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Thin Coat Render tinting colour consistency, why are batch quantities important?

Why is batch to batch consistency an issue? What are the pitfalls of ordering little and often? Is ordering small quantities just an added cost? Is ordering more than enough better than just enough? Surely a “British Standard” colour is the same wherever I buy it from or whoever produces it? How do I avoid creating a moving target? These are all related to the same topic and the net results being the same, a potential problem; A colour difference.

All thin coat renders are a blend of constituent parts, each part made independently and joined together at least once, to create a coating. Some ingredients are joined together to make a part that goes in to making another part and so-on. Every time one component is produced, it is manufactured to a tolerance. By definition, where there is a tolerance there is the opportunity for a variance, this in turn can lead to inconsistencies and in render terms it can lead to appearance differences.

The moment you order or require additional render for an existing job, by definition it is a new product/batch of render. Yes, the same formulation may be used but if the constituent parts are slightly different tolerance the end result will be slightly different. You may have noticed that wall-paper has a batch number on every roll and that you need wall-paper from the same batch to ensure the patterns align correctly. The same wall-paper producer, producing the same pattern will recommend the use of the same batch. If the wall paper rolls are not from the same batch the patterns will not usually match up, even if in only one small segment of an edge. This is because the one of the constituent parts in the same factory (paper, inks, printing or cutting machinery) is different from the alternative batch. The same can be said for renders, particularly thin coat renders.

How can these situations be avoided? It is not as straightforward as ordering a specific RAL/BS level and be assured it is going to be the same colour. Every render manufacturer has their “own version” of a shade which falls within “their tolerance” of the colour. If you request the same colour from the same manufacturer, the colour may be slightly different due to the forementioned tolerances in the constituent parts. The only way to be sure of getting a consistent thin coat render colour throughout is to make one batch of the right size. Assuming this is thoroughly mixed it will ensure that the first tub is the same as the last tub in this batch. Any thin coat render produced in any other way could have variations, however small. As tint and binder stocks rotate, a variance one way or another may lead to changes, most are so small that they are un-noticeable. These changes can magnify over time as more and more batches are produced. What are the answers? For most manufacturers it is not commercially viable to produce single render batch in quantities of less than 1000kg and so the chances of every tub being exactly the same colour is limited. So, the next best thing is to order enough thin coat render to complete the job in hand as this will at least remove one link from in terms of batch-to-batch risk. When ordering a tub or two at a time, the risk is increased due to the “turn-over” of constituent parts over a prolonged period of time. Better to have 10 x 25kg tubs made at the same time in comparison to 1 x 25kg tub made every week. If you for whatever reason you need additional thin coat render to match an existing job, how do you best avoid batch to batch variances? If you haven’t ordered enough render initially, do not use every last drop of material before starting the next tub, use the original tubs and keep topping-it-up to blend any variances as it is used. Some render manufacturers will supply a batch number and this may relate to the formulation used or possibly a retained swatch of render from that batch. If further thin coat render is required, the batch number can be given and the supplier can produce to the same formulation and check the colour and sheen against the retained panel. If the same formulation is used, the thin coat render supplied may fall within “their tolerance”, which may be visibly noticeable to the eye.  Will a supplier charge you for matching? Arguably yes, arguably no. Should a render company be able to produce the same colour every time? In theory yes, in reality not every time! The need to order enough render at the beginning of the job will invariably come back to haunt you if you under budget on quantity. Hopefully this will give an insight into batch-to-batch variances and demonstrates the benefits of ordering the right amount of thin coat render for every job. This scenario is typical for all thin coat render producers, anyone who mixes thin coat render has the same issue.

A very common misconception is “colour standards”, by definition a “standard” is “something used as a, norm, or model in comparative evaluations”. When this is used in paint or render production it is quickly followed by “tolerance” defined as “an allowable amount of variation of a specified quantity”. A quick explanation of colour before getting in too deep, colours can be decoded and given a numerical position on a colour graph. If you imagine a cross on a clock face, with Yellow at 6 o’clock, opposite yellow is blue at 12 o’clock, Red at 3 o’clock and Green at 9 o’clock, every colour falls somewhere on the clock . That same colour when produced can be measured and as long as it falls within its manufacturers tolerance it is deemed a good commercial match. The problems begin when different manufacturers have different tolerances or the same company produces one batch within tolerance slightly on the “yellow” side of their “standard” and the next batch on the “blue” side of the tolerance, visible change may be negligible or noticeable. The next batch may be “bluer” again and so the colour drifts batch on batch and the potential for change increases.

This blog is not designed to give a clear-all solution, it has been produced to give a wart and all insight into paint production. Batch-to-batch consistency is resultant on the pigments, binders, dispensing equipment and critically quality control. If the pigments and

binders are not very tightly controlled; the dispensing of the formulation counts for very little in terms of consistency. Many car paints cost significantly more than industrial or domestic paints, this is largely born from the quality control of the pigments and binders. Hence why there may be more than two dozen variants of “Arctic” white, this is where the shade has moved over time in a car production plant.

Long story short, if you are unsure please contact us!

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