Hey, Shinobi
I've been a big fan of the stuff from you I've seen around DIYaudio.
I was wondering if you could put up pics of some of the various cracks / lines that you have seen show up. Specifically, the cracks that show up in mdf + wood hardener.
I found this thread after already starting on a finishing project (with wood hardener), you see, and I'd like to see just what it is that's going to happen so that I can wrap up the project in as pleasing a way as possible. I also wonder if the different sealers develop the same kind of flaws, or if they have different looks.
Thx
I've been a big fan of the stuff from you I've seen around DIYaudio.
I was wondering if you could put up pics of some of the various cracks / lines that you have seen show up. Specifically, the cracks that show up in mdf + wood hardener.
I found this thread after already starting on a finishing project (with wood hardener), you see, and I'd like to see just what it is that's going to happen so that I can wrap up the project in as pleasing a way as possible. I also wonder if the different sealers develop the same kind of flaws, or if they have different looks.
Thx
AdamThorne said:
As a matter of fact I took photo's of the baffles on the Perceives when I noticed this problem:
An externally hosted image should be here but it was not working when we last tested it.
An externally hosted image should be here but it was not working when we last tested it.
It got worse too. I ended up putting on obscene amount of primer over that to give a thick layer so as to more effectively hide the problem. Unfortunately it still showed through in much the same way as joints do. Hindsight is a great thing and I now avoid the stuff.
Here's an image of the lines that are showing up on the second epoxy test piece. They're quite fine, but you can feel them, and they're obviously visible.
The lines are very similar on the blocks coated with the other products (though sometimes a little deeper and wider).
There is one constant with all these test blocks - they're glued together using PVA. I wonder if it's causing some moisture/shrinking problems as it dries?
If I get some time in the next few days I might try glueing some blocks together using the epoxy.
Ant, what glue are you using? Good to hear that the veneering process is looking successful BTW.
The lines are very similar on the blocks coated with the other products (though sometimes a little deeper and wider).
There is one constant with all these test blocks - they're glued together using PVA. I wonder if it's causing some moisture/shrinking problems as it dries?
If I get some time in the next few days I might try glueing some blocks together using the epoxy.
Ant, what glue are you using? Good to hear that the veneering process is looking successful BTW.
Attachments
I use PVA from Evostik, the blue one rather than green. Reason for that is I rationalise weatherproof as a stronger formula.
Those lines look pretty severe, especially given the short amount of time that they've taken to show. Give that a few months and it will be visable from the other side of a room unfortunately. Had it been a metallic things get even worse.
Have you found any explanation as to why one of your epoxy peices hasn't got joint flaws and the other has? I remember you saying one had a more generous coating, can you confirm it still has no lines?
Ta
Ant
Those lines look pretty severe, especially given the short amount of time that they've taken to show. Give that a few months and it will be visable from the other side of a room unfortunately. Had it been a metallic things get even worse.
Have you found any explanation as to why one of your epoxy peices hasn't got joint flaws and the other has? I remember you saying one had a more generous coating, can you confirm it still has no lines?
Ta
Ant
I've stopped using PVA as I'm not convinced it dries hard/stable enough. When you sand it it goes all rubbery and cloggy. I now use Extramite (formerly Cascamite) which is almost rock hard. It's still water based but doesn't seem to have any adverse effects.
IMO if PVA were any good they would use it to fix plywood together. They don't they use urea resin, which is what Extramite is.
IMO if PVA were any good they would use it to fix plywood together. They don't they use urea resin, which is what Extramite is.
ShinOBIWAN said:
Yea, me too - and for the same reasons. Interesting... (drums fingers together in a Monty Burns way)
ShinOBIWAN said:
Still no lines. The only thing I can think of is that it's got a really thick coat. It's mad really, as it was done in all the wrong ways - no coverage on the bottom, and got dunked into water numerous times when I was flatting the epoxy/paint/lacquer stages.
BTW I've mailed West, will see if they've got any further ideas.
richie00boy said:
Good points. How long is it workable after mixing the power?
I'm presuming you're meaning this stuff:
http://www.axminster.co.uk/user_sea...-Extramite-Powdered-Resin-Wood-Glue-21688.htm
sploo said:
Maybe the MDF likes you to treat it rough
Considering what you've just said, especially the bit about dunking the MDF, its all a little bizzare.
I'm 'owt for an easy life so is that Extramite stuff available ready to go without mixing? If the answer is no, then what about this Rich:
http://www.axminster.co.uk/pricing/...uct-Titebond-III-Ultimate-Wood-Glue-29225.htm
Yeah that's the stuff. I mix it up into small pots, I think 14 teaspoons of powder is about the most you can make up and apply to joints in one go. But that was enough to do all round all 4 sides to fit the front and back panels, of a 60 litre box, and have a little bit left to brush round joints after to get a nice coverage and fill any small gaps.
