Multiple finish coats without sanding

I'm wondering if there are any functional risks in applying multiple coats of Interlux products (specifically Schooner varnish and Brightside paint) without full cure time and without sanding in between. I've seen comments about folks doing this, and it seems like the general strategy is to wait until the 1st coat is tacky (a couple of hours) before applying another, and to not exceed 2 coats between each full cure and sanding effort. I know there are aesthetic risks to this (it eliminates sanding/smoothing opportunities), but I'm mostly curious if this greatly increases the risk of future delamination, cracking or other degradation in the finish down the road.

I would not normally consider departing from the "instructions on the can" for something like this, but I may need to trim a couple of days off my finishing schedule. I'm working on a Sectional Shearwater Sport in a borrowed space that I only have access to on the weekends, and I need to move out of that space very soon. I'm nearly there and am excited to finish this project, but also want to get it done right!

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RE: Multiple finish coats without sanding

sanding is not that important if you apply multiple, neat, thin coats.

however, you should ensure that you are at the cure/dry times on the cans and, again, keep the coats thin as the dry times on the can correspond to thin coats

putting wet paint, especially, over not dry paint can create a real mess (learned that from experience).  the paints volatile compounds have to evaporate off for the paint to dry...and if you put paint over paint prior to that happening can get a crackling effect which is really ugly.

anyway, that's my experience.  that said, if the temps are hot and you keep the coats thin you can get as many as three coats in a day.   



RE: Multiple finish coats without sanding

Honestly, if you need to shorten your finishing time, the best approach would be to switch to products with shorter dry times.  The wet sanding itself takes very little time.  I just completed a Pygmy Osprey and unless I had a run to sand out, I could wet sand the entire hull in about 15 minutes.

I agree with hspira's advice above to not over coat paint prior to the specified dry time.  The Epifanes mono that I use has a specific warning in the instructions not to do so.  It warns that a coat applied over a not fully cured coat will create a "curtain" which will prevent the underlying coat from ever fully dying.  Brightsides is a very similar paint so I expect that it would have the same issue.

I do not know of any paints that you can overcoat in less than 24 hours but there may be one.  I have used Epifanes RapidClear Varnish on multiple coats with good results.  (My Yukon that won best in show at BLBF last year has this varnish).  You can overcoat in 5 hours without sanding between coats.  

Lastly, as someone with a degree in Chemistry, I would strongly recommend that you follow the instructions on the label with whatever product you use.  If you don't you are really playing Chemical Russian Roulette.

This one is Schooner on the Deck, Epifanes Mono on the hull, and Rapidclear in the cockpit.

RE: Multiple finish coats without sanding

Thank you for the notes hspira and Mark. My main takeaway here is that deviating from the instructions on the can is high risk for paint. So I made sure to allow the full 16-24hr dry time (depending on temp variations), along with some light wet sanding, between each coat on the hull. I was still able to get 3 coats on over a 2.5 day long weekend, and I'm really happy with the results. I suppose that much of the credit goes to the faring effort leading up to the paint application (a process I also learned completely from this forum!) but I'm really appreciating the art and chemistry involved with good finish application.

I did take some liberties with the deck varnish however. Given my limited workspace access that seemed to be the better way to cut some finishing time. For 2 of the 5 coats I did not sand and only waited around 4 hours between applications. I think the results are still pretty solid. I did find it hard to track where the wet edge was without sanding (maybe I still should have done something to knock down the gloss from the previous coat?) but it worked out alright. In hindsight I think I missed some sags that otherwise would have been addressed with more sanding between coats, but I'm probably the only person who will notice those.

Here she is leaving the borrowed workshop in the country for a permanent home in the city:


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