Problems with Matt Varnish

[woodman-79]

Hi all,

Is anyone able to provide some advise on what the problem is with what i'm doing here.

I have made a sample piece of timber with satin varnish which worked perfectly. 5 coats, no bubbles, nice and even etc.

For the life of me i can't get a sample to work with matt varnish. It keeps getting bubbles coming out of the timber on the first coat. It's the same brand as the satin.

The bubbles are not being brushed on, they are actually coming out of the timber as it starts drying. You can see in the photos below that they come out along the grain lines.

I first tried with the varnish straight and thought that i'd messed it up brushing it on, or that it was too thick. After it dried it sanded it all off and tried again thinned with turps but the same thing happened.

Is there where a sealer is required? i have never used one before so i don't know.

Or is there another solution?


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Thanks,
Mike

[Big Shed]

Always better to apply a sealer or sanding sealer first to bare timber. Ubeauts sanding sealer (shellac based) is one you can use.

If you don't want to do that then apply a coat of the satin first, then the matt.

That should fix your problem.

Be aware that the more coats of matt varnish you apply the "milkier" the finish gets due to the matting agent (usually a form of aerated silica) in the matt varnish.

[woodman-79]

Thanks, i might try putting a coat of satin on first. Don't know why i didn't think of that .

It's possible it is the grain/pores in that particular piece of timber that's the issue rather than a difference in the two varnishes. If so i'll give the Ubeaut sanding sealer a shot.

So with a matt varnish, do you general do fewer coats than you would with a satin or gloss, to avoid a milky finish?

[Nanigai]

Hi Mike,
You could sit there with a pin and prick them one by one as they bubble up but it's probably easier to use a sealer.
This will give you a better finish as well. The sealer raises the grain and pop's any figure as well. I recently used some tassie oak to make a couple shave cabinets for a bathroom reno and had no problems at all after using a dewaxed shellac sealer under the polly.
I'm an amateur though so may be someone else may be able to expand on this. Good luck,
Cheers, Ian

[Big Shed]

Depends how many coats the timber needs.

On most hardwoods 3 coats should be sufficient, so if you use a sealer (or the satin as a first coat) then 2 coats of matt would be fine.

If however you need more than 3 coats I would limit the matt to the last 2 coats.

[Arron]

The timber is out gassing. Air trapped in the pores needs to equalise with the outside somehow. You put the finish on, trapping in the air. Normally it makes its way out through the finish but if the finish is too thick it can't penetrate.

Personally, I doubt it's the difference between matt and satin varnish per se, rather something else you are doing without realising it.

Are you doing something to make the air in the pores expand - like putting it in a sunny place to dry after application. Avoid changes of temperature when finishing.

Time of day can matter too. That's why most people with experience of epoxies never apply them late in the day. As the ambient temperature drops, air in the pores will try to equalise and flow out.

Are the samples the same. Obviously it's euro oak, very porous timber and the pores run very deep. Were they cut from the same plank?

Sealing will help, to the extent it fills the pores and stops the transfer of air - but sealing is difficult with euro oak because the pores run so deep. Maybe better to grain fill instead.

Is the matt varnish a lot thicker then the satin? Or older? Maybe thin it a bit.

Finally, if you keep getting bubbles hitting it with a hair dryer might help - activates the finish and let's air pass through.

Bubbling is a standard problem for those of us who spray lacquers. I've largely eliminated it but never fully. Still comes back to ruin a job every now and then.

[woodman-79]

Personally, I doubt it's the difference between matt and satin varnish per se, rather something else you are doing without realising it.

Are you doing something to make the air in the pores expand - like putting it in a sunny place to dry after application. Avoid changes of temperature when finishing.

As time goes on, i'm inclined to agree. I think it's the specific piece of timber rather than anything i was doing differently though. I applied them in exactly the same fashion, at the same time, and in the same place. They were applied and dried in my workshop which is insulated and resonably well sealed so temperature would have been stable at about 18-20 degrees.

