choice of wood for laminating

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I need to replace some laminated beams which support the deck stepped mast on my boat. The existing beams appear to be sitka spruce which would be great to use again but the quote I have had seems astronomically expensive. The only reason I am replacing them is because the 45 year old glue lines are letting go. The timber is still in perfect condition.

Browsing through B&Q today I noticed they had some quite nice looking pine boards in a size which could be thicknessed to suit. The boards were described as 'clean' and were certainly knot free. Thet were also a lot cheaper than sitka.

what do people think? Obviously I need a stable, strong timber but not necessarily as light as sitka would be. I will be laminating with epoxy so I dont suppose that will be a problem for any softwood?

TIA
 
Prescient! It is indeed a Twister. Someone published an article soem time ago.about doing the job in a fibreglass boat in the class association magazine but I've lost the copy I had. Was that John?
 
Probably not necessary to buy any new wood if the current wood is sound and it is just the glue lines that have failed - and if you can get the beam out in one piece. Separate the laminates using a fine toothed band saw or a jig saw if you are careful. This will have the effect of cleaning the faying surfaces then you can make a jig to the right curve and glue back with thickened epoxy. You may want to add an additional laminate to strengthen it and bring it back to the original thickness. 4 or 6mm marine ply would be good as that will help stabilise the curve before you reinstall it. I have done this successfully with laminated tillers in the past.

If you do have to start from scratch then Douglas Fir is a good choice and a specialist like Robbins in Bristol will machine laminates to size for you. Sitka Spruce is OTT for this job, but alternate laminates of fir and mahogany would also look good if it is on show!
 
Pine is suitable for laminating. Stronger then spruce usually, at least equal to Sitka. So I'd guess may replace the existing beams with no problems. Only look out for places with too much resin in them, and such - as usually.
 
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As suggested D Fir is excellant, infact any coniferous softwood is good if free of knots, small ones up to 5p size are acceptable as with laminating it is much stronger than original wood. Mixing different species needs to be done carefully as not all species will bond well to each other and can have different rates of shrinkage which can lead to failed glue lines. Don't bother with epoxy it is expensive, wastefull, not good at gap filling and can be very bad for your health, use a polyurethane such as Lumberjack or any other that is sea-waterproof it usually says on pack. Don't be tempted to use a fast set as you will need time to get the laminates set up with glue on. Former can be blocks of 2 x 2 timber screwed to chipboard base or direct onto floor, place plastic sheet underneath to prevent sticking. For a gentle curve such as deck beam place cramp blocks every 6-9" with a cramp at each position. Ideally have at least 5 laminates so for a 60mm deck beam you will need 5 x 12 mm, The thinner the laminate the stronger the beam will be but the greater the timber costs. More laminates also mean less "spring back" when you remove the cramps. Spring back is usually negligible with multiple laminates but can be several mm if only a few pieces glued up so if you have less than 5 laminates allow say around 10mm extra curve. You may wish to make the beam a little deeper than original to allow for bringing the shape exactly to that of its partners. Some deck beams are reduced in depth where they are dovetailed into the beam shelf.
Allow some extra width on the laminates to allow for cleaning up, if your beam should finish at 50mm than have the timbers at least 55,-60mm allows more leeway with planing up. Not a good idea to use existing laminates unless you ahve had lots of experience with laminating as you will struggle to get the laminates all flush along the edge. It can be done but needs additional cramps to pull the edges all in line. Allow at least an extra 150mm on length it can be awkward to get the ends in line too, better to have some spare to trim off. Don't be tempted to remove the cramps too early allow at least 12 hours at 20C to be safe.
Good luck. you will be surprised at how strong and beautfull your deck beam come out.

Polyurethane glues take 4 days to wear off of your fingers-wear gloves!
 
I'd be a wee bit careful of overcooked cheap softwood, but certainly you could get satisfactory pine lumber from my local builders merchant in the UK. My boom is made from same stuff. I was very picky in going through the timber available and bored and plugged a few knots.

It used to be fairly standard practice to laminate deck beams from left over bits of boatskin. In my case larch.

Epoxy is good stuff and is well known for its strong gap filling capability with appropriate fillers (=sawdust). PolyU is probably better for this job as it is kind to your tools when planing up afterwards.

N.B. it is moisture curing, so temperature makes not a lot of difference to how fast it goes off. Don't think you can speed it up by heating it.
Clamp tight, but not so tight that you squeeze it all out.

My deck beams were done with resourcinol (I think cascophen or aerolite) glue and are OK after 50 years - I saw them glued up but my memory is fading.
 
Why oh why do intelligent people ever go to B&Q for anything bar white paint? especially for wood as most of it is rubbish and very dear. quick grown, ungraded and not air dried.
 
Originally Posted by Paddingtonbear
Why oh why do intelligent people ever go to B&Q for anything bar white paint? especially for wood as most of it is rubbish and very dear. quick grown, ungraded and not air dried.


RobinBirch said:
Who knows but he's obviously not as intelligent as you are.
Click to expand...

I'm guessing that the last comment is intended as ironic? With regard to the first, a review of my original post will, I hope, confirm that I was asking a question which I felt to be valid. Just for the record I will probably not buy my timber from B&Q but the 'clean' range which I was referring to did appear to be a better quality than the vast range of softwoods that they supply.

For everybody who has taken the trouble to offer what appears to be good advice around my original question, many thanks indeed. I am particularly interested in the comments around using polyurethane adhesive rather than epoxy, since I know it is easier to handle (accepting that its notoriously difficult to remove from hands!) I did replace one of the beams 10 years ago using Balcotan but some of the joins have let go. I'm guessing it may have been a combination of poor wood and workmanship though, so I'm quite prepared to have another go. Maybe the timber was't properly seasoned?
 
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I have had success with both Polyurethane and epoxy. The downside with poly is that although it is gap filling the glue that fills the gap has no strength and in laminating you need the strength. However if your laminates have a good surface which is roughened up there should be no gaps. For this job, though I would use epoxy thickened with silica and maybe some brown microballoons if using mahogany to give the glue line colour. Bit harder to clean up so worth scraping off the excess as you go.

Would not use either with bare hands. Either disposable latex gloves or cheap Marigold types from Tescos.

BTW you are right about the strip wood from B&Q - much better than the usual cheap timber, but you will probably find little if any cheaper than Douglas Fir.
 
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