Thinning Glossy Varnish

I have read to not thin the final coat of varnish. With the weather conditions I don’t see how I can get the varnish to flow and lay right unless I use a brushing thinner of 10% or less. Any assistance would be appreciated.

Heat the varnish to 150/180 degrees in a pan of water or double boiler. It will flow out beautifully, cool quickly on the workpiece and dry and harden normally.

My Way said:

I have read to not thin the final coat of varnish. With the weather conditions I don’t see how I can get the varnish to flow and lay right unless I use a brushing thinner of 10% or less. Any assistance would be appreciated.

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Not only do different online "experts" give different advice, but instructions virtually always assume perfect conditions which of course don't often happen. You're absolutely right, the varnish MUST be adjusted for weather conditions and use (first coat, middle coats, last coat, etc.)


Ken

The “final coat” probably should turn into 2 if you are thinning. 23 rain days in R.I. in April. Ugh!

I have Rebecca Whitman’s book on varnishing and will look up your situation.

But from my memory thinning varnish is a no-no. I’ve done it in many ways w no problem but the last coat should be max thick. Probably be good to have max UV protection on the last coat too.

Personally I think the best thing to do re varnish is to apply several to many coats on bare and dry wood w progressively less thinner (turp) and I usually just use Linseed oil. I know Tung oil is better but I’m not convinced it’s much better. And for best penetration I use kerosene for thinner on the first few coats.

The only difference in applying a thinned varnish layer in place of a straight varnish layer is that you will apply less varnish and more thinner. As a consequence you need to apply more layers of thinned varnish to get the same level of protection/resistance.

L

Lou_tribal said:

The only difference in applying a thinned varnish layer in place of a straight varnish layer is that you will apply less varnish and more thinner. As a consequence you need to apply more layers of thinned varnish to get the same level of protection/resistance.

L

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Agreed. The issue with never thinning the last coat is one HAS to take the thickness of the varnish into consideration. Last coat or not, if the varnish has too thick a consistency it will not flow out correctly - and there are definitely circumstances that can cause the varnish to be too thick for proper wet film thickness and and/or flowout.

Ken

Lou_tribal said:

The only difference in applying a thinned varnish layer in place of a straight varnish layer is that you will apply less varnish and more thinner. As a consequence you need to apply more layers of thinned varnish to get the same level of protection/resistance.

L

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I looked in the Whitman book and want to share to or so things.

The last coat isn't to be different in any way from the preceding four.
However some consideration should be given to all the solvent that is still in the previous coats having to evaporate through all the coats including the last. So longer wait times should be considered for later coats.

Attention should be given to the dew point. Some summer days are dry enough much earlier than other days. Paint as early as possible on hot days to apply cooler varnish on a cooler boat.

I could not find her saying never to thin. She talks about thinning 5 to 15% on primary coats and to use a "brushing liquid" in later stages.

Eric: Thanks for posting that. I’ve always thinned, even the last coat, usually between 5-10%. I’ve never given any thought about the thinning solvent but it makes sense. I’ve screwed up a few jobs by rushing the final sanding by not being hard enough. Patience.

Ken and Lou hit the nail on the head. Varnish does need to be adajusted to meet conditions. If it means one or two more coats so be it. You will be rewarded with a beautiful finish.

Rob

I always add Penetrol, just flows better with it.