Sealing Thngs To The Deck

[RuK]

Hi , I have chunky bits of wood attached to my narrowboat hull. They're a real headache to seal on; a stupid design but I'm stuck with it.

 

I've spent lots of time & effort cleaning them up, finishing with Deks Olje & sealing them to the deck with Sikaflex 291 marine sealant, only to find the sealant hasn't held & it's trapping water underneath. Has anyone out there come across this problem?

 

I could take it all off & re-seal, maybe use a different sealant & this time I'll complete the paint job - last time I only got up to having rustoleum ('damp proof') primer on the deck, so I do wonder if water seeped through the primer & caused the sikaflex to come unstuck. But I have very little confidence that sealing them on again will work. I wonder if it's best to use no sealant at all, at least then the water can dry out from the sides when it seeps under. Is this just a hopeless design flaw? I would like to keep them as they're beautiful wood.

[Nine of Hearts]

If it's any help, I used Marineflex to "glue" wooden battens to my hull, and that seems to have worked fine. I have also used it for securing tiles, as a sealant and various other gluey jobs, so if it turns out to be crap my boat will fall to bits. No doubt someone will come along and tell us that it's the same as Sikaflex but with a different label. I live to be informed.

[Timleech]

A bit more detail as to what and where these wooden bits are, and how they are attached, might help.

 

Wood on steel is a constant source of problems, but I would seal/paint both timber and steel thoroughly, and don't squeeze the sealant out too thin when you fasten the two together - a bit of thickness of sealant allows a bit more movement.

 

Tim

[WotEver]

Are these wooden things adhered to bare steel, or to a painted surface? If the latter, then it'll never work. If the former, then you'll need to also seal the gap around the edge (think silicone around a bathtub).

 

Tony

[koukouvagia]

I had precisely this problem on our motor. The back cabin is steel but has a wooden frame. After about fifteen years a gap began to open up and it would have only been a matter of time before rot set in. The solution was to run a half inch wide fibre glass tape along the seam and seal it with epoxy resin. Once this had been sanded down and painted you couldn't see the join and the problem has been permanently cured. (Well, it's still OK after three years.)

 

[RuK]

Thanks for your replies. The worst bits are wood attached to the back deck - it's unavoidable that there will be puddles of water hanging around where the wood joins, which makes me wonder if any sealant can stand up to being in a puddle for long.

 

These bits are attached by bolts through the back deck. I've just taken these bits off, so they can go back onto bare steel or have it painted up to topcoat enamel underneath

 

Koukouvagia - thanks good to know there's something more high tech to try. Not got the knowhow to put fibreglass on yet but may have to work it out if sealants fail again

[Grace and Favour]

I would always 'glue' (if that's the correct term) materials together before painting/undercoating/priming for a good adhesion.

 

If you glue to painted steel (say), then all you are doing is glueing your wood to the paint!

[Timleech]

I would always 'glue' (if that's the correct term) materials together before painting/undercoating/priming for a good adhesion.

 

If you glue to painted steel (say), then all you are doing is glueing your wood to the paint!

 

In the Op's case the timber is bolted to the steel, so the main function of the sealant is to seal the join. If you don't paint beforehand, at the first hint of the sealant failing the steel will rust or the timber absorb water, after which all will rapidly go downhill, so my preference in this case would be to paint thoroughly beforehand.

 

There is no perfect answer, because the wood will always 'move' and almost inevitably any seal will eventually give up. If you have a significant thickness of PU sealant between the two it will allow some movement, though.

 

Tim

Edited August 7, 2013 by Timleech

[blackrose]

If it's any help, I used Marineflex to "glue" wooden battens to my hull, and that seems to have worked fine. I have also used it for securing tiles, as a sealant and various other gluey jobs, so if it turns out to be crap my boat will fall to bits. No doubt someone will come along and tell us that it's the same as Sikaflex but with a different label. I live to be informed.

 

Likewise, the hardwood base for my navigation light mast has been stuck onto my roof with marineflex for about the past 4 or 5 years. I didn't want to make holes in the roof for screws of bolts. (The mast itself folds down if it hits something and is completely removable - apart from the base).

