Tool to Cut Sikaflex

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lpdsn

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Looks like I'm going to have to replace or at least re-bed the portlights in the hull over the winter.

They're held in by screws and sikaflex. Cutting the sikaflex from outside looks like it'll be easy with an ordinary Stanley knife or similar.

To cut the sikaflex on the inside I need the blade to move parallel to the window, which is going to be pretty impossible to achieve with a knife. I've an idea of the sort of tool I want, with the blade at 90 degress on the end of a flat piece, so I can run it around the surrounds whilst it cuts the sikaflex.

I've tried to sketch it up very quickly in the attached PDF. The trapezoid on the end is the sharp bit, but there's no special reason why it has to be exactly that shape, it's being able to cut a 90 deg as it is moved from side to side that is important.

I've never seen anything like this. Any ideas?
 

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I use a Stanley plastic handled window scraper with stanley blade for trimming sikaflex flush after it has gone off completely.A lot easier than attempting a perfect finish by tooling.Drawn across the direction of travel rather than pushed.May suit your detail ?
 
Perhaps this diagram will explain it a bit better than my earlier attempt.

There isn't the space to hold a tool parallel to the portlight, so it needs to be held at the normal but cut around the edges parallel to the portlight.

Should also say that I don't want to use a power tool such as a Dremel because of the risk to damage to the woodwork or portlight.
 

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Sure, I understand the layout. maybe an idea of portlight dimensions and depth of surround will improve the picture further.

For something even more flexible then a piston ring compressor could be adapted (basically a very wide, long watch spring)

Edit: add

Or a grapefruit knife, already bent a bit.

I just removed some, probably much larger, so easier to get to. I didnt do anything to cut the part you are trying to find a tool for. I cut from the outside (the easy to get to cut) and used a couple of pry bars from the inside. Sikaflex in shear (the outside cut) is very strong, but in tension you can get a brittle fracture to run along, so apply force, nick the edge and watch the split run.
 
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Dougal Tolan said:
Sure, I understand the layout. maybe an idea of portlight dimensions and depth of surround will improve the picture further.
Click to expand...

The aperture is approx 3" high, wood to wood. Overlap on portlight and wood is maybe about 1/2", so a bit reluctant to use brute force method.
 
can you introduce high tensile steel wire as used in cutting cheese >


The car window repairs people use it to remove the bond material btw glass and bodywork.
 
sarabande said:
can you introduce high tensile steel wire as used in cutting cheese >


The car window repairs people use it to remove the bond material btw glass and bodywork.
Click to expand...

Thanks for the idea. Not glass unfortunately so the cheese wire would damage the acryllic. Also pretty impossible to lead it through as it'll have to go around a right-angle bend below the portlight through sikaflex the whole way.
 
Try palette knives for oil painting. They come in a range of lengths, thicknesses and widths. I spent a few happy hours in the winter removing windows, and in the end a set of these from the forum's favourite supermarket, Lidl, did the trick. Had to throw them away afterwards, but I went straight out and bought another set.

Perhaps a quick trip to the local art shop?
 
Looked at new sketch - protect the acrylic by pressing a thin blade against it ( e.g a thin blade from a japanese pull saw or a broad spatchel filler blade) then use a thin blade ( like a jap dowel saw or as mentioned a fish knife) sideways into the joint.
 
I had the same problem as you on my Rival 41C, not as extreme but still could not get a blade in to cut away the sealant. What worked best was a flexible scraper, 1 1/2" blade, available from the likes of BandQ. The blade flexes very well and bends in response to pressure, I used the corner to get a start into the gap and then just worked it from there. I did not cut the whole way round but levered the window frame out as soon as I had removed enough of the sealant, about 50% iirc. The new windows were sealed against GRP using Scapa Bedding Tape from Hadlow Marine. If at all possible do not use an adhesive sealant when re-bedding.

I notice that Hadlow do not list Scapa bedding Tape anymore: http://hadlo-43547-001.dsvr.co.uk/Pages/Sealants.html
 
Next time use silicone sealant to avoid the same problem in future. Polyurethane sealants (Sikaflex etc.) are not recommended for acrylic windows as they do not allow the window to expand and contract easily.
 
+1 Don't use adhesive sealants where they're not needed, you're only storing up trouble in the the future. The screws hold the window in place, the sealant keeps the water out.
PCUK said:
Next time use silicone sealant to avoid the same problem in future. Polyurethane sealants (Sikaflex etc.) are not recommended for acrylic windows as they do not allow the window to expand and contract easily.
Click to expand...
 
PCUK said:
Next time use silicone sealant to avoid the same problem in future. Polyurethane sealants (Sikaflex etc.) are not recommended for acrylic windows as they do not allow the window to expand and contract easily.
Click to expand...

Thanks. I'll pass your advice on to the builders if I ever meet them. :)
 
I'm not sure about varnish. It does seem to spread right out though so you would need to bear that in mind if there was any other sealant nearby.

lpdsn said:
Thanks, that's useful. Did you get a chance to discover the effect it has on varnished woodwork? Or find anything that can be used to protect the surrounds when it is being used?
Click to expand...
 
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