High Build up Electroless Nickel Plating (without pits?)

While it could be caused by any number of things, the two most common is not enough or the improper anti-pit (wetting agent) and inadequate agitation (it takes great agitation).

Hello Mr. Rains,
In our experience, no matter how well balanced or pit free an EN chemistry claims to be, above a certain point, the plate will develop imperfections. There seems to be a tendency for certain micro constituents to adhere to the surface, breaking its uniformity. Those irregularities accumulate over time. Twelve to eighteen mils is simply too much to expect a smooth final surface for an electroless plate. Most surely, you will have to do something to smooth it down afterwards.

What type of EN do you use, high P, mid or low?

The best way to prevent pitting is to operate with a very slow plating rate. To accomplish this you have to reduce PH, temperature and concentration.

On top of it, ask you vendor whether the product contains wetting agent. If negative ask him to add it.

What type of agitation do you use?

I am not aware of any commercial EN that will plate that much. Few will go more than 0.003 and I have not heard of one that will routinely do more than 0.005.

Years ago, some people were trying to re-activate and Woods nickel strike the part to get a second 0.003 build up. I really doubt if a third try would work.

I guess that you could have a second EN tank with a different formulation-less stabilizers and brighteners that could work longer, but there is a much higher probability of self destructing the tank.

My experience is in line with Guillermo's. If any chemistry or method could achieve 0.018" without pits, it would be news to me. I would like to hear what Don Baudrand would have to say about it.