Wall coating Problems

Spray or trowel applied exterior wall coatings are often sold as a quick and easy fix or answer to the prevention of water ingress. Also sold as a cure for other damp wall problems such penetrating and rising damp. Within a few days, complete homes, built with old stone, brick or lime based renders can be encased and covered with this impervious textured-plastic like wall paint. So what can go wrong and what can cause wall coating problems

Many people believe they will never have to worry about exterior wall maintenance again and that rain and damp can be kept out and that moisture within the wall can escape. In theory, having the wall of your house spray coated with this material would make perfectly good sense. But in practice, this is often not the case. On cavity wall build or over good dry walls this type of coating process can be a good choice and very successful. Unfortunately, problems can and do occur with wall coatings on all types of walls, If applied without adequate surface preparation or the thick wall coating is over diluted with thinners (spirit based) the coatings can crack and blister, allowing water ingress which traps damp within the wall.

Solid walls especially those without damp proof courses (DPC) rely on a vapour exchange equilibrium within the wall.Moisture is able to escape from inside the wall and surface water on the outside of the wall can evaporate when the weather is dry.The application of inappropriate wall coatings can upset this balance and can actually exacerbate damp problems 

Often promoted as a breathable, microporous paint, thick resin-oil based coatings do not breathe 

Over time the coatings can become brittle and crack, water then gets trapped between the wall and the coating, which also lowers the thermal properties of the wall. In addition, serious damp problems can be caused. If applied over a rendered surface the actual render itself can suffer from freeze-thaw water damage.

Unfortunately, on some applications, soft brickwork or stone is coated with a layer of hard cement slurry primer before the textured coating is applied, this slurry is brushed onto the wall to act as a filler and stabiliser. This slurry-slush coat can ruin brick or stone and can be impossible to remove damaging the surface beyond repair. See this project

This same cement based primer coat can also stop the wall from breathing.

Resin-based heavy textured wall coatings do not normally respond well to sandblasting removal methods, they are not easy finishes to remove. It’s worth noting that the pre-1983 US derived Kenitex formulas can also contain asbestos.

Why have so many homes been treated with this type of exterior textured or smooth wall coating

Depending on the firm involved a typical textured coating sales presentation can include the use of sales aids to demonstrate the supposed microporous nature of the paint such as the bubble pipe, pictured below.

During the sales pitch, in addition to making claims that the textured coating will allow moisture to escape freely, the salesperson may use this bubble pipe apparatus to try and convince people further that the coatings do in fact actually breathe.

This is how the ruse works:

The pipe is filled with a few mm of water on the side that has the textured coating on. The hand pump is squeezed a few times, pressuring the chamber under the coating section. Miraculously air bubbles rise through the coating. It all looks very impressive and convincing. 

Supposed to demonstrate that textured coatings breathe

Meanwhile back in the real world, this demo is nothing more than a gimmick. If a house was pumped up under the same kind of pressure all manner of liquids, vapours and air would escape through the walls.

Claims of breathability by those selling these textured wall coating products should be entirely dismissed. Solid wall houses, thick resin-based spray or trowel applied coatings and their associated cement slurry coats can be a bad combination. Putting this material on an old damp solid wall could be a recipe for disaster and a complete waste of money. Homeowners are often given a presentation to demonstrate the flexibility of the external wall coating product. A flexible piece of plastic on which the coating has been applied is bent from side to side, without cracking the textured coating,  again this looks impressive. But this is normally done at room temperature. If you ask the salesperson to pop the flexible demo thing in your freezer for 20 mins or so you will get a completely different result. The flexible card will no longer be flexible and will snap like a cracker, as the coating will not be able to provide flexibility with the lower temperature just like the kind of temperatures your exterior walls have to cope with in winter. 

Once a house has been covered with this type of paint it can be ruined. It can be extremely difficult and damaging to clean off, some external wall coatings can genuinely ruin houses, sometimes making restoration of them impossible. Often cracking and blistering, lots of these thick resin coatings have created problems for homeowners. Failure of a textured wall coating can be due in part to inadequate preparatory work such as not washing down or stabilising old paint finishes or the lack of primer coats.

Common damp problems are sometimes just down to incompatibility of the wall coating, old solid walls houses, especially those without damp proof membranes can have a much higher moisture content than cavity wall build. This type of textured spray coating on a solid damp wall can stop the wall from breathing, often resulting in some serious damp damage.

Removing external textured wall coatings is not a really a job for the inexperienced or DIY person. Over the years we have removed thousands of square metres of this coating from all types of buildings if you have this textured wall finish on your house and want to be rid of it get in touch with the experts.