Just finishing up my first speaker project, and I'm contemplating my finishing options. The cabinets are MDF. I actually have a gallon of Gel Coat (Pigmented polyester resin used for finishing boats) left over from a previous project that I was thinking of using. Out of curiosity, has anyone tried this before? Did it work or did it crack?
I have used it with good results.
Apply a first layer, somewhat diluted, so MDF absorbs it and becomes harder, when it gels you can apply the definitive layer.
Mind you, I guess you´ll need to have your gel coat "paraffined", not sure of the English term but your supplier will know what am I talking.
Regular gel coat dries hard **in absence of oxygen** , as in against a mold/die surface but tacky (not 100% cured) if exposed to air, the idea behind that being that it should fully cure and "become one" with later coats of resin-fiberglass.
So if you use regular gel coat as the only layer, it will be sticky forever ... in practice until it catches enough lint and dust.
So whe gel coat is intended to be the final ecposed to air surface, sellers add some "paraffin" (I mean the white waxy substance, not what some British and Aussies call kerosene) .
It is not actually dissolved in Gel coat, just tiny droplets suspended, so when curing they are expelled towards the surface and cover it in a very thin layer, letting it dry hard.
Of course, maybe your gelcoat was already formulated to be used as the last layer (as in sprayed boat interiors) , but ask your supplier just in case.
EDIT: almost forgot: it won´t crack on its own, but if cabinet receives a *hard* knock, MDF is softer and will be pushed in forming a cavity, gelcoat isn harder and will slightly crack under strong impact ... but in any case it´s easy to repair: just fillhole with Bondo, sand it if necessary, and respreay that cabinet area , results are invisible.
I once sold a second floor (what in USA is third) Club some PA equipment.
Because of an accident, speakers rolled downstairs for 2 floors, scratching and bunping all the way.
They brought them back to my shop and helped me fill whatever bumped in, sand whatever had splintered out. Then I lightly resprayed them : as good as new, they could not believe it.
Repairs were *invisible*.
Apply a first layer, somewhat diluted, so MDF absorbs it and becomes harder, when it gels you can apply the definitive layer.
Mind you, I guess you´ll need to have your gel coat "paraffined", not sure of the English term but your supplier will know what am I talking.
Regular gel coat dries hard **in absence of oxygen** , as in against a mold/die surface but tacky (not 100% cured) if exposed to air, the idea behind that being that it should fully cure and "become one" with later coats of resin-fiberglass.
So if you use regular gel coat as the only layer, it will be sticky forever ... in practice until it catches enough lint and dust.
So whe gel coat is intended to be the final ecposed to air surface, sellers add some "paraffin" (I mean the white waxy substance, not what some British and Aussies call kerosene) .
It is not actually dissolved in Gel coat, just tiny droplets suspended, so when curing they are expelled towards the surface and cover it in a very thin layer, letting it dry hard.
Of course, maybe your gelcoat was already formulated to be used as the last layer (as in sprayed boat interiors) , but ask your supplier just in case.
EDIT: almost forgot: it won´t crack on its own, but if cabinet receives a *hard* knock, MDF is softer and will be pushed in forming a cavity, gelcoat isn harder and will slightly crack under strong impact ... but in any case it´s easy to repair: just fillhole with Bondo, sand it if necessary, and respreay that cabinet area , results are invisible.
I once sold a second floor (what in USA is third) Club some PA equipment.
Because of an accident, speakers rolled downstairs for 2 floors, scratching and bunping all the way.
They brought them back to my shop and helped me fill whatever bumped in, sand whatever had splintered out. Then I lightly resprayed them : as good as new, they could not believe it.
Repairs were *invisible*.
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Here's an update:
The speakers in question turned out excellent, but for those who are thinking about trying this, here's a few considerations:
1- Spraying anything presents challenges, but if you live in the frozen wasteland that is Wisconsin, doing this in the winter will prove challenging, as gelcoat doesn't respond very well to cold temperatures.
2- Install a dryer (or two) in your airline, and DO NOT run your airline from a warm house, outside where it's 20 degrees, and into a heated garage. The condensation in the line will cause some pretty serious issues with the finish (pinhole voids).
3- I had MUCH better luck rolling the gelcoat on with a paint roller given the temperature and airline issues. I laid it on very thick, then sanded it. 220 grit to flatten it out, and then most of the smoothing was done with 1000 grit, then 4000 grit. Then use a marine polishing compound.
There has been no cracking of the gelcoat to date, although I did use a special sealer that is specifically designed for MDF and gelcoat. If you struggle with spraying finish, rolling it on and then sanding it was pretty easy, though it really helps to have a sander with good dust collection(Festool excels in this area), otherwise the mess is incredible.
The speakers in question turned out excellent, but for those who are thinking about trying this, here's a few considerations:
1- Spraying anything presents challenges, but if you live in the frozen wasteland that is Wisconsin, doing this in the winter will prove challenging, as gelcoat doesn't respond very well to cold temperatures.
2- Install a dryer (or two) in your airline, and DO NOT run your airline from a warm house, outside where it's 20 degrees, and into a heated garage. The condensation in the line will cause some pretty serious issues with the finish (pinhole voids).
3- I had MUCH better luck rolling the gelcoat on with a paint roller given the temperature and airline issues. I laid it on very thick, then sanded it. 220 grit to flatten it out, and then most of the smoothing was done with 1000 grit, then 4000 grit. Then use a marine polishing compound.
There has been no cracking of the gelcoat to date, although I did use a special sealer that is specifically designed for MDF and gelcoat. If you struggle with spraying finish, rolling it on and then sanding it was pretty easy, though it really helps to have a sander with good dust collection(Festool excels in this area), otherwise the mess is incredible.
Gelcoat is used as the "class A" surface of hand laid FRP parts. It consists of polyester resin, inhibited styrene resin,dye(usually white), and Cab-O-Sil. Definitely no wax or paraffin is in gelcoat. Here in the states we can find it at most marina boat shops, Walmart and Amazon also. Or simply buy some fiberglass resin and Cab-O-Sil and make your own. Don't forget the hardener and also a shear mixer blade to properly incorporate the fillers into the resin. Hand apply with your tool of choice, I prefer 4 inah rollers.
Almost forgot, make sure your resin is compatible with the material your roller is made with. And positively do not use this in any living space. My 2 cents worth from 40 plus years of working with FRP
Almost forgot, make sure your resin is compatible with the material your roller is made with. And positively do not use this in any living space. My 2 cents worth from 40 plus years of working with FRP
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