Buying Filler Blocks

[mikiek]

To this point in my career I have never made filler blocks to fit between frames. OK - well maybe back at the transom but as far as side or bow blocks, never. The builds have come out OK so far. I don't think fillers would have made any difference.

 

After some hiatus, I am building Cazador mostly just to get my skills back again. I thought I would have a go at making filler blocks at some of the hull positions and see how that works, if there is really any benefit. The Cazador frames have a fairly large space between them - but typical to most kits I have built so far.

 

The kit offers nothing in the way of filler material. I see a lot of basswood blocks of various sizes for sale online. From 1x1x3 to 2x2x6 to 3x3x10 pieces or some combination. I'm just wondering what makes the most sense. I imagine the smaller pieces would not be useful. But I am stuck between buying some big hunk and cutting pieces to size (probably with a lot of waste) or the medium size pieces. I'm just hoping to be as efficient as possible.

 

There's probably a simple answer to this. Any help would be appreciated...

[Dr PR]

Balsa would be easier to cut and shape. The filler blocks do not need to be strong. They just provide a shaped surface between bulkheads to glue the planks to.

 

You don't need to fill the entire space between bulkheads. All you need is something out at the hull surface. Some people just use pieces of wood dowel, with multiple pieces cut to fit horizontally between bulkheads along the outer edges.

 

Whatever you use should extend out beyond the bulkhead edges a bit so you can sand them down to fair a curved surface between the bulkheads.

[wefalck]

... and the wood should not be much softer than the bulkheads, otherwise there is a tendency to sand hollows into the fillers, which defeats the object. On the other hand, one can always build up the surface again or apply wood-filler putty.

[brunnels]

9 hours ago, mikiek said:

see a lot of basswood blocks of various sizes for sale online. From 1x1x3 to 2x2x6 to 3x3x10 pieces or some combination.

I don't know if you all have Hobby Lobby's down there in SE Texas, but I was in my local Hobby Lobby and they had a pretty good assortment of basswood blocks that I thought would be perfect sizes for filler blocks.

[Pete Jaquith]

Mikiek,

I have used pine or basswood for filler blocks.  Easy to work with but firm enough to provide excellent planking support.  Attached are pictures from my Fair American build.

[manning16]

Hobby lobby balsa blocks..I used them between all frames on my Confederacy..no problem and easier to shape than basswood.  Use them  now for bow/stern scratchbuilds

[mikiek]

Thanks for all the replies. I guess what I am wondering is if it is more efficient to buy a couple of big blocks and cut smaller filler pieces or buy smaller pieces. I'm kinda thinking a big block would be better but there might be more waste.

[mtaylor]

On 3/20/2025 at 8:34 PM, mikiek said:

Thanks for all the replies. I guess what I am wondering is if it is more efficient to buy a couple of big blocks and cut smaller filler pieces or buy smaller pieces. I'm kinda thinking a big block would be better but there might be more waste.

I think there's trade-offs with either method.  You might buy a small sampling of the larger block and test to see how everything goes for you. It's probably a bit more time consuming than the smaller blocks but overall, less money. 

[Snug Harbor Johnny]

  I used both bass and balsa on a hull as an experiment, and found that balsa is a bit soft (but after shaping it can be 'hardened' by applying titebond and rubbing it in a little - then allowed to dry before sanding).  Now some balsa may be denser, but dense balsa if hard to find these days (not so 50 years ago for RC planes).  You need to mind the grain direction of bass as filler - amidships to app reaching bow and stern, the grain should run fore-and-aft for easier shaping/shaving.  Where the curve plunges at the bow, cutting a piece to fit with the grain at a 45 degree angle will limit carving across end

grain.

[Pete Jaquith]

I used 1/8", 1/4" 1/2" and 3/4" basswood sheet laminated for the bulkhead spacing for filler blocks.  If basswood is not available, I would use pine or popular.  Shaping was done with #80 grit paper wrapped around 1" and 1.5" dowels.  They turned out to be very effective fairing tools rapidly removing unneeded material.  This was followed by #120 and #150 grit paper using the same large dowels.

 

After initial shaping with gouges and chisels, I use the same large dowels for fairing laminated solid hulls. 

[mikiek]

Anyone able to provide links to posts that have described the build filler block process? I have seen more than a few and there appears to be no consensus on how it should go.

[wefalck]

Up to you and what materisl you have to hand …

[David Lester]

There's are excellent article on the NGR website. It's Nautical Research Guild - Resources - Articles and How-Tos - Framing and Planking - Constructing Bow and Stern Filler Blocks.

 

I've use this method with success a few times.

 

 

[mikiek]

On 4/8/2025 at 7:57 AM, David Lester said:

There's are excellent article on the NGR website. It's Nautical Research Guild - Resources - Articles and How-Tos - Framing and Planking - Constructing Bow and Stern Filler Blocks.

 

I've use this method with success a few times.

 

 

I appreciate your comments and glad it worked for you, but I really didn't get any real benefit from that article. I'm not about to get into that level of detail just make a few filler blocks.

 

Looks like I'm back to a plank by plank fastened to frame by frame install.

[wefalck]

I don't know this NRG-article, but the point about filling the spaces between the bulkheads is, that in general in POB construction, in particular in kits, is that the bulkheads are spaced too far apart. This makes fairing the edges of the bulkheads difficult and can also lead to sagging or kinks in the planks, if they are proportionally to thin for the distance.

 

What you use as filling material is not really important, but it should not be harder than the material of the bulkhead to keep the effort of fairing at a reasonable level. Too soft is not good either, because than their is a risk of creating hollows, which defeats the object.

 

Some kit manufacturers offer a sort of remedy for too far spaced bulkheads by providing for two layers of planking. However, you have to get the first layer right, otherwise it transmits all fairing issues to the second layer.

 

 

 

[Paul Le Wol]

6 hours ago, mikiek said:

I appreciate your comments and glad it worked for you, but I really didn't get any real benefit from that article. I'm not about to get into that level of detail just make a few filler blocks.

 

Looks like I'm back to a plank by plank fastened to frame by frame install.

Hi Mike, if you decide not to use filler blocks you could try an alternate method that I have used and still use. Glue small pieces of offcut planking to the backside of the planks to keep them in line.  If you dry fit the plank after shaping and/or bending you will be able to see where they need to be placed.

 

 

 

 

I then glue to the bulkhead and edge glue with white pva. After a while you will be able to figure whether the tabs need to be attached to the previous plank or the plank that you are currently working on. Good luck with your build.

[wefalck]

That's a good idea to keep subsequent strakes together and prevent some sagging, but not really an alternative to the fairing aid of fillers between bulkheads. If the bulkheads are not faired properly, you might still kink the planks.

[Paul Le Wol]

4 minutes ago, wefalck said:

That's a good idea to keep subsequent strakes together and prevent some sagging, but not really an alternative to the fairing aid of fillers between bulkheads. If the bulkheads are not faired properly, you might still kink the planks.

Very true.