Re: Gelcoat and Duratec Clear High Gloss Additive
The short answer is, if you are going to sand and buff it, it won?t make much of a difference.
Both opinions have merit. Styrene has terrible UV resistance and turns yellow rather quickly, when more styrene is added to a formula it typically reduces its weathering properties, how much it?s reduced can be in direct relationship to the amount of styrene added. Duratec clear is already high in styrene and MEK (45% or so), will adding 2% more styrene make a noticeable difference?.maybe.
The resin used in Duratec clear is not as inhibited by air as normal polyester, but you still have 50% normal polyester in the mix, so you are trying to overcome this portion of the mix and have it cure. As a backup plan they say to add wax to help reduce any air inhibiting that may take place.
Under cured polyester will turn a milky white when exposed to moisture, this happens in gel coat or resin, depending on the color of the gel coat you may or may not be able to see it. Dark colors show the blushing rather easily, whites may hide it completely. Dark colors may (typically do) turn milky (blush) even when fully cured, this can be an issue with boats left in the water for long periods of time. The same thing can happen to a white, you just can?t see it. Above the waterline there is less of an issue of having the repair turn milky so they say the additional wax isn?t needed.
If the Duratec/gel coat mix cured correctly (temp and catalyst ratio were correct), then even if the surface was slightly under cured from air inhibition, the sanding and buffing process would remove the under cured surface layer. This would eliminate the portion that may turn milky.
The problem is Hawkeye (manufacturer of Duratec) doesn?t know the exact methods or the conditions of how the product will be used, or what it will be used with, so adding wax will help in the curing process with little downside.
My opinion of using Duratec or other thinners for DIY repairs has sort of changed, not because the outcome has changed, only that expectations of the results are different between DIY and the manufacturer.
Any of the thinners, including Duratec, have possibly negative side effects, reduced UV resistance, reduced crack resistance, blister resistance, gloss retention, color change, etc. When these products are added characteristics of the gel coat are changed, most in a negative way, the benefits can be that it sprays and levels better reducing the amount of sanding needed. Duratec may increase the gloss because as you add more resin you reduce the pigment loading, pigments don?t develop a good gloss, resin will, so reducing the amount of pigment in the mix may give a better shine. Reducing the pigment load can also make a color look richer and deeper, sort of like a clear coat, so this may enhance the look too.
The down side is that gel coat relies almost 100% on the pigments for UV resistance, so by reducing the % of pigment you typically reduce the weathering properties. Reducing the % of pigment by even a small amount can also change the color, sometimes a great deal.
When a manufacturer is doing a repair on a brand new boat, the color needs to be exactly the same, plus stay the same over many years of use and exposure to the sun. This can only be accomplished if the gel coat is mixed and used in the same way it was on the hull, this means very little or no thinning, only enough to make the product usable for the repair. Even then many times the repair can be seen after a few years in the sun, add other stuff and the changes are far more likely.
We do testing to ensure the original gel coat and the methods we recommend to repair it will give the best long term results for a manufacturer, at 5 to 10 years down the road the repair needs to still be invisible if possible. People don?t like finding a big repaired area on the hull side of their new boat.
In the DIY arena, plus in repair shops, the very long term results aren?t quite as important as how fast it can be done, or the initial results when you (or the customer) first see it. If after a few years the repair starts to be noticeable the owner may be satisfied with buffing it out to make it look better, or the boat may have already been discarded or sold. The DIY owner or customer already knows there is a big repair and if after a while it becomes more noticeable they frequently accept it as normal and don?t make a big deal out of it, new boat owners tend to come unglued when they find a big repair.
In a complete respray there isn?t really anything to compare it to, so if it changes color you may never notice.
My recommendations are typically aimed at the best long term result, not on how fast or easy it can be done, or the initial look, this is where my opinion is beginning to change. Many DIY?ers frequently want a finished product that looks good and is relatively easy to accomplish, this can trump long term results.
It?s interesting that when it comes to rebuilding the inside of the boat, stringers, floor, transom, the DIY crowd here typically does a much better job than the manufacturer, the attention to detail, products used and thought going into it are at a higher level. Many will only use epoxy because they feel it will do a better job (it may, but the end result is about the same as polyester). The first thing they ask is, ?What are the best products and methods to fix it?. But when it comes to the outside of the boat, an area where the manufacture typically does a much better job (OLD boats frequently look great on the outside and are totally rotten inside), the DIY?er does things that would get an employee fired on the spot.
Good manufacturers have rules in place on how a repair should be done, this includes catalyst % and the amount of patchaid type product used to thin the gel coat. They have tested the methods and only allow it to be done in one way so the results are far more consistent and long lasting. Adding large amounts of anything is not allowed. Some will use a small amount of acetone (2-5%, but most don?t), and surface agent (wax), others only allow a patchaid product made exactly for doing repairs with gel coat, and then as little as possible is added. Very few (none I deal with) use Duratec for repairs or resprays. Not that it doesn?t have a place, just that none use it for this purpose.
Will adding Duratec and other thinners in large amounts make the job easier to do?yes. It?s up to the person doing the job to decide if the possible downside of doing it this way is worth the tradeoff.
Lots of rambling, sorry for that.
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