Roofing Asphalt + Portland Cement Putty

[carioca1232001]

Has anyone actually tried this putty for caulking underwater seams and the like ?

It was presented on the thread concerning linseed oil putty, but no hands-on experience was presented.

Would be grateful for any takes on this.

[Frank E. Price]

As well as here, you might get some feedback from Buehler's website: georgebuehler.com, I think.

Frank

[carioca1232001]

Many thanks Frank.

Looking for people who have actually tried this stuff.

Do not fancy doing experiments on my undersides. :eek:

But cut-and-tried stuff is welcome.

[Paul Stohlman]

We have used this mixture (we call it bear s**t) a number of times. The latest example was a boat we replanked (among other things), and we wanted the seams to be able to move as the boat absorbed water. A year after launching, the owner was able to scrape off the bear s**t that squeezed out and it skinned over again to accept bottom paint.

I love the stuff

[Stan Derelian]

What proportions do you use? How long before launching can you use it?

[carioca1232001]

Yes, I too am interested in more details.

Hope Paul Stohlman reads this

[Stiletto]

Carioca, an NZ book called High Tide calls that mixture shenam, which is what they used to pay the seams in the old scows.

"Mix up tar with a sprinkling of cement, add a dash of tallow. Heat it up, stir well and let it cool. once you get it right it's beautiful to use , like plasticene (modelling clay)It sticks to anything , even oily wood. Prime over the shenam before antifouling. Dont use it on seams above the waterline though or the tar will leach through the paint."

Sounds like a fair bit of leeway in the recipe.

[carioca1232001]

Many thanks Stiletto.

Your recipe calls for a sprinkling of cement into standard tar

Whereas Frank Price´s, extracted from Buehler Boats, mixes cement into roofing asphalt until the latter can take in no more.

Roofing asphalt is readily available in most construction material stores . Me thinks it would be the watered down (with thinners) version of standard tar, not readily available over the counter.

Actually know somebody who has done this, one recipe or the other ?

[Paul Stohlman]

Make sure that the cement is powdery. It sometimes gets lumpy, and it is hard to mix. I put it on a suitably sized pallette (piece of plywood) and fold in the roofing tar (also sold as roofing cement). (Sounds like Julia Child...might as well have some wine).

It should have a consistancy to allow you to work it into the seam with a wide putty knife. Farily firm, not hard.

Work it into the (caulked and primed) seam so as to avoid trapping air bubbles. Work for a few feet, on a few adjacent seams, then scrape it flush, and wipe with a kerosene soaked rag (no smoking please). It gets harder to clean up once it skins over.

Don't skimp on the rags, work it in well. We paint right over it once it skins. You don't need to paint right away, but who wants a boat hanging arount the shop, when you can be sailing.

[carioca1232001]

Paul Stohlman wrote:


Make sure that the cement is powdery. It sometimes gets lumpy, and it is hard to mix. I put it on a suitably sized pallette (piece of plywood) and fold in the roofing tar (also sold as roofing cement). We have two grades of roofing tar, one is as viscous as peanut butter and the other can be spread with a brush.

The manufacturer recommends the viscous stuff for boat seams, aside from roofing applications.

How viscous is the stuff you use ? And how much powdery cement do you add ? Give me some numbers !

Thanks

[Dan McCosh]

I used standard roofing sealant, tube grade, for years as a seam compound. It sticks to anything, even wet, and sets up to a relatively elastic compound. It's messy, and virtually impossible to sand, tough to clean up. I don't know what the cement would do. There also is a variety with fiber mixed in, which is even stronger. As a compound, the caulking-grade roofing sealant has no actual body, hence squeezes with swelling planks. It's a pretty common compound for commercial hulls.

[carioca1232001]

The manufacturer´s tech line in Brazil said there would be no point in adding cement to the viscous variety of roofing asphalt (tar). They recommend using it "as-is", just as you do.

Their reasoning:

Cement grains on the surface of the aphalt+ cement blend could harden after contact with water, thereby providing a more abrasion-proof surface.

But grains within the blend would be isolated , for the simple reason that asphalt does not let water through - or it is not supposed to do so, anyway !

And the viscous stuff aleady exhibits good abrasion resistance.