sploo said:
Point taken about exposure time, though rolling or brushing certainly doesn't put great clouds of the product in the air. I've been hand finishing furniture with solvent based urethane for years, all that's needed is decent ventilation.
Another bonus with rolling or brushing is the coating goes on full strength, not reduced, so one coat will be enough.
Granted, if it's a very large or very complex item to be painted, I most likely would spray it, since the combined time for prep and spraying and cleanup is less than doing it by hand.
PS: Yesterday, I colour-sanded and polished one of the speakers. That's a day after spraying on the 4-6 coats of paint and 5-6 coats of clear. Absolutely amazing.
How's that for reduced production time?
richie00boy said:
Hi Rich,
The solvent based urethane paint or varnish is used as the primer, to avoid introducing water into the raw MDF.
Once it is coated, it will be water-resistant, and application of water based finishes afterwards should not be a problem.
The WB urethane paint (black) is very thick. I'd not be comfortable putting it on raw MDF though, because it is water based. Keeping the MDF's moisture content down seems to help a lot.
MJL21193 said:
That is a good point. Though don't you find the urethane soaks into the MDF (or does it not do that when you're using it really thick)?
MJL21193 said:...PS: Yesterday, I colour-sanded and polished one of the speakers. That's a day after spraying on the 4-6 coats of paint and 5-6 coats of clear. Absolutely amazing.
How's that for reduced production time?
Very impressive!
My questions though are:
1. Surely you have to wait the same amount of time as before for the urethane to cure (and let any movement settle down)?
2. Why not just sand the urethane and apply a clearcoat over the top?
3. Is there any risk that sanding & polishing the final coats so soon after painting will risk showing up paint movement over the next few weeks (or does the WB cure so quickly it's not an issue)?
Cheers,
Gordon
sploo said:
The urethane gets soaked in, but it does it's job of sealing the MDF.
1. A single coat of urethane will cure very quickly. As for movement, that was never a big problem for me.
2. see below.
3. see below.
As I said before: " I colour-sanded and polished one of the speakers. That's a day after spraying on the 4-6 coats of paint and 5-6 coats of clear. Absolutely amazing."
Well, today I had a good look at the finish. I was not happy - the clear went slightly cloudy in sections (not sure why, but I have a few ideas). Also, the parts where the clear was clear, you could see the texture of the previously sprayed black (orange peel). This was completely unacceptable to me.
I had no other choice but to repaint. (yeah, I'm turning into Ant)
Seven coats of black WB urethane. Finished spraying by 2:00, finished colour-sanding both baffles about 1 hour ago (4:30).
I have the first baffle polished now.
I'm not sure if the paint is fully cured (my guess would be no) but it's plenty hard. Like I said, this paint is amazing.
Right, some good news with the 2K Isolack...
I sanded one of the raw MDF blocks this weekend, and applied 5 coats of 2K clearcoat. Unlike the 1K Isolack, the 2K didn't react with the clear (and discolour).
I think the block probably needed a few more coats of paint before sanding, as there's a slight hint of the MDF showing on one face, though it is pretty subtle.
I'll give it a week to cure, and then sand/polish it, along with the two other test blocks (one raw MDF, one primed with Cascamite).
John, the latest speaker pic looks great. Amazing that you can sand and polish it on the same day as spraying.
I was thinking about the urethane coating - I'm amazed that a single coat is enough to seal the MDF. Is the stuff you're using really thick when rolled/brushed? Even the 1K Isolack I'm using (which is thicker than the 2K version) will sink into MDF edges after many coats.
I sanded one of the raw MDF blocks this weekend, and applied 5 coats of 2K clearcoat. Unlike the 1K Isolack, the 2K didn't react with the clear (and discolour).
I think the block probably needed a few more coats of paint before sanding, as there's a slight hint of the MDF showing on one face, though it is pretty subtle.
I'll give it a week to cure, and then sand/polish it, along with the two other test blocks (one raw MDF, one primed with Cascamite).
John, the latest speaker pic looks great. Amazing that you can sand and polish it on the same day as spraying.
I was thinking about the urethane coating - I'm amazed that a single coat is enough to seal the MDF. Is the stuff you're using really thick when rolled/brushed? Even the 1K Isolack I'm using (which is thicker than the 2K version) will sink into MDF edges after many coats.
