Mounting stuff on GRP

[DGR]

I've done a search on screwing things into GRP to secure them, but I'm unclear on a couple of things - so before I stick a drill into my console...

I'm only attaching small things which won't need to take huge loads, i.e. extinguisher ports on the engine box, air vent on the console etc. From looking at the threads there seems to be different ways of doing it:

1) drilling the pilot hole and self tapping into the GRP, or

2) over drilling the hole, filling with sikaflex, and then drilling/self tapping into the sikaflex.

Is there a 'best' way of doing it to give the best finish?!?

Dylan...

[Erin]

I always just pilot drill a hole through the gel coat with a drill larger than the screw thread, and then let the screw self tap into the fibreglass beneath. I find that if you don't break through the gel coat then it fractures when the screw gets driven through and can look unsightly.

Worth putting a bit of Sikkaflex behind whatever it is your'e mounting to add a bit of waterproofing.

Keith

[DGR]

OK - so just to get this straight...

(1) You drill an oversized hole just through the gel-coat laywer to stop it cracking and looking messy

(2) and then let the screw self-tap through the GRP (i.e. you don't drill a pilot hole all the way through the GRP first?)

(3) and once finished, just put a bit of sikaflex on the back where the self-tapper has penetrated the console on the inside to keep waterproof?

Is that right?

D...

[slimtim]

The way I have always done it is to drill a pilot hole smaller than the thread all the way through (I guess it could be half way...doesn't really matter), then cover the thread and underside of the screw head with silicon sealer (less of a glue than skiaflex which means it'll be easier to take out), then screw it in nice and tight. The sealant will squish out around the screw as its tightened up but it can then be wiped off with a rag to make it look neat. This way it minimises the risk of water getting into the hole and soaking into the laminate.

Tim

[Erin]

Yeah pretty much right but depending on the size of screw you may need to pilot drill a hole right through the GRP. Also best to put the sikkaflex or sealant on the outside face of the console before tightening up the screw as mentioned above.

[DGR]

Thanks guys - much happier now.........

[nugent]

i actually prefer s/steel nut and bolt on every thing if you can get behind it + silkaflex or every day silicoln will stop any water absorbing into glassfibre.

i have large bag of M4-m6+ machine screws and nyloc nuts awaiting my rib to arrive..friday i ope in case i need to change any self tappers that are present, as they allways work loose in the end