because i was doing shelvs and the sides are thin spray was not really working but was perfect for the bigger flat parts. more the edge but i guess i could paint then sand then after that spray should work for the smoothness.
i sure i brush was crap and out side was bad idea tho bits floating on it
thanks i will have a look into them brushes never heard of it
the roller way was not to bad but leaves a different pattern not tried the gloss roller bit tho
thanks
i sure i brush was crap and out side was bad idea tho bits floating on it
thanks i will have a look into them brushes never heard of it
the roller way was not to bad but leaves a different pattern not tried the gloss roller bit tho
thanks
richie00boy said:
For me, the end grain raises above the face hence my inclination towards no 1. Running my hand over the tweeter cabinet on the LGT's confirms this.
But I can also see the glue line in the joint has depressed compared to the face. So could be both unless the MDF face has expanded but at a lesser rate than the end grain causing the dip on the joint.
larksp said:
Washed? Water??
Nooooo... not on MDF!!
That will effectively undo your 1200grit sanding.
Damp wipe at most.
The 1200 grit sanding should come AFTER an initial coating of whatever you are using.
Ok, so maybe you were sanding 1200 after coating... i dunno.
In which case some polishing will bring back gloss, if you are looking for that... for no brush marks - spray.
But, to make paint go smoother, buy a commercial paint aditive that is intended to improve "flow"...
_-_-bear
The foam rollers are great, but can take some practice to get smooth.
I use to roll coat fine art prints by hand with acrylic glaze and a small foam roller. It does take practice to get a smooth finish with no lines or bubbles. A light touch helps a lot.
Every surface and paint or medium will be different, so practice with what you will be using. It can be done and look very nice. But the first few won't. =)
I use to roll coat fine art prints by hand with acrylic glaze and a small foam roller. It does take practice to get a smooth finish with no lines or bubbles. A light touch helps a lot.
Every surface and paint or medium will be different, so practice with what you will be using. It can be done and look very nice. But the first few won't. =)
richie00boy said:
Yea, I had visions of someone intercepting it and trying to do a couple of lines. That'd give 'em a surprise
No worries on visiting - just give me notice when it's OK.
ShinOBIWAN said:
Some good points there. I've only done a few cabs with butt or rebate joints, and come to think of it, you're probably right about the slight raising of the cut end grain. However, the sinking glue line is always far more severe for me.
I've had a response from West, and they confirm that the epoxy should completely seal what's being covered (from both air and moisture).
Interestingly, they did indicate that more coats (applied with a roller) may be needed to get a good seal - especially considering I'm flatting the cured epoxy. The first test piece (and something I'm working on right now) had coats applied with a brush, and hence got a much thicker covering.
It'll be a while before the current piece gets painted, but I'll report on the results.
A quick update on the glue/MDF/movement issue...
My local area (Oxfordshire) has an annual event in which local artists and businesses open their premises up to the public (artweeks). It's well worth your time BTW.
I was chatting to a guy at a bespoke furniture manufacturer, and he noted they sometimes use MDF as a core (with veneer) specifically because it doesn't 'move'. He was talking about it in relation to veneering over real wood though.
On the subject of glues, he did think there might be something in the PVA issue. They use Extramite to attach veneers to MDF, because it dries hard and brittle, as oppsed to PVA which dries slightly rubbery.
I mentioned it was for loudspeakers, and he wondered if a brittle glue might have problems with a speaker cabinet under pressure, but I don't think that would be a big problem.
Anyway, nothing conclusive, but certainly a few more gentle prods in the direction of harder drying glues...
My local area (Oxfordshire) has an annual event in which local artists and businesses open their premises up to the public (artweeks). It's well worth your time BTW.
I was chatting to a guy at a bespoke furniture manufacturer, and he noted they sometimes use MDF as a core (with veneer) specifically because it doesn't 'move'. He was talking about it in relation to veneering over real wood though.
On the subject of glues, he did think there might be something in the PVA issue. They use Extramite to attach veneers to MDF, because it dries hard and brittle, as oppsed to PVA which dries slightly rubbery.