The paint, straight from the can is quite thick and has no problem sealing the edge. The clear urethane solvent based is not as thick but will still seal the edge. It seems as though it has all been absorbed but that's not really the case. Remember, one of the reasons why I use it as a primer is that it is highly stable, It doesn't separate when applied to a porous surface.
Given my recent experiences with the WB paint and clear, I believe the way I will paint MDF from now on is like this:
1. Sand smooth. Really smooth, especially the edges with 320 grit paper on the sander.
2. Prime/seal with solvent based clear urethane, brushed/rolled/sprayed on. Let dry overnight, then lightly sand.
3. Several coats (spray) of WB clear urethane. This is for "fairing" the surface as it will be sanded smooth with 320 paper to give a good base for the paint.
4. Paint (spray) several coats, enough to guarantee good colour-sanding results without burn through.
5. Polish, using all the usual suspects (buffer, compound, etc.)
Given my recent experiences with the WB paint and clear, I believe the way I will paint MDF from now on is like this:
1. Sand smooth. Really smooth, especially the edges with 320 grit paper on the sander.
2. Prime/seal with solvent based clear urethane, brushed/rolled/sprayed on. Let dry overnight, then lightly sand.
3. Several coats (spray) of WB clear urethane. This is for "fairing" the surface as it will be sanded smooth with 320 paper to give a good base for the paint.
4. Paint (spray) several coats, enough to guarantee good colour-sanding results without burn through.
5. Polish, using all the usual suspects (buffer, compound, etc.)
Finally, I can offer what I hope to be a conclusion to my experiments in finding a suitable coating for MDF.
The 2K urethane blocks were sanded and polished a couple of weeks ago, and none have shown any signs of lines appearing.
I was following Ant's "How-to for a high gloss finish" thread, and to be honest, I haven't done a great job (they're a bit scuffed) but all (2K urethane and 2K urethane + 2K clearcoat) look like they will take a nice shine.
To summarise...
All below were finished with black cellulose paint and 2K clearcoat:
The above blocks that worked well were left for a long time (many weeks) indoors after glueing, and several weeks before sanding and 2K clearcoat. I left a couple of weeks before final sanding/polishing the 2K clearcoat.
Of the urethane painted blocks, a Cascamite glued block was given several coats of 1K white urethane, with a week drying time between each coat. This has shown no lines, but even weeks later is just slightly soft (it will take a fingernail). Coating with 2K clearcoat is not possible, as it reacts and discolours.
The three rectangular blocks have been discussed in previous posts, and were all Cascamite glued then painted with 2K white urethane. One was sealed with Cascamite before painting. The other two had the paint applied to the raw MDF (like the 1K urethane block mentioned above). One of the raw coated blocks was finally given a coat of 2K clearcoat.
All these blocks were given 2-5 days between coats, as the 2K dries very quickly.
So, my recommendations:
The 2K urethane blocks were sanded and polished a couple of weeks ago, and none have shown any signs of lines appearing.
I was following Ant's "How-to for a high gloss finish" thread, and to be honest, I haven't done a great job (they're a bit scuffed) but all (2K urethane and 2K urethane + 2K clearcoat) look like they will take a nice shine.
To summarise...
All below were finished with black cellulose paint and 2K clearcoat:
- PVA glued + very heavy epoxy coat -> good
- PVA glued + thin epoxy coat -> some lines
- Cascamite glued + polyurethane varnish coat -> good
- Cascamite glued + thin epoxy coat -> good
- Epoxy glued + polyurethane varnish coat -> good
- Epoxy glued + thin epoxy coat -> good
The above blocks that worked well were left for a long time (many weeks) indoors after glueing, and several weeks before sanding and 2K clearcoat. I left a couple of weeks before final sanding/polishing the 2K clearcoat.
Of the urethane painted blocks, a Cascamite glued block was given several coats of 1K white urethane, with a week drying time between each coat. This has shown no lines, but even weeks later is just slightly soft (it will take a fingernail). Coating with 2K clearcoat is not possible, as it reacts and discolours.
The three rectangular blocks have been discussed in previous posts, and were all Cascamite glued then painted with 2K white urethane. One was sealed with Cascamite before painting. The other two had the paint applied to the raw MDF (like the 1K urethane block mentioned above). One of the raw coated blocks was finally given a coat of 2K clearcoat.
