Review: A Comparison of System Three MetlWeld and WEST System for Metal Bonding

Needing several small metal fittings for the sail rig I was building for my canoe, I chose the somewhat unconventional approach of forming them from laminations of thin aluminum sheet. As a user of WEST System products, I knew that Gougeon Bros. has extensive instructions on using WEST System for bonding hardware and thought this would be a good opportunity to try it out. It worked out well and although a bit messy, everything cleaned up nicely and I got some lightweight, strong, and very trim custom fittings.

With one piece left to make, I came across System Three’s MetlWeld quite by chance while browsing their online site. Up to this point, WEST System was the only major brand we commonly use that I knew supported metal bonding. So I was intrigued by System Three’s MetlWeld for bonding metal and other dissimilar materials. It’s designed specifically for this purpose and doesn’t need any sort of filler added, as is typically the case when modifying epoxy to make an adhesive. I ordered a small sample kit of their SilverTip products to try it out.

MetlWeld can be used at temperatures as low as 50F. However, at a room temperature of 67 it seemed rather stiff. I warmed the room up to 72 overnight in hopes of making it a little more pliable. That didn’t seem to make a lot of difference. Also, the hardener looked as though it had separated slightly from its filler so it seemed prudent to stir it before measuring out. Because it comes already thickened, mixing resin and hardener was a bit of a chore, even in the small amount I was using (2 oz.). I didn’t have a lot of confidence in its getting thoroughly mixed so I stirred a full five minutes before I felt it was ready to use. This is in contrast to the usual method of mixing thin resin and hardener for 1 – 2 mins. before adding filler. Since the epoxy is thoroughly mixed at that stage, stirring in filler is not so critical and the amount can be controlled to suit the application. The material that came with the sample kit didn’t include anything in the way of instructions for modifying MetlWeld’s thickness.

Also, because of its thickness, I found it virtually impossible to apply the MetlWeld without getting too much on. This particular application is inherently messy with quite a bit of squeeze out anyway, but the thickness of the MetlWeld added to it. Squeeze out typically takes place over about 15 – 20 mins. or more as thickened epoxy responds slowly to the clamping pressure. In this case, it became too tacky to manage after about 20 – 25 mins. and I was left with squeeze out that had set too firmly to wipe off. This isn’t serious but it does mean there’s more cleanup to be done after it’s cured. Other than that, cleanup was the same as with WEST System.

System Three says to let MetlWeld cure at least 48 hrs. (at 77F) before putting a load on the joint. It certainly bonds well to aluminum and makes a strong joint. But I was surprised to find I could bend the new piece by hand. I simply can’t do that with the pieces I bonded with WEST System. That doesn’t automatically mean MetlWeld has less ultimate strength than WEST System but it clearly isn’t as rigid. In this application ultimate strength is not an issue–the pieces are too lightly loaded. The MetlWeld job is probably rigid enough for my purposes. Whether or not there’s any difference in long term durability will have to wait until both have been in service for a while.

My take on it at this point is that MetlWeld is a reasonably adequate alternative for what I’m doing but I definitely prefer WEST System in this application. WEST System is easier to use, much easier to control (using that word loosely), ends up with a neater job and takes a heavier load before deforming.

There are a couple of caveats that should be noted here:
One, given the non-critical load on these fittings, I didn’t feel the need to pursue System Three’s technical support so this review is absent any helpful perspective they could provide.

The other is that this is a specific application done under one set of conditions and shouldn’t be taken as a general indication of MetlWeld’s suitability for bonding. In this case, it didn’t work nearly as well for me as WEST System.

Review by Charles E. Campbell
Reviewed: System Three MetlWeld
Date Reviewed: 5/10/06