richie00boy said:
Only discovered Bonda recently and only use it on the externals anyway. I've always used a PVA mix for the internals since its quick and cheap.
Over what period do you find the joints shift/expand? My latest cabs were sanded until I couldn't feel the joints to the touch. It's been a week and I can feel them again already. I was waiting to cut the port hole before applying anything on them.
I think the lesson here is that you need to seal the cabs quick sharp after sanding 🙄
edit: or do these expansions only occur when soaking up paint?
I think the lesson here is that you need to seal the cabs quick sharp after sanding 🙄
edit: or do these expansions only occur when soaking up paint?
Understanding equilibrium is important here. Consider the max./min's. of relative humidity that occur over the course of a year. If casework is sealed during one of the extreme conditions you are going to witness movement during the alternate. It may be expansion or contraction. It depends upon where you start.
If new material used for a project is stored in an unheated garage it is most likely accumulating moisture from the air. The exception to this is for those of you living in the desert. When that material is moved to a heated space (or you turn on the heat) it will lose moisture until reaching equilibrium with it's surroundings. A vapor barrier slows the process. Maybe to acceptable levels. It does not stop it.
Maintenance of an environment that replicates the "norm" where the finished casework will reside is important. Climate control is key. If you must store material where it is subject to moisture swings, consider purchasing only what is needed as it is needed, so as to limit the exposure to moisture gain.....and get it inside as quickly as you can.
If new material used for a project is stored in an unheated garage it is most likely accumulating moisture from the air. The exception to this is for those of you living in the desert. When that material is moved to a heated space (or you turn on the heat) it will lose moisture until reaching equilibrium with it's surroundings. A vapor barrier slows the process. Maybe to acceptable levels. It does not stop it.
Maintenance of an environment that replicates the "norm" where the finished casework will reside is important. Climate control is key. If you must store material where it is subject to moisture swings, consider purchasing only what is needed as it is needed, so as to limit the exposure to moisture gain.....and get it inside as quickly as you can.
What glue did you use? If PVA based the joint may be every so slightly still shrinking for a bit after it has seemingly set. This would pull it tighter together hence pronounce the lip again.
Paint sinking
Hi Vikash,
In my experience, "speed" of application doesn't have much to do with this.
With dissimilar substrates, the long-term 'sinkage' with paints will vary according to the substrate, no matter what.
MDF end grain is very much different here than the highly 'compressed' surface of MDF, as another poster has pointed out.
Even if one thinks one has overcome this problem (by whatever means) in my experience, and in the fullness of time, the paint will 'sink' differently, and, regrettably, you will see the joins.
I have been doing this kind of thing for many years, and whatever finish is used (I started with cellulose over 50yrs ago, then synthetics, then 2 pack etc., and latterly polyurethanes, acrylics, plastic coatings and whatever) and given sufficient time, you will always see the difference in 'sinking'.
Unfortunately, it seems to be a fact of life and needs to be taken into account when deciding on what finish to apply.
Hi Vikash,
In my experience, "speed" of application doesn't have much to do with this.
With dissimilar substrates, the long-term 'sinkage' with paints will vary according to the substrate, no matter what.
MDF end grain is very much different here than the highly 'compressed' surface of MDF, as another poster has pointed out.
Even if one thinks one has overcome this problem (by whatever means) in my experience, and in the fullness of time, the paint will 'sink' differently, and, regrettably, you will see the joins.
I have been doing this kind of thing for many years, and whatever finish is used (I started with cellulose over 50yrs ago, then synthetics, then 2 pack etc., and latterly polyurethanes, acrylics, plastic coatings and whatever) and given sufficient time, you will always see the difference in 'sinking'.
Unfortunately, it seems to be a fact of life and needs to be taken into account when deciding on what finish to apply.
Re: Paint sinking
The sink your referring to is usually called die-back or shrink back and refers to the paint actually shrinking and tightening as the solvent within the paint are released causing it to lose mass and shrink. Or at leasts that's the way I've read it.