I think that piece of timber had larger pores on one side of it where the grain curved in a different direction to the bulk of it.

Are the samples the same. Obviously it's euro oak, very porous timber and the pores run very deep. Were they cut from the same plank?

Yep, all of the samples (made 6 in total) were from the same board. I think the problem bit was right at the end and the grain may have been a bit more porous than the rest of it.

Sealing will help, to the extent it fills the pores and stops the transfer of air - but sealing is difficult with euro oak because the pores run so deep. Maybe better to grain fill instead.

What is grain filling? and how does it differ from sealing?
I'm new to finishing as i've primarliy just used oil before, but i would really like to become proficient at finishing. It really is a world of it's own.

Is the matt varnish a lot thicker then the satin? Or older? Maybe thin it a bit.

Both are Feast Watson purchased at the same time (one may have been on the shelf for a while.. not sure about manufacturing dates). They feel about the same consistancy.
I tried thinning it twice after the first failed attempt. First time just thinned a bit, then thinned a lot. Didnt seem to make a difference to the bubbling up.


I have this morning applied the first coat with satin and it appeared to be working well by the time I left home. Haven't got home yet to check the dried (almost) results but I think it worked.
I did however use a new sample piece I had left over, so i will not know whether it worked because it was the satin varnish or because it was a new sample of timber.. I will clean up the old bit and try it with satin though for my own sanity.

Thanks for the replies.

[woodman-79]

Ok, now i'm getting frustrated!

I made a new sample and gave it a coat of satin varnish which worked perfectly. Completly bubble free and nice and even and smooth.

Once dry, I again tried to give it a coat of the matt varnish and within minutes of applying it, it blistered up... what the hell am i doing wrong?

I'm applying it exactly the same way as the satin which works perfectly every time.


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[Arron]

It appears to be a different and quite unrelated issue.

My guess is that there is some sort of contaminant on top of the satin varnish.

Are they both oil based?

[Big Shed]

OK, that is a different problem to what you had before. The matt is lifting the satin which by the look of it had not dried enough before recoating.

How long did you let the satin dry before putting the matt over the top?

Which brand are you using, are they both the same brand, what is their recommended drying time before recoating?

[woodman-79]

It appears to be a different and quite unrelated issue.

My guess is that there is some sort of contaminant on top of the satin varnish.

Are they both oil based?

I dont believe that is the case, the issue has only occured with the matt varnisih.

To go back to the beginning, I made a sample with matt and satin at exactly the same time initially. They were applied in exactly the same manner, and dried in the same environment. Subsequent coats of both were also applied at the same time as well etc.
The matt sample, did as the above pictures shows, but the satin was perfect.

I then sanded the matt one all the way back to raw timber and tried again, thats when i noticed that the first coat was having the issues shown in the opening post above. Thats why I ended up putting a succesfull layer of satin onto a fresh piece of wood, to try and seal the timber as it appeared that the issue was stemming from gas escaping the timer.
There were no contaminants on the dried satin first coat at all, I can guarentee that.

Yes, they are both oil based.

OK, that is a different problem to what you had before. The matt is lifting the satin which by the look of it had not dried enough before recoating.

How long did you let the satin dry before putting the matt over the top?

Which brand are you using, are they both the same brand, what is their recommended drying time before recoating?

Yep, they are both the same brand and same manufacturing date.
It was dry, it was applied 12 hours after the first coat, which is as per manufacturers instructions.

I will also note that, this is no different to what i did with the satin sample i made in terms of drying time, which did not have this issue. I did, i think, 5 coats, all 12 hours apart and had no issues at all. It's perfect.

I'm not entirly sure that it is a different issue to the opening post. I tend to think it just appears different because it's on top of varnish not raw timber.
As mentioned above, the blistered look above, is actually the issue I initially had with my matt sample, before sanding all the way back and starting again, which is when i noticed the bubbles as per first post.


What makes no sense to me is,
1. Why would satin not have the issue shown in the first post but matt does?
2. Why would second coats of satin not have the same blistering issues but matt does?

