Why I HATE Silcone Sealant

this appeared in an online publication of SailWorld...too good to pass up, Brian


Many of the yukkiest, most pointless, timewasting activities in boat building and repair are all down to the misuse of silicon sealants. Generally if there is a leak some handyman type will try and fix it with this awful stuff. It is absolutely fine in bathrooms and houses but it just does not belong on boats. Why?

You can't paint it.

You can't sand it.

It doesn't stick well enough to be structural or to stop boat type leaks in its own right

It doesn't stick poorly enough to be easily removed.

When the thinners from paints hit it they spread its unpaintability to nearby areas which it hasn't contacted directly. YOu can the wash and sand to try and get rid of the residue and it just spreads it over the whole area so that the paint bubbles in an intermittent sort of way.

The only place it works is underneath fittings that are bolted or screwed to the boat - but ONLY on boats that will never be painted - even fibreglass boats may be painted one day - so what boats could they be?


Sikaflex, yes, yes, yes. - .. .
Use a polyurethane sealer like sikaflex. It can be sanded, painted and it doesn't really cost much more. It also seals gaps in a structural way - so if the bits move relative to each other it will still keep on working.

In fact you can glue a whole boat together with sikaflex - not that I'd recommend it - epoxy does a better job in most cases - but there are places...

Disclaimer - if I sound bitter it's because of bitter experience. I worked as a professional boat painter and varnisher over several years - silicone sealant was the #1 reason for having to redo work that we thought was finished.

About the author:
Michael Storer supplies Wooden and Plywood Boat Plans for Amateur Boatbuilders. They specialise in Light, Elegant, High Performance, and Simple Construction. You can buy his plans with Detailed Step by Step Instructions by going to his website

 

I've run into this many times and it's a pisser for sure. A quick trick I've found that works is to seal the stinking buggers where they lie with shellac. It takes paint and clear coats and will lock down the damn things, that seem to get many feet away from the place the first bead was applied.

 

Does it burn out? - with flame or acid - (similar treatment may work with silicone breast implants - similar misuse of a product)

 

used it again under a pulpit only becouse it was laying around but the old kit told me it does not even work properly underneath fittings that are bolted or screwed to the boat

 

I run into the same problem on airplanes all the time. Absolutely despise the stuff. The owner saves himself $25 on a tube of proper sealant only to squander 4 or 5 hours removing it from around ONE WINDOW a couple of years later! What a deal! And why remove it? The leak has returned

 

Silicone actually is a fantastic product, but really not for working on fiberglass or joining panels good grief !

Silicone is quite nice to form a rubber seal with, ie like for a port hole that can be opened. The structure gets applied with an even strip of the silicone and the window part can be covered by ie vaseline so the silicone does not stick to it. Close the port and wait for silicone to dry out some. It makes for a perfect fit rubber seal

Silicone has to be removed mechanically, elbow grease. Mostly chemical resist and can withstand high temperatures - used widely to seal leaking exhaust flanges, so my guess is you'r going to burn the boat out before the silicone gives

 

That is what I was implying - get the owner to do it...

 

masalai,

Yes my friend, silicone can easily be burned out of the boat. One of the easiest ways is to let off a flare in the bilge, the resulting fire is sure to remove all the bloody silicone that some dumbwit has inserted within a few minutes. Just love your thoughts!

 

It's not a matter of thinking inside or even outside the box but "OVER THE TOP", and to have a reputation as a communist fish thrower helps in the "Ahhh, Now I understand" the logic Its a part of being entertaining and keeping them on their toes? - - and shitting some people off.....

 

I use it in some applications where it has advantages, for example the deck beam seals on my catamaran. If I use Sika I would never be able to get the boat apart again, its actually quite a job with the silicon sealant that I use. I have found that the adhesive quality varies quite a bit between brands, silicon ain't silicon. Much prefer Sika if the job is permanent. I was once told that the secret to getting a good seal with silicone on deck fittings was to apply the sealant, fit the bolts, settle the fitting to within 1mm or so of the surface and then let it dry. Once dry tighten it down and trim.


Box? There is a box?

 

I know that Silcone sucks, it will not even stick to dried Silcone very well. The guys at the hardware store sell it, but often ask customers what they are intending to use it for and often tell people just to use caulk.

I have not heard of Sikaflex before. I will be looking for it and may use it on my hovercraft repairs and modifications if need be.

Sikaflex
http://www.sikaindustry.com/ipd-ma-products

Lots of different products in the link.

Which one would you guys use on fiberglass boats?

 

It depends on the adhesive strength required, I think that 295UV is up the top end of the range. Slow cure is stronger from memory. The chandlery that I use stocks 290DC, 291, 291T & 295UV. Its a very similar product to the stuff that they stick modern auto windscreens in with. Some Oz boat manufacturers use it to attach windows to F/G production boats with no fastenings. Be very sure that you want what ever it is stuck permanently as the big problem with this stuff is getting the fitting back up if you need to. Practice a bit before you go for a bigger job, turps clean up but it can be very messy and it sticks to everything in sight if you are not careful.

Sika belongs in the hall of fame, one of those products that actually works!

 

3M 5200 is another very good product, same as the Sika story.

(For some strange reason though, Sika users get the stuff from ******** to ear hole on a regular occurrence, 3M users seem to get more on the job and in the right place.)

 

LOL, Using Sika cleanly is a skill! Not sure if that says more about the users or the product. I have not seen the 3M stuff, will look out for it.

Cheers

 

Meanz Beanz,

No mate it is definately not a skill associated with the product, even the unskilled manage to get it all over the place!