Just pondering ideas and wondered why I had never seen anyone use polyurethane on boxes or anything else car audio related? Seems to me like it would be a great finish on the outside, as well as good sealant for the insides of the box. Polyurethane has a very smooth glossy finish which I would think would be great for ports and such.. Which leads me to wonder why it hasn't been used in place of fiberglass in some scenarios. Does anyone have any experience with polyurethane or know why it's never used?

One idea I had, was covering an enclosure with playing cards (or anything really) with adhesive spray, then going over the cards with a few layers of poly to give it a sweet glassy look with the cards underneath.

Example of Polyurethane on MDF.

http://media.photobucket.com/image/polyurethane%20mdf/jeeposaurus/Picture9-1.png

thats an awsome idea but you would know what would look better use beer tops lol

haven't got a clue on how I would apply PU on MDF ... I personally think it looks nice ...

Kinda like this:

I put a sticker over the fiberglass panel, then did a coat of resin + cab-o-sil (or talc) over. Originally I scuffed everything up so it had a matte finish, except for over the sticker, there it was clear. After sitting in a car for a hours, it got hot enough that the matte finish turned back into gloss. I probably didn't give it enough time to cure, and you can see the sticker wrinkled and came up.

I can't say that I know anything about polyurethane, just thought I'd share the above. Coat of resin sounds like it would work for you if polyurethane doesn't.

Check out fiberglass forums, there's a lot more people there that are familiar with chemical products and finishing.

Edited March 16, 201213 yr by stefanhinote

I would use a brush or spray it on.

thats an awsome idea but you would know what would look better use beer tops lol

Well, I went to Lowes a picked up a quart of some oil based gloss PU to test out on some scrap MDF. The results after one coat and 24 hour cure was pretty neat.. It left the natural wood a dark tint, very smooth, and hard as a rock. I haven't tried sanding and mulitple coats yet. The only problem I saw with it, is that it makes the MDF swell up about 1/8" or so. The swelling seemed to be even across the wood, so no bubbles or anything of that sort. So I don't really a problem there as long as all pieces are assembled completely before covering with PU.

Note: The fumes that this stuff puts off is STRONG. I'd advise anyone else who tries it to use a mask and a very open and ventilated area. The product still has a pretty strong smell after 3 days of curing on the wood.

Well, I went to Lowes a picked up a quart of some oil based gloss PU to test out on some scrap MDF. The results after one coat and 24 hour cure was pretty neat.. It left the natural wood a dark tint, very smooth, and hard as a rock. I haven't tried sanding and mulitple coats yet. The only problem I saw with it, is that it makes the MDF swell up about 1/8" or so. The swelling seemed to be even across the wood, so no bubbles or anything of that sort. So I don't really a problem there as long as all pieces are assembled completely before covering with PU.

Note: The fumes that this stuff puts off is STRONG. I'd advise anyone else who tries it to use a mask and a very open and ventilated area. The product still has a pretty strong smell after 3 days of curing on the wood.

Cool, you'll have to post pictures later.

Will definitely post pictures. I think I'm going to build an enclosure for a single ported 12 or something and use the PU on it to see what the results are (inside and outside of the box).

Another note about PU: I'm not sure how pricey fiberglass materials are for I've never dealt with FG, but a quart of PU is roughly $10-12 which supposedly covers 125sqft. To me, that isn't bad at all. And it looks much easier to work with.

if it swells.. perhaps you should try it on birch, plywood or oak.

Will definitely post pictures. I think I'm going to build an enclosure for a single ported 12 or something and use the PU on it to see what the results are (inside and outside of the box).

Another note about PU: I'm not sure how pricey fiberglass materials are for I've never dealt with FG, but a quart of PU is roughly $10-12 which supposedly covers 125sqft. To me, that isn't bad at all. And it looks much easier to work with.

You can get decent resin for the same price, but like you said it's a little more involved.

I actually had the same thought as you. I'm planning on painting my box black, then doing a coat over to give it a piano type finish. Hopefully this method works.

My concern would be the added weight. Unless you use Birch to start with.

if it swells.. perhaps you should try it on birch, plywood or oak.

this

So, I tried the fiberglassing idea.. it was a fail. The PU does not dry hard/thick enough on material surfaces that arent solid such as wood or plastic. However, I did manage to put 2 more coats on a scrap piece of MDF with a good bit of sanding between each coat. The results were very nice.. a very smooth shiny finish, and hard as a rock. And just for fun, I left the piece outside overnight during a rainstorm. Checked it the next morning, and the PU'ed part of the wood was in perfect condition. Beat it against the corner of my metal fence pretty hard, and barely a dent. So, this could even be used for potential waterproofing if you have a leak in your trunk or using wood somewhere that moisture could get in contact with the wood. This stuff works great. It dries very evenly and the finish is glasslike if applied correctly. I'd suggest a foam brush or something of the likes. My next experiment will be with birch as stated above.

Stefan, I also thought about doing the same idea you have with the paint underneath. I say go for it! Looks like this stuff would work great for it.

My concern would be the added weight. Unless you use Birch to start with.

This stuff doesn't really add weight.. it doesn't weigh any more than paint does. It's not thick like you see on some restaurant tables where it's raised almost a 1/4". I guess it could be if you spent a month adding about 25 coats. But 3 coats is plenty sufficient for a great finish.

I used some poly hardwood floor coating on my birch enclosure. It requires lots of light coats and plenty of blocksanding to get it smooth and glossy. I have well over 20 coats on it now.

I used some poly hardwood floor coating on my birch enclosure. It requires lots of light coats and plenty of blocksanding to get it smooth and glossy. I have well over 20 coats on it now.

restaurant table subwoofer enclosure???

nice!!!

So, I tried the fiberglassing idea.. it was a fail. The PU does not dry hard/thick enough on material surfaces that arent solid such as wood or plastic. However, I did manage to put 2 more coats on a scrap piece of MDF with a good bit of sanding between each coat. The results were very nice.. a very smooth shiny finish, and hard as a rock. And just for fun, I left the piece outside overnight during a rainstorm. Checked it the next morning, and the PU'ed part of the wood was in perfect condition. Beat it against the corner of my metal fence pretty hard, and barely a dent. So, this could even be used for potential waterproofing if you have a leak in your trunk or using wood somewhere that moisture could get in contact with the wood. This stuff works great. It dries very evenly and the finish is glasslike if applied correctly. I'd suggest a foam brush or something of the likes. My next experiment will be with birch as stated above.

Stefan, I also thought about doing the same idea you have with the paint underneath. I say go for it! Looks like this stuff would work great for it.

How can you fail with fiberglass resin? unless you didnt use enough hardner.