JJ,
12 corners?!
Haven't decided, but I'm thinking:
6 corners rounded, 2 square
5 rounded edges, 7 square
Hard to imagine from what I've just said, but it's a sub box with a surfboard shaped open baffle panel above. The shape is too complex to describe in words, and I'm still working on it.
MJL,
Beautiful work!
That's the kind of look I'd like for the sub part.
Is it a good idea to use HDF where the edges will be routered?
Amp guy,
When you use gel coat, how do you apply it? Do you just do it over the edges or over the whole box?
12 corners?!
Haven't decided, but I'm thinking:
6 corners rounded, 2 square
5 rounded edges, 7 square
Hard to imagine from what I've just said, but it's a sub box with a surfboard shaped open baffle panel above. The shape is too complex to describe in words, and I'm still working on it.
MJL,
Beautiful work!
That's the kind of look I'd like for the sub part.
Is it a good idea to use HDF where the edges will be routered?
Amp guy,
When you use gel coat, how do you apply it? Do you just do it over the edges or over the whole box?
Hi paulspencer sorry I missed your question Ive been camped out on a houseboat out of reach of the net, cellphones and T.v. .
I spray the gelcoat on the entire exterior , then sand when it is fully hardened , then i usually use spray can Laquer from the autopart store. As far as treating cones I have experimented with throw away speakers with all sorts of varnishes etc, Damar was the only one that wasn't dentrimental to the sound , but that is my opinion. good luck
I spray the gelcoat on the entire exterior , then sand when it is fully hardened , then i usually use spray can Laquer from the autopart store. As far as treating cones I have experimented with throw away speakers with all sorts of varnishes etc, Damar was the only one that wasn't dentrimental to the sound , but that is my opinion. good luck
I have just finished a sub box made from 3/4" mdf. I am going to have it spraid at a car body repair shop, they will be using 2 pack paint (obviously) I told the guy I would seal it prior to bringing it to him..
I was going to use wood hardener as per OP's advise but now even the OP on some posts says this causes cracks in the MDF.
Are the cracks only when the MDF is left in adverse conditions? I am planning on keeping this box indoors now.
If the hardener is not the way to go what is cheap and available for me to use?
thanks guys.
I was going to use wood hardener as per OP's advise but now even the OP on some posts says this causes cracks in the MDF.
Are the cracks only when the MDF is left in adverse conditions? I am planning on keeping this box indoors now.
If the hardener is not the way to go what is cheap and available for me to use?
thanks guys.
Do you think Shinobiwan would leave his beautiful creations in adverse conditions 
I've got some of this to try
I spoke to Rustin's technical support and they managed to convince me it's better than watered down PVA as it is acrylic based so harder.
There is also a sealer made by Bonda called "G4 Damp Seal", in a white and orange container that is worth trying.
I've got some of this to try
An externally hosted image should be here but it was not working when we last tested it.
I spoke to Rustin's technical support and they managed to convince me it's better than watered down PVA as it is acrylic based so harder.
There is also a sealer made by Bonda called "G4 Damp Seal", in a white and orange container that is worth trying.
An externally hosted image should be here but it was not working when we last tested it.
rich - they have that in my local wilko's.
Problem is it has taken me so long to get this box up to scratch I am reluctant to try stuff out.. indeed I scrapped the first attempt.
If you spoke to the tech and they convinced you I may give that a go.
I am sure I read that the piece that the great shin noticed cracks in was left in his garage
Problem is it has taken me so long to get this box up to scratch I am reluctant to try stuff out.. indeed I scrapped the first attempt.
If you spoke to the tech and they convinced you I may give that a go.
I am sure I read that the piece that the great shin noticed cracks in was left in his garage
needmorstuff said:
I keep all the MDF in the house, only time it goes outside is to work on it.
The sealer I mentioned at the beginning of this thread does cause problematic hairline cracks in the thickness portion of the MDF, note I never noticed this problem on the face.
Ignoring my own advice and wanting to see if the flaw would repeat itself, I did the 50mm thick MDF plinths of the last speakers I built with the wood hardener. I got cracks again but quite a bit worse than last time. In the end I went back and shaved around 5mm off each side to get back to the sound MDF and avoid problems with finishing.
