UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > General Vintage Technology > Cabinet and Chassis Restoration and Refinishing

Notices

Cabinet and Chassis Restoration and Refinishing For help with cabinet or chassis restoration (non-electrical), please leave a message here.

Reply
 
Thread Tools
Old 13th Sep 2020, 8:44 am   #41
PsychMan
Octode
 
PsychMan's Avatar
 
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,619
Default Re: What causes this in polyurethane varnish?

Yeah will definitely check it out Steve. Once I’ve done my top coats and buffed all this up I’ll have to decide if it’s worth all the work next time, I suspect maybe not!
PsychMan is offline   Reply With Quote
Old 13th Sep 2020, 9:31 am   #42
MurphyNut
Heptode
 
MurphyNut's Avatar
 
Join Date: Apr 2016
Location: Croxley Green, Hertfordshire, UK.
Posts: 817
Default Re: What causes this in polyurathane varnish?

Quote:
Originally Posted by ajgriff View Post
A combination of applying coats too thickly and insufficient curing time between coats I suspect.

Alan
I would agree with this wholeheartedly, Sometimes it takes more than a day for the varnish to really set hard. Also it's important to mix the varnish really well between coats.
__________________
Clive
MurphyNut is offline   Reply With Quote
Old 13th Sep 2020, 2:57 pm   #43
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 10,100
Default Re: What causes this in polyurethane varnish?

Quote:
Just and update, sure enough merlinmaxwell was correct.

After waiting just over a month I have sanded the piece, re applied varnish and there are no wrinkles or abnormalities at all.
My reputation (such as it is) didn't get a knocking, what a relief.
__________________
Cats have staff, it's dogs that have owners.
merlinmaxwell is offline   Reply With Quote
Old 14th Sep 2020, 8:16 am   #44
Michael.N.
Pentode
 
Join Date: Apr 2011
Location: Bradford, West Yorkshire, UK.
Posts: 172
Default Re: What causes this in polyurethane varnish?

In my day job I do both spirit and traditional oil based varnishing, mainly brushed on but sometimes French polished in the case of the spirit. I've next to no experience with poly although I once bought a tin to varnish a table. I took an instant dislike to the stuff. They are obviously trying to rid us of the VOC's (understandably). The stuff will obviously work but it's probably a matter of becoming accustomed to it's properties and it's propensity to certain finish problems. All finishes can and do go wrong, perhaps some more than others. There are a lot of alternatives for the home varnisher. Tru oil is a pretty simple product to apply. It's not the hardest finish and is only really suitable for relatively small objects such as table top radios. Some of the boat varnishes such as Epifanes are well established and well regarded, not the cheapest.
Michael.N. is offline   Reply With Quote
Old 14th Sep 2020, 8:50 am   #45
PsychMan
Octode
 
PsychMan's Avatar
 
Join Date: Jun 2013
Location: Fleet, Hampshire, UK
Posts: 1,619
Default Re: What causes this in polyurethane varnish?

Quote:
Originally Posted by Michael.N. View Post
In my day job I do both spirit and traditional oil based varnishing, mainly brushed on but sometimes French polished in the case of the spirit. I've next to no experience with poly although I once bought a tin to varnish a table. I took an instant dislike to the stuff. They are obviously trying to rid us of the VOC's (understandably). The stuff will obviously work but it's probably a matter of becoming accustomed to it's properties and it's propensity to certain finish problems. All finishes can and do go wrong, perhaps some more than others. There are a lot of alternatives for the home varnisher. Tru oil is a pretty simple product to apply. It's not the hardest finish and is only really suitable for relatively small objects such as table top radios. Some of the boat varnishes such as Epifanes are well established and well regarded, not the cheapest.
I really like the results of a good polyurethane finish, very glossy, very smooth, and hard wearing. But if there are varnishes that can achieve 90% of that, then I will definitely try those out. I'm very new to finishing, and like many things I dive in head first, balls it up a few times, and re do until im happy with the results

Part of the reason for using poly on this project was the grain structure of the veneer, while also being very thin. I tried a few grain filling options but didnt like the results. With poly, the coats are thicker than aerosol lacquers, so its viable to fill the grain by building up coats with it, and that's what I've done. I did of course go wrong with the coats being a tad too thick, and not allowing enough curing time between them.
PsychMan is offline   Reply With Quote
Old 14th Sep 2020, 10:33 am   #46
Michael.N.
Pentode
 
Join Date: Apr 2011
Location: Bradford, West Yorkshire, UK.
Posts: 172
Default Re: What causes this in polyurethane varnish?

