Bubbles in Varnish


New member
23 Jul 2001
I am getting tiny air bubbles in the final coat of varnish. I rub down between coats, clean with a tac rag,stir the varnish slowly and let it stand so there doesn't appear to be bubbles in the pot. I don't "twirl" the
brush when I apply it and try not to over brush. -- Ideas please.
16 May 2001
After initially applying the varnish I tend to "lay it off" with full length brush strokes from one end to another of the workpiece. This ensures an even coating and no sags or runs. This does not work however if the ambient temp. is too high as the coat has started to dry. Best results are obtained in lower (around 5-10C) temperatures when bubbles and brush-marks have time to even out before the varnish sets. This is a feature of modern thixotropic coatings where fast drying seems to be a requirement. More traditional oil based varnishes take far longer to become touch dry so don't suffer from this problem but can be exasperating when one comes back next morning to find runs on vertical surfaces.

So is too high a temperature your problem? Could be.

Steve Cronin


Active member
7 Sep 2001
The temp is too high, I get it when the sun gets on my new varnish, shield it or keep it cooler. I also put my varnish in the fridge, if the temp outside is too hot, like in the meddy.


New member
28 Mar 2004
This is always because of too fast reaction( polymerisation). If the varnish is 2 components than reason for bubbling can be catalisator (too fast) or if the varnish is 1 comp. than sun heating can be reason.
If you are varnishing with 2 K than after mixing with catalisator leave varnish 10 min to obtain first reaction in pot - not on finish area.


New member
25 Jul 2002
Tampa Florida USA
Surface is too hot(varnishing)

as others mentioned , sounds like surface is too warm.
If that is the case and if you can not control surface temperatures . this is something you may want to try.
This technique actually worked better in air-conditioned environment , and I have not try this out doors. However . test pieces has been in Florida sun for nearly eight years.
I have tested this technique with the regular oil varnish as well as single part polyurethane varnish with amazing results, if you are interested . I can send you a photograph.
First , I prefer to use high-quality oil varnish as a base coat . After the usual preparations if you are going to do this out doors, shade the workpiece from sunlight and warm up the varnish on the food warmer to around 175° F. Without any thinner, if it is a new can continue warming for about 15 minutes before starting the varnishing, with this technique takes about one hour for the first coat to be ready for the next coat or as soon as it becomes slightly tacky.
With above temperatures you should be able to put on three to four Coats as soon as each coat becomes tacky.
This many coats of varnish would be unthinkable in the usual way of varnishing
temperatures above 200° F. allow me to put on 12 coats in 24 hours and end result 28 coats in three days. I'm not sure if this temperature or the number of coats made the resulting finish very slightly darker.
All of the above coats were put on without sending in between and soon as each coat became tacky to dry.
After the sixth coat I switch to using single part polyurethane varnish and reasoning behind this is because polyurethane is very difficult to remove if it is used on bare wood, but it is very durable.
Normally end of first-year the brightwork will require slight sending and then a couple of coats of varnish and if we waited longer varnish will take on crazed look were . it will require much more aggressive sending to prepare for varnishing
with the above technique varnished surfaces stayed in full sun without any noticeable changes . for 15 months , and gradually became as if it was just sanded no crazing whatsoever . what appears to be ready to varnish over after just wiping down with the mineral spirits.
Next time I would like to try something slightly different , which involves using a acrylic sealant as a base , which I think will make it resulting surface slightly lighter in color if you do try the acrylic sealant . make sure it is not UV reactive, the same manufacturer makes one that is photoreactive as well as one that is not
just out of curiosity , how many of you use a technique called backstroke . I believe that's the right terminology.(For painting and varnishing) .
Good Luck :)

PS: I'm sure you all know but I want to put this reminder warming up the varnish should be done with a double container . like the one that used to be used for warming up furniture glue even more importantly . no open flame should be used. And all necessary precautions should be taken and should not be attempted by those considered themselves the beginner DIY etc.


New member
19 Mar 2004
Re: Surface is too hot(varnishing)

In days gone by when I did more varnishing than was good for me, I used to use a product called Penetrol as an additive which helped a lot particularly in the tropics where I did most of my varnishing work.

Try not to work too fast as this sometimes causes the bubbles to form (but not too slow either ...).


23 Oct 2004
NSW Australia
How clean was your brush? I had a similar problem when using a high quality old-favourite brush this morning - when I'd had no problems with earlier coats using (very good) cheap throwaway bushes. I assumed it was due to my technique for cleaning brushes.


New member
27 Oct 2011
Coppershield, Hello, I just came across this post and since I see it is several years old I was wondering if you have anything to add in terms of refining your technique at all? I'm about to revarnish my cap rails and deckhouse after stripping back to bare wood, and the idea of being able to put on even 5 - 6 coats a day really appeals, especially without having to sand in between. I am planning on using Epifanes High Gloss Clear Varnish with Extra UV Filter. I've used this product a lot before and have had good results "with the conventional method" ie a coat a day, light sanding or scuffing between coats. I'm going to try your method on a small section and see how it goes, though it may be difficult to keep the whole area in shade. Your thoughts would be most appreciated. Thanks!