Priming MDF boxes

[richie00boy]

Sploo like you I wondered about the warning on the tin or wood hardener. I actually rang Ronseal tech support and talked it over with them. They said basically it's just intended for use on rotting real wood, not MDF. He couldn't really say why it's not a surface treatment other than it's for damaged patches of wood rather than big areas.

However, it won't stop me using it as the results are good. It's just a shame it's so expensive.

I'd be really interested in how you get on with the epoxy again. Maybe instead of the West Systems (which is expensive?) you could try normal stuff used by car bodyshops. You can get it from Halfords, in yellow tins.

[ShinOBIWAN]

Originally posted by richie00boy
Sploo like you I wondered about the warning on the tin or wood hardener. I actually rang Ronseal tech support and talked it over with them. They said basically it's just intended for use on rotting real wood, not MDF. He couldn't really say why it's not a surface treatment other than it's for damaged patches of wood rather than big areas.

However, it won't stop me using it as the results are good. It's just a shame it's so expensive.

I'd be really interested in how you get on with the epoxy again. Maybe instead of the West Systems (which is expensive?) you could try normal stuff used by car bodyshops. You can get it from Halfords, in yellow tins.

Rich, has any of the MDF ever cracked with the Ronseal Hardener. When I say cracks I mean tiny almost hair line fractures in the MDF as you look at the crosssection rather than face.

I say this because I have the first test piece I tried this out on in the garage still and came across it a month or so ago and discovered lots of these fractures. I've got older bits of untreated MDF up there and they're fine. I can only assume its something to do with the hardener and the climate. I never noticed this problem on the Perceives though.

I'm wondering if thats what the tech support and warning labels were trying to get at?

BTW I used the Bonda stuff but it looks to be the same thing as the Ronseal.

[sploo]

Originally posted by richie00boy
...However, it won't stop me using it as the results are good. It's just a shame it's so expensive....

...I'd be really interested in how you get on with the epoxy again...

Well, I'll give it a go and see what happens.

The West System epoxy isn't cheap - 16 quid for about 600g. However, the coverage is pretty reasonable. I don't have the figures in front of me right now, but I think it was something like 6-8m^2 per kilo.

Hadn't thought about getting something from Halfwits. Will have to take a look the next time I visit.

Originally posted by ShinOBIWAN
...I say this because I have the first test piece I tried this out on in the garage still and came across it a month or so ago and discovered lots of these fractures....

Did you coat it completely, or just one side? I'm wondering if stabilising only part of a section of MDF results in moisture changes (from the other side) which then causes cracking on the side that's 'fixed'.

BTW I'm reading through your 'LGT' Construction Diary, and I'm stunned at the stuff you're doing without any CNC gear. I still make plenty of foul-ups, but it's a little easier now that I'm running a CNC router.

[ShinOBIWAN]

Originally posted by sploo Did you coat it completely, or just one side? I'm wondering if stabilising only part of a section of MDF results in moisture changes (from the other side) which then causes cracking on the side that's 'fixed'.

I did all side except for the rear face. Your probably right about the moisure getting through the untreated part and causing the MDF to expand at different rates. That would quickly and easily explain the fractures.

I never observed anything like that with a fully treated cabinet though, which adds further weight to what your saying.

BTW I'm reading through your 'LGT' Construction Diary, and I'm stunned at the stuff you're doing without any CNC gear. I still make plenty of foul-ups, but it's a little easier now that I'm running a CNC router.

Thanks, most of the stuff you can do with CNC can be done with good handtools its just that the accuracy isn't always as good and the setup time for guide rails, measurements, markings etc. all add up, so you need a fair bit a patience and diligence.

[richie00boy]

I coated both sides, and it's maybe not been long enough to for faults to show yet. Also the cabs have been kept in the house so maybe big moisture changes have not been seen.

Handy to know somebody with a CNC router

[larksp]

sorry just a small question rather than a new thread richie00boy
did u upload that program yet ?

[richie00boy]

You would have been better just posting again on the thread in question, it then shows up to me that a new reply is there

No I said I would do you a design if you gave me the details I asked for, as the program was not at a stage I was happy to release.

[larksp]

ok thats cool. was not to make anything with just see how it work but anyway different subject back to priming lol

[sploo]

Originally posted by ShinOBIWAN
...I never observed anything like that with a fully treated cabinet though, which adds further weight to what your saying.

I'm hoping that might be the same reason I'm seeing some small lines on my original test pieces - as I didn't coat the bottom of the stacks. Will make sure they get completely coated this time.

Originally posted by ShinOBIWAN
Thanks, most of the stuff you can do with CNC can be done with good handtools its just that the accuracy isn't always as good and the setup time for guide rails, measurements, markings etc. all add up, so you need a fair bit a patience and diligence.

Tell me about it. I built a set of five speakers a couple of years back, and it took weeks. I even have a decent router table I made, but it's all the measuring (as opposed to the cutting) that eats up the hours.

These days, I can get home from work, draw a few lines and circles in a CAD package, wander into the garage, and have something cut, all in a couple of hours. Well, apart from when I make one of about 500 different type of mistakes (I'm very inventive - always working out a new way to screw up ).

Originally posted by richie00boy
I coated both sides, and it's maybe not been long enough to for faults to show yet. Also the cabs have been kept in the house so maybe big moisture changes have not been seen.

Handy to know somebody with a CNC router

Sounds like the right thing to do (a full coat). I'll see what happens in time.

The CNC gear is useful (took me long enough to save up for it)! I'm based in Oxfordshire, so if you're after stuff cutting, then I'm quite happy to discuss the possibility.

[richie00boy]

Thanks, it would likely be odd smallish panels really. Stuff that would be hard to do by hand.