethane shell, which gives high thermal insulation performance (carbon dioxide does not conduct heat well).

The mixing of the two components takes place in a special gun under high pressure. To obtain the perfect foam, the components must be heated to 45°C (there are heated supply hoses, and there are special heaters). Under pressure, in the form of very fine dust, the components are mixed in a gun and sprayed onto the surface, where they foam and then harden. This is the insulation with polyurethane foam.

To achieve the declared qualities of the material, diisocyanate and polyol must be supplied in equal proportions. Even a slight increase in one or another component adversely affects the characteristics of the material. Worse, if there is more diisocyanate – such a foam quickly “sits down”, then collapses, loses its heat-insulating characteristics. If you overdo it with polyol, the picture is a little better – the foam becomes brittle, but it fulfills its tasks, although it has a higher thermal conductivity than stated. This is precisely one of the disadvantages of polyurethane foam insulation – the end result depends very much on the qualifications of the workers and the class of equipment used.

It is possible to mix the components in the given proportions almost perfectly exactly using high-pressure installations. Therefore, when choosing a company, you need to pay attention to the equipment that they have at their disposal – with low-pressure installations, you will most likely get a non-uniform coating with poor thermal insulation characteristics.

But different equipment is not everything. There are also different types of polyurethane foam by cell type and density:

• Open-cell lightweight PPU. According to its characteristics (thermal conductivity), it is very similar to mineral wool, with the same main drawback – it is hygroscopic, while it costs much more than mineral wool. That is, when using lightweight polyurethane foam (density 9-11 kg / m³) it will be necessary to provide its hydro- and vapor barrier from all sides, to organize a ventilated facade – to remove excess moisture. As a plus, you can write down a higher sound insulation (compared to mineral wool). It is extremely rarely used for insulation of external walls and roofs, since it simply does not cope with the tasks set – it gets wet and loses its thermal insulation properties. With all that, it costs more than mineral wool. But for the insulation of internal partitions and ceilings it is used successfully (in combination with all hydro / steam insulating layers), also providing good sound insulation.
• Closed cell polyurethane foam. Regardless of the density, it is not hygroscopic, it adheres very well to almost any surface, with the exception of polyethylene. There are the following types:
  • Medium density – 28-32 kg / m³. The standard solution when using sprayed thermal insulation on walls, ceilings, unused roofs. Provides good thermal insulation with a thermal conductivity coefficient of 0,02-0,028 (for air 0,022, lower only for vacuum). Vapor permeability is average – 0,05 (comparable to wood).
  • Medium density for filling cavities. The characteristics are similar to those described above, but it expands more slowly, it freezes only after full foaming. It is used in the construction of layered walls, roofs, etc.
  • High density polyurethane foam – 40-80 kg/m³. It is used for insulation of exploited roofs, under a screed, in other places with a high mechanical load. Due to the higher density, it has a slightly higher thermal conductivity coefficient – 0,03-0,04, the vapor permeability is the same – 0,05.

If we talk about prices, then the cheapest is lightweight open-cell polyurethane foam. But if we add the need for a hydro- and vapor barrier, then in general the price of insulation will not be so low. At the same time, it is still unrealistic to achieve perfect insulation, and it may well turn out that this type of PPU insulation will be cold. So that you can navigate the prices, we give approximate prices for different types of foam (material + work):

• light with an open cell from $180 per cubic meter;
• closed-cell medium density – from $ 650 per cubic meter.
  

Closed-cell polyurethane foam, per cubic meter, is much more expensive, but it does not require any additional layers, except for finishing. It is not afraid of water or steam, it has been fulfilling its tasks for a long time (more than 25 years). The exact price of insulation with foamed polyurethane foam depends on its density and layer thickness, the size of the sprayed surface. Considered individually.

Advantages and disadvantages

Let’s start with the merits:

• To date, polyurethane foam insulation is the most effective. This is due to the cellular structure of this insulation and the carbon dioxide contained in the cells. Ideally, this system gives a thermal conductivity coefficient of 0,02, which is even lower than that of air (0,022).
• Continuous, seamless coating that eliminates the presence of cold bridges, further increasing the effectiveness of insulation.
• The possibility of spraying on the surface of any, the most complex shapes.
• Low hygroscopicity. Simultaneously with the insulation, you improve the waterproofing characteristics of the surface. This property is used in the insulation of foundations, wells and other similar structures.
  

• Excellent adhesion to any surfaces and materials except polyethylene. Excellent adhesion (adhesion) in some cases can be considered as a disadvantage – it cannot be washed off with anything, since there is no solvent for PPU. It is cleaned only mechanically, often with fragments of the surface on which it was applied.
• Long service life – up to 25 years with the declared characteristics, later carbon dioxide is replaced by air, thermal conductivity increases, but not catastrophically, sprayed thermal insulation continues to work.
• If during the first year polyurethane insulation did not cause any complaints, there will be no complaints for the next couple of decades.
• When using high-pressure plants, polyurethane spraying takes a short period of time, and without compromising quality.
• Sufficiently high vapor permeability of polyurethane foam – 0,05-0,06, which allows excessive moisture to be removed through the walls, as well as before insulation (if the walls are vapor-permeable).
• Does not support combustion (self-extinguishing).