I mentioned it was for loudspeakers, and he wondered if a brittle glue might have problems with a speaker cabinet under pressure, but I don't think that would be a big problem.
Anyway, nothing conclusive, but certainly a few more gentle prods in the direction of harder drying glues...
Hi Spoo,
PVA glue for MDF is as strong as needed. I use yellow carpenters glue, which is stronger than the white variety. Apply a generous amount, then clamp tight.
Not enough glue in the joint might be the cause of your lines, it could also be that the pieces weren't clamped tight enough.
The biggest problem with priming MDF is the end grain. Everyone knows that it absorbs quicker than the face grain, but the real problem is that it can suck the solvents and/or resins out of the paint and leaving an inferior finish. It will literally seperate the paint as it's being applied.
Treating the edge grain with a urethane based finish prior to priming will block this absorpsion problem.
In the pic below is a speaker baffle that is laminated with 2 layers of 5/8" MDF. The first layer was glued, clamped and screwed to the box. the second layer was just glued and clamped - no screws. As can be seen, there is quite a curve to it (about 5" out of line). It took considerable clamp pressure to curve the MDF, and the only thing holding it on is yellow carpenters glue.
It's strong enough.
PVA glue for MDF is as strong as needed. I use yellow carpenters glue, which is stronger than the white variety. Apply a generous amount, then clamp tight.
Not enough glue in the joint might be the cause of your lines, it could also be that the pieces weren't clamped tight enough.
The biggest problem with priming MDF is the end grain. Everyone knows that it absorbs quicker than the face grain, but the real problem is that it can suck the solvents and/or resins out of the paint and leaving an inferior finish. It will literally seperate the paint as it's being applied.
Treating the edge grain with a urethane based finish prior to priming will block this absorpsion problem.
In the pic below is a speaker baffle that is laminated with 2 layers of 5/8" MDF. The first layer was glued, clamped and screwed to the box. the second layer was just glued and clamped - no screws. As can be seen, there is quite a curve to it (about 5" out of line). It took considerable clamp pressure to curve the MDF, and the only thing holding it on is yellow carpenters glue.
It's strong enough.
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MJL21193 said:
Hi John, I was hoping you'd reply to this thread.
I've been effectively 'painting' on glue before clamping together, so I was hoping that would be enough.
I must admit I saw a professional company laminating sections of plywood (to then slice as kitchen table tops) and the glue was pretty much spraying out the sides... I don't use that much.
What urethane products are you using? I'll see if I can get them here in the UK.
Love the curved baffle - but I notice what looks like lines in the finish down the left hand side of the image. They appear quite similar to the problems I've been seeing. Are they an artifact of the camera/reflection of something else/a different problem?
ShinOBIWAN said:
This reminded me of speaking recently to a mate of mine who's in a band - I was wondering about having a summer+gig party in my garden, and asked him what amplifier gear they'd need. "9kW PA!" was the response
Wonder how those speakers are glued together!
Hi,sploo said:
Paint (or any urethane based paint):
http://www.overflex.com/product.asp?frm_product_id=617&SBL=5
Use non-water based polyurethane(clear) to seal the edge if the finish is going to be different (not urethane based). Urethane doesn't seperate easily, so it will seal the edge grain completely. Let dry at least a day, then sand smooth. Urethane is highly resistant to other solvents when dry.
Part of my sucess with this problem is the products I use. When built up thick it seems to have some flexibility. It's not as hard and brittle as some finishes. I've also used Tremco Rust Enamel and Sherwin Williams All Surface Enamel Alkyd - all fairly cheap stuff. The only drawback is how long it takes for the paint to cure.
The area you pointed to is the side of the box, and is un-finished (just hit by overspray). It will be given a layer of cherry veneer plywood. Only the curved front baffle is finish painted. As I mentioned before it's two layers of MDF glued together. No line is visable at the joint, in fact it appears to be a single solid thick piece. The picture is a few hours after painting (10 coats).
Here it is before primer:
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