I'm looking for a place to buy a "pre-formed synthetic rubber flashing
boot" to make a waterproof seal around a pressure-treated 4x4 on a deck.
I've seen such things mentioned in books, but can't seem to find a source
for them. I've not exhaustively checked my local building supply as that
would take forever but the biggest ones do not have them.
Help appreciated, flames ignored.
This may not be the answer that you are looking for, but here it
is, anyway. In 35 years of construction I have never seen such
an animal. To waterproof post penetrations, we use a combination
of flexible flashing and a roll on or paint on waterproofing
Flexible flashing is the way to go.
I agree with Mr. Allison.
Rubber boot flashing is made for pipes penetrating a roof and similar
Flashing for penetrations with flat sides like your 4x4 can be made up
from sheet material.
What you're looking for may exist, but I've never heard of one. The
standard thing is to make one up out of either metal flashing (you can
buy them pre-made but they're unnecessarily expensive), or to make one
up out of fiberglass flashing mesh and embedded in roof cement.
Google 'pitch pocket' to get an idea of a typical type.
Here's the most typical one you see, where the flashing has a 90
degree bend at the top and fits into a horizontal kerf cut around the
There's really no need to advertise what you'll do if and when you
feel you are attacked. I mean someone flaming you won't read the
warning and think, "Uh oh! This guy means business and he's going to
ignore me if I flame him!" Right?
Not to necessarily disagree with the other posters because I don't see
it working with a 4x4, but to answer your question,
You might contact this company and see if you can find a dealer in
They DO make a flashing detail for things like posts, but they
are not all rubber or neoprene and they are wildly expensive.
This is one that we have looked into buying but realized that we
could make something on site that worked just as well, if not
better. Plus our method cost about 1/25th as much as the product
sold for. Take a look at this site and scroll down to the
bottommost picture on the right. Notice the rubber boot inserts
and you will see that one of them is square.
Thanks Robert, T, Brian and Ricodjour for sharing your expertise! Fellows
like you make this a really good group.
I tried making a boot out of Grace Ice and Water Shield, but it was really
difficult to get the joint where all 3 planes intersected to be strong and
to last. I wasted a ton of time in the shop trying to pre-fab the flashing
& counterflashing out of copper, and I saw the phrase "pre-formed synthetic
& rubber flashing
boot" show up in a google search (even referencing 4x4 posts) I thought it
looked like a better solution. But when I tried to drill further to find a
source it proved elusive.
While it will probably wind up being another time-burner, I'm currently
trying another approach which is to make a mold master from a 4x4 bolted
onto a flat base, make a fillet around the base with bondo and then cover
the whole thing in wax or some other mold release.
I'll over lay that with strips of coarse nylon cloth (the stuff used for
speaker covers) which have been soaked in a mixture of GE silicone
dissolved in VM&P Naptha. The cloth adds some strength to the silicone and
being a bit stretchy itself allows the end product to conform to odd shapes
If it works, I'll make it into a small injection jig so I can turn them out
next time without a lot of work.
Thanks again to all,
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