Mdf finishing

[g_hinton]

I don't usually work with mdf but I am doing some plunge routing and can't seem to get rid of the hairs when finishing. I have tried primer, sanding sealer, shelac and 2 different brand new router bits. What am I doing wrong? All help is greatly appreciated.

[khaos]

I heard someone talking about a torch. Lightly going ofer the hairs with a little propane torch action cleared the hair without singing the work!

HTH,

[harryball]

I find the type of MDF makes a big difference. Trupan cuts clean with few if any hairs. Some of the stuff I get from HD leaves hairs. Using a torch works. I've also found priming with Kilz2 then sanding lightly works well too.

/RB

[sam_harbold]

Look for Premier Plus or Double Refined MDF. A world of difference over the standard MDF when it comes to machining.

[khaos]

FYI: That torch post was in this thread http://www.talkshopbot.com/forum/messages/315/30750.html and regarded pressure treated wood. no idea why it wouldn't work for MDF...

[myxpykalix]

I use bits from www.centuriontools.com (http://www.centuriontools.com) and i don't have any hanging hairs. They cut real clean and are good and sharp.

[jseiler]

Torch also mentioned in this thread:

http://www.talkshopbot.com/forum/messages/312/13496.html

Dremil abrasive puffs work pretty well too if you can fit them in. 3m makes abrasive disks (they look little disks with nylon abrasive hairs hanging out of them) that work in for fine detail. I think foredom has them on their site.

John

[br928]

Check out Danny Ray's MDF finishing techniques here.

http://www.talkshopbot.com/forum/messages/312/30834.html?1211429456#POST68351

Gary, try this and let us know if it works for you.

[joe]

We been using a very simple painting technique on all composite wood surfaces. It's called High Build Primer. Like sanding sealer, it's lacquer based. The big difference is it's made as a filler. Not a sealer. No sanding and sanding and sanding.

Any automotive paint store has High Build Primer. It's thick and needs thinning. Two coats and it sands to a slick finish with 400p.

[br928]

Joe,
Do you do an initial sanding prior to the first coat?

Danny feels the sanding sealer soaks in and provides a harder more durable surface. Do you think the high build primer has the same effect?

Since you both are coming from different application backgrounds (signs / furniture), I am wondering if your approach is application specific. i.e. one better for signs, the other better for furniture.

I guess I am lazy and should just try both and see for myself but this forum saves so much time! (Hey, just using my resources right?)

[Gary Campbell]

Gary, et al...
We recently had a refinish training seminar in our shop updating us to the latest products that M.L.Campbell has to offer. Even tho it doesnt apply to us, one of the items covered was finishing MDF & similar materials.

Using a pad sander the instructor did a once over lightly on the flat surfaces & edges with 120 grit stearate paper. He then switched to 320 grit and did the edges well. Using Clawlock primer unreduced, he put a fairly heavy coat over the panel & edges.

The panel was set aside for an hour, then sanded complete with 320 grit. He then sprayed post catalyzed semi gloss finish over the panel & edges. I was impressed with the results, short turnaround times and lack of fuzzies, hairs and saw kerf showing up.
Gary

[dray]

M.L Campbell came to our shop and did the same demo.

I really liked the products, but the dry time was too long for my painters as the campbell stuff is water based. It is also about double the price of what we use.

P.S. Signs need a good UV protected polyurethane which does not soak in as well as laquer based sealers. Interrior I use laquer, exterrior I use UV protected Polyurethane.

[myxpykalix]

Danny you might be able to answer this (or anyone else). When i was making the wainscoting using mdf I found that the parts of the mdf that was cut into soaked up much more primer/paint and the parts with the paper face tended not to soak in enough and were more prone to running (maybe my spray technique was too aggressive) but is there a combination of primer/paint/sealer/whatever that would allow me to get a more consistent coat between the cut/uncut parts of the mdf?

[Gary Campbell]

Danny...
This is not the water base product, it is a post catalyzed lacquer type heavy body primer. Even in our 90%+ humidity it is ready to sand in an hour to hour and a half, and can be stacked in 2.

I have tried water based products from MLC, SherWil, Target and others, never to get satisfactory results. I have since vowed to never put a waterbased product on wood. "It just ain't right!!" These post cat products are pricey, fortunately for us, our customers can afford the good stuff.

