Priming MDF boxes

[sploo]

Oops. "files" should of course be "flies". Long day at work...

BTW I forgot to note - it's been mentioned to me in the past that putting several coats of paint onto a surface with inadequate flash off time can lead to the bottom layers never setting (as the already cured top layers prevent the drying of the layers underneath). I am worried that might happen with the urethane, as it's formed a pretty decent skin.

 

[richie00boy]

The bottom layer issue is also one that I've been concerned with.

Today I have been mostly emailing Blackfriar and Rustins regarding their MDF sealer products. I'm going to my local (very good) hardware shop tomorrow to see which they can get, they stock both brands in various products.

I've worked out a way to cut blocks with perfect edges with my flush trimming bit, turning the block over for each pass.

 

[ShinOBIWAN]

Offtopic but ontopic 😀

I found some excellent examples of paint defects at various stages of finishing. The examples also include the possible causes as well as remedies for all stages from mixing through to application as well as during and after drying.

Paint Defects

 

[ShinOBIWAN]

Oops. "files" should of course be "flies". Long day at work...

BTW I forgot to note - it's been mentioned to me in the past that putting several coats of paint onto a surface with inadequate flash off time can lead to the bottom layers never setting (as the already cured top layers prevent the drying of the layers underneath). I am worried that might happen with the urethane, as it's formed a pretty decent skin.

Yep that's true. I had to sand back a tweeter enclosure on my speakers because the gloss had lost its shine. On close inspection of clearcoat I could see what looked like a very fine frosting pattern on the surface.

John mentioned that he had something similar and that it was primer related. Sure enough once I'd stripped back the clear and base coat I found the the primer was rubbery - dry but not hard. Bare in mind that this primer layer was applied over a month before stripping the cabinet back, so I very much doubt it would have ever dried.

As to the cause; I remember spraying a lot of primer coats in a short space of time because the weather was unfavourable. I'm not 100% sure if it was the weather or me rushing and not allow correct flash off time whilst building up coats. What I can say is that I hadn't had that before when I allow the correct flash off time recommended for my primer.

 

[MJL21193]

...cured top layers prevent the drying of the layers underneath). I am worried that might happen with the urethane, as it's formed a pretty decent skin.

If this is the case, it will still dry - it'll just take a lot longer. I have had 1" of urethane harden right through in the can.
I can't comment on the particular formulation the manufacturer uses for the paint you bought, but the one I use will harden completely in about 2 weeks. Yeah, it's a long time, but that's how I do it.
You've heard about how fast cold molasses will run uphill? 🙂

If you want a faster dry time, with near equal performance in a 1K, use alkyd based paint. Should be easier to find than the urethane.

Yep that's true. I had to sand back a tweeter enclosure on my speakers because the gloss had lost its shine. On close inspection of clearcoat I could see what looked like a very fine frosting pattern on the surface.

John mentioned that he had something similar and that it was primer related. Sure enough once I'd stripped back the clear and base coat I found the the primer was rubbery -

The time you are refering to I used a different primer, sprayed it on thick, then didn't give it enough time to cure. I beleive the top coats re-activated the primer (same as yours Ant, rubbery).
A royal mess. I actually scraped it all off with a chisel.

With my work schedule, I usually wind up painting during ideal spring conditions - not too hot, not too cold, moderate humidity. I have a large garage that I spray in, open air. A ten coat paint job will take most of the day (and a few cold beers 😀). It's dry enough to move indoors the next morning.

All in all, perhaps the total length of time needed for my paint job to fully cure adds to the stability of the MDF.
It can be up to a month with paint on before final polish.

 

[ShinOBIWAN]

All in all, perhaps the total length of time needed for my paint job to fully cure adds to the stability of the MDF.
It can be up to a month with paint on before final polish.

That's roughly how long I leave mine, 4 weeks with the film thickness I build up is just right. After that time it gets the final finishing. I used to give it only 2 weeks but found that in the preceding weeks following that I often needed to go over it again with fine cutting compound because the paint was still shrinking.

 

[troystg]

ShinOBIWAN-

Was it you that had a website with pictures of your enclosures?

I recall seeing a website with a 10" 3way in a single enclosure with parallel sides on bottom, tapered on the sides at the top and I'm not having much luck finding it again.

EDIT: It was a black and wood grain enclosure, 5* tilt back.

 

[sploo]

...I found some excellent examples of paint defects at various stages of finishing...

