Caulking over silicone

M

Minnow

New member
I'm trying to re-caulk the leaky joint in my shower floor. It had flex in the floor that had caused the factory silicone joint to open up and leak when we used the shower.

I scraped/cut-out as much of the old silicone as I could. I plan on fitting supports between the raised floor and the hull to minimize the flex, and then caulking/fastening with something more permanent like poly (4200, 5200?)

I cleaned-up with some MEK solvent, but there is still silicone residue.
What are the chances of anything adhering over the old silicone?
 
Other, non-silicone caulking doesn't stick well over silicone. I have used Marine Formula by Debond to soften silicone, etc. It works on silicone, 5200 and whatever that #@%%^& Bostik is called. One has to scrape off the residue, and I used a plastic spatula. Fingernail also works well.

Boris
 
You're discovering why I detest silicone. To my mind there is always a better choice. I have never tried to adhere more silicone to old silicone, because I hate it too much to do so; for other materials you really do need to get it all off - including the invisible residue. Sometimes that literally involves removing some of the substrate beneath it. Nasty stuff and I feel your pain (literally, as I had to remove some today on my boat :amgry).
 
Darn that Sunbeam--he always nails it! No you cannot depend on silicone over silicone, or anything else over silicone to bond well. Boat painters hate silicone even more than Sunbeam does....

I have had the best results with various debonding agents, and then using the Mr Clean white pads--finally a light sanding with wet and dry. If there is a crack, you might want to consider a permeant repair rather and just a sealant. The floor of showers should be one piece molded. (I know that not all of them are) You may have to use a resin and cloth. I would choose vinyl ester in this cases, because you will want to gel coat over it to match. We had a similar problem when we rebuilt our Cal 46. Had to use 6 oz cloth over a crack--and then faired it in, and gel coated it.

Another problem with Silicone is that mold will grow in/on/under it---sure that are supposed to be silicones resistant--but they all break down eventually....
 
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