Cracked radar arch repair

davidbrooks

I know this is a fairly common issue as i have heard others chime in that they have also seen the gelcoat crack on the base of the radar arch.  Mine is just on the port side.  The outside has a fine spiderweb crack but i am going to leave that for the time being.  The inside though actually had chunks that were starting to pop out. I started doing some chipping and i thought i would show you what i am finding.    So these arches are galvanized aluminum. It looks like on mine at least it was damaged at some point.  The inside has a crease or dimple going in.  I don't see how this happened on the boat. More likely in my mind it was damaged prior to installation.  Just rough handling with a forklift.  Anyway.  The main culprit is corrosion or oxidation.  Everything that i have read says that after you take the finish down to bare metal you have to coat it with body filler immediately.  This is just using a putty knife and rubber mallet.  Next up is a sander and steel wool.  I need to do a little more research on body filler.  I am used to work on fiberglass but i need something designed specifically to be applied directly to metal.  Suggestions are always welcome.  Bondo and 3M currently look like good candidates.  No comments on the mold on the rail for the side panels.  That was wiped off right after i took the pic.  

mbnarney

I will take a stab at it. In keeping with similar metals, there is a product called All Metal that is imbedded with aluminum, I used it years ago and it was pretty darn strong. Eastwood also sells a similar product called Contour. Its tough to tell from the picture, how deep you had to go, but for smoothing things out, I always used a glazing compound. 

YYZRC

I had this issue with my 330 arch. It cracked due to water freezing prior to me purchasing it. I reached out to SEI (arch manufacturer) and they recommended to fix with bondo. I did and it worked great. No pics of the crack repair but I did take this pic of a similar repair I made below the TV antenna. 

The paint I used was this, it was a perfect match. @aero3113 also found a match. Not sure if yours is the same color. 

aero3113

Yes, I used Bondo also and it worked great. I think you have an off white arch so our paint won’t match. Sorry my pics are out of order.

davidbrooks

I am going to try using the Bondo Metal Reinforced Filler.  I looked at the All Metal filler recommended but got a little concerned as it has both steel and aluminum in it.  They state there isn't an issue with the different metal interacting but i am a little skeptical.  I haven't measured the deepest part that needs to be filled but i am thinking it is about 3/16 at the deepest.  So the plan is to get it down to bare metal any where it is cracking, get a layer of bondo on it immediately. Then apply an epoxy fairing compound on top of the bondo.  I would really like to try and stick with gelcoat to paint it but it may prove to be a little too much.  I am going to give it a shot though.  I am only planning on doing the inside of the arch this year.  If it goes well i may do the outside next year.  It isn't as bad.  I will come back and post pics as i go.  

YYZRC

Is the metal reinforced harder to sand?

I wouldn’t worry about the strength of the filler - it is the bond between the filler and the bare metal that matters. 

davidbrooks

@YYZRC That is exactly why i was going with this one.  The bond between it and the arch is the most important.  I am not as worried about sanding as it is a flat surface.  It isn't going to be the final layer either.  I learned the hard way from the remodel of the dash. 

davidbrooks

The repair is done and now i am wrestling with gel coat.  I am likely going to have to wait till spring to finish the gel coat.  I just cant keep it warm enough to cure.  I did try the disposable spray bottles but IMO they were a fail.  i ended up simply painting a layer of gel coat over the final layer of fairing compound to protect it.  I will have to sand it down.

Ian

Mine needs doing but I don’t have the skills to do this type of stuff.

davidbrooks

@ian if you can do drywall repair you can do what i have done so far.  Literally it is just sanding to get to metal, wipe it clean with acetone and cover immediately with bondo.  That gets you close.  Then you add a layer of a fairing compound which is just a putty you mix 1:1.  It is easier to sand and gives you a smoother coat to paint.  You really just take your time to get it smooth.  Now painting it.  That is a different story.  Gelcoat requires a PHD in chemistry, 4 years of apprenticeship to a sorcerer and an offering of your first born to ensure it hardens.  In general if i can get it close i feel like that is a big chunk of the labor.  Then i can find someone to help me finish the gel coat for a lot less than outsourcing the whole thing.

Ian

I guess I can repair drywall but the “take your time to get it smooth is” is the hard part.