Very useful, thanks.

The bottom layer issue is also one that I've been concerned with...

...will harden completely in about 2 weeks. Yeah, it's a long time, but that's how I do it...

I can hear it calling me... 2K... 2K... 2K 😀

That, unfortunately, is looking like becoming more difficult, as I've been having 'fun' working out compressor requirements.

Most air fed masks seem to require around 6CFM. So, you find a 6CFM compressor. Well, no, a compressor advertised as 6CFM is likely to be 6CFM 'displacement', but you apparently need 6CFM 'free air delivery' (FAD). Unsurprisingly, that costs more.

I found a couple of suitable units, and was planning a purchase, only to be told that a 6CFM FAD compressor would be working flat out to supply a mask, hence I'd probably need twice that, at 12CFM FAD.

Anyone got any (real) experience with this and could tell me what's actually likely to work (HP, litres, CFM etc.)?

 

[ShinOBIWAN]

Sploo

Can't you get one of the resevoir-less continuous run types?

The mate who got me into all the spraying using compressed air does exactly this with 2k paints and it works fine. He sticks the mask compressor outside the garage runs the air line inside and then opens the front doors and has two large 36" industrial fans that pull the fumes out.

Works great and he sprays for long periods like me. Had never complained about lack of air to the mask just that the air gets warm after long prolonged running.

 

[ShinOBIWAN]

ShinOBIWAN-

Was it you that had a website with pictures of your enclosures?

I recall seeing a website with a 10" 3way in a single enclosure with parallel sides on bottom, tapered on the sides at the top and I'm not having much luck finding it again.

EDIT: It was a black and wood grain enclosure, 5* tilt back.

I don't think it was who built what your looking for. I tend to always spray my speakers instead of veneer.

Sorry I couldn't help.

 

[troystg]

ShinOBIWAN

Ok. Thanks for the prompt reply.

Back to the search...

 

[sploo]

...Can't you get one of the resevoir-less continuous run types?...

That would seem ideal - but what I know about compressors you could write on the back of a postage stamp. Where could I get one of these things?

A while back I had considered a (maybe not that) crazy idea of using a breathing tube - kinda like a long snorkel. I'd add a valve system, so you'd draw air in through the tube (from the outside) and breath out through another valve (into the working area).

I figure at the end of the day, all you're trying to achieve is to breath air that's not where you're spraying. I guess the issue with the tubes is that you'd need something with a large enough diameter so you could draw air at lung pressure through a tube of, say, 5 meters. I don't know what the static load issues would be on that, but I'd expect something in the order of 2" diameter would be OK, if a little cumbersome.

 

[ShinOBIWAN]

The oil-less ones are pretty expensive, I thought otherwise when I mentioned them to you earlier.

Looking around, something like this would be fine:

http://cgi.ebay.co.uk/AIR-COMPRESSO...1QQihZ007QQcategoryZ30906QQrdZ1QQcmdZViewItem

That 3HP so you can expect between 9-10cfm(FAD). More than enough air for a mask. Unfortunately its got a 50 ltr tank attached meaning it will be quite bulky and heavy considering its just for the airfed mask.

This 2.5HP 7.3cfm(FAD) might be better with its smaller 25ltr tank. That is if space is a problem.

http://cgi.ebay.co.uk/WOLF-SIOUX-AI...2QQihZ005QQcategoryZ30906QQrdZ1QQcmdZViewItem

With these types you'll need an air line filter to get rid of any oil or moisture in the air:

http://cgi.ebay.co.uk/SCHRADER-AIR-...ryZ30906QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

 

[TerryO]

I may be off base here, however many of the 2-part paint formulas are very risky to use without a pressurized hood. The idea is not merely to prevent breathing the fumes, but to prevent absorbing any of the paint mist through the eyes or mouth. The catalized 2-part epoxy and urathane paints can cause a lot of irreversable damage, if I'm not mistaken. I would certainly check this out with the manufacturer before proceeding, as only one exposure can ruin your health permanently.

Best Regards,
TerryO

 

[MJL21193]

Health Effects of Isocyanates

Isocyanates are highly reactive chemicals typically found in the hardener of two-part paints and primers. Isocyanates are present in two forms, monomer and prepolymer. The isocyanate monomer content is frequently indicated in Material Safety Data Sheets (MSDS), but this is only a small part of the total unreacted isocyanate present. Both forms of unreacted isocyanate are a risk to health when they are released into the air during paint or primer spraying.