The downside to Extramite is that you do have to mix it up.
I haven't used any Titebond I, II or III so can't comment really other than when I was researching glues a little while ago I discounted them for some reason, but I can't remember exactly what that was now.
edit: now I remember. It was because it is a poly glue that foams slightly as it cures, i.e. expands.
I haven't used any Titebond I, II or III so can't comment really other than when I was researching glues a little while ago I discounted them for some reason, but I can't remember exactly what that was now.
edit: now I remember. It was because it is a poly glue that foams slightly as it cures, i.e. expands.
Basically bit of water, then the powder then mix. Then add a little more water to finish and mix off. The ratios are given on the tin. Apply with a small paint brush.
I can see how it could be a bit of a pain if you have a load of gluing to do, and doesn't clean off your hands quite as well as PVA, but it is water clean up.
On the other hand, it's great for applying to veneer or sticking panels together as it can be slapped on easily and you can to a degree control the viscosity.
I think Laver's in town stock it Ant.
I can see how it could be a bit of a pain if you have a load of gluing to do, and doesn't clean off your hands quite as well as PVA, but it is water clean up.
On the other hand, it's great for applying to veneer or sticking panels together as it can be slapped on easily and you can to a degree control the viscosity.
I think Laver's in town stock it Ant.
I just ordered the smallest tub of that and the Titebond3 Ultimate.
I think you could be onto something with the glue used. Its the one constant I see between my own experiments and Sploo's. Lets face it, we're both approaching the problem with pretty hard hitting tactics that should work nicely but yet that isn't the case, glue is something I've overlooked.
I think you could be onto something with the glue used. Its the one constant I see between my own experiments and Sploo's. Lets face it, we're both approaching the problem with pretty hard hitting tactics that should work nicely but yet that isn't the case, glue is something I've overlooked.
Sploo I'm happy to send you a bit of Extramite and the mixing instructions if you want to have a go with it on another block test.
My logic is that the PVA joint allows a tiny bit of movement between the panels. You can prove this because you can stick your fingernail quite easily in the dried glue, so it must have some give/flexibility. If the joint is locked solid with a glue that doesn't move or flex then I think it should all act as one solid block.
My logic is that the PVA joint allows a tiny bit of movement between the panels. You can prove this because you can stick your fingernail quite easily in the dried glue, so it must have some give/flexibility. If the joint is locked solid with a glue that doesn't move or flex then I think it should all act as one solid block.
richie00boy said:
No.
"They" would not use PVA, no matter how good a glue it might be!
That is because Plywood is made as a continuous process, on a high speed production line. Not one sheet at a time, with dry time available for glue. It is done with high pressure/high temp fast/instant setting glues.
Ok?
_-_-bear
ShinOBIWAN said:
The reason I'm wondering if it's the glue is that (for me at least) it always seems to be the joins that move.
OK, I'm sure the joins will always be the weakest point, but you would've thought you'd see some cracking/folding in the paint if the whole surface of the cut edges were shrinking/expanding.
I've got a few days off next week, so will try to glue some bits together using the epoxy.
richie00boy said:
Thanks. However, if you're after coming round for me to sort out those sub panels it's probably better to do it then, rather than sending me a sachet of white powder in the post.
richie00boy said:
Exactly. Which would explain why it's always the joins that are visible.
Ant - remember John (MJL21193) saying he wasn't having any problems, when he was using coatings/techniques that didn't appear wildly different to some of the stuff we're doing. Perhaps he's using a different type of glue (can't remember if he mentioned it).
sploo said:Thanks. However, if you're after coming round for me to sort out those sub panels it's probably better to do it then, rather than sending me a sachet of white powder in the post.
LOL that could be quite funny. I'll have to sort out coming soon though, which could be a bit difficult.
sploo said:
I did wonder about that myself.
That just it though, it could be any of the two most plausable explanations:
1. The entire end grain is expanding leaving a depression on the joint because the glue doesn't follow suit.
2. The end grain is relatively stable and the PVA is shrinking/moving revealing the joints.
Its hard to tell just which of those is happening or maybe its both. All we know is that despite our best efforts we get a channel appearing along the joints at some point after finishing - could be days or could be months depending on the treatment.
I shall try to remain open minded about whats causing it but I just have a feeling and instinct for this now thats tough, for myself, to deny. My money is on number 1 and we'll see exactly the same thing regardless of glue used. I hope I'm wrong because that would solve the whole thing pretty nicely.
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