Here the top edge of a structural member was sliced off and the rotten or wet wood was removed. Next a thick (1/4”) layer of polyurethane sealant was applied along the bottom of the opening. This will seal the concrete and allow the concrete to expand without damaging the hull. The concrete will be poured before the sealant is fully cured.
After the off the top edge of the structural members were sliced off a chain saw and a large wood auger were used to remove the plywood.
The picture shows a small portion of the marine plywood removed from the structural members. The wood in some members was so rotted it could have been removed with a spoon. Other members had solid but wet wood. Water had penetrated 100% of the wood. In some cases the openings that allowed water intrusion were as much as 10 feet away.
Use pre-coated epoxy rebar about every four inches. Use through bolts to (1) support the rebar as you are pouring the concrete and (2) mechanically fasten the fiberglass walls to the concrete structure when the concrete is hardened. We do not want a bond between the concrete and the fiberglass. Instead we want mechanical fasteners that allow for differences in expansion between the concrete and the fiberglass.
Here concrete is being spread into the structural member by using a metal bar. The rebar is being temporarily pushed aside. Note, plastic cups have been cut and pressed into the holes in the structural members used for plumbing, etc. The plastic cups are then filled with rags so they do not collapse.
Here the port member of the structural grid surrounding keel is being filled with concrete. The last rebar is being placed on the top. To finish the job the loose concrete will be vibrated by holding a Sawsall without a blade against the fiberglass wall. Note the structure is slightly bulged in the center. That is because the through bolts holding the rebar have been left a little loose on purpose. After the concrete is vibrated, the bolts will be tightened to a uniform width. Note, the starboard structural member has been completed and allowed to set up for one month before the port side was started..
A motor mount can be gutted and filled with concrete just as any structural member. The bolts that secure the motor will go through a fabricated metal plate that is temporarily held in place inside the hollow mold. Not shown here.
To finish the job grind off any loose surface coating and clean the surface well. Then give the surface a coat of Polyurethane sealant. Vulkem 45 is self leveling and can be used for horizontal and curved bilge surfaces. Vulkem 540 is designed for vertical surfaces. Unlike gelcoat these coatings are elastic and will allow the hull to expand without cracking the coating even though the coating may be over 1/8 inch thick in places.