Best caulking for acrylic shower base

I recently installed an new shower with acrylic base and have been having terrible problems getting the caulk to seal at the base. It just does not want to stick to the acrylic and water seeps underneath it. The first application was made immediately after removing the plastic protective film so I assumed it was spotlessly clean. After a few days water was seeping under the glass and from the corner where the aluminum supporting rails meet the glass. I removed the silicone and throughly cleaned with isopropyl alcohol and re-caulked. Again after a few days it had detached again. I have been using GE silicone II and it has absolutely no problems sticking to the tiles, glass or aluminum rails but just doesn't want to stick to the acrylic base . Any ideas why or suggestions for a better product that will stick properly to the acrylic base.

Does your pan flex much?

There is very little to no flex. I emailed the manufacturer and here's the response I got:

Hi,

Acrylic has no porosity, that is why silicon doesn't adghere to it.

Use masking tape and leave approx 1/4" of acrylic...use a fine sand paper to scratch the acrylic surface...then the silicon will adhere.

Thank you

Interestingly the installation instructions don't mention anything about this and unlike other pans I have since looked at does not have a raised edge that would have prevented water seeping over the edge in the event of caulking failure.

That is interesting. But silicone will stick to glass. I wonder what is different about acrylic?

The acrylic could still have some mold release on it, which would make it tough to stick anything to it. Also keep in mind that some of those caulks, while they may get a skin on them fairly quickly, take up to a week or more to actually cure. Wetting them before full cure will cause them to fail.

OK, I found it. The stuff is called Lexel and it sticks like sh** to a blanket. Once I knew what to look for a quick Google search reveals that it is highly rated for this type of application but unlike silicone doesn't have a huge market penetration. Unfortunately up here in Canada I could only find one source locally and only stocking small tubes of clear - I would have preferred white but clear is better than a leak.

So far so good but only time will tell how is stands up.

dirtmover - just wondering if you could give me an update on how your caulking has held up. I have an acrylic tub and surround. For the seam between the top of the tub and the bottom of the surround, my contractor used caulking that didn't adhere so I had to remove it (assuming 100% silicone). I contacted American Standard (the manufacturer) and they recommended Loctite Tub & Tile Adhesive Caulk (see photo). This stuff adhered really well but grows mold daily. I've tried drying it off after each shower and tried putting car wax on it to help seal it which hasn't helped much. Any advice on a good mold-proof caulk that will adhere to acrylic tub/surround or something I could use to better seal the existing loctite caulk would be greatly appreciated. I have thought about trying to put 100% silicone caulk over the existing. I'd rather not remove the existing if possible.

There was a lot of flex between the tub and the surround before I put this new stuff on it, so the caulking/adhesive needs to help hold it together rather than just seal the joint. Thanks!