PS Advisor: 06/06
My situation relates to the article about caulks and sealants in the April 2005 issue. I have a leaky main hatch. My main hatch sliding frame is made of teak; it is cut out so that a piece of Lexan fits into it, picture frame style. The problem is the Lexan/teak seal. Some sealers adhere to one but not the other. I thought I had it solved with a Boatlife primer followed by a Boatlife sealant. Still leaks. Any ideas?
After talking again (to the same industry experts we consulted for the April 2005 article), we garnered support for what we suspectedóand it isnít simple. Like deck leaks, hatch leaks can try oneís ingenuity and logic. The water often does not come out anywhere near where it sneaked in. Oneís sanity is threatened when, after making brilliantly considered repairs, the thing still leaks!
What you probably have is not a sealant problem, but either contaminated surfaces (the teak is the prime suspect) or different coefficients of expansion for the Lexan and teak.
Dealing first with the contamination, what you need are really clean teak and Lexan. For your teak (which is no doubt impregnated with oil, dirt, old caulk, soap, and who knows what else), use a putty knife to remove any sealants that might remain in that 90-degree joint. Then sand it carefully until you get new teak; itís hard work. With an old toothbrush, scrub the joint with acetone, which will hopefully remove the last of the dirt and the teakís natural oil.
Next, mask off the edge of the Lexan on the side that will face the teak, clean it with whatever works, scuff it up with 80-grit sandpaper, and wipe it clean. (ltís always a good idea to rough up anything to be glued, painted, or varnished.) The surfaces now are ready to be joined.
Choosing a sealant isnít simple, either. Epoxy is not a good choice. It doesnít like the sun. In addition, if you get it wrong, youíre in trouble.
Polysulfides or any sealant containing the sulfur atoms are out, too. The sulfur attacks the Lexan and polysulfides generally do not adhere well to any wood containing oil.
Your choice realistically is between a polyurethane or a silicone. The polyurethanes tend to be permanent, so the safe bet is a silicone.
Because silicone (often called silicone rubber) has the best flexibility and good adhesion, it also would be the best choice to protect against uneven expansion and contraction between the teak and the Lexan. If the materials differ, an edge can pull loose, unless it can be accommodated by the caulkís flexibility. Apply a smooth bead to the joint, and firmly press the Lexan until the caulk oozes out all around. You canít sand or paint silicone, but when the silicone sets up, you can trim it neatly and easily with a razor blade or X-Acto knife.
We recommend you try laying down a smooth bead of silicone on a piece of scrap wood before you tackle the hatch. Itíll also give you a chance to get a feel for the trimming, which requires a slicing stroke.
On one occasion, we had good luck sealing a teak joint with a thinned liquid epoxy, which when sanded, provided good adhesion with the caulk.
If you can manage, it would be good to remove the hatch and do it on a workbench. Weíve rebuilt several hatches during the winter months and find that the level of workmanship is superior to dockside work. Doing it on the bench also would permit you to closely examine the corner joints and, if theyíre suspect, seal them up neatly with thin epoxy applied judiciously with one of those West System eyedroppers.
This being a difficult subject, PS invites comment from any quarter.