Sealing joints

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Sealing joints

Postby gaff » Tue Jan 01, 2013 2:16 pm

I have been advised to fill gaps in cedar strips with sealant.

There are some superficial gaps that are not very wide or deep.

Is there a rule of thumb as to what should be done with sealant and what can be filled with epoxy fairing putty?


Thanks

steve
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Re: Sealing joints

Postby Torchie » Thu Jan 03, 2013 3:59 pm

Be careful as some sealants are just like adhesive. Make things hard to take apart if you ever have to.
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Re: Sealing joints

Postby Phill Blank » Tue Jan 08, 2013 6:53 am

Gaff,

I recommend using Boat Life as a filler on cedar strip boat. It can be forced down into smaller voids and can be used along with string packing for wider voids. It remains flexable and can be sanded aand painted when totally cured. Thompson used white lead and linseed oil to make a paste they filled the voids with. On the wider gaps they used the cotton strip packing withthe paste to fill the voids. I found a few of these voids between strips withthe string packing on a 12 footer I stripped down to bare wood.

The string packing is the type that has many threads loosely twisted together to form a larger diameter string and is off white in color. Johnston has it available in their catalog, but it can also be found in most office supply stores for less money. I remember it was commonly used years ago for tying packages for mailing. It is thicker then the string that was used in the stores to secure items when wraped in paper. (I guess I just dated myself, didn't I.)

With the many threads you can pull it apart to fit the width of the gap being filled.

Some very small voids can also be filled using thined primer and allowing it to fill the voids and repeat after sanding until void is filled then sand and put on final coat of primer.

Hope this helps.

Goo dLuck,

Phill
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Re: Sealing joints

Postby sayuncle » Tue Jan 08, 2013 12:40 pm

Phil, do you think that when they built these cedar strip boats at the factory, that there were gaps between most of the strips at the area between the bottom of the boat and the side of the boat? The area on the back half of the boat where the hull is rounded. I made some test strips for my boat and in this area there is no gap on the inside, but there is a small gap on the outside. I centered the matching profiles when making the strips which works good when installing in an area where there is only a slight curve. But maybe they need to be offset to one side a touch when installing these strips where the curve of the hull is the greatest?

Brad
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Re: Sealing joints

Postby Phill Blank » Tue Jan 08, 2013 3:01 pm

Brad,

The original planking, cedar strips, were concave on oneside and convex on the other with a small area in the center of the convex side that protruded slightly beyond the convex surface. This was what Thompson refered to as "compressed seam planking". Thompson was the only manufacturer that used this as far as I know. This slightly raised area would be compressed when the strip was clamped in place after steaming and was screwed in place. This made for a tighter joint, but there would be some gaps between the outer edges of the planking in the sharper curved areas of the hull and where the planking met the garboards.
In these areas Thompson used the string packing to fill the larger voids and then covered the hull with the mixture of white lead and boiled linseed oil paste to fill all voids.
The hull would then be lightly sanded and painted. On those boats that had mahagany planking above the spray rails they mixed in mahagany stain with the paste filler.

If you have the Thompson DVD the planking cross section is shown in the sales literature. I know it is shown in the front of the 1953 literature on Page #3.

As i mentioned before i found the string packing in the larger voids filled with white lead filler when I stripped my 12 foot Super Deluxe runabout some years ago. Whe I was cleaning out the larger voids I found the string packing had been force down into the gap with filler and then move filler over the top.

You have to remember Thompson was building these boats as fast as possible and all seams where not always as tight as others. Thompson was not building a high end boat like Chris Crafts. Thompson built boats for the average people for daily use and not the show boats well to do people. The filler was used to give the hull a smooth look when painted.

Good Luck,

Phill

Phill
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Re: Sealing joints

Postby sayuncle » Mon Jan 28, 2013 5:51 pm

Thanks Phil, I will have to look for the string. I need to experiment with the shape of the strips. The router bit I purchased has the matching profiles. I made some strips out of pine to test. The strips on the inside are really tight but there was a full 1/16 on the outside where the curve is the greatest. I think I can do a better job than that. First I need to finish the ribs.

Brad
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Re: Sealing joints

Postby Phill Blank » Tue Jan 29, 2013 10:34 am

Here is the detail as shown in Thompson's literature. I have no idea of what the actural radius was that they used for their cutters. Right now with the snow I can not get to any of my boats to see if I could detrermine the radius at this time.

Image

Hope this is of help to everyone.

Good Luck,

Phill
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