How to coat previously lime-washed walls

A large number of old buildings, particularly in rural areas, have been coated with lime-wash ( also referred to as white-wash). Restoration of these buildings is a complex affair and needs to be undertaken by a skilled contractor who is prepared to pay attention to detail.
The external walls of many of these structures can be anything up to 50cm thick, built without a cavity or damp-proof course. Lime-wash does not seal these walls, so in winter months the walls get very damp, but due to their thickness this moisture never reaches the interior. During summer months the walls dry out, and the lime-wash allows this moisture to permeate though it unchallenged. The paint coatings applied to the exterior of these walls has to be breathable i.e. they should allow moisture vapour to pass through them at a high rate. Matt coatings, with an excess of pigment over binder content, are suitable, and less expensive than the sheen coatings usually used on exterior walls.
Before coating, all lime-wash needs to be removed from the walls. This is best done by scraper and bristle brush as high pressure water-jetting is not an option on old clay brick walls. This is a tedious process, requiring a lot of patience and perseverance. Once all the lime-wash has been removed, and the inevitable repairs to the plaster have been completed and dried, apply one coat of an alkali resistant Plaster Primer and allow to dry overnight. This primed surface can then be top-coated with an interior-exterior matt finish paint such as MattCoat 40.

What are 'high-traffic' coatings

Work-space floors can have very different requirements due to the activity that takes place in that particular area
From high people-traffic in school or office block passageways, to heavy vehicle load-bays or work-shop floors - each area has its own set of challenges. Substrates can vary from wood, to galvanised iron through to screeded concrete, and it is essential to take these factors into account when selecting a suitable coating.
When it comes to coatings (as opposed to self-levelling screeds), twin pack epoxies tend to be the product of choice. They are self-priming on cured cement (due to their chemical resistant properties) and can be applied directly to bright metal - although priming with a twin-pack etch primer would give better long term results.
On wooden floors - where high traffic is expected - it would be better to use a twin-pack polyurethane. They are, in general, more flexible and do not yellow over time so that the natural appearance of the wood is not affected.
Passageways, depending on the volume of traffic, the substrate, and in the case of schools - the budget, can be coated with twin-pack epoxies (best option) or single pack polyurethane enamels. The single pack polyurethane enamel, although not as abrasion resistant as the epoxies, is far cheaper and can be applied by less skilled applicators.

How to identify the type of coating currently on a surface

When selecting the coating type to apply to a previously painted surface it is important to know whether incompatibility could result. The best way to avoid this is to first identify the coating type currently on the surface. Quick tests can narrow the options down to a level where a potentially expensive compatibility problem is avoided.
Without becoming too technical, dry coatings exhibit solubility, or a lack thereof in certain solvents, and this can be used to identify the coating type on the surface.
The method used is to rub the surface of the coating with a rag wet by solvents 15 times back and forth (known as 15 double rubs), and inspecting the rag for dissolved paint.
If 15 double rubs using Lacquer Thinners as the solvent caused no dissolution of the paint coating, then the product on the surface would be a twin pack epoxy or polyurethane.
Similarly, if a high aromatic solvent dissolves the coating, a water-based coating is indicated.
If the high aromatic solvent does not dissolve the coating, but Lacquer Thinners does, then a single pack solvent based product is likely to be on the surface.
Although this is not a fool proof method of testing a paint film, it does give a good idea of what one is faced with, and helps when selecting a new top-coat option. Costly mistakes are avoided when the correct information is at hand when specifying coating systems to be applied to previously painted surfaces.

Honest advice vs making a sale

A conflict arises when visiting a site between making a sale and giving the customer the best advice possible. We like to solve coating problems, and if the problem can be solved by using a product on our range, then a sale is possible. It is better to walk away from a sale than to offer a solution that is not guaranteed - your own personal integrity, as well as the technical integrity of your products remains intact. For a technical person this is probably easier than for a salesperson driven by commission, or sales targets, but we pride ourselves on the fact that we do not fall into that trap. This is why we have technical consultants rather than sales-people. Many a time have we advised customers to tile rather than paint, to go for cheaper options in certain applications, or simply questioned the reason for wanting to paint in the first place. Paint cant solve all issues, and the customer needs to be told when this is the case, so that more cost-effective alternatives can be looked at. In the same way, customer expectations of coating systems need to be managed - by giving accurate information with regard to life-expectancy of the coating - so that later disappointments are avoided.

