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Outdoor table top advice needed

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peterrr

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Hi All,

I'm replacing a table top (previously a ceramic mosaic which the winter killed) and have chosen to use Siberian larch planks. Unfortunately, the planks are only available around here in 3m lengths and the table is 1.57m long so, to avoid wastage, I'm planning to put a breadboard at the ends so that I can then get 2 lengths out of each plank.

My question is, how should I joint the planks to the breadboards? Also, should I do anything else to help keep the tabletop in shape? I was thinking about using half lap joints. I don't have a table saw, just a circular, jigsaw and compound mitre and nothing esoteric like biscuit jointers etc. I'm aware that the planks will expand and contract across their width whereas the breadboard length won't change so unsure about how to keep it all flat in the beautiful Stockport climate...

The table frame is a metalwork grid with a lip around the edges so I'm planning to just rest the top in there rather than fix to the base. The planks are 143mm wide, there will be 6 of them with approx 6mm gap between each.

Hope that makes sense! Any advice gratefully received.
Pete
 

Sgian Dubh

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I'm guessing your intention is to make a solid (gap free) wood top with edge jointed boards which are then joined to the clamped (breadboard) ends, something like below. This sort of construction would be likely to fail quickly in a garden table; there's a great deal of expansion and contraction that would need to built in to the clamped ends, and water would pool on the surface probably leading to panel joint failure, severe warp, and likely rapid rotting.

1618848286329.png


In reality, what you should be aiming for would be something like the example below, or a variation on this theme. Essentially, there's an exterior framework M&Td at each corner with slats spanning the width morticed at each end into the long side rails, with gaps between each slat. The gaps allow for expansion and contraction in each individual slat, and for water to drain away leading to fewer warping problems, and providing greater longevity to the table top, i.e., it won't rot away so quickly.

I've no really negative comments on your wood choice, except to say larch is relatively soft and classed as moderately durable, so you might get 15 - 20 years out of all the wood not in ground contact, fewer years in soil contact, which wouldn't be the case here because your plan is to put a new top on to an existing frame, based on what you said in your first post. Slainte.

1618848239056.png
 

peterrr

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Thanks so much for your detailed reply @Sgian Dubh !

As I mentioned in the 1st post, I'm aiming to leave around 6mm or so between the planks for expansion/drainage (Could also expand this gap if needed). My main confusion is that if I fix the planks to the breadboard using screws/glue , will the 6mm gap be enough to allow expansion/contraction or will it still fail as the ends are fixed and the breadboard won't expand with them due to grain direction.

Apologies for such noob questions!
 

Sgian Dubh

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Just a small addition to the above. The framework of the table top has two long rails, two short rails at either end, and a mid-rail, the one with a hole at its mid-length for an umbrella pole. These rails are all tenoned into mortices in the long rail, but each of those M&Ts were glued with polyurethane adhesive and draw-bored from the underside but with the pin stopped short of emerging through the top face. This was to prevent creating a gap between the diameter of the pin and the table's top surface into which water could penetrate so that rotting opportunities were minimised. The slats, also with tenons about 20 mm long were fitted dry into their mortices, i.e., no glue or draw-boring used, just shoved into their mortice. Slainte.
 

Sgian Dubh

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My main confusion is that if I fix the planks to the breadboard using screws/glue , will the 6mm gap be enough to allow expansion/contraction or will it still fail as the ends are fixed and the breadboard won't expand with them due to grain direction.
No apologies needed. I suggest leaving a gap of about 8 - 10 mm. What I'm not sure about is how you plan to simply screw the parts together. I'd think you'd need some sort of rebate in your side and end rails, and a matching tongue worked on the end of each slat to fit into the rebate and then you glue and screw the parts together. It doesn't sound like you have the tools to do that really, but maybe you do, e.g., router, chisels, mallet, saws. I'd think you'd need fairly thick material to do that successfully, e.g., about 36 - 38 mm thick.

From what you say, I don't think you're really making what are called clamped (breadboard) ends, just rails around the outside into which you're fixing slats. I wouldn't normally put slats following the long direction (assuming there is a long direction, because your existing metal frame may be circular), but if you have a grid underneath to support them that could be okay. Normally I'd look to put those slats across the short length, although there isn't really an only way to orientate slats, e.g., they can be fitted diagonally as long as none of the slats are too long and whippy, and it also depends on how thick the slats are, i.e., thicker slats are stiffer and less likely to bend too much under a load.

I'm not sure I've helped you much with this post, and maybe added to your confusion - sorry. Slainte.
 

peterrr

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It's all helpful. Thanks again. I'll definitely go for your suggested 8-10mm gap.
 

Sgian Dubh

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It's all helpful. Thanks again. I'll definitely go for your suggested 8-10mm gap.
Maybe, as you already have a metal base with a lip to hold things in place, you could simply make something that resembles the top of a pallet, i.e., four pieces around the edge and screw slats to those four pieces ... something like that. Slainte.
 
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