The Teak Deck Seat in the bow of Grand Day Out needed some TLC and repairs. (Thankfully, the main teak deck, probably original is in good shape.) First, the front trim piece became unattached on the left (port side) end. It is attached to a bowed fiberglass section below, so the stress of adhereing to a bowed surface caused it to raise up or straighten out. I reattached it by drilling a new hole, filling with epoxy to seal it and installing an additional screw. Then installed a new teak bung to cover the screw. I then removed the existing bung and screw and found that it had no bearing surface--the hole was bigger than the screw head. (I thought the screw had pulled loose but in fact the screw was not holding down the board--only adhesive that had failed.) Filled hole with epoxy, redrilled and countersinked the hole, then installed the screw and a new bung. (I felt that the mechanical force of two screws on each end would hold the board down more securely.) For good measure, did the same to the right side. Sanding changed the color and made it apparent that the other teak needed some TLC. Many of the teak boards were loose, and apparently years of cleaning the surface has removed the soft portion of the teak between the grains, so the boards looked unsightly and rough.
To remove a teak bung, you use a 3/8" Forstner bit and drill till you meet the screw head. To countersink for a teak bung, use the same 3/8" Forstner bit. Careful positioning allows the precision removal of a bung and the point will fall into the slot of the screw head, combined with a slight rolling oscillation of the drill and bit will keep the bit and screw from being damaged.
I made some inquiries on the Trawler Forum. I had anticipated using screws to hold down the teak boards, but most of the guys on the forum advised that I should just "glue down" the boards. I watched several youtube videos and researched several websites.
To my surprise, the install was nothing like I expected or what I had seen as "examples". The boards were 3/8" thick, but instead of a 1/4 gap being filled with caulk, the boards were an "L" profile shape with the edges tight to the next board. I think this caused a bit of a buckeling force when the boards became hot in the sun and absorbed some moisture. It appeared that previous sanding has reduced the depth of the "L" groove.
I decided to remove all of the loose boards (15) and just sand those that were solidly attached (22). This would allow me to add a bit of distance between the boards I removed to provide some room for expansion hopefully reducing the probability of the boards buckeling up and coming loose in the future. (Sanding the boards reduced thickness 0.030" from 0.390" (3/8" plus) to 0.360 (3/8" minus)
Removing the boards turned out to be very difficult. They were loose on one end, but very solidly attached on the other. Required careful use of a putty knife and some bending stress on the board. I broke two boards in the process. Fortunately I was able to mend them with epoxy. (I was surprised at how well epoxy works with teak---just "prime" the wood with some acetone to reduce the oil in the teak and you get a strong bond. Sanding and skilful use of a sharp wood chisel allows a very nice restoration, even with severe fractures. 5 minute works well but only if you mix it VERY carefully and apply it quickly. Slower cure is probably better, but requires more patience during the clamping stage. 5 minute requires at least 15 minutes of clamping time.)
All the literature recommended having the groove as deep as it was wide, so I needed to renovate the "L" shape profile. I built a jig to allow the use of a conventional router rabbitt bit. See photos below.
Here are the tools...Orbital Sander (80 and 100 grit), Router, Surfing Tool, 1" Wood Chisel (very sharp---sharpen with honing stone), Special Teak Decking System Scraping Hook, Calipers, and a 5" Circular Saw.
A cool cloudy day with a light drizzle made the prep work more pleasant, without sweating, but you need a "weather window" without rain to apply the adhesive and later the caulk. After gluing the boards in place. I will place sandbags over the boards to hold them down and in place for a few hours, then to be safe to insure no water gets into the open slots, I will cover with plastic overnight. Once glued down with the Sika 291, it must be cured for 24 hours minimum--48 hours to be sure.
The picture shows the application of the Sika 291 adhesive. I combed it with a 1/4 inch comb. I did not "butter" the boards, but did use the rubber mallet to "seat" the boards and also slid them fore/aft and side to side a little to get a good bond. (I remembered that this stuff really holds, and sometimes a board needs to be removed, so a "perfect" 100% contact bond may actually be undesirable.)
My next issue was the best choice for the material to use for caulking the seams. Sika does not recommend 291 for that job. It would probably work, but it is not very UV resistant.
Seems like Teak Decking Systems has done some great marketing for their SIS 440 Teak Deck Caulking. It comes highly recommended in most of the forums. So, I ordered one 10 oz tube. I foolishly underestimated the amount of caulking required. A 10 oz. cartridge for a typical caulking gun only provides 20 feet of 1/4" bead. That is 240 inches more or less. When I figured the total length of the seams I needed to fill, my estimate was closer to 700 inches! So one tube would not do. I needed three or four!
I took this opportunity to rethink my choice.
