Waterproof finish for MDF

[snowman]

A friend has asked me to build the cabinet for a record cleaning machine. The plans call for it to be made out of MDF, but it will need to be waterproofed, as the cleaning process uses fluids which could spill onto the surface.

What is the best waterproof finish to use? Should I use a silicone based sealant and then paint over it, or paint it first and then apply a varnish?

Any suggestions?

[rodm]

Have you thought about melamine with edging or laminexing the cabinet?

[snowman]

Thanks - It's certainly an option. I usually work with solid timber and don't have much experience with laminates. I was concerned I couldn't cut laminated board without chipping as I don't have a table saw with a scribing blade.

I thought a waterproof finish might be simpler, but if that's not a sensible option I'll have to consider using laminated board.

[rodm]

Sorry, I am not saying not to build it out of MDF as there probably is a suitable waterproofing covering. I'm sure somebody will be able to advise on this.
As for melamine it is cheap enough to get a small sheet and experiment. The chipping can be overcome by using a fine blade and cutting slightly oversize. Plane (hand or machine) to the required size. I use a 80 tooth blade on a 10 inch table saw (no scribing blade) and only get a minimal chip on the downward face. It is really quite minimal damage and you need to examine the edge closely to see it. Because it is always on the downward edge I make sure the finished faces are always pointing up when cutting. This means that any chips are on the inside of the box. On the doors I fix any chips up with liquid paper. Sounds funny but you can easily build up the thickness to be higher than the surrounding melamine. It dries real quick and then I use one of those snap off blades and run it flat on the face of the melamine and it cuts the liquid paper back to the melamine. Chip vanishes. You get a real buzz if you stick your nose over the brush while you are working so be careful.

[DarrylF]

There are blades specifically made for cutting melamine - CMT make one for instance. They do a good job.

Use HMR (Highly Moisture Resistant) melamine - the type they're supposed to use in bathroom cabinets etc. The core usually has a green tinge to it. Otherwise it's going to get water damaged and swell.

There are plastic type finishes that will waterproof MDF for a while - but as soon as you get chips or scratches in the finish the MDF will soak up water like a sponge.

[Shane Watson]

No finish is completly waterproof...

[soundman]

As shane says no finish is totaly waterproof BUT.

Its not as if you are making a sink of thet the surface will be constantly swimming in fluid.

I say make sure you use HMR mdf, use a better glue ( but don't go over board) yellow PVA should doo (AV Syntec AB180 of similar)
doo your preparation well.

What ever finish you use you will need to make sure a total coverage is achieved.

Often we apply a finish that is porus to say the least but that can be appropriate.

start with the appropriate sanding sealer, sand & re coat till the surface is well consolidated.

then procede with several coats of top coat.

A pre catalised lacquer is probably the best option.
as the water & alcholl resiatance is quite good ( some record cleaners contain some alcholl) and the results are achievable for most people (I asume you are spraying).

or

Bulid the sucker sand it good & smooth & take it to a two pack spraying company.

There are fellas who just spray two pack.
No mess no probs & no health risks (for you anyway.
)

[snowman]

I've just joined this bulletin board and this was my first post. I would like to thank you all for your helpful replies. I'm going to take soundman's advice and go with the sealer and laquer finish. I also appreciate the valuable advice for working melamine without chipping, and will investigate the blades if I do another project with manufactured boards.