French wood screw or carriage bolts?

[DennisCA]

I am building a deck with a roof and the entire design is a bit like a sandwich with joists in different layers. The posts are essentially two joists and the upper bearer and railings go in the middle. Now I wonder, I have only "angled" the joists together with 6x120mm wood screws and 6x90mm. I've screwed so that the holes are as hidden as possible.

I think I probably need some reinforcement through the posts, especially at the top and bottom of the posts. Now I have the choice between inserting some lag screws or alternatively carriage bolts straight through.

Carriage bolts would definitely be the stronger solution, but it won't look as nice on one side where you have to stare at a washer, nut, and bolt sticking out. Of course, at the very bottom, it will likely be okay since it's built in and won't be visible afterward.

 

[fribygg]

I don't think it's necessary, but if you're worried you can complement it with some galvanized nails.

 

[DennisCA]

I think the "lamineringarna" in certain places are not as tight as they should be, which is why I'm considering large French wood screws or carriage bolts to really press the parts together.

 

[Stefan1972]

Today, there are coarse mounting screws that are significantly better than classic French screws, which are actually completely useless in that regard.....

 

[fribygg]

If you have access to large clamps, you can nail-glue or screw-glue the posts together.

 

[topmount]

Yes, the main beam is likely hanging in the screws (no support underneath), so careful consideration is needed. It feels like construction screws have taken the place of French wood screws and are a bit more discreet.

 

[DennisCA]

Well, the screws have to take all the load there too.

I don't have clamps strong enough to pull together even though I have clamps that can reach around.

What do these construction screws look like?

 

[Kane]

https://www.essve.com/sv/produkter/bygg-och-traskruv/konstruktionsskruv

 

[Ursviken]

Threaded rod with dome nuts where it is visible?

 

[DennisCA]

Dome nuts were a good idea...

 

[DennisCA]

Bought carriage bolts and will combine them with acorn nuts.

 

[Dilato]

classic French screws that are actually completely useless

❤️👏

 

[z_bumbi]

So the screws are taking all the load there as well.

I don't have clamps strong enough to pull it together, even though I have clamps that will fit around.

What do these construction screws look like?

If the clamps can't pull it together, the timber is too warped to be pulled together with screws. Unless you're trying to pull it together with existing screws already screwed in?

 

[Harald Blåtumme]

Try the modern replacement for the French wood screw: Big Dog. Examples can be found here but I think I've bought similar ones at Biltema as well. https://www.beijerbygg.se/privat/sv...digt/traskruv-big-dog-c4-10x50-40st-915608062

It's crazy how strong they are with their fairly coarse Torx fittings, typically T40. I've used hundreds of coarse 10mm x 140mm with an impact driver at 340 Nm with no problems at all. Available in all interesting dimensions just like the old French wood screw. Insanely effective.