MDF vs. ply for molds

jturk · Post by **jturk** » Thu Jul 23, 2009 6:53 am

I am about to purchase material for molds for my first canoe. Looking at the plywood at the local big box made me look arround. The MDF looks like an option. What are the pros and cons of using either material?
Thanks
Jim

Big Woody · Post by **Big Woody** » Thu Jul 23, 2009 6:02 pm

I actually used cheap particle board for my forms.

Pros: It was cheap.

Cons: the sheets were extremely heavy and I almost injured myself getting them down into the basement where my project is happening.

I would not recommend particle board if you're working where there might be high humidity. Since I'm building stapleless I do not know how well the particle board would hold staples. I nailed my sheer strips in place with small nails to the forms and they held fine for me.

I work a lot with MDF and LDF in connection with my job and don't really like them.

Perhaps somebody who has built more boats can give you a more informed opinion.

Selwyn · Post by **Selwyn** » Thu Jul 23, 2009 7:45 pm

I've heard of some people have trouble with clamps sliding on MDF unless you really crank them down. Not and issue if you are going the staple route. Also MDF swells like mad if it gets wet and even after it dries it's shape wont be exact. The only issue I've heard of with ply is it can be hard to find a sheet with no twist in it. But keep in mind that the boat will take its own shape due to the force of the strips trying to pull true again. So a little twist won't ruin your whole boat. Ply also has some texture so clamps won't slide but it can make it hard to trace your plans onto it.

Just my 2 cents

jturk · Post by **jturk** » Thu Jul 23, 2009 9:40 pm

Thanks for your imput. sounds like I should lean back towards ply and just search thru the stack for a couple of relatively flat pieces.
jim

mtpocket · Post by **mtpocket** » Thu Jul 23, 2009 11:05 pm

I've always used particle board, 1/2' thick. To combat humidity, I always apply a coat of varnish. Two coats on the edges and the glue push out won't stick the boat to the forms. Works for me.

ov10fac · Post by **ov10fac** » Fri Jul 24, 2009 7:23 am

I haven't actually built my forms yet, but I found some old table tops. Formica surface with three quarter MDF core. I plan on using these. Hadn't considered the clamp slippage issue though.

Pros - Free. Formica should help with the dampness issue.
Cons - Don't know until I actually build the forms.

David James · Post by **David James** » Sat Jul 25, 2009 7:32 am

I drive drywall screws through my clamps just far enough so there is a point sticking out the opposite side (the side in contact with the form) about 1/16". I tried glueing 60 grit sandpaper to the clamps but had little success. My clamps don't ever slide with the screws in them, and they are easily repositioned.

just an idea...

Dave

alick burt · Post by **alick burt** » Thu Aug 27, 2009 5:30 am

I used 1/2"md f for my forms and stapled my planking as per canoecraft.It all worked fine and shaping forms from mdf can be slightly easier on your tools.
It is important to keep them dry though as mdf will swell like a sponge if wetted.I waxed the edges with a candle to prevent the glue sticking which worked a treat.
I have only built one boat so far but i'm sure my forms would be ok for another and I may use them again.
regards
Alick Burt

waterlover · Post by **waterlover** » Thu Oct 15, 2009 3:42 pm

MDF is my choice...no slivers, holds screws well...doesn't chip...glue,epoxy easier to scrape off...it's heavy, so you might need help with 4x8 sheets.

Tim Eastman · Post by **Tim Eastman** » Thu Oct 15, 2009 8:02 pm

One canoe finished with 1/2" particle board forms with the edges varnished. Worked better than I ever would have hoped using staples. Started a second canoe with 1/2" particle board forms (Freedom) and going stapless with rubber bands believe it or not and again - it's working remarkably well.

Obvious note but some interchange MDF and particle board as the same stuff and it's not.

Adamv · Post by **Adamv** » Fri Oct 16, 2009 10:33 am

I used MDF and really liked it. It was cheaper, and very stable. Being heavy is a drag when lifting it, but a benefit when the strongback is all set up, because it makes the whole jig much more stable on the floor (I did not glue it to the floor as per Canoecraft).

It is easy to cut and shape. Just use a good dust mask when working with it. I've been told there are some pretty nasty chemicals in the glue that makes up most of the MDF that you don't want to be inhaling.

I also liked how easy it took a pencil line. And I had no problems with my clamps sliding on it (built stapleless with jigs, also made of MDF, as per Canoecraft).

I will definitely be using it again on my next build (in fact, I've already cut the molds for a 17' Freedom with 1/2" MDF).

Cheers,
Adam

Ben · Post by **Ben** » Fri Oct 16, 2009 6:04 pm

I made the forms for my Freedom 17-9 from MDF as well. The benefits were:

Tracing pencil lines is easier on MDF than plywood.
More stable to cut and sand because of the lack of grain.
Cheap!

The only issue I had was trying to put a screw into the edge of a sub-form near the bow. I didn't pre drill and it split the form. I should have known better but the glue was wet and I was in a hurry.

I also used packing take on the edges of the forms. It worked well, but got ripped up on top when I cut the centerline for the football.

The Bear Mountain Boat Shop

MDF vs. ply for molds

MDF vs. ply for molds

MDF vs Ply