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Old 13th Sep 2020, 8:44 am   #41
PsychMan
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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!
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Old 13th Sep 2020, 9:31 am   #42
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Default Re: What causes this in polyurathane varnish?

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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.
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Old 13th Sep 2020, 2:57 pm   #43
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Default Re: What causes this in polyurethane varnish?

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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.
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Old 14th Sep 2020, 8:16 am   #44
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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.
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Old 14th Sep 2020, 8:50 am   #45
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Default Re: What causes this in polyurethane varnish?

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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.
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Old 14th Sep 2020, 10:33 am   #46
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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.
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Old 8th Jan 2021, 5:23 pm   #47
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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.
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Old 8th Jan 2021, 5:26 pm   #48
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Default Re: What causes this in polyurethane varnish?

forgot the photo
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Old 8th Jan 2021, 10:51 pm   #49
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Default Re: What causes this in polyurethane varnish?

Product data sheet for Epifanes. Use a foam brush. Only first coat needs thinning.
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Old 18th Jan 2021, 2:04 pm   #50
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Default Re: What causes this in polyurethane varnish?

Interesting info. I will be trying various other varnishes in coming months, 2 pack and other water based varnishes for other projects. I suspect 2 pack would have finished this cabinet project for me months ago!

Ive progressed with the poly though, as I've had no choice - I was in too deep.

I am getting to the point where Im happy with the results, which I will share on here when its done. Its not perfect, and it wont be, the surfaces arent perfectly flat, there are flaws, the gloss isnt as perfect as I'd like, but given its my first serious attempt I think its decent, and the defects are ones most people cant see.

Theres been many bumps in the road getting here, lessons learned etc. As ever, very grateful for all of the help and advice. Im proud of what Ive achieved, but boy, WHAT A LOT OF WORK!!!

Ive been used various sand paper grades, and trying to get the surfaces as fine as possible, then switching to t-cut, followed by a slightly less aggressive meguiars car polish. Its a LOT of work, particular the t-cutting, but it gets there. I've tried buffing wheels and so on, but they simply dont work well with t-cut and I need that level of abrasion.

Im really looking forward to being able to glue the damn thing together, and fit the deck and the electrics - which by far will be the easiest part of this project!

Adam
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Old 18th Jan 2021, 2:09 pm   #51
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Default Re: What causes this in polyurethane varnish?

Like I said months ago Adam, polyurethane is a LOT of work. I used it many times and was never happy with the way it went on and never really happy with the results even after much corrective work. You know what my favourite finish is.
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Old 18th Jan 2021, 3:06 pm   #52
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Default Re: What causes this in polyurethane varnish?

It is a lot of work. Well done for keeping going. It's made marginally easier by keeping patient at the beginning and doing really thin coats, as you've discovered. It's so easy to be a bit too thick because it doesn't look like it's covering, then find out that the next coat's softened the one underneath.

I look forward to seeing your end result!

I wondered why you didn't glue it together first, as surely the joints will require extra treatment as at least some will be visible. Didn't you want to varnish them in situ?
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Old 18th Jan 2021, 3:54 pm   #53
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Default Re: What causes this in polyurethane varnish?

Indeed Steve, I was in too deep to change the varnish at that point.

I looked at your posts, you said it was water based and ďmilkyĒ varnish. Do you have a product name or what the core ingredient is?

@Uncle bulgaria, the reason Iím doing these pieces separately is I anticipated some sanding, and buffing, and couldnít see how I could achieve that if it was pre assembled, with internal corners and so on. I agree it makes lines hard to hide, and I will have to cross that when I come to it. Iíve been selectively sanding and dremeling bits of it to try and get it fitting as tight as I can. Beyond that itís going to be best endeavours in bodge city!
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Old 18th Jan 2021, 5:12 pm   #54
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Default Re: What causes this in polyurethane varnish?

It's Wilko Quick Dry varnish. Available in matt, satin and gloss, and in different stain colours too.
https://www.wilko.com/wilko-ultra-to...E&gclsrc=aw.ds
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Old 18th Jan 2021, 6:25 pm   #55
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Default Re: What causes this in polyurethane varnish?

Cheers. It doesnt say what it is, but I wonder if that's water based polyurethane.
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Old 18th Jan 2021, 6:44 pm   #56
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Default Re: What causes this in polyurethane varnish?

I'm not sure, all I know is it works great. Whenever I need to finish wood, out comes the Wilko Quick Dry Varnish. A few days later, job complete and looking good.
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Old 18th Jan 2021, 6:52 pm   #57
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Default Re: What causes this in polyurethane varnish?

It is a water-based PU varnish - it says so on the tin...

Alan
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Old 20th Jan 2021, 11:35 pm   #58
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Default Re: What causes this in polyurethane varnish?

Get an air brush and spray really thin coats and this will happen no more.
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