If I were to hazard a guess as to what was happening I'd say the treated part vs. the internal untreated part of the MDF has some movement interaction and causes the problem ie. one expands/contracts whilst the other remains more stable.
For this reason I'd strongly recommend not using the Bonda wood hardener I did.
My favourite method for best finish over joints is veneering then priming over that. Its an effort but I don't mind.
Alternatively spraying polyurethane sealing coats works well according to investigation done by forum member sploo.
If you want an almost flawless gloss finish then sadly there isn't an easy fix from my own experiences.
Let us know what you tried and after some weeks once the cabinets are finished tell us if problems appear. You may find something others have missed.
auto paints
If you are planning to apply auto paint as a finish ( which I highly reccomend) be sure to seal using a product compatable with laquer type paints . Gelcoat resin will absorb into the mdf giving it a hard surface that will take a surprising amount of abuse without damage. this is a two part resin that is colored white. this is the topcoat when molding composites. I have never encountered cracking or cazing.this can be applied with a brush for those without spray gear. the surface can be sanded to a mirror finish then a sealer intended for auto paints can be applied
Two part epoxy sealers are worth the cost here.
if this all sounds costly and labor intensive that is because ...well it is but this is the ultimate finish (in paint that is). don't overlook painting some parts and using wood for others that is extra spiffy too.
If you are planning to apply auto paint as a finish ( which I highly reccomend) be sure to seal using a product compatable with laquer type paints . Gelcoat resin will absorb into the mdf giving it a hard surface that will take a surprising amount of abuse without damage. this is a two part resin that is colored white. this is the topcoat when molding composites. I have never encountered cracking or cazing.this can be applied with a brush for those without spray gear. the surface can be sanded to a mirror finish then a sealer intended for auto paints can be applied
Two part epoxy sealers are worth the cost here.
if this all sounds costly and labor intensive that is because ...well it is but this is the ultimate finish (in paint that is). don't overlook painting some parts and using wood for others that is extra spiffy too.
Also make sure the box is kept in the house at all times and at least a week before sealing it. This will keep the mousture level down.
Look forward to hearing how you get on. The Rustins sealer is supposed to be highly compatible with other finishes, one other reason I was swayed towards it.
Out of interest what glue did you use to do the joints? As I think that plays a part in the problem as well. PVA based wood glue does have a tiny amount of give to it. Myself and sploo now use only Extramite which is a little less convenient as you have to mix it up yourself but it works very well and was recommended by the MDF Council or whatever the UK trade body for MDF is called.
Look forward to hearing how you get on. The Rustins sealer is supposed to be highly compatible with other finishes, one other reason I was swayed towards it.
Out of interest what glue did you use to do the joints? As I think that plays a part in the problem as well. PVA based wood glue does have a tiny amount of give to it. Myself and sploo now use only Extramite which is a little less convenient as you have to mix it up yourself but it works very well and was recommended by the MDF Council or whatever the UK trade body for MDF is called.
richie00boy said:
I used the evo stick blue bottle pva glue (the external stuff) and at least three "F" clamps on every surface being joined.
I now have the rustins and will be coating tonight and taking to body shop hopefully b4 the weekend. Most of the joints are silky smooth at present but one or two could do with a little more attention.. I will do this during the sealing/sanding back process. Final grit of 320.
I will look into the adhesive you mention.
The box was in the garage for the vast majority of the construction - I brought it inside about a week ago, just prior to flush trimming edges and rounding over etc.
Spoke to body shop guy and he told me to bring another piece of MDF sealed with rustins for him to try b4 finishing my work. That kind of common sence sometimes escapes me.
richie00boy said:
I used decorators cauk to seal all internal joins (acrylic)
the driver does not have a backing of any type where it will contact the MDF, will the rpessure be sufficient at creating a seal or should something else be employed? (draft strip..) I remember taking the drive rout of my BK sub and the metal just butted straight up to the mdf.
I have a thread at another forum.. are we allowed to cross link?
**edit** do you mean all the internal panels with rustins? I wasn't going to but i can if it will help.
Personally I think caulking the seams is pointless, if your glueing is good and your panels pretty straight cut then it's doing nothing.