 

 

It's still as well-sealed as the day I stuck it there. The whole idea of flexible adhesives like marineflex and sikaflex is that they will compensate for the different thermal expansion/contraction rates of different materials. If you've used sikaflex before and it didn't work perhaps you used the wrong one? Sikaflex has a confusing amount of variants. Give Marineflex a go - it's half the price of sikaflex too. Give both surfaces a key and clean with white spirit first.

Edited August 7, 2013 by blackrose

[Stormbringer]

Just an addition to blackrose's excellent advice above.

When I did my caravan engineer training we were told to always clean with white spirit first, but that it ( the white spirit) left a residue which should be cleaned off with a bit of meths prior to applying the sealant.

I have no chemical proof of this but have never had any problems sealing caravans using this method either, so may be worth a try ...

 

HTH

Andy

[gbclive]

If the wood is teak or similar it has a high oil/resin content (the reason it is favoured for marine and garden use) and presents a significant challenge to boatbuilders trying to glue it.

 

Advise is to clean the joint using acetone a few minutes before gluing, leaving just enough time for it to evaporate before applying the glue. Avoid substituting nail polish remover as these may have oils and other additives.

 

It is also suggested that initially sanding the surface with a medium grit can help if the surface is shiny from planing.

 

These ideas are specifically referenced to gluing, but perhaps relevant if the problem is the bond between the sealant and the wood?

Edited August 10, 2013 by gbclive

[blackrose]

Just an addition to blackrose's excellent advice above.

When I did my caravan engineer training we were told to always clean with white spirit first, but that it ( the white spirit) left a residue which should be cleaned off with a bit of meths prior to applying the sealant.

I have no chemical proof of this but have never had any problems sealing caravans using this method either, so may be worth a try ...

 

HTH

Andy

 

I think white spirit might be the solvent used in marineflex, so it shouldn't need cleaning off itself. As long as the surfaces aren't wet with it. I use a cloth dampened with white spirit to clean up too.

[smileypete]

Bit of a 'piece of string' question, much more detail would help.

 

Like how wide/long/thick is the wood, what tree species, is it through bolted, was it bare wood to bare metal via Sikaflex, what loads on the wood, what is fixed to it, pictures with ruler and diagrams with dimensions would help, the more the merrier.

 

Sealing deck hardware with Sikaflex is meat and potatoes to the rag and stick brigade so it should be quite doable.

 

cheers, Pete.

~smpt~

[bowten]

Also put some cross cuts in the wood with a sharp knife or chisel this will help the adhesive penetrate the wood.Don't forget the adhesive bond will only be as strong as the paint surface so remove some of that as well.

Edited August 10, 2013 by bowten

[blackrose]

Instead of mounting pumps etc directly onto bulkheads which means drilling holes into the steel, I've used marineflex to stick a small piece of ply to the bulkhead and the next day just mount the pump onto the ply with screws. It's much easier and just as permanent.

 

The heat exchanger and pump in this picture are mounted in this way, and the cables running down the engine beds are clipped onto strips of wood marineflexed to the steel.

 

Now, I've just got to repaint the engine hole...

 

Edited August 10, 2013 by blackrose

[Ex- Member]

To solve the particular OP's problem simply use neoprene sheet. If this wood is bolted to steel then I assume it can be tightened and compressed against the steel. Neoprene is the solution as it needs no adhesion just simple compression to avoid any water ingress. It can also be purchased in different thicknesses so will cope with almost any amount of movement whilst maintaining a permanant seal.

 

Also brilliant for all types of boat fittings, port holes especially, it really makes sticky sealants redundant in many instances.

 

http://www.ramgaskets.com/gasket-materials/rubbers/neoprene/

 

It's probably quite an expensive solution depending on the area you need, however how much is continual failure costing?

[smileypete]

IF it's a large section of thru bolted timber with a lot of seasonal expansion and contraction, then it sounds like there needs to be a proper expansion joint to take up the shear movement between timber and deck.

 

cheers, Pete.

~smpt~

Edited August 10, 2013 by smileypete