chemical resistance

[olleorama]

Originally Posted by David Brown

Yes. Although not with a sink, but other applications. There is plywood made for outdoor and marine purposes. Wood in boats and ships is specially treated, etc. Particle board and MDF are not and will disintegrate if it gets wet. It will fail. I am not disputing that it could probably be coated with enough plastic or other material to make it initially water proof, but if the protection gets a break in it, and the particle board does get moisture, it will swell up and begin to come apart. By the time one puts enough effort and expense into making a water proof wooden sink (or boat), it would not be much more expense to simply use a proper wood substrate in the first place. Just my opinion, of course ...

Thanks, I appreciate it. The risk you are talking about is mechanical damage to the coating, in this application (which isn't really a sink per say) that is unlikely.

[Fluidphoto]

I've had good luck with 1/2 in plywood (the cheap stuff) coated with fiberglass resin. A 24x60in sink cost me about $25. Just have to watch that you use the resin or epoxy outside as the fumes aren't too good for you.

[David Brown]

Originally Posted by Ian Grant

David, MDF is treated unlike chip board (particle board) so has very significantly better water resistance which is major a reason for it's popularity.

Ian

Ian:

My "personal experience" was with MDF. It may not all be created equal.

[Bob-D659]

Exterior grade OSB is lower priced than marine grade plywood, and easily obtained. Not all MDF's are created equal.

[adyphot]

Olleorama, the best bet is to build the sink properly with rails underneith the marine ply bottom and sides, well sealed with a waterproof glue or silicone on the sides and rails (screw them tightly to the sealant from under the rails), and take the sink to a shop to have it fiberglassed. I built my sinks and rack for my vertical washers that way, with a black gel-coat finish on the fiberglass. Make sure the gelcoat is fully cured before putting it in use. The gelcoat on mine stained a bit, but I've had no issues with mine in over 20 years or more of use. The bottom slopes to the drain, and I used plastic grids made for fluorescent fixtures, with trimmed pieces of PVC pipe glued to the bottom to level them up. They are light weight and easily removed for cleaning the sink if necessary.

Aaron

[totalamateur]

My understanding is that marine grade plywood is put together with the same glue as regular plywood. The difference is that the interior sheets are higher quality, being free of knots and inclusions.

I believe the glue in OSB is "more" waterproof than the stuff used in Plywood, but it's still fiberboard. I've used epoxy coated Grade 2 plywood for the backs of fishtanks. The main point of failure is where joined edges were not cut perfectly straight and square.


Good luck.

[richard ide]

Marine plywood is made with waterproof adhesive and the type I use is mahogany as well as being 3x the price. Plywood with no voids in the core laminations is commonly known as Baltic Birch. I have used some which (either Russian of Finnish) was waterproof with a thermally activated adhesive. The material I have bought in the last couple of years; I don't want to say it is for sure. As far as MDF - If I am putting expensive labour into something, I will use the best material possible.

[ralnphot]

The outer surface of MDF does have some water resistance, but not much. Once you cut into it, the edges will readily accept moisture and start to swell. Even when it accepts a sealer, it will swell from the application of sealer. You can use MDO, which is commonly called "signboard" , it is for exterior applications, and made from exterior plywood faced with MDF for smoothness. If you are making a sink, use a product called "sturdifloor" it is 3/4" exterior grade plywood with a moisture resistant finish and adhesive, plus it is fairly smooth.

Rick