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SMP: Silicone-modified Polyester Paint

In today’s marketplace, most pole buildings are roofed and sided with silicon-modified polyester paint or SMP.

SMPs create a middle ground between PVDFs (Polyvinylidene Fluorides) and polyesters. Also known as silicone-protected and siliconized polyesters, SMPs use polymerized silicone to improve polyester’s chalk performance and gloss retention. Companies initially experimented with varying levels of silicone, and marketed high levels as superior to lower levels, but silicone became less important as the polyester resins themselves improved. Most SMPs now contain 30 percent or less silicone.

Steel Paint LayersSilicone-modified polyester systems vary greatly in quality. Polyester quality outweighs silicone content in importance, but SMPs still outperform straight polyesters in chalk resistance. A more important difference is in pigment type and quality. Some formulations use the same ceramic pigments as PVDFs; others rely on simple inorganics or organics. Since the better resin does little to prevent an organic pigment from fading, paying for silicone is no excuse for going cheaper with pigment.

SMPs vary in gloss from 20-60 at 60 degrees (semi-gloss to medium gloss). Realistic warranties for SMPs vary between 10-20 years and can feature impressive chalk, fade, and gloss retention promises. There are companies which do offer unrealistically long SMP warranties – I would encourage the reading of the actual warrantees closely, before paying extra for a product with a drastically high fade rate over time.

Like polyesters, SMPs are harder than PVDF resins, making them more resistant to rough handling. They are also more brittle, and tiny fractures can form on bends during roll forming. Manufacturers have generally considered these microscopic fractures insignificant, however some companies are warming their SMP coil before sending through the roll former.

Most paint decisions are compromises between performance and costs, with SMP being the middle ground in both as compared to polyesters or PVDFs. Color is an important consideration. Light colors reduce the appearance of chalk, and are readily formatted with inorganics. Some companies will offer polyesters in a light color range, but shift customers over to an SMP for darker ones.

With a chalk/fade advantage over polyesters, and a scratch/abrasion resistance advantage over PVDFs, SMPs are the most widely-used paint system in the non-commercial building market. SMP is still a good paint system – it just allows for more chalking and fading over a given time period than PVDFs such as Kynar®.