[Big Shed]

The photo of the matt over the satin is a classic case of the topcoat lifting the basecoat, I have been involved in the paint industry for most of my life.

You described the original problem as "bubbles rising through the wet varnish", which is not what this problem shows.

If these are a one-pack polyurethane then I would suggest that 12 hrs is an absolute minimum before recoating.

As I cannot inspect the wet varnish I would guess that the matt is thicker than the satin so therefore you are putting a thicker wet film on than you would with the satin giving more chance of lifting the base coat.
It could also be that the solvent blend in the matt is different to enhance flow, which in a matt is somewhat impeded by the silica matting agent. It could contain a slower evaporating solvent to give the matt a longer "open time" which means the solvent stays in the wet film longer, thereby giving it more time to lift the satin base coat.

To prove this one way or another, recoat a satin sample with the matt after at least 24hrs. If it doesn't lift then my diagnosis is correct, if it still does I would get on to the technical dept of the paint company involved and get their opinion.

Edit:

I see you are in Kinglake, if that quoted 12 hrs includes an overnight period (ie 7pm to 7am) then that would further reinforce that the satin has not dried properly as even here in Bendigo we have had overnight temps of below 10C.

[woodman-79]

Thanks Big Shed,

I will do as you have suggested and try a new satin base coat dried for over 24 hours.

Yep, the matt is a bit thicker than the satin, it doesnt flow as well. Is it worth also thinning it a bit with turps?

Regarding temps, the satin base coat I did yesterday was applied early in the mornig, bout 7am and left inside my house through the day. It would have been around 20 inside all day.
I made a very good decision that i am constantly appreciating, while we were building to add extra insulation throughout the house, including all the internal walls. It's the best decision I made and keeps the house very stable. I did the same with my workshop (garage) which has also been a blessing.

[Big Shed]

For a direct comparison it would be better not to thin the matt, but as you will probably have to thin to use it under actual conditions you could do so.

[soundman]

OK you have a couple of problems here.

1/ you have an open pored hardwood, typical of oak and many others.
Viewed under magnification the timber looks like a whole bunch of straws glued together, those straws are full of air.

Pretty much all top coats regardless of type can benifit from some sort of sanding sealer or primer ..... most top coats have a matching sanding sealer.

what you need to do is fill up those tubes and seal em up.

You need something that will penetrate and is both fine enough in its resisn and liw enough in viscosity to enter into and seal those tubes.

Expect to sand after you use a sealer and maybe several coats till you have worked up a sound base ..... a fully choked out finish

One tip for these porous woods ........ warm the timber thru and thru ...... apply the finish and then put the piece in a cool place to slowly cool

It helps to have the finish warm too

this will do a number of things .... because the job is warm the finish will flow and be absorbed better ...... as the timber cools it will the air within will tend to contract rather than expand ...... less of a problem with bubbles.

2/ Any time there is blistering there is either a solvent compatability problem.

either the uver finish has a more agressive solvent mix or the underfinish has not properly cured out.

Polyeurathane is mongrel stuff, it goes thru several distinct stages of curing ..... and these stanges vary from product to product.

but there is "not off" , "not quite off", "yeh sort of off", "yeh its off", "realy off", "realy properly off" and "fully hardened out"

You have to pick your recoat times and this varies from product to product.

you can lay up wet coat on "yeh sort of off" this will redisolve and bond with the previous coat, IF you are carefull and quick.

then ya go thry a can't win stage, before its "realy off", then you can recoat.

If you want to sand between coats you need to wait for it to be "realy off".

But if you wait for it to be realy properly off or fully hardened out, you can not recoat without sanding because you will have adhesion problems.

And there are can't win stages of one type or another between all the stages of curing.

I'd strongly sugest you do not try to mix your mats finishes ... stick to one top coat product.

Shelac is a realy good sealer, because once it is fully cured out you can go over it with virtually anything.

cheers