Caulk for Bathroom Use

Not knowing what you are trying to adhere/what the gap is in (other than the bathroom). The usual approach to reduce caulking sag, total volume and run out for large gaps is to first fill the gap with a backing material usually called a backer rod, and made from closed cell polyethylene foam, the closed cell is important as to not soak up water. For applications that are not for expansive stress relief, there are a lot of alternatives, you could use such a timber, solid plastic or even grout.

Your application, aesthetic appearance requirements and skill as a caulker will be your deciders on what caulk to use as well as budget.

For High grade caulking for non expansion type joints, the best permanent caulking I prefer to use is a 2 part epoxy known as Pecora Dyna Poxy, it is a high solids epoxy that sets extremely hard, it has very good adhesion properties, and is a hammer and chisel affair to remove from most surfaces it will accommodate a small amount of expansion in most cases (when I write about expansion joints I refer to the types in bridges and building panels). It can be coloured using the pecora tints or with most epoxy paints prior to application. It is extremely good for high abuse and wet environments. Unfortunately it is only available in a 1-1/2 Gallon pale, but can be mixed in small quantities and applied with a 10floz disposable caulking tube. Even when opened the pales contents will last a few years as long as the a-b parts remain unmixed. This is superior to any single part silicone or polyurethane like GE kitchen and bath or vulkem, the finish is professional grade especially if the joints are masked off to give a straight edge (the tape should be removed shortly after the caulk is applied).

Please look at the www.Pecora.com and http://www.tremcosealants.com/commercial/products/product_category.asp?category=1 websites for information on good quality caulks and sealants for all applications.

First you should see if you can make the gap smaller with a piece of wood or something else. You should never use caulk to fill anything over 1/4" inch (.25) or at least that is what is recommended. However, I know your situation and have done it myself before. I have had the best luck with clear silicone. I used the white caulk around the bathtub and had the same problem. Silicone seems to take the expansion better and does not crack and you can buy a paintable silicone also. Surface preparation is key.

• The surface must be clean and dry, use alcohol to clean it with, this will get any oils off of the surface.
• In order for it to adhere very well you need to scuff the surface or sand it til it is a little rough, this will give the caulk something to hold on to.
• The last thing is probably the most important... DO NOT PUT MORE THAN A 1/4" BEAD DOWN AT A TIME... I have failed twice because of this. If you get in a hurry and fill the crack up, it will only crack again, it will take too long for the large amount to dry and it will come out soon. Only put a bead at a time down and let it dry for the recommended time before applying another bead. repeat this step until it is filled. In the meantime keep it as dry as you can and low humidity until it is cured. If you have to, cover the area so that it will not get wet before the job is finished.

Let me know how it turns out. Good Luck!

To minimise the stretch of the caulk where there are large movements, weight the area before filling:

for example, when filling around the bath, half-fill the bath first. This will allow a larger bead into the gap. The bead will then compress when the tub is empty, and stretch when it is completely full, so the caulk only has half the work to do.

That would be my old stand-by, 3M 5200 marine adhesive / sealant....

3M 5200 Marine sealent/adhesive is great stuff and available in the sporting goods department of Wal-mart. A gentelman turned me onto that stuff in Florida when I was trying to get the shower sealed up in my motor home. Still no leaks. Just don't use it where you may want in later.

First I would find the reason for the gap and repair it. It sounds like the floor might be the culprit and needs some reinforcement. Maybe it even needs to be replaced, as dry rot in a bathroom floor is not uncommon and will cause sag, gaps, and other annoying defects. As with all mechanical problems attack the cause -- don't just hide it because it will probably get worse.