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Scuff sand CPES before varnish?

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Scuff sand CPES before varnish?

Post by JacobErdey » Thu Dec 05, 2019 9:54 am

So I have my boat stained and sealed with CPES, now as I wait on that to cure, I'm trying to clear things up before varnish.

1. Am I supposed to scuff sand the cured CPES before I apply the first coat of varnish? Or just wipe with tack cloth or a rag with some solvent?

2. Once varnish starts going on, as far as I can tell, the process is: apply three coats of varnish, sand to snow, wipe with tack cloth, wipe clean with alcohol or brushing thinner, apply three more coats and repeat the same process, etc. etc. until 18-22 coats are built up, then allow 2 weeks to fully cure, then buff to glass finish. That sound about right?

Thanks for any input
Current Project: 1950 Chris Craft Sportsman 18'

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Re: Scuff sand CPES before varnish?

Post by Bilge Rat » Thu Dec 05, 2019 11:44 am

There will be a lot of opinions on this process I'm sure, but I will comment on the CPES question.

There should be no need to scuff up the CPES before first coat of varnish. Although the CPES may look a bit lumpy, the subsequent coats of varnish will fill that in nicely and after build coats and sanding, it will level out. Some people may thin the first coat or two of varnish but I think that is a bit of a throw back to not using a sealer after staining.
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1953 Chris Craft Sportsman 22 foot "Summerwind"

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Re: Scuff sand CPES before varnish?

Post by tkhersom » Wed Dec 18, 2019 7:12 am

As far as building coats of varnish without sanding in between, I believe that will depend on the product being used. Some varnishes allow for no sanding in between coats while others suggest sanding every coat to help adhere the next coat. It would be a shame to have poor adhesion between boats 9 and 10 if you are going to apply 20+ coats of varnish. Read the manufacturers recommendations. :wink:
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Re: Scuff sand CPES before varnish?

Post by kiitos » Sun Dec 22, 2019 6:46 am

It is my opinion that you should sand between coats but I would start by sanding with a scotch bright pad. I find the burgundy color is best. Use that for at least the first 5 coats. Don't "sand to snow" or "white-out" as some people call it, until you get about 10 coats on or you risk sanding through to the stain. Be very careful of the edges. The edges sand through quite easily. It has been my experience that sanding between coats makes it easier to see where you are varnishing because you have a dull finish as a background. If you try to hot coat it is easy to miss small areas as there is no contrast. You are laying down a shiny coat of varnish over a shiny coat of dry varnish. You may also want to try using high build varnish to reduce some of your coat count.

As for buffing I would try to avoid that unless you simply cannot keep the dust level down. I refinished the decks of my CC 25 and had to buff because of the amount of dust in the final coat. The final buff job is a level of shine below the unbuffed varnish finish.
'78 Chris Craft 30' Sportsman
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