waterproofing mdf?

[thunderstruck]

I need to waterproof some mdf, and so far I've come up with a few options.
Marine varnish, seems like best option at the moment and its clear so it may allow a painted finish underneath. Would the varnish allow acrylic paint underneath or would it mix with it and go funny?
Acrylic paint, like school paint which cleans up with water but might be ok in water once it dries?
Acrylic paint over pva glue, again same issues with the paint but added layer of pva glue may add to waterproofness. Only problem is pva glue starts to degrade in water.
Melted hot glue spread thinly over the mdf. Seems like a surefire way, but would be expensive for the area I need done and time consuming.
Spraypaint. Would pressure pack spraypaint create a good enough sealant from water?
Any ideas or advice would be greatly appreciated.

[Mantikore]

mdf is just glorified cardboard

but remember, anything you put on it may eventually get a scratch or something, then water will eventually make contact

[Alamo]

Is waterproofing this mdf the best option? Can use a tarp or plastic coating and using sealant at the edges ect. As for waterproofing it the Acrylic paint I guess could do it but I would put it on thick with a good couple layers to make sure edges or somewhere its thin isn't showing.

If I may, what is it your doing with the mdf?

[thunderstruck]

Originally Posted by alamo

Is waterproofing this mdf the best option? Can use a tarp or plastic coating and using sealant at the edges ect. As for waterproofing it the Acrylic paint I guess could do it but I would put it on thick with a good couple layers to make sure edges or somewhere its thin isn't showing.

If I may, what is it your doing with the mdf?

I've found some fiberglass resin in the garage which should work and should be clear enough to do over the paint so that the paint wont rub off in the water.
Me and a friend made a small boat (smaller than a dinghy) because we had a motor and time on our hands. It should work a couple of times before becoming a soggy horrible mess if we can waterproof it enough.

[eesakiwi]

Theres proper waterproofing stuff for MDF. The hardware store will have it.

I was told to use it before applying glue to hold down tiles I was putting on the MDF.
Then the guy says 'just apply a very thin layer of the same glue you are using, then let it harden, then apply more glue before attaching the tiles."

It was a ADOS glue, yellowy/greenish colour, for tiles etc.

[thunderstruck]

I ended up doing 2 coats of marine varnish, 1 or 2 thick coats of acrylic paint and then a coat of fiberglass. I'll probably do a coat of polyurethane or slate sealer on top of that as well, and then decking oil or the same polyurethane stuff on the inside. It should work alright hopefully.

[Virus]

Originally Posted by thunderstruck

I ended up doing 2 coats of marine varnish, 1 or 2 thick coats of acrylic paint and then a coat of fiberglass. I'll probably do a coat of polyurethane or slate sealer on top of that as well, and then decking oil or the same polyurethane stuff on the inside. It should work alright hopefully.

Hopefully it will work, but out of curiosity, what are you building?

MDF is probably the worst choice for something that has to be exposed to water. I would have gotten marine ply. If I couldn't get ahold of marine ply, exterior ply would be option two, then coatings.

[Euda]

Good choice. I've always gone with an epoxy resin.

[thunderstruck]

Originally Posted by Virus

Hopefully it will work, but out of curiosity, what are you building?

MDF is probably the worst choice for something that has to be exposed to water. I would have gotten marine ply. If I couldn't get ahold of marine ply, exterior ply would be option two, then coatings.

Me and a friend are making a small dinghy with an electric motor of a sea scooter (modified to go a bit quicker). And yes short of bricks it was probably the worst choice for what we wanted to do, with that said though neither of us knew or thought it would be that hard to make the thing waterproof.

[Virus]

Originally Posted by thunderstruck

Me and a friend are making a small dinghy with an electric motor of a sea scooter (modified to go a bit quicker). And yes short of bricks it was probably the worst choice for what we wanted to do, with that said though neither of us knew or thought it would be that hard to make the thing waterproof.

So will it act like a brick thrown into water?

I hope you have a great design, because MDF isn't exactly fantastic for structural members.

[thunderstruck]

Originally Posted by Virus

So will it act like a brick thrown into water?

I hope you have a great design, because MDF isn't exactly fantastic for structural members.

Lol The structural bits are pine so it miiiight be ok.

[thunderstruck]

Well it worked. Then I decided it wasn't quick enough and needed 24v instead of 12 and I stripped a gear in the gearbox.

[Alamo]

Make it skip across the lake, this might be hazardous to your health but do it for science.

[Virus]

Originally Posted by thunderstruck

Well it worked. Then I decided it wasn't quick enough and needed 24v instead of 12 and I stripped a gear in the gearbox.

Awww man.

[thunderstruck]

Originally Posted by Virus

Awww man.

It's alright, or should be. I've got a bigger high torque motor and am in the process of making a waterproof enclosure thing to place it in. The motor's a 24v one with a lot of torque so if i can run 2 car batteries in parallel it should be good and a bit quicker too with a 1:1 drive ratio. Here's a couple of pics of it as the fiberglass or urethane was drying

[Alamo]

Hahah that's awesome, looks viciously fast OOOO!!

No rudder? Also how stable is that in the water just curious.

[thunderstruck]

Haha I sort of forgot a rudder as I was building it, but there will be one by the time it's finished. It's not that stable wen you're getting in, but once you shift your weight around a bit to make it sit flat in the water it isn't too bad. I had it with me and 2 car batteries in my pool and I had 10-15cm between the waterline and the tops of the sides so it was a lot better than I thought.

[thunderstruck]

So after fitting the new motor I've run into yet another problem. It draws a lot of current and heats up the small wiring on it. With that said its about the same speed on 12V, actually works on 24V now and is quicker but without a rudder is kind of dangerous and really heats the wires. Also it was powerful enough when I turned the polarity to reverse that it pulled the propeller off.