Plywood Cracking!!!

[Guest]

Anyone got any ideas? The cracks have been there for some time but just recently expanded more. The port lights were replaced about 6 months ago, sealed in with sikaflex and bolted (bolt holes slightly bigger to allow movement).

This is the port side, the starboard side has no cracks!!??

[wheels 543]

I assume the Bolt shown is the bolt holding the frame? What is the frame made from and how substantial? I suspect the frame is expanding with heat and the bolts are simply pulling the ply apart. You may be best to either make a bigger hole in the ply for the bolt and then fill it with sika to allow movement, or fit several more smaller bolts around the frame, or bolster up the inside area with resin and glass tape.

[Guest]

Thanks all for the help!! The windows are perspex mounted outside (no frames) on a "bed" of sikaflex then bolted but NOT tight and the holes slightly larger than the bolts (already considered expansion etc before installing the new port lights!!). Same was used starboard but no cracking!!??? Any ideas or remedies? I thought epoxy and sucking it through with a vacuum cleaner or blowing it in with a compressor than bracing the inside?? She's an old Van de Stadt built in 1966. I was thinking mast flexing (keel stepped) might be the cause but this is not opposite the mast and there is no sign (YET!!) of cracking on the starboard side.

[Guest]

where is it ?

[Guest]

Thought of that too but the Tamaki River swings both ways with tides so each side would probably receive the same amount of sun exposure???

[Bogan 8]

Two things at once:

 

The windows were glued on later winter with the timber at its highest moisture content - and now we're in the height of a very dry summer. So the wood is shrinking as much as it can.

 

Meanwhile the window is expanding as much as it can in the hot sunny days. According to one spec sheet a 1.2m lenght of acrylic will expand 5mm for a 60C temperature change. That sort of temp change seems high, but if the sheet is tinted it might reach some pretty high temperatures in the sun

 

How wide is the bed of Sikaflex? That stuff is pretty tenacious. With the relative change between the plastic and the ply (one expanding, one shrinking) a wide bed like that could have enough shear resistance to tear the ply apart.

 

Regarding the different sides, perhaps the ply on the other side was not as damp when the windows went on, or the windows on one side went on on a colder day than the other?

 

If you take of the windows, you may find the cracks close up. Then if you redo them (now) on a hot day, they will tend to pull inwards instead of tearing the ply apart.

[Guest]

Thanks everyone. After some research and a good chat with the guys at Lloyd Stevenson, going to have a crack ('scuse the pun..) at getting epoxy into those cracks!! Will let you know how it goes.

 

...or it could be all those vindaloos on the stove!!