TDS SIS440 is a silicone based product. It is really a silane based product, but silane is a sub group of silicone based compounds. It is an excellent product...very good UV protection..BUT. A) It does not adhere to polyurethane caulk; and B) It does not have good resistance to petroleum based fluids.
So, TDS SIS440 might not do well as a "repair" caulk. And, although the technical support people at TDS say SEMCO Teak Sealer can be used carefully, I became concerned that using SEMCO, that is 75% mineral spirits (according to their SDS), might soften the caulk and maybe even allow the caulk to stain clothing or shoes.
Sika recommends its polyurethane 290DC caulk for teak decking. In Europe you can buy it in 10oz cartridges, but in the US, only in 20oz sausages, requiring a special caulking gun. And, 290DC is not offered by my major suppliers: Defender Marine nor Jamestown Distributors. Seems like there is one sole distributor of 290DC in the US, based in FL, according to Sika's Marine Tech Support at 203-453-3090.
Pretty sure that the caulk on the decks of 36 year old Grand Day Out are polyurethane, so a polyurethane caulk would be good for repairs and polyurethane caulk is generally more resistant to petroleum solvents. So no worries about using SEMCO to keep my teak brown colored.
The whole debate of allowing teak to oxidize to a silver gray color or to treat it with something to "preserve" the brown color is just that--a debate. My research indicated that SEMCO Teak Sealer was the easiest and best product for that purpose--I intend to use that instead of varnish or other glossy coatings on all of the considerable teak on the Grand Banks 36. I also concluded that the silver gray look just seemed to scream "maintenance deferred" or "old-like a gray haired old man" and part of owning a boat is the pride of maintaining it at a high level. (Must be the Navy/Maritime tradition of my family coming out.) To me, wood should look like wood--teak should look like teak. (See picture of the USS Missouri battleship at sea with it's beautiful natural brown teak deck!)
So finding the Sika 290 DC seemed a chore, and dispensing using a sausage was less attractive than the familiar 10oz cartriges in a standard caulking gun.
I found that Sikaflex 1a had very similar specs. Seems like 290DC is marketed for "marine wood" use where 1a is marketed for "industrial wood, metal and concrete" use. The only major difference seems to be "tack free" curing times: 70 minutes for the 290C and 3 hours for the 1a. (This actually is an advantage for a DIY'r like me---I would be able to lay in all of the seams and then be able to tool all of the seams at the same time. 70 minutes would not be enough time for me.) The "Elongation at Break" and "Tear Resistance" and Hardness ASTM specs are almost indentical. Sika's Marine Tech Support confirmed this info. And, Sikaflex 1a meets Federal Spec TT-S-00230C, Type II, Class A which includes a requirement for UV resistance.
Sikaflex 1a is available at Jamestown Distributors and from Amazon. It is half the price of 290DC. An important note: Although some polyurethanes are more resistant to UV radiation than others, silicone based materials are much more resistant. So, if you were installing a completely new deck, and then allowing it to turn silver gray, TDS SIS440 would probably be a very good choice. But for repairing a deck, previously caulked with a polyurethane, or where SEMCO or Teak Oil will be used to maintain the "wood color", Sika 1a would probably be the best choice. Finally, your choice would have to consider the fact that polyurethane is more wear resistant to foot traffic than silicone. So it becomes a balance between resistance to wear, chemicals and sunlight.
Here is a comparison chart of the three main types: Polysulfides, Silicone/Silanes, and Polyurethanes.
Some caulk without tape, but I decided that limited taping would reduce the amount of sanding needed. After the caulk cures for 48 hours, you can sand it with 80 grit disc in an orbital sander.
Almost...
Be aware that polyurethane caulk can be applied at temps up to 100F, BUT---in direct sunlight an above cabin deck can easily reach 130F on a 80F ambient temp day. At 130F, bubbles will form. 😒
Unfortunately, although I was applying caulk in 80 degree F air, the surface of the decking was much hotter---130 F. This created air bubbles that could not be removed.
To fix, after letting it cure 48 hours, I sanded the caulk, flashed it with acetone and applied another layer. Fortunately, this polyurethane Sika 1a sticks to itself well, so the second application produced a reasonably good result. This time, I applied the caulk under a "tent" to shade the surface from direct sunlight.
Even under a tent, the surface temp of the wood was hotter than the air.
Below is the "finished" product after applying Semco Teak Sealer-Gold Tone. Not perfect, but very pretty.
After being exposed to rain, I noticed a couple seams that showed signs of water impregnation. These were strips that I had not removed or recaulked---so sanding must have disturbed the bond to the teak. So I cut out the caulk, taped and refilled these seams.
Interestingly, even on a 72 degree day, in direct sun, the teak was getting too hot. So I used an umbrella to shield the area.
