no-screws in grp

[eyesec]

After mulling over the replies to my previous post about fixing wooden slats to grp, I have come to a management decision not to glue them on, but to bolt them on using either rawl anchor bolts which expand as you tighten them, or spring toggle bolts which open like a butterflys wings as you tighten them (thanks to refueller for that idea). Two questions, what bit would you use - wood drill or metal for drilling through grp, and more important, as I have an aversion to using anything except brass or stainless steel in my boat, does anyone have a source for the bolts I mentioned in brass or stainless? Builders merchants etc do stock them, but only in zinc plated or ordinary steel. Thanks in anticipation.

 

[Boathook]

Metal bit for drilling GRP.
Nothing having read your previous post I would do all I can to avoid drilling holes in GRP because it is something else to leak. Modern adhesives seem to work ok and the blocks holding my whisker pole are stuck to the deck with adhesive/sealant.

 

[S2Jimlad]

I would certainly use an epoxy adhesive. In my opinion, over time the bolts will be subject to movement allowing the holes to work open, thus allowing moisture in. GRP is much better left intact if at all possible.

 

[seumask]

What are the slats for. If they are decorative, then glue only. Only if they are subject to significant lateral or tension loads would I go beyond a good glue to supliment with screw or bolts. Echo comments above about not puncturing the fiberglass if you want to retain watertight integrity. Always glue and bolt.

 

[eyesec]

Thanks everyone. The boat is only a 16ft ex ships boat, the slats are to go on top of the glassed in buoyancy tanks which run fore and aft. The only weight they will have on them is bums. They will also protect the grp from weights dropped on them - crab pots, anchors etc, they will also (hopefully) stop stuff falling off onto the deck.

 

[lw395]

I think rawlbolts as I understand them will put too much stress on the grp as they expand, they are meant to go in a deep hole in brick/concrete.
For light duty fixings, plastic 'hollow wall' plugs plus a stainless screw and sealant can be used, I've done this in the past where a hole had worn to about 8mm dia, with no acccess to the back. Apologies to the purists.
Another possible is the 'well nut', a rubber moulding with a brass threaded insert, these are quite widely used to hold panels of motorcycle fairings together. They are good until the brass corrodes and spins in the rubber.
I would prime the backs of the wood strips then use sika flex or similar, probably with a few self tappers to hold it in place while the sealant sets.
I would try to ensure the strips won't retain a pool of water, mabe cut drain grooves across the back at intervals?

 

[seumask]

IMHO this is one to try sticking on with the appropriate Sikaflex or equivalent as these are bouyancy tanks which if punctured will not be bouyancy tanks when you need them most. I'm often amazed with what good preparation and careful sticking can produce with sikaflex.

 

[castaway]

Yes me too.. I have my Spi pole in blocks held down with Sikaflex and they get kicked every time someone goes fwd....

Less holes the better... and not really neccesary with modern adhesives and certainly wouldnt use commonly available rawl or butterfly anchors.

Regds Nick

 

[Refueler]

I wouldn't use rawlbolts unless you really need strength - then you need to be careful about hole and expansion.
Rawlplugs - the plastic type are much better ....

Being on top of buoyancy tanks - liberal sealant around the fittings when bedding down.....

 

[Drascomber]

I suspect that the reason no one has answered your original question (in addition to offering their advice) is that no one has come accross the type of fastening that you describe in a metal suitable for on-deck marine use.

I have seen nylon fastenings of the type that have "wings" that open out when you tighten them - but the chocks that my anchor sits in - and is secured to - on the foredeck are stuck down with polyurethane adhesive sealant (except that it came from a builders merchant and didn't say Sikaflex on the tube).

I reckon you are "stuck" (sorry about that) with either screwing them down either directly or into plastic rawlplugs of some sort - or glueing them down.

 

[Refueler]

I have a bag full of 6mm / 8mm brass inserts that you can press / glue into grp / whatever material. When bolt is wound in the insert expands a small amount to lock in place. The expansion is not so great as rawlbolts / plugs. Cost about 10p each in local builders merchants.

 

[Boathook]

Best to avoid holes in buoyancy tanks !!
You could even try no-nails waterproof ......... Bright blue in colour, but as only required to hold slats in place will possibly do ok.

 

[snowleopard]

I too would go for adhesive. I found that it didn't work too well on the teak so switched to Sikaflex. If you are dead set on a mechanical solution, use self-tappers. I use them all the time - No 8 screws in A2 stainless. It's amazing what loads they will take provided you drill to the right size first and if you screw through a blob of Sikaflex you should get a watertight seal.

 

[fluffc]

In agreement with several others, I think that sika is the way to go. It won't budge if you've cleaned down the grp first.

As a side thought though, would very much not recommend brass screws in a seawater environment - they are an alloy of metals and disappear to nothing. If you are on a freshwater environment, then Brass would be okay i guess.

If you really don't like the look of stainless, then bronze would be the 'proper' way to go if you can afford it. Marinestore in maldon have these available on their website, or Anglia Stainless in colchester if you need lots.