My name is Brenda. I have been a member since March 2008 and doing stained glass mosaics for about one year. I was offered a small commission to make 2 house number signs. These signs were to be left outside all year long. I live in Maine where it does get below zero sometimes. I did lots of research. What I used was:
MDF 1/2 inch thick, sealed with Welbond 100% no dilution
Liquid nails poly adhesive
mapei keracolor grout
I mosaiced the entire piece of MDF...top and sides included. I drilled holes for 2 eye hooks for hanging. The sign was GORGEOUS!!
The grout and glass started coming apart after being hung up for one week. The weather was not cold enough at night for a frost. I think it was the MDF (not exterior) that was the problem. Can you help me? Should I have used hardibacker board with a piece of plywood in the middle? How would I have hung that up? Help as I need to make 2 more. Thanks
I've got a book for garden art and in one of the stepping stone instructions it says:
Apply three to four coats of mosaic sealer to all sides of the project. Let dry.. Allow to cure one to two weeks before setting the stone outside.
I hope this helps. I don't know if there is a big difference in sealers, but the mosaic sealer I used on a grouted Bowling Ball has done a good job so far and it has been out all summer. Now I don't know how it will do in the winter.
I don't know if using outdoor mastic instead of liquid nails would have helped. Maybe making a quick one that you can use as a test would help. Let us know what you do.. I'm interested in knowing what worked.
Gourd, I wish I would have experimented first! That would have saved lots of time. I applied 2 coats of sealer but I did not let it cure for one or two weeks before setting it outside. It was only 2 days. I have done pavers and used grout with an additive and they have been outside all summer and not one crack. I think I was okay using the liquid nails and now I believe the problem was the wood. When examining it, you can see the wood has swelled. Not sure how the moisture got in there though...It was suggested to me by another person on this forum to use backer board and plywood in between. I am going to give it one more try, this time experimenting on a small piece to see what happens.
Maybe you can frame the sign with metal, then attach the eye hooks/hangers to the metal frame. I can see where the wood would swell, I wonder if you could mosaic a concrete square block/stepping stone with the address? That would be too heavy to hang, but maybe set in a frame also, it would work.
I'm thinking the cement backerboard would make a difference. It's designed for moisture, and MDF is not. If swelling in the background is the issue, that might solve your problem. I believe I've read that MDF put in a bucket of water will swell and break down.
Maybe you could do an experiment with a piece of MDF and a piece of cement backerboard in a couple of 5-gal buckets and see if there's a difference before you invest more time and energy into a new piece?
I don't know this from experience, just stuff I've heard from my tile guys and read in some of my tile books...
The problem has to be the MDF. I have never had a problem with mosaics over hard surfaces like cement or hardibacker but when I have used wood the swelling creates problems. The sandwich idea sounds good to me.