Personally I'm not a great fan of really flat high gloss finishes, the type you can use for observing Neptune. I once varnished a guitar and did the usual steps of going through all the grits , polishing compounds and buffing. When I eventually finished I stood back and so admired the brilliant gloss finish I had produced. The very next day I looked at it and decided it had to be all rubbed back. It was just too plastic wood looking. The more I looked at it the more I hated the effect. There's no doubt that it results in great optical clarity but it's just too cold looking for my taste. These days I tone it down a little with the French polishing cloth, deliberately putting in very straight 'micro lines' to lessen the gloss a little. I would still call it a glossy finish (most people would). It's just not glass hard reflective as some.
That's just my personal taste though. There isn't a right or wrong about this kind of thing so do as you please. Most finishes can be taken to a pretty high reflective gloss. Usually the harder finishes a touch more.
As for the curing time you have to learn to judge that. With the solvent finishes you can literally put two coats on every hour or so. Alternately you can wait months between any two coats. The new layer will solve into the underlying coating. With finishes that cure through polymerisation it can be tricky. If you leave it too long you can get two very distinctive layers. When you rub back it can produce witness lines, rather like contour lines on a map. I'm not sure if that applies to the modern polyurethane finishes. My real experience is with old fashioned linseed/tung oil/resin based varnishes. Many of the modern finishes are cold solved, low VOC - very different beasts.

Last edited by Michael.N.; 14th Sep 2020 at 10:42 am.
Michael.N. is offline   Reply With Quote
Old 8th Jan 2021, 5:23 pm   #47
Andy 1964
Triode
 
Join Date: Jan 2021
Location: Leicester, Leicestershire, UK
Posts: 20
Default Re: What causes this in polyurethane varnish?

I know all about this, from my other hobby/sport. The photo shows my sailing boat with 4 coats of clear epoxy and 8 coats of Epifanes water clear 2 pack varnish, prior to mirror finish polishing after 2 weeks full cure. This is my preferred supplier and cheapest. https://www.pinbax.com/index.asp?Det...ssc=&ordering=

So, back to your first photo, what you have there is surface tension. Think of water on your polished car, exactly the same. Dont use white spirit as a pre wipe, it can have greasy deposits, which again cause surface tension. Best cleaner of bare wood and inter-coats is Isopropanyl mixed with equal amount of water. Any recoat may wrinkle because of still evaporating solvents. Avoid Ronseal, used it once, never again.

Then you have 2 different re-coating bonds, a chemical bond happens with fresh coats, a phyisical bond when sanded because previous layer has exceeded reccomended re-coating time. I always do next day and flatted back with 240g wet/dry. Just enough to remove any peaks and reach the valleys. The chemical bond is preferred by 2-pack products, because most solvent will have evaporated by dust dry time.

Too dry/cured a coat will have the wet car effect, unless sanded.

1-pack can be applied over 2-pack. 2-pack should not be applied over 1-pack, its too chemically aggresive.

Back to the deck in photo. This has to withstand phyisical abuse as well as extreme weather abuse. The varnish has UV filter to protect the epoxy coat. The epoxy coat protects the wood from moisture. Epoxy coat not needed on a radio. Because the varnish is water clear there is a 2-tone effect as you walk around it and the sunlight angle changes on the grain. This boat always gets admiring comments every time I take it out.

What will your veneers look like when varnished? Just wet it with clean water, it will naturally be darker.

If you are sanding back to bare wood, wetting it will show up areas where varnish still remains. Meths is good for this, as it quickly evaporates you can get back to sanding those spots you missed.

On bare wood use Acetone and a brass suede brush to remove any old varnish deposits in the grain.

Always work on a test piece first, an A4 piece of plywood will do. Then you know exactly what will happen to you lovely restoration. Use the test piece to test your polishing technique.
Andy 1964 is offline   Reply With Quote
Old 8th Jan 2021, 5:26 pm   #48
Andy 1964
Triode
 
Join Date: Jan 2021
Location: Leicester, Leicestershire, UK
Posts: 20
Default Re: What causes this in polyurethane varnish?

forgot the photo
Attached Thumbnails
Click image for larger version

Name:	119859952_2696612460576543_8311237438711968829_n.jpg
Views:	124
Size:	52.5 KB
ID:	224143  
Andy 1964 is offline   Reply With Quote
Old 8th Jan 2021, 10:51 pm   #49
Andy 1964
Triode
 
Join Date: Jan 2021
Location: Leicester, Leicestershire, UK
Posts: 20
Default Re: What causes this in polyurethane varnish?

Product data sheet for Epifanes. Use a foam brush. Only first coat needs thinning.
Attached Files
File Type: pdf epifanes_polyurethane_gloss_varnish.pdf (715.3 KB, 15 views)
Andy 1964 is offline   Reply With Quote
Reply

Thread Tools



All times are GMT. The time now is 9:10 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2021, vBulletin Solutions, Inc.
Copyright ©2002 - 2020, Paul Stenning.