As you can see, a decent list of advantages that contribute to the fact that thermal insulation with polyurethane foam is gradually becoming more and more popular. But there are also disadvantages:

• High price – 1,5-2 times higher than with mineral wool insulation. But if you calculate for a year of service, it will turn out no more expensive.
• The end result is highly dependent on the equipment used and the experience of the duster. Good results are achieved only with full observance of technology.
  

• Due to the use of high-tech equipment, polyurethane foam insulation is very, very difficult to do with your own hands. There is a way out – to buy equipment in pool for several owners – in this, given the prices, there is a reason. But the question of having experience remains – it is very difficult to achieve normal indicators on your own.
• The material does not burn, but when burned, it emits a lot of acrid and harmful smoke.
• Fear of ultraviolet. Under the influence of sunlight, the foam fuses, the white surface becomes dark brown. But a film of a certain thickness protects the underlying layers from further destruction, so that with a sufficient thickness of the foam, it can even be left open. But the appearance of the surface insulated with polyurethane foam is far from the best, so a finish is still expected.

The main limiting factor in the spread of PPU insulation is the high price. Although, when compared with the cost of insulation with extruded polystyrene foam, the prices do not seem so high, and despite the fact that the sprayed thermal insulation is laid several times faster in time, it gives the best result. In general, if you are planning to insulate your home, this technology is worth exploring.

Application conditions and surface preparation

Even with good adhesion, which distinguishes polyurethane foam insulation, surface preparation will not be superfluous. First of all, you need to remove everything that crumbles – and first of all the old paint. Grease stains are also subject to mandatory removal and neutralization. They shouldn’t be.

Everything that should not be covered with foam should be covered with polyethylene, fixed with adhesive tape. It is necessary to fix carefully, without gaps – it is difficult to tear off the foam.

When insulating a roof with polyurethane foam, there are two ways to apply thermal insulation. The first – they make a permanent continuous crate, on which foam is poured. The second – make a temporary frame, consisting of two parallel planes.

If the outer walls of the building are insulated with polyurethane foam, it is assumed that there is a finish. And after cleaning the surface, you need to make sure that something can be strengthened – it will not work on foam. To do this, most often, wooden or metal planks are stuffed onto the walls, to which the exterior finish is then attached. This completes the preparation. But the application of polyurethane foam is only possible on a completely dry surface, at temperatures above +10°C. There are no other conditions.

Spray process

If you have entered into an agreement with a company, a minibus arrives at the appointed time. It has spray equipment. The pressure washer requires 380 volts to operate. If you only have 220 volts, a generator is usually run to supply the required voltage. A low-pressure apparatus can operate from a 220 V network, but, as mentioned below, the quality of thermal insulation will be much worse.

Usually, only hoses are pulled into or around the house, through which components are fed into the gun to form foam. It’s comfortable. Workers who spray thermal insulation are wearing protective suits, they are wearing a respirator, gloves and goggles. A respirator is necessary, since the components of the foam are toxic before hardening, and everything else is to protect the skin from getting PPU, which then cannot be torn off.

The foam is applied from the bottom up, in small portions. Pour everything, without gaps, trying to prevent the formation of shells. As the foam expands, ensure that the layer thickness is not less than required. After the foam hardens, the excess can be cut off, and the lack cannot be made up for.

Sprayed insulation parameters

It should be said right away that, as for any other insulation, it is preferable to insulate the walls of buildings from the outside. If you insulate from the inside, then the outer wall will freeze through. How many defrosting / freezing cycles it will withstand depends on the material, but rarely such a house will last more than 10 years.

When insulating with polyurethane foam from the outside, a final exterior finish is required – the surface has a very unattractive appearance. But there are no problems with freezing of the walls, the building will serve for a long time.

There are no problems with the roof at all. Roofing materials are designed for repeated freezing, so insulation with polyurethane foam of the roof can also be done from the inside, spraying it directly on the “wrong side” of the roofing material or on the crate.

Outside, insulate the house or figured out from the inside. Now a little about the layer thickness. Insulation with polyurethane foam is usually made of large thickness. This is not due to the fact that small is not enough. Usually, just according to the thermal characteristics, a thickness of insulation of 2-3 cm is required, but they make at least 5 cm. This is so that under any conditions the dew point is in the thickness of the thermal insulation, and not in the wall material. Since PPU is non-hygroscopic, it cannot get wet, condensation simply does not occur, and excess moisture is removed naturally due to the vapor permeability of the material.