Sikaflex expectations, vertical surface.

SiteSurfer

SiteSurfer

Well-Known Member
Joined
18 Jun 2015
Messages
1,262
Visit site
Reviewing some notes for upcoming jobs, I noted that 3 small pads supporting my Webasto exhaust offset mounts had come away from the bed of sikkaflex i'd squirted on them when installing. I had left the Sikkaflex to dry overnight and had tested their strength prior to wiring on the exhaust.

The rationale for this was to avoid screwing/bolting through the locker with its associated water ingress possibility, that and avoiding drilling more holes..

However I wonder if I've gone beyond the design expectations of Sikkaflex, would the collective like to offer an alternative glue/fix for this task? I'd really really like to not have to screw them in - but if that's what it takes then I'll go put some small countersunk bolts through and seal with some butyl tape rolled around the head.

The photo shows how they are fixed (prior to coming adrift).



 
SiteSurfer said:
Reviewing some notes for upcoming jobs, I noted that 3 small pads supporting my Webasto exhaust offset mounts had come away from the bed of sikkaflex i'd squirted on them when installing. I had left the Sikkaflex to dry overnight and had tested their strength prior to wiring on the exhaust.

The rationale for this was to avoid screwing/bolting through the locker with its associated water ingress possibility, that and avoiding drilling more holes..

However I wonder if I've gone beyond the design expectations of Sikkaflex, would the collective like to offer an alternative glue/fix for this task? I'd really really like to not have to screw them in - but if that's what it takes then I'll go put some small countersunk bolts through and seal with some butyl tape rolled around the head.

The photo shows how they are fixed (prior to coming adrift).
Click to expand...

You dont say which Sikaflex you used

I have found that things don't stick well to old fibreglass. Perhaps if you had abraded to expose a fresh clean surface or even cleaned with acetone they might have stuck better,

Personally I get good results with car body filler ( Isopon or even plastic padding) if the surface is prepared well. If anything is critical i glass over the wooden pads as well. It sets sufficiently quickly ( compared with epoxy) that if the surfaces are warmed fit with a hot air gun I can hold the pads firmly in place while it cures
 
Last edited:
Oh, its the Sikkaflex sold in chandlers - I must admit to not really looking at it beyond having heard of it as a good solution.

<quick google> I used 291 in white.
0000018794.jpg


Am I right in thinking that the area that I have previously used Sikkaflex on is now unuseable due to contamination? I have West systems epoxy on the boat doing nothing and some matting so could glass them in - which never crossed my mind.

My only concern would be how to support them whilst the epoxy was going off, allthough I'm sure i could fashion something.
 
I might well have used Sikaflex 291 in that situation and I wouldn't expect it to fall off, so I was a little surprised that yours has. That said, I'd have used a much thicker layer than I can see in your pictures, think rubber mounting bed rather than squirt of glue (291 isn't officially an adhesive), and at minimum I'd have given the surface a good scrub with acetone first or perhaps a quick sand with 80-grit followed by acetone wipe.

If you want to be really sure, sand to rough up the surface, scrub well with acetone, then use epoxy thickened to "peanut butter" consistency with microfibres. For the timber surface, paint a little of the unthickened mix on first, to penetrate the fibres. But this is really going over the top for some pipe mounts.

Pete
 
One of the tricks I picked up from the fora many moons ago was that polyester layup resin has a little wax to stop the stickiness of the free /non mold surface.

To remove the wax the recommendation was to rub surface with a web green scrubbing sponge washing with water until the water stops beading.
 
Right. Lots of avenues to try then.

Plan of action:
Rough up the area and clean off old adhesive.
Wipe down with acetate
Clean up mounts.
Apply liberal amounts of Sticks Like Wotsit
Hold in place
Go sailing.

If that fails:
Repeat clean up.
Dig out epoxy kit and glass the buggers in.
 
Thickened epoxy will be much stronger.

To avoid clamping in place, often you can put in a few short wood screws (not through, just into the core) to hold it while it cures. They do not hold the actual load, but they do allow you to keep working. Very neat and fast.
 
Have used 291 successfully as an adhesive for light loads. Perhaps a bit thicker than in the photo. Perhaps it was the preparation or the thickness that led to failure. Otherwise there is a much more adhesive Sikaflex (221). May not be stocked so much as the shelf life is shorter. This will certainly do it.

If you use epoxy, thicken it with a filler - eg low density filler, and use it as an adhesive. Very strong, but so is 221.
 
IIRC, doesn't 291 need over 24 hrs? I know when I did my log fitting, the instructions were to lightly tighten the inside nut, then wait 24 hours to tighten to final torque
 
Gladys said:
IIRC, doesn't 291 need over 24 hrs? I know when I did my log fitting, the instructions were to lightly tighten the inside nut, then wait 24 hours to tighten to final torque
Click to expand...
The rationale in this particular case is that you shouldn't tighten it up so much that all the sealant is squeezed out. If you first just 'nip it up' and then wait 24 hours before tightening fully, you will effectively have a made a gasket of sealant which should efficiently keep out moisture.
 
Last edited:
You must log in or register to reply here.

Share this page

Top