Jack...
You might want to try to apply it thicker. It will lay on top of the machined areas better, not run on the smooth parts, and require less coats.
Gary

[beacon14]

I have also used Clawlock. It is worth trying out if you need to paint MDF.

[gene]

I use M.L.Cambells Magnaclaw primer also uncut and it does a very good job . The only downside i have found is the cost. around 145.00 for a 5 gal I guess this is one of the things you get what you pay for?
Danny What are you using that dries faster and cost less?

[joe]

Any auto paint store has both catalized and plain good old HBP.

I'm considering of coming out with my own brand of HBP. I could just change the labels, like Cambells has done, and call it "Dr. Crumleys Rootin Tootin Magnafangs" high build primer. Double the regular price and retire.

Joe
www.normansignco.com (http://www.normansignco.com)

[dray]

Jack, yeah you cant treat it the same as ply goods. Have to use the "process"

[weslambe]

Use titebond 2 and water mixed about 50/50 60/40 (water to glue) or so and spray it out of a cup spray gun. let it dry then sand smooth. nothing works better or is cheaper. titebond 2 is water resistant when dry.

btw, I've been cutting mdf for over 5 years and I've tried all of the other methods. try the glue.

[joe]

Great tip Wes,

I've never tried titebond 2. Is it different from regular Titebond. A few years ago I painted, sealed off, some letters with diluted Titebond and couldn't get paint to stick. That was a disaster. Is this different?

[br928]

The glue and water mix is what I have been using for years with good success. The sign I made for my business was routed then sealed both sides with glue mix and painted with good quality latex paint. (From the recommendation here by the way). The glue mix must dry overnight before finishing.

I asked in an earlier post if someone knows the difference between these processes. One that works fine for signage may not work as well for furniture. Both processes may be perfect for their respective end use.

My question is there enough of a difference between the two?

Danny thinks the laquer based sanding sealer soaks into the MDF making it harder and therefore more suitable after finishing for furniture. However more sanding is required. This dries faster and can be finished before the glue type sealer.

The High Build Primer reduces the sanding but must build on the surface of the MDF covering the imperfections. Is the result of the HBP as durable (hard) as the sanding sealer? If not this process may not be as suitable for furniture.

What do you guys think?

[john_l]

With the glue... do you not get as much of the "hair" standing up? Or do you still get that but it is just easier to sand off with the glue before finishing coats?

[Gary Campbell]

Stan...
All are good methods and seem, of course, to work best in the hands of the well practiced.

We used to use a 24% HiBUild Lacquer sanding sealer from SherWil. It dries very fast, but requires multiple thin coats to do the same job as the 54% solids post catalyzed lacquers we use now. 1 coat unreduced equals 3 of the SW sealer. A side benefit is no blushing in our high humidity. If the solids level is as high in the automotive high build primer and it is catalyzed, then it may have similar properties.

Even tho others have good experiences with them, I have never had good results putting water based products on wood or wood products as they swell them and raise the grain more than solvent based. They are much cheaper tho.
Gary

[weslambe]

John,

Give the glue a try. What happens is the mixture causes the fibers to stick up then they dry that way. The glue gets hard and when you sand it down you get a very smooth surface for painting.

One big tip is to spray the entire surface of your project with the glue mixture and wipe off the excess from the unrouted areas before it dries. What I have noticed from not doing this is minor differences in the appearance of the paint after it has dried. Spraying the whole piece (in my case doors) assures a uniform paint appearance.

[erniek]

I've painted a lot of MDF cabinet doors over the years and let me tell you they can be a lot of work. I usually use the clawlock as the first and second coat, sanding after each coat. Sanding before the first coat doesn't seem to do much for me other than knock off the sharp edges. Depending on the door style, I find I have to sand each door for 15 minutes to get rid of the fuzzies on the routed parts.

On the last couple of door sets, I've done I tried something different that required mimimal sanding. First I sanded, to knock off the sharp edges, maybe 1 minute per door. First coat was Benjamin Moore Enamal Underbody Oil based primer. I spray the edges a second time. Next paint with an eggshell latex paint. Next glaze with another watered down latex paint off a different colour, applied with a rag. And lastly a coat clear coat of Aquavar. The finished look turned out excellent and with no sanding between coats.

[weslambe]

Ernest is right about sanding first. Any mdf part should be sanded with a sanding pad. Buy the ones that look like scouring pads and are made out of plastic. They work wonders and come in many grits down to 000. With these, you are able sand in the nooks and crannies far better than with sandpaper.