Breathing unreacted airborne isocyanate can cause coughing, chest tightness, fever, fatigue and sensitization. Once a worker is sensitized, further exposure to even very small amounts of isocyanate will cause distressing asthma-like reactions. The reaction may occur immediately or several hours after exposure. One exposure to a high airborne concentration or several exposures to lower concentrations may result in sensitization. There is no proven method for predicting whether any particular person will become sensitized if exposed to Isocyanates.

Direct skin contact with isocyanates may cause rashes, blistering and reddening of the skin. Repeated skin contact may cause skin sensitization.

Eye exposure to airborne isocyanates can cause eye irritation and temporary blurred vision. Direct contact with the eye may cause damage to the cornea.

Some brain food...

 

[ShinOBIWAN]

Terry and John speak the very best advice.

I've used 2k and had a minor scare with it. I have to ask the question to anyone who isn't trained, equipped and confident with the use of it, is it really worth the health risk given that even a short but high concentration exposure can cause permanent damage and for what? A paint coating that dries harder and faster?

This is a hobby, I'd want danger money for spraying that stuff again.

Sploo if your really wanting to do this then do like I did and hire self contained breathing apparatus (similar to enclosed suit Terry mentioned). Just remember to never get complacent with the 2k as its totally unlike celly finishes. One minute you feel fine and the next your throat's on fire and you can't breath. Sounds like I'm exaggerating but far from it.

 

[sploo]

...That 3HP so you can expect between 9-10cfm(FAD). More than enough air for a mask. Unfortunately its got a 50 ltr tank attached meaning it will be quite bulky and heavy considering its just for the airfed mask...

I'd been considering one of these (which is pretty close to what you're describing): http://www.toolsnstuff.co.uk/produc...sor-50ltr-Direct-Drive-30hp&products_id=17331

What's set me back is that when I spoke to them they indicated that I'd probably need 12CFM FAD to drive a 6CFM mask. The more I look, the more conflicting information (and probably a fair bit of *rse covering on their part) I encounter.

Thanks for the heads-up on the filter - it's not something I was aware of.

...without a pressurized hood. The idea is not merely to prevent breathing the fumes, but to prevent absorbing any of the paint mist through the eyes or mouth...

An excellent point Terry. When I spray anything I do wear goggles and cover all skin, but I am also spraying outdoors - so there's fairly low concentration of dangerous stuff in the air. If in an enclosed space, the need for good air round the eyes is probably going to be very important. That probably knocks the breathing tube idea on the head (and also explains why the half face mask kits are not rated for isocyanates, despite the wearer still being fed good air).

...Breathing unreacted airborne isocyanate can cause coughing, chest tightness, fever, fatigue and sensitization...

I have caught a breath of it on a couple of occasions, especially when mixing, and yea, you really don't want to be breathing it.

...anyone who isn't trained, equipped and confident with the use of it...

Now come on Ant, on a daily basis, you, me, and most of the rest of the nutters here attempt things we're not trained, equipped or confident about doing. Otherwise we'd never get anything done. 😀

...hire self contained breathing apparatus (similar to enclosed suit Terry mentioned)...

I did find a place that hired some of the stuff, but it's a fair distance from me - certainly not the sort of last minute thing where you decide to do some spraying today, as a hiring would have to be planned.

Plus, when I worked out the costs, it was going to be many tens of pounds for one weekend, so you'd only have to use it a few times to reach the cost of buying the gear yourself. Oh, and with a reasonable compressor on hand I guess you could use some of the decent air tools available.

Finally, it's an airfed mask; would you want to stick your head in where some other bloke has been? 😉

 

[ShinOBIWAN]

I have caught a breath of it on a couple of occasions, especially when mixing, and yea, you really don't want to be breathing it.

That's when I had that turn, for some stupid reason I only considered using the breathing equipment when spraying. During mixing I just used a normal VOC mask which does absolutely nothing to filter isocyanate's. Apparently some folks are more sensitive to it than others. Once its got you though, your weakened to it and subsequent exposures are more severe and can be triggered by small concentrations. So that's why I don't bother with the stuff now.

