Prepping MDF.

[Aegwyn11]

I never did get to try it last night...I was freekin tired! I think I made it to 9:30 before falling asleep on the couch. Maybe tonight. Glad to hear the sandpaper should work okay. Based on what you're saying, I'm really wondering if my can is funked up.

Regarding higher quality stuff, from what I've read Clawlock (ML Campbell) is actually some of the better stuff out there. I chose to use Kilz because its easier to get for me (there is only one dealer in town that has ML Campbell stuff and they close at 5, so I'd have to leave work early). Plus, my exposure to MDF is going to be limited...once I finish my ClearVue pieces, I'm probably not going to use the stuff at all except maybe for jigs. I'm sure I could have gotten better quality out of a better primer, but for this purpose, I decided Kilz was fine.

Also, regarding Sikkens, I used their SRD semi-transparent on my deck (heavily used the RO150 for that project ). Seemed to work really well...how it looks next year (and the year after) will be the true test.

I get that, but at the same time it doesn't make sense to me. I've seen lots of remarks that people sand the primer between coats, but with the scumming problem I had that would be totally impossible without using up a box of paper each time.

I know close to nothing about the products you use in America, but after reading what the manufacturer says about Kilz original, it seems to me there is something not right with the Kilz original you used. According to the manufacturer you should be able to sand and paint it after an hour. If the formula generally dries that quick, there is no way it is normal that it will scum your sandpaper after 12 hours drying. Perhaps your can of Kilz was past its shelf life or it was produced faulty.

I just thought of something...could my problem be because I'm using Brilliant2? Should I be using Titan2 as the Kilz is oil based?

There is nothing wrong with Brilliant2. It's the best sanding paper Festool offers for paint, especially oil based paint. I work almost exclusively with oil based paint and do 80% to 90% of my sanding with Brilliant2.
 
For me, it would be very strange to use a product like Kilz. For wood, I never use products that take such a short time to dry. Seems almost unnatural. I use top notch products from the Sikkens brand, made by Akzo Nobel, and the primer takes just as long to dry as the finish paint, a minimum of 16 hours.

 

[Aegwyn11]

Okay so I tried some sanding last night. At that point, it had been 3 days since last application of the Kilz original. I tried using Brilliant2 180grit with my RO150 in RO mode, low speed (about 2), with the CT set on the turtle. It  went better, but not great. Instead of getting the little round corms in a few seconds, it took a few minutes. After a few minutes, the same little corms started appearing and the efficiency of the sandpaper went WAY down WAY fast. I think I'm going to go try to grab some Clawlock during lunch today and give that a try on the next piece.

 

[Brice Burrell]

Aeg, I've used Kilz oil in the past, if you brush it on heavy and the humidity is fairly high the dry time is much longer. I agree with Pete about the Zissner BIN shellac primer, I've used the spray cans but most of the time buy the regular gallon and brush it on.

Alex, I love your advice - keep going.

Peter

I too like Alex's advice, good job!

 

[peter halle]

Aeg, I've used Kilz oil in the past, if you brush it on heavy and the humidity is fairly high the dry time is much longer.

You can always try adding a little japan drier to shorten the drying time.

Peter

 

[Brice Burrell]

Aeg, I've used Kilz oil in the past, if you brush it on heavy and the humidity is fairly high the dry time is much longer.

You can always try adding a little japan drier to shorten the drying time.

Peter

Or just do it right the first time around and get a shellac primer. ;D

 

[peter halle]

Absolutely. ;D ;D ;D

 

[Aegwyn11]

Best results - Zissner BIN Shellac based primer - spray can works best.

Dries fast - soaks in - hardens mdf fibers - topcoat with anything.

Or just do it right the first time around and get a shellac primer. ;D

Agreed! So far, I have to say I'm VERY happy with the BIN primer, especially coming from Kilz. I went to the tool store this weekend fully planning on buying a cheap spray gun so I could spray Clawlock, but couldn't bring myself to spend even $70 on something I honestly know nothing about. So, I went to big blue and bought a few cans of BIN spray for $7/ea. I suck at rattlecanning, so I had massive drippage the first coat, but sanded my runs off and tried again last night with much better results. Also, no corms on the Brilliant2 180grit I was sanding with! I did notice that it seemed to seep deeper into the MDF much more than the Kilz.

On a side note, the whole process I read about sanding cut MDF edges to 600 grit prior to priming (instead of glue sizing) seemed to work very well. Not sure if I actually saved any time, but gave me something easy to do that I could teach Tanya (wife) a few hand sanding techniques on.

-Nick

 

[Peter Hamilton-Scott]

So far, I'm happy with the filling procedure. The countersunk screw holes were filled with a typical wood filler and I also slightly scored the joins with a sharp knife to give the filler something to bind to. I'm happy to report that after sanding, the filler did a very good job. I put more into the screw holes than I needed to, to allow for shrinkage, and they are now as smooth as the proverbial baby's bum. The next step is to try and source some shellac primer. I also sanded off the pen lines and they too are now but a distant scribe in history.

The only bummer is that my Fein MM went berserk and refused to run at any speed except the maximum. I've only used it about four times in the past year and the warranty has now expired. I took it to the local dealer (a Festool shrine) and asked them to give me a quote to repair it. They were very sympathetic and said that's unlike any Fein MM to give a problem. He phoned them about it and they said to send it in and they'll do it as a warranty repair and hence no charge to me. That's really very decent of them as they were not obliged to. When you deal with an excellent shop and a quality manufacturer it's been my experience you get more than just a power tool.

