: Planning to build my first kayak soon, and wondering about what to use for
: forms and a strongback. I can buy 4x8 sheets of 3/4" MDF for $20
: locally, and was wondering if this is a reasonable material to use for
: forms. It seems everyone talks about using 1/2" plywood? Form cost
: seems small compared to everything else involved, so I guess a few dollars
: either way for a better material isn't going to break the project. What
: thoughts can you share on the ideal form material? MDF vs MDO vs particle
: board? 3/4" vs 1/2"? I especially like the flatness of MDF, and
: the ease that it takes pencil marks. Conversely, I've always disliked the
: waviness of plywood. I haven't decided on staples/brads vs none, if that
: makes a difference.

: Thanks.

: Mike.

Hi Mike

Out California way we have Particle Board, MDF ( multiple Density fiberboard ) and Underlayment.

Particle board is usually solid on the outside, but loose on the inside and a little grainy on the surface. Bigger flakes of wood, say 1/8" or smaller. MDF is very fine, almost the consistancy of sawdust,with even color and glue mix that's pressed into solid sheets. It's a little lighter, more solid and a little stronger, but will chip away fairly easily. Underlayment is made up of a more solid mixture of glue and the same size material as Particle board, but, is very hard and smooth and a lot stronger than both the above. It usually only comes in 5/8" thick, for flooring and used to be used for cabinet bases. I would avoid Particle board, and I would avoid the thinner sheets of MDF and go with 5/8" or 3/4". My choice, if I had to go with these materials would be the underlayment as it is hard, will hold staples very well and is cheap.
HOwever, if I had My Druthers, I'd go 3/4" fir plywood all the way. It's not that much more expensive, much lighter than any of the above, holds any type fastener much better and if you decide to go the staple-less route, and use the groove method with clamps, it will hold the clamps on the edge without tearout, which the particle boards and MDF material won't. Depending on what boat you are building, the cardboard or foam ideas will probably fall to the wayside as well.

The particle and MDF materials are definitely the cheapest, at from $6.99 to probably $14.00 and the MDF, as you mentioned is more, but, if you are going to go that route, then the CDX fir plywood is about the same price and twice the strength and durability. I've heard too many posts where folks have had some problems with 1/2" plywood to even consider it over 3/4".

Then, it depends on what kind of use you are going to get out of it. 1 boat, 2 boats, ?????? Durability is a factor as well. Then the real factor will be the cost. What can YOU afford to spend in order to get the results that you want, with the least amount of problems.

Being new, I'd stay away from the foam, cardboard, and cheap particle board all together. Then it's a matter of price verses durability. If you are only building one boat.... Take a chance on the 5/8" MDF or 1/2" plywood. If more than 1, then go to the Underlayment, 3/4" MDF or 3/4" plywood. If more that two or three, I'd only consider the 3/4" plywood. It's the only one that will last through the abuse and the price is only a couple of $$ more.

Personally, I wouldn't go with anything but 3/4" plywood regardless. I don't like to cut corners to save a couple of $$ on a Thousand $$ project. You may just end up with more headaches than it's worth. Where quality and price collide is a personal thing for you to decide.

Just My Personal Opinion.

Rehd