Subject: What do I do now? (deck seam repair)
Date: Wed, 20 Oct 2004
In July of 2003, I purchased caulk, Elastuff 120 and Rhino Top to cover
the boat deck on our research vessel. I applied the coatings in November, 2003 and it worked well that winter. During the summer, the seams started
to open in small cracks and after yesterdays storm, it was raining inside
the boat. It has been suggested that I put down marine plywood, caulk the
seams between sheets, and recoat the deck again. Any suggestions? I am
going to try to seal the open seams and coat them with the Elastuff before
applying another coat of Rhinotop before it rains again.
Thank you, Byron
Redwood City, CA
Wood is one of the more difficult building materials to maintain.
Regular lumber swells and shrinks a considerable amount with the
movement of moisture into and out of the wood. That is one of the
appeals of plywood. Having the layers glued together makes plywood a
very stable building material.
I suspect that the original coatings were applied when the wood was
relatively moist, and therefore somewhat swollen. Since the moisture was
prevented from entering the wood in the winter, when summer came the
wood achieved a dryness that it hadn't gotten to on previous summers.
Moisture moves out of the wood very gradually, taking months rather than
Since the wood has now achieved equilibrium at a lower moisture content,
if you were to repair the cracked seams you would likely have no further
cracking issues. I would recommend taking a utility knife and some sharp
blades and cutting out a vee into the caulk seams where the cracks are.
I would then prime the crack with CPES, and when this cures for 24 hours
fill the vee with some polyurethane caulk like 3M™ 4200. This
would certainly be easier than filling with Elastuff, and
then could be top coated with Rhino Top as you suggest.
If I am right, and the wood has stabilized at a lower overall moisture
content, this should be a lasting repair. If you have further trouble,
you could certainly go to an overlayment of thinner plywood. The
stability of plywood would reduce the chance of future problems, except
for at the seams in the plywood.
Come back if you have further questions.