Varnish

i am using Interlux Schooner Vanish. The instructions say sand between coats. I like the idea of applying 3coats of Vanish before sanding, to prevent the endless cycle of applying a thin coat, the sanding most of it away.  I feel as though I have been dying that with the thin coats of Epoxy , that I have been applying.

Has anyone used this Varnish and successfully applied two or three coats prior to sanding?


13 replies:

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RE: Varnish

I have. That's my usual varnish and modus operandi. I also use #400  wet and dry paper to wet sand.

Laszlo

 

RE: Varnish

Unless you are really experienced with varnish, I would recommend following the directions and wet sanding between coats.  A light wet sanding with 400 will scuff the surface so that the next coat can get good adhesion, without removing much material.  I can wet sand an entire kayak in about 30 min.  I don't doubt that an expert like Lazlo can skip the wet sanding but the timing has to be right.  If you wait too long between coats, the surface will be fully cured and the second coat won't stick well.  I did this once and tape would pull the top coat right off.  If you apply the second coat too early, it will form a curtain and prevent the bottom coat from fully drying.  The result here is a soft varnish coat that is easily scratched.  

If you really want to skip the wet sanding, there are several products that are formulated for that purpose.  One of them is a semi-gloss by Epifanes called RapidClear/RapidCoat.  I used it on my skiff and am very happy with both how quickly it went on and how it looks.  So far, it seems to be just as hardy as Schooner.

    

RE: Varnish

   Recoating varnish without sanding is a matter of hitting a window in time.  As mentioned, it's about being dry enough, varnish is a film finish that requires the solvent to gas off in order to cure, but uncured enough to allow a good chemical bond.

If totally cured, the sanding allows for a good mechanical bond.

Insofar as sanding.  If your only sanding to enable "key", or a surface for the new varnish to grip, about anything will work that removes the gloss.  Don't necessarily have to use 400, or wet sand.  If your sanding keeps clogging up the sandpaper, it's simply not dry enough to sand.  It's probably uncured enough to repost without sanding....

If it creates a nice white powder easily, just remember to keep cleaning your sandpaper, I simply clap it.  My then wife though I was continually applauding myself! Geesh....  I've got an ego, but not that bad!

One of the reasons for sanding between coats, is to make the final product more shiny, by allowing varnish to accumulate in the low spots, and sanding off the high spots.  This can basically only be done by "candling" and block sanding.  This is what good auto body men do...  And after the requisite number of coats will leave a surface that reflects an image without distortion, like a mirror.  

In the course of block sanding, you will leave low spots that won't get sanded at all between coats, which is where simple hand sanding with something really fine comes in, not enough to really change the flatness of the surface, but removes the gloss for good mechanical adhesion of the next coat.  Or, that's where the wet comes in, allows you to sand without clogging the sandpaper, the coat being green enough that good chemical adhesion will still occur in the spots that don't get sanded.  

Mike

RE: Varnish

Maybe I'm just the luckiest varnisher alive, but I've never worried about the timing for varnish. I just apply very thin coats so they won't drip and run, and when they've hardened I apply the next one, with or without sanding, depending on how smooth the surface is. If it's smooth and clean, I don't sand unless it's one of the outer layers. Once I get to the last 3 or 4 layers, I start sanding.

I wet sand not because the paper is clogging, but to keep the dust levels down.

YMMV,

Laszlo

RE: Varnish

   I'm with ya... It's not necessarily a tiny window.  One small caveat is that I noticed one day I really don't even know what varnish is anymore.  All of the sudden, mainstream suppliers have polyeurathane varnish... Hmmm... I remember the days of deciding which I wanted, poly OR varnish.  And then I started rebuilding a plane, and them folks have epoxy varnish!  Wha?

The point is, some of the newer I guess synthetic "varnishes" seem to have very specific instructions when it comes to recoating.  I've had good luck following their specific instructions to the letter...  Ive had decidedly bad luck mixing brands sanding sealers, thinners, reducers, etc. and/or not following temperature or time guidelines. 

Mike

RE: Varnish

Mike,

I think you hit the nail on the head with the different types of varnish. Schooner is a traditional solvent-based varnish which doesn't depend on polymerization or cross-linking. That makes it a lot more forgiving since it doesn't have a "chemical" vs. "mechanical" bond. The solvent from a new coat will simply dissolve the top of the previous layer allowing the dissolved and suspended solids to merge. The only way that can fail is if the previous layer is contaminated, something that's fixed by sanding the contamination off.