All these blocks were given 2-5 days between coats, as the 2K dries very quickly.
So, my recommendations:
- Keep the MDF indoors (in a dry location) as much as possible.
- Glue with Cascamite (now I believe called Polymite) or epoxy.
- Apply plenty of pressure on the drying surfaces.
- Epoxy works well if you can spend the time building up many smooth thin coats
- Solvent based urethane works very well, though the (safer) 1K version doesn't seem to dry as hard as cellulose, let along as hard as the 2K version.
- Take your time - the longer you leave between coats, for the paint to sink and shink, the better.
- Gently sand between coats - especially to attack the glue lines if the paint has sunk.
Attachments
Hi Rich.
I forgot about the Bonda G4 blocks. They were painted with 1K isolack - a bit too heavily to be honest, though it was the first time I'd used that paint.
They never really cured properly, but I did use them to experiment with the 2k clearcoat - and they reacted badly.
Because the isolack works well on its own, there's probably not much point in adding another step of pre-coating with the G4. Using a sealer coat (of G4 or Cascamite) does reduce the initial absorption of paint, but what you gain in not having to spray so many coats, you lose in the time it takes to brush and sand a sealer.
Will respond to your mail... I've been really busy for the last few weeks, so I'm just catching up now.
I forgot about the Bonda G4 blocks. They were painted with 1K isolack - a bit too heavily to be honest, though it was the first time I'd used that paint.
They never really cured properly, but I did use them to experiment with the 2k clearcoat - and they reacted badly.
Because the isolack works well on its own, there's probably not much point in adding another step of pre-coating with the G4. Using a sealer coat (of G4 or Cascamite) does reduce the initial absorption of paint, but what you gain in not having to spray so many coats, you lose in the time it takes to brush and sand a sealer.
Will respond to your mail... I've been really busy for the last few weeks, so I'm just catching up now.
Hi Ant,
Kinda surprised you mention that epoxy is cheaper than Cascamite. I was using the West System epoxy, which is pricey, but a little of the Cascamite seems to go a long way, and a big tub is only a tenner.
I also find it nicer to work with, as it's a bit less dangerous for your skin, and much easier to clean up.
On the subject of 2K... I bought a couple of Coolermaster Aero PC fans (a squirrel cage design). A single fan will push way more air than you'd need, through a 32mm internal diameter vacuum hose (no serious static pressure losses as far as I can see). Given the simplicity of the Devilbiss mask, I expect a DIY alternative wouldn't be world's hardest job.
At some point I hope to actually get somewhere with this project, and will post results...
Kinda surprised you mention that epoxy is cheaper than Cascamite. I was using the West System epoxy, which is pricey, but a little of the Cascamite seems to go a long way, and a big tub is only a tenner.
I also find it nicer to work with, as it's a bit less dangerous for your skin, and much easier to clean up.
On the subject of 2K... I bought a couple of Coolermaster Aero PC fans (a squirrel cage design). A single fan will push way more air than you'd need, through a 32mm internal diameter vacuum hose (no serious static pressure losses as far as I can see). Given the simplicity of the Devilbiss mask, I expect a DIY alternative wouldn't be world's hardest job.
At some point I hope to actually get somewhere with this project, and will post results...
Can't remember if I posted this before... but if you want a realy high gloss finish, see if you can get some Glatex 8, even with a regular 2 inch small foam roller you can get an almost glass smooth and highly durable (they use it on yachts) finish. Little expensive though, expect to pay north of $15 a can. I have done wood surfaces that have almost none of the texture of wood left... it looks like it was made of smooth plastic almost. It is pretty thick and a few coats fills small holes effectively, comes in clear as well as a number of cool bright colours, I think black too..
Hi Nordic,
A Google search on "Glatex" hasn't brought too much up, certainly not UK related. Can you give us some more info?
The issue we had wasn't specifically around getting a high gloss finish - there are many routes to that. The problem is that glue lines between sheets of MDF telegraph through many finishes over time.
John (MJL21193) has made some good points with regard to the issues that you need a sealer that won't separate due to some part of its chemical makeup being absorbed by the porous surface. I also wonder if a slight elasticity in the cured product helps (though the 2K isolack dries rock hard, so that may not be an issue).
