Melamine vs PU

Two of the most popular transparent/natural wood finishes are melamine and PU(Polyurethane). Melamine and PU are both synthetic hydrocarbon polymers which form a film over the wood surface that is coated, thus laminating it. The purpose of lamination is to preserve the wood by not allowing the moisture of the wood to escape, preventing it from damage from the elements and protecting it from wear and tear from use. Both finishes enhance the aesthetics of the wood by allowing light to refract inside the transparent layer formed by them. Both the finishes have a similar application procedure by spray. So, what is the difference between the two?

The main difference is in the life of the coatings and its resistance to the elements.

PU Finished Door

Melamine was a great improvement over wood polish as a transparent wood finish when it was introduced in the Indian market in the late 80s and the 90s and is popular to date due to its economy. But melamine has its limitations. The film formed by melamine is only moderately resistant to water. It deteriorates when exposed to sunlight. The film easily yellows and looses lustre. The film begins to crack at the wood joints over time.

With the advent of polyurethane (PU) in the late 90s, most of the shortcomings of melamine were covered. PU forms a tougher film than melamine. It is more scratch resistant. It is flexible and does not crack with the movement of the wood joints. It is UV resistant and can be used on woods that are used in exteriors, such as entrance doors and windows. It does not yellow easily and gives a high lustre. The lustre is also retained longer due to its UV resistance.

PU gives clear advantages over melamine as the application procedure remains the same for both and there is no new skill required to apply PU. Thus the work involved takes the same time and effort on part of the applicator.

Consider wood finishing as a one time investment as reworking of wood finishes takes up lot of resources, skill, time and money. Go for the best coating for your expensive teak or other exotic woods as it will not only preserve the wood but also enhance its aesthetics.

Some things to note when applying Melamine or PU

Melamine or melamatt polish as it is popularly known among the painting contractors is usually sprayed over French/hand polished surfaces, which is not the intended procedure of application.

A study of melamine shows that for all intents and purposes, as in PU, was not originally developed as a wood coating. It is a product of innovation and adaptation that these products are used as wood coatings. The adaptation requires a specific application procedure for the product to perform as a wood coating. These application procedures are grossly ignored by applicators and contractors.

A damaged French Polished door

Applicators apply generous coats of French polish and NC Based Sanding sealers as a preparation for the final coating by melamine or PU. They do this as their skill set for colour matching of wood is based on French polish techniques.

The melamine and PU films often fail as the solvents in the French polish and NC sealers are not compatible with solvents used in PU and melamine coatings. Also, the solvents in the French polish applied under transparent coatings are exposed to light and begin to evaporate and cause blisters in the polymer film formed over it.

It is thus highly recommended that application of French polish be avoided when any such coatings are applied. Wood coated by French polish has its own charm and should not be over coated by polymer coatings.

There are much simpler and compatible colour matching techniques for melamine and PU using wood stains, which we shall discuss in another post.

For a huge range of wood finishes visit http://paintnhardware.com/20-wood-finishes

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Why it is worth investing in quality paint for mild steel fabricated structures

Mild steel fabrications such as entrance gates, safety grills, rolling shutters, collapsible gates, sliding doors etc are known and used for their strength amd durability. They take a short time to be fabricated and can be quickly installed.
They however have a high initial cost and are meant to last a lifetime.

Mild steel has an achilles heel though and it is rust and corrosion. Expose to water, sunlight, dust and pollution cause the structure to corrode and loose its strength and its lifespan quickly shortens. The high initial cost comes to no avail.

It is wise thus to preserve the mild steel structure using anti corrosive paints and coatings.

Normal enamels and metal primers available in the market such as redoxide and zinc chromate primers are prepared using alkyd based binders. These binders typically have a lifespan of 1-2 years on exposure to the elements. The binder being the main film forming and barrier forming medium in the paint heavily influences the life of the paint. Due to the  inferior quality binder, the regular enamels begin flaking and chip off in a short span of time, leaving a small area of mild steel exposed. Smaller areas of exposed mild steel corrode much faster and begin to rust. Rust being more voluminous than mild steel causes the paint in the area around the corroded spot to chip off, causing even more rust, snowballing into a much more serious problem.

To save your invested time and money, it is hence worth investing in a good quality coating for your metal structure. It is also worth following best practices while applying the coating.

To coat any mild steel structure, the following is the best coating procedure.

Start off by removing any corrosion or rust using a rust remover and if necessary use a wire brush. Pay special attention to weld joints and corners as these are the most stressed and are prone to rust. Apply a coat of epoxy based metal primer generously over the surface. Zinc phosphate based epoxy primers are the best ones as the zinc phosphate acts as an active rust inhibitor. Allow the primer to fully cure. Fill dents, crevasses and holes using a polyester based putty, commonly known as a body filler. Give ample time for the putty to set. Apply another coat of the zinc phosphate primer. Allow to cure. To finish the coating aesthetically and to build resistance to deterioration of the coating from exposure to UV, apply a polyurethane based enamel as the final coat. Apply 2 coats of the PU coating, typically using spray equipment.

The above treatment will provide an extremely durable finish and a long life to the mild steel structure.

Special care must also be taken to protect parts that are sunken in the ground. 2-3 coats of the epoxy zinc phosphate primer must be applied before installation. The primer coat must not be damaged during the installation.

Thickness of the coatings on parts that are exposed to hand and foot traffic must be built up using an intermediate hi-build coating to resist wear and tear.

For a wide range of industrial paints and paints meant for mild steel, visit our site : www.paintnhardware.com
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