Have fun,

Laszlo

 

 

RE: Varnish

Thanks again for all the experienced input. I should have proof read my original post.I meant to say. I have been applying thin coats of Epoxy, then sanding most of it away before applying yet another thin coat.

I did not want to do the same with the Varnish coats. I ended up sanding between the first two coats, and even though I was using 400 grit wet sandpaper,and being careful not to over sand, it seemed as though I was removing most of the Varnish.

Then I saw a post on another boat building forum suggesting that Scotch Brite pads were a better alternative. I was finishing two Kits at once, and had already wet sanded the deck of one. I finished using the Scotch Brite pads and did the second completely. The Scotch Brite still scuffed the shene off the Varnish, but did not remove as much. I had a few flaws that still required a little wet sanding, prior to recoating, but I stopped a 4 coats, only because our weather was unusually dry and warm, in March and I was anxious to try them both out, before the weather changed.

The deck that I had wet sanded before switching to Scotch Brite, required a fifth coat to match the rest of the Kayak. 

RE: Varnish

I believe epoxy takes a very long time to dry fully and it can be recoated without sanding for days (maybe weeks). The only reason to sand between coats is to create a smoother finish.

Varnish also takes a fairly long time to dry fully and in my limited experience one can apply multiple coats in a single day, have good adhesion, and have a durable final finish. I think one only needs to wait until the varnish or epoxy is dry to the touch before recoating. Adding additional coat(s) promptly increases the chemical bond between the coats . . . but it delays the time until the finish coat is fully hardened and ready for hard use. (Basically, the undelying coats are not fully dry and it is harder for them to dry because of any additional coats on top.)

Personally, I would rather apply epoxy (or varnish) fairly rapidly without sanding between coats. As long as I get chemical adhesion, I'm happy. . . . But I have to use my boats very carefully for the first weeks (or months) while the various layers of epoxy and varnish are reaching their final hardness.

I have not yet had any problems with adhesion. 

RE: Varnish

   My original post was near the end of March.Since then I started another Shearwater Sport (this one was using the original Kit parts mostly),and now Ian ready for any required sanding, prior to the first coat of Varnish. The trouble is, the final coat of Epoxy looks so good, I am finding it hard to use any sandpaper on the finish. I know that there are a few marks that I may or may not be able to remove, but the finish looks way better than I was able to achieve with my first two builds, even after hours of sanding. The point is, it has been less than 24 hours since I applied the final coat of Epoxy to the deck. Is it risky to go ahead and apply Varnish, without sanding at all?

RE: Varnish

Yes, very risky.  Varnish over fresh uncured epoxy may not cure.  If the epoxy finish is that good, then it will take very little sanding before varnish.  Just a light go over with 220 until the entire epoxy finish is light grey and not reflective.

 

RE: Varnish

Yeah, wait a while to make sure the epoxy is cured. It doesn't dry as in evaporate solvent but it takes a while to finish cross linking. Most will say 72 hours but if you can sand it and make only dust, you are there. You want that epoxy to be stable with no chance of reaction with the solvents in the schooner varnish.

RE: Varnish

You can't expect a chemical bond between epoxy and varnish. That is going to be a mechanical bond, so you will need to scuff up your lovely epoxy surface. (How I envy you for getting such a smooth final coat of epoxy!)  If you can't dent the epoxy with your fingernail, you can go ahead and sand it and then apply varnish.

 

RE: Varnish

   No need to envy. On my first Shearwater Sport I used a squeegee and bristle brush, and missed a lot of runs,thus leading to a lot of extra sanding.

My second kayak was a Chesapeake 17LT. This time I used a foam roller along with the squeegee on the first coat only, and the roller, and foam brush only on subsequent coats of Epoxy. Very few runs this time, and much better looking final coat of Epoxy.  When I said I didn't want to sand, after my intended final coat of Epoxy, I spoke to soon. Yes at first the finish looked much better than the finish I settled with on the first Shearwater . After scuffing the shine with a Scitchbrite pad, I could see areas that needed more sanding, so I went ahead and wet sanded the entire boat with 220 . Now I realize that I need another coat of Epoxy on the deck. I have been applying very thin coats of Epoxy, especially on the deck. So thin that after 4 coats the cloth was barely covered. Hopefully this will be the final coat of Epoxy on the deck. I will hold off on the Varnish for three days at least to be sure that the Epoxy has a chance to cure. Thanks for the great advice, I was was rushing ahead thinking that 24 hrs was enough time to wait.

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