Art Finish on MDF

      An architect asks for a bizarre bleaching and staining job on MDF panels, and a finisher seeks professional help. April 30, 2009

I'm looking at a potential project, spec'd by architect. His finish schedule calls for bleaching MDF 2-4 times prior to dye stain then clearcoats. The part I am the most concerned about is the bleach. I have little experience with bleach. This is a good size project - 100+ sheets. I was told bleach around lacquer dust can be explosive. Does anyone have experience with large bleach projects and potential issues within a midsize finish facility?

Forum Responses
(Finishing Forum)
From contributor A:
Please elaborate on this "Art-i-tech's" vision. I never heard of anyone bleaching MDF before.

From contributor C:
What about the issue of the MDF swelling when you put a lot of water/bleach on it? Why bleach it if you are going to stain it.

From contributor F:
Don't you just love architects? I had to do a fairly large scale job like this a few years back. I can see the architects desire for a bleached finish because the MDF was not consistent enough from one piece to the next to produce a consistent color with the dyed finish. The cut panels all had to go next to each other in sort of a geometric pattern and like most architects this one went ape over color consistency. I toyed with the idea of bleaching but quickly canned the idea after trying a few samples with different products.
The problem is that all bleach products that I found are water based.

Water on any cut or routed areas of MDF would swell the fibers and make it impossible to sand smooth, it was just too much to deal with on the scale of the job (roughly 4000 panels averaging 8 sq. ft. each).

The best we could do was seek out premium MDF for the best shot of anything resembling color consistency of the substrate, but even then we had to hand separate the sheets by color, assigning them to different areas on the job site. Then spray all the pieces that were for a particular area together at the same time.

From the original questioner:
The client want the MDF to be stained and clear coated. The colors they are trying to achieve are both pastels and bright colors. Some of the colors have white in them so the coatings manufacturer did samples for the architect to attempt a match. In order to get a match they bleached, up to four applications to fade out MDF. It is not the process I would have choose but at this point one being specíd. I know itís far from green with bleach and acetone reduced dye, but as long as it is done of site they don't care. Again my concern is that many applications of bleach on mega panels in a fairly busy finish shop.

From contributor F:
I hate to advise anyone to turn down work in this economy, but if you cannot talk the architect into finding a way to eliminate the bleaching step, maybe painting a solid color on the lighter/pastel pieces? I would run. The problem with matching samples, especially for an architect (or any customer who does not understand the finishing process) is that matching a small sample and doing the same thing on an entire job are two very different things.

From contributor C:
How are you going to achieve a pastel color with dye stains?

From contributor R:
I did a job like this and would never do this type of finish again. It was for the architectís own office and as all architects, this one knew everything about everything. The issues we ran into were the MDF was not consistent to begin with and even after bleaching it (some panels more than once) the overall results were that the panels still were not all that consistent.

Sanding through the factory finish on the MDF was ok but after bleaching there was such a texture on the panels that it made the dye stain absorption just as inconsistent as the original coloring of the raw MDF panels. This architect contacted the manufacturer of the MDF panels and insisted that they make a special run of panels just for him, he would not take no for an answer.

The company just quit returning his phone calls and he eventually got the point. Every sample we made was rejected for whatever reason was handy that day.

I have seen some super light colored panels that thinking back, we could have utilized, but they were not available at that time. I would say that if you could eliminate the bleaching step you have a pretty decent shot at pulling off the architectís request. If you havenít submitted the bid yet, you might consider putting a few more zeros after the decimal point.

From the original questioner:
This forum is great. The major fact remains; this is an integral part of a multi-million dollar project specified by the very reputable architectural firm. To be blunt, the specs suck. However thatís what they want. Thanks to some of the responses I may be able to help shed some light on their need for finishing education. That's what makes this so helpful. Anyway, thanks again. If anyone has specific incidents about two component wood bleach mixed with other dry coatings (lacquer dust) explosiveness, please let me know.

From contributor R:
Make sure the container that you mix your bleach up in is real clean and if you decide to apply the bleach solution from a pressure pot I would insert a pot liner. Stainless steel fittings would also be a good idea. Bleach is corrosive but not flammable by itself. A spark could possibly cause a room full of lacquer sanding dust to combust. Whoever mentioned the dust and the bleach being explosive would be your best bet for more information on this possibility.

From contributor S:
If you Google dyed MDF, you will find there are manufactures who sell colored MDF. I have samples of these in several colors, and the color does go right through.

From contributor G:
If all that's required is a light color with MDF "grain" showing through, you can spray a light-colored pigmented wiping stain and then not wipe. It will absorb into the surface, lightening and still showing the "pattern of the flakes" in the MDF.

From the original questioner:
Thanks again for all the input. I don't think oil stain or analyne dyes either would work on their own. Again the sanding the MDF would help but we have a finish shop not a woodworking shop. Yea, we could do it but that would be cost prohibitive to sand each of 100 plus panels. If we went to that extent sanding the panels for complete even stain penetration some other finish shop would be doing this job. That certainly isn't my goal. I think I can come up with a satisfactory process. Again the problem is the Architects bleach specs.

From contributor G:
In another life, I worked in the bleach plant of a pulp mill, making and preparing bleaches from liquid chlorine through chlorine dioxide, hypochlorite, hydrogen peroxide and liquid oxygen. Every single one of them are water based.

Unless someone knows of a bleach that I don't that isn't water based, I'm going to say that any bleach you use will swell the MDF fibers. This is going to cause a lot more work than sanding and spraying. Since your lacquer rep is making samples for you, get them to try using the suggestions you've gotten here and show the architect. You might want to ask the architect what the plan was when bleached MDF was chosen.

From contributor F:
The finish supplier who did the samples should have known better than to suggest bleaching MDF. To me whether or not bleach will cause any fire hazard when combined with sanding dust is a moot question. You say you do not have time to sand all the panels, but if you bleach it will cause a need for even more sanding. Sounds like a catch 22 situation to me. My continued advice is to avoid the bleaching step at all costs, by hook or by crook any way you can.

From Paul Snyder, forum technical advisor:
One part of a two part wood bleach contains hydrogen peroxide. That's probably what someone was thinking of when they told you about a fire/explosion hazard. I've used two part bleach many times without a problem and have never heard of it causing a fire or explosion. Get a copy of the MSDS sheet for the product(s) you plan to use and follow the safety procedures. You can also get an MSDS for hydrogen peroxide and sodium hydroxide (the other part of the bleach) to see what they advise to safely use those chemicals individually.

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