How to Re-Deck a pontoon

Before the project:

   Taking off the old deck of a pontoon can be a difficult task.  Often the fasteners are rusted or so set that they need to be broken to get them off.  These fasteners will need to be replaced to put things back together correctly.  Do NOT throw any of the fasteners out until the project is finished.  Using a similar or identical fastener will make reassemble a much easier task.

    The plywood that is used to build a pontoon deck is a marine grade or boat grade plywood.  Using construction grade (especially treated plywood) will be a very temporary solution to a rotted deck.   The cost of marine grade is much higher as well as the quality.  Doing a project this involved requires the right supplies. 

    Marine grade plywood is a no-void lamination.  This means that the layers (or plies) are solid wood with no holes.  A boat grade is also available at a lesser cost that is considered no-void as well.  Boat grade plywood has a lower level of tolerance and does have some small voids (usually less than a 1/4" diameter).  The other primary difference between marine/boat grade and construction grade is the glue used in the marine/boat grade is made for the marine environment. 

    The problems with construction grade plywood is the voids and the glues used.  Construction grade plywood is generally used on vertical or angled surfaces.  It is rarely used as a flat decking surface except in indoor flooring.  Even in the wet areas of the buildings a special sub-flooring is used for laying tile or vinyl floor coverings.  The voids in plywood used on a horizontal exterior surface gather moisture and cause delamination of the plies of the board.  They do this when the moisture freezes in the winter and expands.  The glues on construction plywood are not designed to handle grease, oil, or fuel spills without breaking down.  These types of spills are highly unlikely in building construction, however they are very common in boat construction.

    The recommended plywood is a pressure treated boat grade plywood that has been kiln dried.  Using this will make the job go faster and lets it last longer with low or no maintenance.  The board is no-void, has treated fibers that will resist rot without any water treatment being applied, and kiln dried flat so there is no warping of the board after installation.  This board can be found in 5 ply and 7 ply.  Many of the manufacturers of new pontoons are using 5 ply 3/4" x 4' x 8' pressure treated.  The cost of 5 ply is lower and the strength and durability is not much less.

The project:

    The most difficult part of this project is getting the deck off.  The cross members (joists) are usually made of aluminum.   There are as many shapes and forms of these cross members as there are manufacturers of pontoons.  (This is the reason to keep the fasteners that come off so they can be matched in size, type, and quantity.)  If a bolt is particularly difficult to get off grinders can be rented at an equipment rental store for a day.  Grind the head off the shaft from the top / deck side.  Do not damage the cross members any more than is necessary.  It is a good idea to sketch out a drawing of the deck boards and how they are bolted / screwed.  This simple sketch will save trouble from any memory losses later on.

    Once the deck is completely removed place the new boards on the deck the way the previous ones had been.  Make any cuts necessary at this time.  If the boards were bolted down mark the holes from under the deck along the cross members using a marker.  Pre-drill the holes by taking the board off the deck and turning it over.  If the deck has been screwed down with self taping screws mark a line on the board to indicate the location of the center of the cross member.  Most self tapping screws do not need to be pre-drilled.  Attach the first board and then do each board the same way.  Attaching each board with only 6 or so bolts / screws at first.  Then if everything looks square and satisfactory finish the rest of the bolts / screws.

    Now the deck can be re-carpeted and put back together in the same way that it came apart.  One step at a time.