Major project ! First a hatch reseal

[Bycrick]

I’ve got 3 large (say 2’ x 2’) aluminum frame hatches. After trying all the fancy caulks, with poor results, I ended up with Dow 795. They didn’t leak and weren’t easy to get out when the plastic need replacement.

Steps:
1. Get rid of all the old caulk. Then sand the aluminum with 80-100 grit sandpaper until every trace of the old caulk is gone. Clean the frame with 100% alcohol.

2. Mark, remove the facing and sand the edges of the plastic where they touch the frame. Bottom AND edges with 60-80 grit sandpaper and clean with alcohol. Acetone is very specifically NOT recommended for acrylic.

3. Spread the sealant, making sure there’s enough to press out of all the joints. Put small spacers around the edge of the frame so that you get a thick seam on the bottom of the plastic. Within reason, a thicker seam is better.

4. Let it cure for 24 hours before pulling out the spacers.

If I were going to change something in the process, I might think about using 3M high-bond tape on the bottom seam, but so far I haven’t needed the extra adhesion.

The other posts cover anything I might have missed.

[Smokeys Kitchen]

Originally Posted by mitiempo

Skip the butyl, Dow 795 is all you need. It is not expensive.

Butyl is very good when an item is bolted to the deck.

A big +1 for the Dow 795. Re-sealed our front Vberth hatch lens 4 years ago and it has been fine since. Living on it full time and one winter up to Alaska and back.

[Northbound44]

Originally Posted by wingssail

In hot weather the butyl can run like hot tar, and drip into the interior of the boat.

Service temperature of butyl is 275F, service temperature of acrylic is 160F. Take note that Lewmar Ocean hatches use butyl and silicone on their hatches.

Ref. Acrylic
https://www.curbellplastics.com/getm...514&height=304

Ref. Butyl
https://www.bestmaterials.com/detail.aspx?ID=16309

Silicone adhesion on acrylic sometimes fails due to acrylic expansion. Butyl act as a second barrier.

[Northbound44]

Originally Posted by Northbound44

Service temperature of butyl is 275F, service temperature of acrylic is 160F. Take note that Lewmar Ocean hatches use butyl and silicone on their hatches.

Ref. Acrylic
https://www.curbellplastics.com/getm...514&height=304

Ref. Butyl
https://www.bestmaterials.com/detail.aspx?ID=16309

Silicone adhesion on acrylic sometimes fails due to acrylic expansion. Butyl act as a second barrier.

Here is a good video explaining how to proceed:

https://youtu.be/eD3Hp8W07yY

[Rmccormi]

On my C&C Landfall I utilized a Plexus adhesive. Plexus is a two part structural adhesive which is not cheep, it also requires its own application gun. The benif it is it bonds to acrylic and remains flexible. After the acrylic was installed in its frame (Plexus is a two part adhesive and sets up very quickly) I finished off the installation with a black silicone sealant (Boatlife ) After 10 years no issues.

[mitiempo]

Here is a link to the advice of Tony at Select Plastics, the largest hatch re-manufacturer in the world. They are the only authorized Lewmar hatch repair in North America.

https://selectplastics.com/which-sealants-to-use/

[Rmccormi]

In the past, I tried Sikaflex 295 with primer, but I did not have any success. I simply may have messed up on the primer application.

[mitiempo]

Originally Posted by Rmccormi

In the past, I tried Sikaflex 295 with primer, but I did not have any success. I simply may have messed up on the primer application.

The other advantage of using Dow795 is that it is a lot less expensive than Sika 295 and primer.

[johnn33]

Hi AliArcher
You could try in the UK
795BL - CRL Black Dow Corning® 795 Silicone Building Sealant - Cartridge
They are a USA company with overseas entities including the UK
John

[Rmccormi]

Originally Posted by mitiempo

The other advantage of using Dow795 is that it is a lot less expensive than Sika 295 and primer.

On my C&C landfall, after 16 years it’s time to replace my cabin a acrylic windows. I am planning on utilizing 3m VHB tape with Dow 795 to seal the windows. Although Dow 795 does have some structural properties I would not recommend utilizing it to be the primary component to secure the acrylic panel. (I have heard that in humid environments the VHB has failed, since I primarily sail in the San Francisco Bay, I hope this will not be an issue)

[Rubicon King]

Originally Posted by AliArcher

Trying to find it in the UK, we have DOW products but not that number! I’ll keep looking

I have 12 tubes of Grey, that I can part with. PM me.