Use a plastic spreader to apply the fairing putty. It’s not a good idea to try to fill deep holes in a single application because a layer of epoxy that’s too thick can cause excessive heat build from the exothermic curing reaction.
For holes that are deeper than ½", apply the fairing compound in two or more layers. It’s easier to apply a few times in low spots because it builds up easier with greater control. Take care to follow the manufacturer’s recommendations for sanding and cleaning between applications of fairing compound.
Filling the Voids
- Fill the low areas proud (meaning just above the fair level) so you can sand them down to fair without having to refill.
- To avoid extra sanding after the compound cures, use the spreader to smooth out the compound as close to the desired shape as you can. Blend it into the surrounding areas.
- For fairing larger areas, use a spreader to apply the compound, slightly overfilling the area to be faired. If the surface is very unfair, use a notched spreader to apply the fairing compound. To level the applied compound, bend a plastic fairing batten so it matches the contour of the surrounding fair areas, and drag it slowly over the filled area.
- Allow to cure completely before sanding.
- You may need repeat the process of filling and sanding low spots until you are happy with the fairness of these areas. Before you know it, your hull will be fair and ready for priming.
If applying a fairing compound made from the recipe method of epoxy resin, hardener, thickening agent, and filler, the cured surface may develop a film of amine blush, depending on the particular brand of epoxy resin. If amine blush is present, it must be removed before sanding. You can remove it using a ScotchBrite pad and water, and allow the area to dry completely. It’s not hard to do, but it does add extra time, especially if you have a number of areas to fill. Check with the resin manufacturer to determine if amine blush is an issue.
If it is, you can prevent amine blush, by placing a layer of peel ply over the applied fairing compound. Peel ply won’t react with the epoxy, and it’s easy to peel off after the epoxy cures. Be sure to remove the peel ply before sanding. Amine blush is not an issue if you’re using a pre-mixed epoxy fairing compound.
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