Like you say, ineviatably you'll see the joints reappear no matter what. But its usually to a much lesser extent if you take precautions before hand.
Ed also made a good point with the MDF not being left in extremes. I always bring my work inside after working on it and never leave it in the cold damp shed.
Bobken said:
The sink your referring to is usually called die-back or shrink back and refers to the paint actually shrinking and tightening as the solvent within the paint are released causing it to lose mass and shrink. Or at leasts that's the way I've read it.
Like you say, ineviatably you'll see the joints reappear no matter what. But its usually to a much lesser extent if you take precautions before hand.
Ed also made a good point with the MDF not being left in extremes. I always bring my work inside after working on it and never leave it in the cold damp shed.
hey guys
im wondering, this effect of expanding mdf has been kicking me in the *** for the last 2-3 projects iv made.
highly annoying.
i cant seem to find any products resebeling this one here up north, but i wonder..
i got the thought of making the cases, placing them in a heated room with a moisture reducer, and then spraypaint then internally and externally with a 2k primer. do you think this will seal the mdf good enough?
or is it the sprayinh that is a problem? can it be if the paint\primer is not waterbased?
thanks
marius
im wondering, this effect of expanding mdf has been kicking me in the *** for the last 2-3 projects iv made.
highly annoying.
i cant seem to find any products resebeling this one here up north, but i wonder..
i got the thought of making the cases, placing them in a heated room with a moisture reducer, and then spraypaint then internally and externally with a 2k primer. do you think this will seal the mdf good enough?
or is it the sprayinh that is a problem? can it be if the paint\primer is not waterbased?
thanks
marius
2k primer will be soaked up by the bucket load. It's also porous so would not seal especially well. The epoxy sealers such as Bonda is a good choice.
I also wonder if something like Extramite (Cascamite) or an epoxy glue might be better for the joints.
I also wonder if something like Extramite (Cascamite) or an epoxy glue might be better for the joints.
And as feared, any chemical like the one you use is banned from norway, the closest i came was fungie killer, the light version, and thats not really what im after >_<
a bloody shame is what it is, i really wanted to do my new speakers the best way i can, im not planning a uppgrade for a long time.
Richie, epoxy sealer was nemptioned earlier.
one that does not evaporate, and thats thinn enough to be used in a spray gun, does one exist to your knowledge?
a bloody shame is what it is, i really wanted to do my new speakers the best way i can, im not planning a uppgrade for a long time.
Richie, epoxy sealer was nemptioned earlier.
one that does not evaporate, and thats thinn enough to be used in a spray gun, does one exist to your knowledge?
Demo....
Do a national search for West Systems epoxy,
variuos viscisties used for boat building, sealing, etc....
like here:
http://www.njordforum.no/tema/lim_eopxy_fenol/lim_epoxy_fenol.shtml
or here:
http://www.westsystem.no/
Do a national search for West Systems epoxy,
variuos viscisties used for boat building, sealing, etc....
like here:
http://www.njordforum.no/tema/lim_eopxy_fenol/lim_epoxy_fenol.shtml
or here:
http://www.westsystem.no/
demogorgon,
Follow the link to a post on Parts Express' site. Aaron Hero started a thread showing how he deals with mdf: lots of heat to drive the moisture out. His work is interesting.
http://www.pesupport.com/cgi-bin/config.pl?read=321628
Follow the link to a post on Parts Express' site. Aaron Hero started a thread showing how he deals with mdf: lots of heat to drive the moisture out. His work is interesting.
http://www.pesupport.com/cgi-bin/config.pl?read=321628
Not that this will add much, but I recently noticed that a set of boxes I built is starting to get cracks around the butt joints. I sealed them with Bondo (the stuff for car body work) but that doesn't seem to have done the trick. It may have been that I sanded too much off and re-exposed the end "grain," but with the weather changing this summer the boxes started shifting.
