In its simplest form, fettling is removing as much of the imperfections as possible and hopefully without degrading the galvanise surface too much, It’s the name given to the mechanical process using handheld power tools i.e., grinders, orbital sanders, and similar. This is applied to the galvanise substrate to improve its appearance once it has been through the galvanise process.
The answer depends on what is being fettled. If you have products, like gates or railings, then you will want them to look appealing once powder coated or painted. When you receive galvanise work back from the galvanisers, they will inevitably need fettling before the coating process to make the surface even and take off the lumps and any excess build-up of galvanise this can sometimes affect the quality of a product or stop it from fitting in with other components.
Also, by fettling you will rough the surface which will promote better adhesion with the coating system you have specified for your work.
If you want your galvanise product to look good, then it’s a must-do, unless you use hot zinc spray which eliminates these issues.
When do protective coaters need to fettle?
When items have been hot-dip galvanised, they need to be fettled, all hot-dip galvanised items will need some sort of fettling before the coatings can be applied. Think of it like rubbing down your woodwork before you paint, the smoother the finish, the better the end result. Hot dip galvanise is a process of submerging items in liquid Zinc and this can lead to problems like pooling in and excess build up in areas, this has a knock-on effect for the coater to get a nice smooth finish. If the coater does not fettle galvanised items before applying primer or topcoat, it’s likely that any imperfections will just show through in the finished product. A smooth and fettled sub straight is the key to achieve an acceptable galvanise finish.
Is Fettling Needed on Every Item?
It isn’t when you use hot zinc spray (HZS). Hot zinc spraying involves spraying metal items with molten zinc. Not only does this allow the zinc to be applied evenly and give metal products a nice finish, but it also protects them from environmental damage, like rust and corrosion. All HZS items are always shot blasted to SA3 standard (white metal) this will remove all rust, corrosion, and scale giving a perfect key for the HZS layer to adhere to.
If you’re creating an item that will be kept used outside, then hot zinc spray is a cost-effective alternative that both saves you time and gives your products a longer lifespan. With HZS there is no need to fettle, just a light rub down with medium grade sanding paper by hand and the surface is ready for the next stage.
How can fettling be avoided?
The best way is to use a quality protective coater who will firstly shot blast any items to ensure they are smooth and free of any imperfections left over from the casting. Second, we would recommend that items are hot zinc sprayed, this allows an even, smooth application of zinc to ensure the items need no fettling. After a light rub down the primer and topcoats can be applied, leaving you with the perfect finished product.
Experts in HZS
At NSP we only use HZS to protect our work, we think it gives a superior finish and we trust it so much it’s a part of our 60 year guarantee.
Hot zinc spraying is lower in cost and much quicker than other alternatives, like hot dip galvanising. It gives your products a professional finish while preparing them for the outdoors, increasing their lifespan and overall value.
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