Yes I meant coating the inside panels, this will reduce the moisture getting into and out of the panel, which is what causes the glue lines to show.
It wouldn't hurt to use draught excluder on the driver seal. Take care with the screw holes though, I would slit a cross into the seal where it covers over the hole to allow the screw to pass through. If you just ram the screw through it tends to distort the seal (speaking from experience).
Yes I meant coating the inside panels, this will reduce the moisture getting into and out of the panel, which is what causes the glue lines to show.
It wouldn't hurt to use draught excluder on the driver seal. Take care with the screw holes though, I would slit a cross into the seal where it covers over the hole to allow the screw to pass through. If you just ram the screw through it tends to distort the seal (speaking from experience).
richie00boy said:
excellent tips - thank you. I have sealed the outside and will make sealing the inside the last job.
The rustins makes some "hairs" appear on the surface so I will sand these back with 320 and give it a final coat of sealer.
I did by some inserts off madaboutsound (vikash) but they aint logn enough for my double width (1.5") baffle. I have some long t-nuts and will either use them or just screw straight into the MDF with 50mm spax wood screws.
I took a quick look at some of the test blocks I did (all stored in the house, all well over 6 months old).
Nothing's changed - the epoxy (2 part West Epoxy) coated blocks are generally good. If you get enough thickness of epoxy it works, too thin and it doesn't.
The two part polyurethane coated blocks (using poly for both primer/sealer and paint) are fine. The single part poly block is also good, however it will still take a fingernail (though you have to press very hard).
For those without breathing gear, the single part poly is a good option. In fact, I felt it had better adhesion and was less susceptible to running than the two part version. I got it from Paints4u (Isolack by LECHSYS).
The two part stuff is amazing - dries rock hard in a day or so, but is obviously very dangerous (isocyanate based).
The problem with the poly coatings is that the MDF absorbs loads of it, and you do seem to need to load it to the point of saturation, let it dry, sand the nibs smooth, then apply paint coats. Makes it pretty expensive on paint.
Epoxy is a ballache to apply in thick enough quantities - it's the consistency of treacle, so quite hard to get flat. It dries rock hard, so sanding smooth is a pain, and it's very messy to use (plus it's not cheap either).
I've been recommended a clear single part poly called Varathane, but every attempt to get it here in the UK have failed. I'd be interested to see the results of the Rustins product.
I've tried a poly floor varnish, but I wasn't convinced - plus using the two part poly over the top was incompatible (it caused the varnish to crinkle).
Nothing's changed - the epoxy (2 part West Epoxy) coated blocks are generally good. If you get enough thickness of epoxy it works, too thin and it doesn't.
The two part polyurethane coated blocks (using poly for both primer/sealer and paint) are fine. The single part poly block is also good, however it will still take a fingernail (though you have to press very hard).
For those without breathing gear, the single part poly is a good option. In fact, I felt it had better adhesion and was less susceptible to running than the two part version. I got it from Paints4u (Isolack by LECHSYS).
The two part stuff is amazing - dries rock hard in a day or so, but is obviously very dangerous (isocyanate based).
The problem with the poly coatings is that the MDF absorbs loads of it, and you do seem to need to load it to the point of saturation, let it dry, sand the nibs smooth, then apply paint coats. Makes it pretty expensive on paint.
Epoxy is a ballache to apply in thick enough quantities - it's the consistency of treacle, so quite hard to get flat. It dries rock hard, so sanding smooth is a pain, and it's very messy to use (plus it's not cheap either).
I've been recommended a clear single part poly called Varathane, but every attempt to get it here in the UK have failed. I'd be interested to see the results of the Rustins product.
I've tried a poly floor varnish, but I wasn't convinced - plus using the two part poly over the top was incompatible (it caused the varnish to crinkle).
the rustins stuff is very runny.. consistency just thicker than water, it leaves very little mess behind as it readily soaks in the mdf on first coat. The 2nd coat hangs a bit more but still dries quickly.
I sanded back after both coats 2nd less than first. It isn't a hard wearing coat and is purely for sealing the mdf. I am placing all my finishing on the automotive paints tbh.
I sanded back after both coats 2nd less than first. It isn't a hard wearing coat and is purely for sealing the mdf. I am placing all my finishing on the automotive paints tbh.
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