Project ongoing but at least the end is in sight.

 

[Peter Hamilton-Scott]

My local hardware stores don't seem to stock a shellac primer but I could widen my search. I've found an unopened tin of general primer that I bought a few months ago. It's targeted at interior and exterior wood priming but no where on the tin does it lay claim to being usable on MDF. I could save it for another project but I'd like to know if I could use it on MDF or whether I should buy a general MDF primer? A tin of normal MDF primer will cost about 10GBP so it's not a budget wrecker by any means. I'm not sure what it is about an MDF primer that makes a general wood primer less ideal for use on MDF. Any suggestions?

 

[Aegwyn11]

Biggest thing is to make sure whatever you use is NOT water based. If it is, the MDF will swell, especially on the edges. Based on my experience (detailed above in the post), if you use an oil based primer, you might have to wait a judicious amount of time to sand.

Again, based off the research I did, the key difference between a 'general' primer and 'MDF' primer is that the MDF primer probably has a much higher solids count. I'm not a paint expert, so this could be inaccurate.

FYI, I sanded down my overzealous first coat and did a second coat of the BIN shellac primer. After sanding the second coat with 180grit, the pieces are starting to stick together from the vacuum when stacked. Thats pretty smooth  ;D

 

[sw1211]

My local hardware stores don't seem to stock a shellac primer but I could widen my search. I've found an unopened tin of general primer that I bought a few months ago. It's targeted at interior and exterior wood priming but no where on the tin does it lay claim to being usable on MDF. I could save it for another project but I'd like to know if I could use it on MDF or whether I should buy a general MDF primer? A tin of normal MDF primer will cost about 10GBP so it's not a budget wrecker by any means. I'm not sure what it is about an MDF primer that makes a general wood primer less ideal for use on MDF. Any suggestions?

Here's a distributor in the UK for Zinsser products.  Maybe they carry shellac primer

United Kingdom & Ireland
Ian Prest, Managing Director
Zinsser (UK) Ltd.
Wetherby House
7 Market Place
Wetherby, West Yorkshire LS22 6LG
Email: sales@zinsseruk.com  Tel:  01937 584411
Fax: 01937 584422

 

[jonny round boy]

My local hardware stores don't seem to stock a shellac primer

Peter,

If you can't find shellac primer, then try knotting solution, it seems to be very similar. I've got an up-coming project out of MDF, and as a test I applied some to the edge of a scrap piece of MDF, just wiped on with a cloth (2 coats). Once dry (doesn't take long) just very light sanding & the edge is sealed, ready for painting.

I must admit I haven't painted the test piece yet, but it may be worth trying on a scrap piece yourself.

 

[AlexThePalex]

Again, based off the research I did, the key difference between a 'general' primer and 'MDF' primer is that the MDF primer probably has a much higher solids count. I'm not a paint expert, so this could be inaccurate.

It's quite the opposite. MDF primers have less solids but more liquid that is designed to be sucked into the mdf ...... in order to prevent it to suck up the real paint. By saturating it. Normal wood primers have more solids in them to fill out the wood grain, which MDF doesn't have. 

 

[Aegwyn11]

It's quite the opposite. MDF primers have less solids but more liquid that is designed to be sucked into the mdf ...... in order to prevent it to suck up the real paint. By saturating it. Normal wood primers have more solids in them to fill out the wood grain, which MDF doesn't have. 

Yet again Alex points out a great point! I looked up a few things just for fun...both BIN primer and Clawlock are just over 50% solids by weight. As a comparison, Zinsser's own High Hide Cover Stain and a PPG epoxy primer (automotive) have much higher solids...closer to 75%-80%.

 

[JeromeM]

My local hardware stores don't seem to stock a shellac primer but I could widen my search. I've found an unopened tin of general primer that I bought a few months ago. It's targeted at interior and exterior wood priming but no where on the tin does it lay claim to being usable on MDF. I could save it for another project but I'd like to know if I could use it on MDF or whether I should buy a general MDF primer? A tin of normal MDF primer will cost about 10GBP so it's not a budget wrecker by any means. I'm not sure what it is about an MDF primer that makes a general wood primer less ideal for use on MDF. Any suggestions?

If you want it premixed or you want to DIY then get it from axminster.
Chestnut Shellac Sanding Sealer 500ml is 7.99 GBP

or
Liberon Shellac Flakes - Blonde Dewaxed 250g 11.20 GBP
then you need about 1.5 litres of methylated spirits

 

[woodguy7]

Peter,

Contrary to what some say, i do use water based products on mdf with very good results.  I used to use a dedicated mdf primer (which was water based) but as you say it is a tenner.  I have experimented with plain ordinary emulsion which works great, soaks in & seals everything.  I sometimes mix up fast set filler with water & smear that on the edges.  Once dry, usually about 1 hr i hand sand the edges with 180 on a block of wood & take the sharp edges off with sandpaper in my hand.  The mdf can now be coated with any paint you want to use.
Like i say, i have done this many times with excellent results.  Sometimes things can get a bit technical & complicated when there is no need.

Woodguy.

 

[Deansocial]

i use zinner bin as is dry so quick