I did use a good quality Latex primer externally, but I did not think to seal the insides (a mistake that will not be repeated). The next time I build a set of boxes, I will definitely dry them thoroughly first and then finish inside and out.
I am quite used to accounting for wood movement in the hard wood projects I build, but for manufactured wood products I have never noticed this movement before. (Then again, I have never tried to make a smooth, exposed butt joint before!)
Anyway, thanks for all of the tips! At least it will help someone!
David
I did use a good quality Latex primer externally, but I did not think to seal the insides (a mistake that will not be repeated). The next time I build a set of boxes, I will definitely dry them thoroughly first and then finish inside and out.
I am quite used to accounting for wood movement in the hard wood projects I build, but for manufactured wood products I have never noticed this movement before. (Then again, I have never tried to make a smooth, exposed butt joint before!)
Anyway, thanks for all of the tips! At least it will help someone!
David
Auror, thanks for the tip, and the same to you Ed!
looks interesting to say the least.
the price on the epoxy is a bit out of my league (and not to nemption unpractical to get) , but the forced heater seems interesting.
i was thinking along the same lines my self, alltho im going for more moderate heat and a airmoisture remover.
gonna use a 1k oil paint, or scout around some more specialized shops for some moisture blockers.
there may be some good stuff left in someones basement if i ask subtle enough 😉
looks interesting to say the least.
the price on the epoxy is a bit out of my league (and not to nemption unpractical to get) , but the forced heater seems interesting.
i was thinking along the same lines my self, alltho im going for more moderate heat and a airmoisture remover.
gonna use a 1k oil paint, or scout around some more specialized shops for some moisture blockers.
there may be some good stuff left in someones basement if i ask subtle enough 😉
Is this what causes the line where MDF is butt jointed?
I just had a look at a subwoofer that my dad and I built together. He spray painted it with just a regular gloss black and a few coats. There is a line where there is a butt join, at the junction between the end piece and the surface.
ShinOBIWAN,
Are you saying that this product when applied will prevent that from happening?
I plan to do some high gloss black finish soon.
I just had a look at a subwoofer that my dad and I built together. He spray painted it with just a regular gloss black and a few coats. There is a line where there is a butt join, at the junction between the end piece and the surface.
ShinOBIWAN,
Are you saying that this product when applied will prevent that from happening?
I plan to do some high gloss black finish soon.
It will reduce it. I think the best way is probably to veneer over the joints (or you could use mitre joints) and then spray them. Eventually the lines will always show through otherwise...
The problem is I'd like to chamfer the corners. What if I were to insert a piece of quad so that there is in fact no MDF edge present. Or am I creating new problems by using MDF and timber?
paulspencer said:
Vik pretty much has it spot on from my perspective.
Wood hardener/Polyester resin reduces but sadly doesn't completely eliminate the problem. I've also noticed it can create hairline fractures within the MDF (not sure about other materials). I don't think these affect structural rigidity but certainly show through under paint.
I stopped using it because of that.
The veneering works very well. Over a year after finishing these there are zero indications of the lines showing:
Joints:
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Veneer over joints:
An externally hosted image should be here but it was not working when we last tested it.
Paint job one year later:
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This method works good but you might be able to avoid the extra finishing steps and find something else which does an equally good job. But for me, this method is a safe bet now.
Dumb idea of the day...
What if ,instead of wood veneer ,you just used a wipedown of glue and a wrap of butcher's paper?
My 2c
Jorge
What if ,instead of wood veneer ,you just used a wipedown of glue and a wrap of butcher's paper?
My 2c
Jorge
That's another suggestion. Not sure of the results though.
I think its important to point out that you only need to do this if you experiencing problems with joints creeping back. I know a couple of folks (not in the UK climate) who've said they don't need to use anything more than good primer and thorough filling/sanding prep.
I think its important to point out that you only need to do this if you experiencing problems with joints creeping back. I know a couple of folks (not in the UK climate) who've said they don't need to use anything more than good primer and thorough filling/sanding prep.
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