I shall have to precis this a bit but I hope that I can include some helpful detail.

Our front windows (above V berth), aluminium window frames, acrylic window.

Remove the black ‘Herzim’ strip covering the screwheads on the outside; remove 32 screws from each window. Here you hope the previous owner did not reseal with a silicone sealant which will make them harder to remove. Work an old (rounded corners) wallpaper stripper behind the frame and keep working around till you can get the whole frame out. Don’t use a screwdriver to lever as you may bend the frame.

Put some covers inside the boat to shield your upholstery then scrape etc, clean up (try white spirit) all around the big holes you just left in the boat, and then put a nice big tarp over the whole lot.

Get the frames home and on a nice flat surface. Covered patio table works well. Now get all the old sealant off the aluminium frame edge ie where the screws go through.


Next job is critical, This is to scrape out enough of the old sealant material between the frame and the window (carefully – as my window is not glass). Ideal tool is an acrylic cutter (hook shape end) but you could do a fair job with a snapped hacksaw blade


Have a good rake out all the way round inside AND outside … something like 4 to 5 mm deep. Clean well but avoid white spirit as it might affect the new sealant. I used builders alcohol wipes. If someone has used silicone, be patient and as thorough as you can.



Squidge with sealant and smooth with finger ? … ABSOLUTELY NOT. Big masking job (I used the blue stuff). Inside your sealant will fill the gap and be ‘flat’, outside you need to mask up so as to give you a sealant bead at about 45% to the window.


Sealant – ARBOMAST Autograde black butyl. Never sets, it just skins over. It’s a longish tube so be sure that it will fit in your sealant gun. Cut nozzle for a small bead and run in on the inside. Squidge the sealant down into the gap you made (I used a small plastic spreader from a car body repair kit). Be patient,




Run another line round and squidge down again. Using a tool (wiped with alcohol) to give a nice finish. Carefully remove your masking tape Do the same outside. This will take more sealant. Your 45 degree edge will take a little patience but keep squidging and smooth off nicely with a tool. Carefully remove your masking tape. You might need another little gentle smoothing here.


I bought some hard wood smoothing tools with the sealant – they were brilliant.


Set the whole lot aside for a few days and let the sealant skin over.


Take it all back to the boat, take your tarp off.

Sealant ARBOMAST BR grey butyl (I didn’t want black between the aluminium and the cream gel coat). Cut the nozzle to give you about a 6mm bead and run a line of sealant all the way round the frame & covering the screw holes. I needed help here as my screws go right through the GRP into an inner aluminium frame. Place the frame back in the hole. I used new stainless self tapping screws with help inside to hold the inner frame in position. Quite a lot of the grey sealant will exude, but go all around with screws. DON’T fully tighten, leave yourself half a turn in case you need to nip up in future. Use a scraper or similar to remove most of the unwanted seal and smooth and clean up with alcohol wipes . The grey is a little more sticky than the black. Just be patient.

Replace Herzim strip with new strip (on a cool day) and don’t stretch it. You can buy a tool but I found a pizza cutter very useful, mitre corners and where they touch use a little super glue to stop the strip shrinking back.

…. Job done.

Benefit of using BUTYL: it never fully sets, it’s easy to do again in future, it will dissolve in white spirit AND its cheaper than silicone.


Costs (£)

Tarpaulin                       17.00    (Toolstation)

Wipes                           6.99      (Screwfix)

Masking tape                0          (had it already)

Spreader                       0          (had it already)

Scrapers                       0          (had it already)

Turps/white spirit           0          (had it already)

Finishing tools              5.91      (Dortech Direct)

Arbomast Autograde     2.47 x 2 (Dortech Direct)

Arbomast BR                3.22 x 2 (Dortech Direct) only needed one

Screws                         5.00      (Seascrew) 100 of 3/4 inch  x 8

I had an opening window to reseal also so 2 extra items were

Window seal                 25.75    Delta Rubber 15mm x 10mm self adhesive expanded

Contact adhesive          3.08      Homebase

Total                             75.11

The quote I had to do the reseal (EXCLUDING remove and refit) was a little under £800

Time taken. Probably 10 to 12 man hours. I did not hurry. Result was 100% success.


I also replaced ALL our Herzim strip (total about 40 metres). It would have been about £80 from SEALS DIRECT but I went to BAINES at Tunbridge Wells and got whole roll deal 110 metres for 30 quid !

 Martin Smith.