# Drylok and measuring for background size



## natpodu77 (Jul 18, 2014)

Hello,

I have a 55 gallon tank that I am making a background for out of extruded foam and I have read a lot of other posts where they recommend making the background smaller by an inch around to accommodate the cement, however I am using Drylok and painting about 4 layers directly on top of the foam and was wondering if this would apply to my background as well?


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## Deeda (Oct 12, 2012)

The Drylok layers are thinner than the cement layers so you'll just need to compensate for that.

Do you already have a post detailing your plans for the DIY background? I have seen you've asked some questions on other posts but every DIY is a little bit different so if you can, post some pics or plans for yours.


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## natpodu77 (Jul 18, 2014)

Thank you so much for your response, I am really looking for some feedback-I have never done anything like this before, just going based on over a dozen of other builds and trying to make it work for me...
Yes I did post plans for my build and asked for recommendations, but didn't get too much feedback based on what I has posted, just what they had done or links to look at other builds. 
First I am building this to install in an already established tank. Upon installation I will be removing all of my plants, driftwood and rocks as well as fish and then putting them back after the background is installed and I do a water test after an hour or so.
I am using 1" extruded polypropylene foam (pink insulation). I was going to cut the form to fit the back of tank, then add a 5 or 6" foot/base running the entire length of the bottom of the background with silicone so that I can put my substrate and maybe a rock or two to help keep it in place. I am going to cut out various sized rocks, ledges and mini-"pots" to silicone to the 1" board, and try and accommodate the intakes for my 2 Filstar filters behind some rocks and ledges, maybe add a mesh screen to help with clogging issues.
Not sure if I should cut it into 2 or three pieces to help with the installation, my tank has the support running down the center of it. To attach the magnets I was going to make some depressions on the back to eventually silicone the magnets, then I was going to paint it with 3 or 4 coats of drylok-topping the 2nd layer with some sand to give it more texture and adding pigments to the last layer to paint in some details. Since I am not securing it to my tank with silicone, I was going to paint it on both sides-well at least 2 coats on the back side. 
I was also going to add silicone trim to the edges of the background (right and left) so that they sit in the tank more securely, and rest against each other without scratching each other. I guess with the Drylok I don't have to worry about adding bulk to the base, so I can measure more accurately to the tank, minus maybe 1/2"?


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## Deeda (Oct 12, 2012)

I think the problem with adding a 6" foot to the bottom of the background is that it will increase the buoyancy of the entire unit and if you (or the fish) should move any of those rocks, the unit will pop out of the tank.

The usual recommendation for getting the background to fit in tanks with braces is to cut them in a couple sections to ease installation. Don't use straight cuts, angled ones are usually easier to hide.

I have never done a DIY styro background but there are quite a few members that have done them successfully. Most if not all of them have been siliconed in place due to their buoyant nature.


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## natpodu77 (Jul 18, 2014)

Oh I didn't think of that, Maybe attaching with silicone to some slate tiles would work better? I know home depot sells them in 4"x4" tiles-or they used to, bough some a while ago for my box turtle-though I would never use them on a tank since he has had them for quite some time. I hope they will be okay in the water...

I thought egg crate, but I want a flat surface that would add weight.

As my tank has fish I cannot attach with silicone, and I wanted it to be removable so I purchased some heavy duty encased magnets. Thank you for the suggestion to cut it at an angle. I did not think of that, but it will definitely fool the eye.


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## Kanorin (Apr 8, 2008)

> As my tank has fish I cannot attach with silicone, and I wanted it to be removable so I purchased some heavy duty encased magnets. Thank you for the suggestion to cut it at an angle. I did not think of that, but it will definitely fool the eye.


I'm not gonna say it's impossible, but I'd say it is extremely, extremely challenging to design and install a foam-based DIY background into a tank while the fish are in the tank. 
The only way I can think of doing it is to lower the water level way way down (to maybe 3 inches of water), brush your substrate forward from the back wall, put the pieces in, lean some very large rocks against it, and brush the substrate back. Then fill the tank back up. Be warned that this is quite risky - if the rocks dislodge, the whole background will flip up violently and probably take out any lights, fish, tank tops, etc that are in its way. Do not underestimate the buoyancy - you can get a sense of how buoyant they are in your bath tub.

I experimented with magnets a bit - couldn't get them to work. Either they were too weak and the background went buoyant - or - they were strong, but I couldn't attach them to the foam securely enough and the foam just ripped and the background floated up while the magnets stayed on the tank.


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## natpodu77 (Jul 18, 2014)

I was actually going to take a day to remove the decor, plants and then fish to separate containers, drain the tank, install the background and then replace everyone to install the background.

I also purchased some strong rare earth magnets that are already coated in plastic to attach to the back, I will be cutting into 2 sections with 3 magnets on each with a force of 3 lbs and one magnets with pull force of 9lbs. I will also be attaching the background to 6x6 inch slate tiles with silicone for added weight, which will then be covered by about 3" of my Eco-complete fine sand substrate. I am hoping that will counter the buoyancy of the piece.

What I can't seem to get an answer to is: if I am painting the foam with 3-4 layers of Drylok, what I should do measurement wise? Should I measure exactly or subtract 1/2 to 1 inch for the Drylok layers?


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## Kanorin (Apr 8, 2008)

OK, this more detailed plan seems more feasible. Drylok goes on pretty thin. I'd subtract no more than 1/8 or 1/16 of an inch.


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## natpodu77 (Jul 18, 2014)

OMG thank you so much you are the first person that has actually answered my question and I have it on multiple forums!!!! :dancing:

I can now get to cutting my board. I was going to start with taking 1/2 inch off-but will go with 1/8 instead...THANK YOU! :thumb:


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## Kanorin (Apr 8, 2008)

You're welcome. I hope it works out, because it was just an educated guess!


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