Joe,
The difference between the glues;
Titebond = not water resistant
Titebond II = water resistant after it dries.
Titebond III = water proof (I haven't tried mixing water with this one yet. LOL)

BTW the mixture should be milky not yellow so the ratio may be 70/30 water to glue. Test, test, test.

[richards]

I've just tried Danny Ray's method using Sherwin Williams "Promar" E-Z Sanding Lacquer Searler B44FT8. It worked great. I used three coats applied 30 minutes apart, sanding with 300 grit sandpaper between each coat. I also followed his method and first sanded with 150 grit, then 220 grit before applying the first coat.

In the past, I've used the high build primer. The problem that I had with that method is that the primer didn't seem to have good adhesion to the MDF. It didn't peel or flake, but it didn't take a lot of effort to scrape and scar the surface.

I've also used Wes Mason's method of using Tiebound with water. I used it 50/50, which, according to his post this morning is too thick. I had problems with 'gumming' and adhesion. I'll have to try his method again using the proper dilution.

[weslambe]

Mike,

I've never really checked the ratio. I just mix it until I can put it into a detail sprayer. That's usually pretty thin. Like I said, testing is the key. The glue mix should be so thin that it will run like water. I have used all of the other methods and found that they don't work any better than the cheap glue sizing.

I really think that once you get the ratio right, you will be sold on this almost free method.

regards
wes

[gene]

One thing everyone seems to be overlooking is the proper preperation of the mdf. You must sand it with a high grit paper prior to sealing . A good 320 grit will close the pores of the mdf so it will limit the soaking up of the finishing materials, Yes its 1 more step but it will cut down on fuzzing and yes you do need to sand between coats. Remember the whole project can be ruined by a bad finish job .

[joe]

Mike Richards,

HIGH BUILD PRIMER

"In the past, I've used the high build primer. The problem that I had with that method is that the primer didn't seem to have good adhesion to the MDF. It didn't peel or flake, but it didn't take a lot of effort to scrape and scar the surface."

HBP readily soaks into MDF and will not peal. Since it's a primer, soft and receptive, for good paint adhesion it will show scuff marks. That's good.

Products like this are for proessionals. You'd be well served to leave it alone.

[richards]

Joe,

I agree about leaving some of this stuff to the professionals. Painting and plumbing are two things that I never get right.

My problem with High Build Primer is that it seemed to allow the finish coat to scrape and scar more easily than other 'primers'. The best way that I can describe it, is that the HBP seems to be spongy. In other words, it seems to allow denting more easily that other materials that I use. Granted, the cabinets and bookcases that I build are beat up and abused by my customers, so I'm always looking for products that reduce or eliminate denting.

[Gary Campbell]

Mike..
We are going thru some of the pains of the learning process on these finishes now. The lacquers we used are getting negative feesback from our customer base due to high VOC & HAPS numbers. The high solids catalyzed finishes lower all these numbers to aceeptable numbers. There are 2 other advantages in that they have a much lower offgassing of odor when installed and they do not soften in the truck when transported in a 100+ degree trailer.

The main disadvantage is that we have had to go to a pressure fed HVLP spray system that is pricey. We were able to upsize tips and nozzles on the two 2.5 gallon presure pots we used with the lacquer, and have added two 2 quart pots also. The 2.5 gal units are $800+ and the 2 qt setups are around $500. Add another $200 for an air agitator on the large units and you can see that it is not for the occasional user. Maybe one of the discount tool people out there have a 1 qt pressure gun that is affordable.

This pressure fed HVLP delivery system allows us to apply triple the material (dried) in a single application that we were able to with the lacquers. As long as we sand prior to application, we are geting the same results with much less handling and spraying time. They are also much less prone to the blushing that the lacquers had when spraying in our 90/90+ heat and humidity. Even tho this product costs more per gallon, since we dont have to add the thinners, or use multiple coats, it costs much less in the long run. I am a firm believer in using the product that works for you. We all have different ambient temps and humidities and what may work in one area, may be impossible in another. We tried water base products first, but with our humidity, experienced poor results. If we were able to lower the humidity by 30-40 points, I bet we would have good results.

We have a scrap of 15# HDU and I am going to test on this week. That should be a good test of locking in a soft pourous surface.

Gary