A Google search on "Glatex" hasn't brought too much up, certainly not UK related. Can you give us some more info?
The issue we had wasn't specifically around getting a high gloss finish - there are many routes to that. The problem is that glue lines between sheets of MDF telegraph through many finishes over time.
John (MJL21193) has made some good points with regard to the issues that you need a sealer that won't separate due to some part of its chemical makeup being absorbed by the porous surface. I also wonder if a slight elasticity in the cured product helps (though the 2K isolack dries rock hard, so that may not be an issue).
http://www.woodworkforums.com/archive/index.php/t-10932.html
Finding very litte about it on the web, probably marketed under some other name these days... allthough my local DIY shop still have shelves of the stuff.
It is a 2 part finish...
Look towards the botom of that link, you'll see some guys talking about it... it is super durable, and I doubt it would "sink in" over time... it basicaly changes the wood into something with the consistency of bacelite.
Oh it is made by a local company called Plascon. I have never seen varnish that can give an equivalent smooth finish, so I guess it is your best bet at filling cracks and keeping them hidden... some people also use it to coat tool handles.
Finding very litte about it on the web, probably marketed under some other name these days... allthough my local DIY shop still have shelves of the stuff.
It is a 2 part finish...
Look towards the botom of that link, you'll see some guys talking about it... it is super durable, and I doubt it would "sink in" over time... it basicaly changes the wood into something with the consistency of bacelite.
Oh it is made by a local company called Plascon. I have never seen varnish that can give an equivalent smooth finish, so I guess it is your best bet at filling cracks and keeping them hidden... some people also use it to coat tool handles.
Something like this sounds like it may be similar.
http://store.nationalpaintsupply.net/blwapoto.html
I would love to find a durable high gloss finish I can use which doesn't need to be sprayed on.
Plenty of marine paint here in the UK too http://www.boatpaint.co.uk/acatalog/index.html and I've asked them to recommend a non-spray high gloss paint.
?? http://www.boatpaint.co.uk/acatalog/Seajet_132_Polyurethane_Topcoat___2_pack.html
http://store.nationalpaintsupply.net/blwapoto.html
I would love to find a durable high gloss finish I can use which doesn't need to be sprayed on.
Plenty of marine paint here in the UK too http://www.boatpaint.co.uk/acatalog/index.html and I've asked them to recommend a non-spray high gloss paint.
?? http://www.boatpaint.co.uk/acatalog/Seajet_132_Polyurethane_Topcoat___2_pack.html
Alright I'm reviving this super old thread as it seems to have a lot of good information in it. Sploo, do you still have all the test blocks? I would be really interested in hearing if anything has changed over 9 years.
Do you guys still use cascamite/polymite? I'm pretty sure it's illegal in a lot of places now haha. What glue did you use as "PVA"? I'm wondering if the popular glues now like gorilla glue or titebond II have the same issues as the PVA from 10 years ago?
Do you guys still use cascamite/polymite? I'm pretty sure it's illegal in a lot of places now haha. What glue did you use as "PVA"? I'm wondering if the popular glues now like gorilla glue or titebond II have the same issues as the PVA from 10 years ago?
The moisture activated Gorilla glue certainly has issues with swelling if project not thoroughly clamped for duration of curing cycle - which is much longer than the current crosslinked yellow PVAs such as Titebond II or II. It also penetrates and stains raw surfaces and is rather a bitch to sand any hardened foam exudation.
While I generally avoid MDF, I'd be inclined to the yellow glue, and don't wet wipe any squeeze-out - wait for it to cure and scrape off, machine any edge profiles, then follow with several coats of high solids primer, etc, etc.
While I generally avoid MDF, I'd be inclined to the yellow glue, and don't wet wipe any squeeze-out - wait for it to cure and scrape off, machine any edge profiles, then follow with several coats of high solids primer, etc, etc.
It has been 9 years. Wow. That makes me feel old
I do still have several of the blocks - though they've lived at the back of my damp garage, so they're not really a good measure of how they'd behave in a home environment. I could dig them out and have a look.
Whilst I've not really done any spraying work for years I have since started using Titebond, which does appear to dry much more hard/brittle than PVA, so I wonder if that might be better.
That said, if I recall correctly, even Cascamite sunk - it was mostly a case of 2k paint working well (which is obviously nasty stuff).
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