Now come on Ant, on a daily basis, you, me, and most of the rest of the nutters here attempt things we're not trained, equipped or confident about doing. Otherwise we'd never get anything done. 😀

We're not talking about cutting wood here though but OK I'll say no more on the subject. Everyone has a line they draw somewhere. You know how I feel about 2k - leave it to the pro's who get paid for it and have ££££'s of equipment that totally isolates the sprayer amd his lungs from the hazardous material.

I did find a place that hired some of the stuff, but it's a fair distance from me - certainly not the sort of last minute thing where you decide to do some spraying today, as a hiring would have to be planned.

Plus, when I worked out the costs, it was going to be many tens of pounds for one weekend, so you'd only have to use it a few times to reach the cost of buying the gear yourself. Oh, and with a reasonable compressor on hand I guess you could use some of the decent air tools available.

The local hire station near me charged just over £70 for 2 weeks and £10 for each extra bottle(they're refillable). A bottle gives around 30-45 minutes of breathing time depending on if your breathing normally or heavily.

Considering I pay nearly £70 for 1.5ltr of paint, then that's nothing to me when it comes to my health. If your doing this regularly and you feel confident that the results outweigh the risks then at least invest in competent equipment and certainly don't jury rig a bit a pipe onto a traditional respirator. That's just asking for trouble.

Finally, it's an airfed mask; would you want to stick your head in where some other bloke has been? 😉 [/B]

Yeah, wouldn't go down too well if the bloke before you was a garlic fiend. You'll find the types I'm talking about are modular and you'll get a fresh silicone breather with it. The head/face cowl, overalls, bottle and mixer were all used but hygiene mattered little with those.

 

[ShinOBIWAN]

I'd been considering one of these (which is pretty close to what you're describing): http://www.toolsnstuff.co.uk/produc...sor-50ltr-Direct-Drive-30hp&products_id=17331

What's set me back is that when I spoke to them they indicated that I'd probably need 12CFM FAD to drive a 6CFM mask. The more I look, the more conflicting information (and probably a fair bit of *rse covering on their part) I encounter.

Thanks for the heads-up on the filter - it's not something I was aware of.

Well if your needing 12cfm(FAD) then you'll need to be looking at 3 phase(400v) belt driven piston compressors. 3hp or about 10cfm(FAD) is about the most you'll get from single phase 240v.

I've just bought a 3 phase 4hp belt driven twin cylinder compressor with a 200ltr tank. Its 15cfm(FAD) which would be enough for a face mask if the advice you've received is to be listened to. Problem is the price, I paid £420 and it was a display model off ebay at that.

That seems an aweful lot to pay to 'properly' run a face mask. At that price I'd go the full monty and go for a 7.5hp 270ltr belt driven type these offer around 30cfm(FAD) and normally have dual outlets so you can run the mask and gun. There's a couple on ebay right now for around £700. New ones are normally around £1500.

Personally I think the folks who've given you the advice are overly cautious, trying to sell you something or think you need this for professional rather than occasional use. A compressor with 7cfm will be working non-stop to supply air to the mask and perhaps they consider that a bad thing but your only going to be using the breather for short periods because your working outside rather than in an enclosed space which would need you to be wearing it constantly even when taking flash-off breaks between coats.

Maybe when you speak to them next time be sure to give as much detail about your spraying habbits and the fact your doing this outside. It might change their advice.

But at the moment, if your needing 12cfm then this will be expensive.

 

[TerryO]

Originally posted by sploo:
"I have caught a breath of it on a couple of occasions, especially when mixing, and yea, you really don't want to be breathing it."
~~~~~~~~~~~~~~~
Sploo,
This isn't something you want to take a chance on, if you got an exposure once, then consider yourself extremely lucky and take the proper precautions from now on. This stuff is nothing to fool around with. When this stuff first came out there were painters with decades of experience with conventional finishes that used this stuff for the first time and it was the last paint job they ever did. IIRC: there were several that actually died.
~~~~~~~~~~~~~~~~~~~~~~~~~~
~~~~~~~~~~~~~~~~~~~~~~~~~~

And then Sploo states:
"Now come on Ant, on a daily basis, you, me, and most of the rest of the nutters here attempt things we're not trained, equipped or confident about doing. Otherwise we'd never get anything done."

Well, I'll just paraphrase the old saying about pilots:

There are old painters, and there are bold painters.
But, there are no old, bold painters!

I truly hope that you'll heed the advice given about using this stuff. It's easier to think that it probably wasn't necessary, than to spend the rest of your life wishing to God that you had listened.

Best Regards,
TerryO