Has any one used MDF to build with ?

[Trout Slayer]

I want to build a small rowboat or punt out of some MDF board i have at the shop. everything I have read says to use exterior grade or marine ply. I dont see why i cant use the MDF if i coat the bottom of the boat with resin. dose any one see a problem with this?

[duluthboats]

Weight for one, it’s about the same density as oak 680-830 kg per cubic m. It also doesn’t like to bend without damage. No reason you can’t build a small boat from it, but there are many better materials to use.

Gary

[Dr. J]

If it were my project, I would steer clear from using m.d.f. for anything marine related except when building molds. It is excellent for that. If you are planning to build something small then you might want to consider using it as plug material and building the boat out of glass. You can get some gentle curves out of MDF,I have even built aft trunk/curved staircase molds for 120' luxury yachts out of it. However it doesn't bend well into compound shapes without fracturing. Basically the stuff is dust and glue pressed into boards.Therefore, it will not stand up to moisture. Perhaps a flat bottomed skiff or duck punt of simple design would a good approach. Remember to prep the plug well prior to gelcoating/glassing.

[B. Hamm]

Might take a look at the newest edition (I think) issue of WoodenBoat magazine, there's a letter I think from a guy that left a piece of MDO outside for an extended time, had no delam problems at all.

Bill H.

[PAR]

MDO and MDF are very different animals and shouldn't be confused. I've had a piece of MDO in a bucket of water for close to a year and a half now, no paint, CPES, epoxy, poly, nothing at all on it. It's resin face has faded a bit in the tough Florida sun, but hasn't delaminated. MDO carries the APA's marine grade. MDF can't come close to the 1-95 rating or the BS1088 rank which is higher. I use MDO all the time, it's good stuff, but you have to be selective and know your product as the quality has been going down over the last 10 years or so.

MDF has no place on or near any moisture. The very nature of the construction will provide little of the qualities we love in other types of sheet goods like plywood. It has no tolerance for torsional loading, bending, flexing and all the things we need it to do as planking or bulkheads in a boat. It eats up saw blades at an alarming rate and isn't strong enough to support it's own weight.

Think I'm kidding? Rip a 2" wide piece down the edge of a sheet on your table saw and clamp this to the end of a work bench with 7'9" still hanging off the end of the bench. If it doesn't break as you're setting it up, just place your framing hammer on the end of the strip that's hanging in air. The weight of a 22 oz. hammer is enough to crack the stuff.

[Chris Krumm]

PAR is totally right. MDF ( medium density fiberboard) is a cabinetry substrate for paint grade or veneer work for indoor use only. Dense, stable, machines well, but will expand into a pile of soggy kleenex if in contact with water - pretty much like particleboard does when it gets wet.

Chris Krumm

[Dr. J]

To make matters worse, the dust created when cutting it is so fine that you need a good respirator to prevent inhaling the toxic stuff. There are, however plenty of plans available using only a few sheets of marine grade plywood to build yourself a small punt or rowboat/skiff. River dories ,which were common in your area at one time, might make a great project.

I am an Architect (building construction, not marine). My speciality is building investitgation (forensics).

I love MDF since it is so moisture sensitive it expands readily even with fluctuating humidity, making it easy for us to locate leaks and moisture problems. It is similar to OSB (oriented strandboard or ordinary S*%T board) in its unstable characterisics when damp or in a humid situation.

OSB is another product that should not be used in or near water or high humidity. Some good structural engineers are not allowing OSB in exterior walls used to transfer shear forces, since it is so likely to fail because of moisture exposure.