Importance of identifying the needs of the substrate

In many cases we have been to sites and viewed substrates that have different requirements for different areas of the same substrate. A factory floor often will have high and low traffic areas in the same work-space. Wine-cellar walls often have wet areas where lower sections of walls need more specialised coatings than the remainder of the wall. Exterior walls often have exposed plaster or brickwork below the damp proof course that need a different coating than the upper walls.
It is important for a contractor or specifier to identify these requirements before coating work commences, so that the correct combination of products can be used. This saves a lot of money in the long term and keeps the coated structure looking its best for the longest period of time possible.

Solvent Sealer

Solvent Sealer is a clear, solvent based pure-acrylic penetrating coating. It was originally formulated to seal coloured floor screeds, but has since its launch found many other areas of application. Being a pure acrylic, it is non yellowing, making it an ideal choice to seal interior or exterior cementitious substrates. Flower pots, planters, face brick walls and paving, concrete walk-ways and stoeps have all been successfully sealed by this product. It is a low viscosity product that penetrates and binds the substrate, with little film build-up on the surface, so that the character of the surface is minimally affected. The product is xylene-based resulting is a very quick drying time. The abrasion resistance is appreciably lower than that of twin-pack coatings so only low-traffic areas should be sealed with this product.

"Food-grade" paint

We get a regular stream of calls asking for food-grade paint for coating interior walls and equipment in food processing areas. The short answer to the question put to us is that there is no such thing. Additives such as colourants, preservatives and flavourants that are used in processed food and beverage production are sold as food-grade as they are consumed. Paint, on the other hand, will hopefully not be consumed. Dry paint films are, in the main, non-toxic and are safe when it comes to contact with food. Over the years many of the known toxic raw materials used in paint production have been banned and replaced with safe alternatives. Low VOC (volatile organic compounds - basically solvents) coatings are available to be used when called for, further reducing the chances of consumables being tainted during production. A range of FDA approved biocides has been offered to us for use in products destined for use in food or beverage processing plants - the use of products will contribute further to the safety of the coating supplied. Good planning of maintenance during plant shut-down periods will ensure that no contamination of consumables occurs during the application phase, and that a fully cured and thus food-contact safe coating protects and decorates the interior of your food or beverage processing plant.

Previously coated wine tanks

Many of the older wine cellars still have steel wine tanks in use. These tanks are typically decades old, and often have been coated on the exterior with many layers of a variety of coating types. On number of occasions we have been called in to advise on the route forward with regard to the rehabilitation of such tanks. After sterilizing and cleaning the tanks - Fungal Wash followed by Tornado Degreaser - it is possible to get a good look at what is being dealt with. Now rust can be removed and treated, before selecting a suitable top-coat. We have, in many instances, gone the route of recommending Druiwebakverf (Fruit-bin paint) - a quick-drying solvent based acrylic/chlor-rubber bound coating incorporating an anti-corrosive pigment. The acid resistance of the coating is a big advantage, and the cost relative to twin-pack materials is favourable. It can be applied to substrates where alkyd based coatings were previously used, which is often the case.

Cleaning and sterilizing of wine tanks

Maintenance of cellar hygiene plays an important part of over-all cellar maintenance. We advocate a pro-active approach to the control of fungal growth, rather than waiting for the inevitable unsightly appearance of contamination before treatment is considered. This applies equally to coated surfaces as well as stainless steel tanks. Regular sterilization and cleaning of tanks ensures that they remain in a bight and shiny condition. After the application of Fungal Wash to the contaminated surfaces, the tanks can we washed down - either by high pressure water-jetting, or by manual scrubbing - using Tornado Degreaser. This is a very simple and inexpensive treatment that will keep one of the components of the cellar in great shape.

These are examples of well maintained tanks from different cellars in the Western Cape. Some of the tanks we see are very badly contaminated, and the "before photographs" would be quite alarming.

Densification of cement plasters

Cement floor screeds or wall plasters can be densified by application of a solution of sodium silicate.
Sodium silicate is a liquid glass, that, simply put, bonds to the cement/sand matrix and reduces the spaces between particles in the matrix. This results in the hardening of the upper layer of the plaster, as well as reducing the porosity without fully sealing the surface. It is inexpensive, non-toxic, odourless and very easy to apply. This makes it an ideal option in certain applications, particularly where legislation does not call for the substrate to be sealed. There is no need to wait for the product to dry before walking over the applied area, as no film is forming on the surface. Lithium silicate is a slightly more costly variant, said to have better properties with regard to hardening.