Gasp horror, the lewmar site suggests silicone as a bedding compound for its deck hatches. This cant be right --can it?
I am about to replace the sealant on some deck hatches. They are not leaking but the sealant looks a bit gruby so I thought I would do it while the sun is out.
I bedded them in with Sikaflex 5 years ago and I can tell already they will be a ***** to get out. However back to the silicone that cant be right can it?
What should you use?
sika 11 fc or some v expensive 3m ****
look these kids in the Lewmar office, wot they know? cant even paint silocon, and now sika have a uv product cos I had some failures in my Qld boats after 7 years there was some breakdown of the sika
There is nothing wrong with that suggestion, but they probably mean the silicone compound for marine use, without the smell of vinegar. Moisture in the air does the curing process, the end product is much more flexible than polyurethane (Sika) and absolutely impervious to UV.
UV can do terrible damage to the bedding of hatches (2-3yrs) when using a 1 pack polyurethane product like Sika. I remember Rondal advized a silicone based product as well. These specific silicone based products seem to have a better resistant to UV and salt. It might cost a bit more, so do check after curing, with water, for any leaks.
Well what about Sikaflex 295 UV ? I dont think I can get silicone UV marine that does'nt smell of vinigar,--I do know what you mean though.
I think CDK is talking about what's known as a "neutral cure" silicone. You would probably want a low modulus, UV resistant type for hatch bedding. Dow, 3M, Tremco and GE all make products that might be suitable. I don't think it's necessary for it to say "marine grade" on the tube- just go by the mechanical and chemical properties. A low modulus neutral cure silicone intended for exterior use with acrylic or polycarbonate should be fine, boat grade or not. (Dow in particular is notorious for selling the exact same product under two or three different names, at different prices, the only difference being tech support and warranty.)
I don't see any reason why neutral cure silicone would be a bad choice here; the acetoxy types (that reek of vinegar) might attack the clear plastic of the hatch. The trick is getting them to bond- scrubbing the substrate with isopropanol, then drying it, can help. Once bonded, the silicone should outlive the boat.
Sikaflex 295 is specifically designed for bedding acrylic and polycarbonate windows and hatches. It is a moisture cure polyurethane; I don't know how long-lived it would be.
Personally I have bad experience with the adhesion of the 295. The 291 was even better but can't resist UV. Therefore we recommend ARBOSIL 1081.
I have looked up the pds. See attachment.
Its an alluminium hatch suround not plastic windows.
I am very limited to what I can get, but I have just come from town and I did see some roof repair silicone and it even suggested it was for boats. Its only 2 dollar a tube!! I cant get 3M or any of the others mentioned but sikaflex is available everywhere.
On the lewmar site it shows a real nifty way of using a G clamp to pull the frames out. Ive made some blocks of wood ready to have a go but I think they will really be a *****--*****. One window did show signs of a leak so I just gunned around it and cured the leak promising myself I would do all of them when the sun shone again which is now.
The biggest job will be removal. I am reluctant to use Sika again because of the "***** factor".
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