Remove 3, maybe 4, decades old PVA glue from Lego

Question

A friend of mine gave me a large crate of Lego that he found in the house he just bought.
It appears to be several sets from the late 70's. (I spotted the building instructions for the 850 and 851 Technic sets in there.)

Unfortunately that crate also contained a bunch of other stuff, including a large plastic squirt-bottle of PVA wood glue. The bottle burst open and the glue leaked into some of the Lego.
I have about 500 bricks fused together with several booklets of building instructions into a sort of modern sculpture.

I would like to get the glue off, without destroying the bricks, but this glue has been there for 30, maybe 40 years.

The usual approach for dissolving old PVA glue is soaking it with hot water, white vinegar or methylated spirits (in order of aggressiveness).

But would that be safe for the Lego?
As far as I know hot water, if too hot, might soften/deform Lego bricks.
Methylated spirits is, in general, not safe to use on plastics and will probably affect the plastic used in Lego bricks.
White vinegar is, as far as I know, safe to use on Lego.

So I'm thinking of just soaking everything in warm water (say 40 degrees Celsius) for a couple of days and seeing how that goes. If that doesn't dissolve the glue I can try again with white vinegar.

Does anyone see a problem with that? Does anyone know a better way of doing this?

Answer 1

Take it for what it is, I am not a material scientist and this is not a guarantee that the following information will work in your case.

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I believe your approach is correct, or at least as good as you'll be able to get considering the material properties of the bricks and the glue.

LEGO bricks are made of ABS plastic (at least after 1963).

According to data from the Cole-Parmer Chemical Compatibility Database, ABS plastic is very susceptible to damage from nearly all the normal solvents used to remove PVA glue.

Chemical	Compatibility with ABS plastic
Acetone	D - Severe Effect: Not recommended for any use.
Methanol (Methyl Alcohol)	D - Severe Effect: Not recommended for any use.
Vinegar	A - Excellent

Vinegar looks like it may work, especially if you expose the glue to soften it before attempting to remove it from the bricks. Unfortunately, the instructions are almost certainly beyond saving.

Concerning heat, ABS appears to be safe until around 80°C (176°F) when it starts to deform. This is good considering PVA softens as early as 30°C (86°F). However, as Alex points out, LEGO recommends using water no warmer than 40°C (104°F).

You might try submerging the LEGO-berg in hot water for an extended period of time (articles I found suggested multiple hours, changing the water as needed) then using a syringe or spray bottle to apply vinegar to one area at a time. With some force, the weakened glue should release. Assuming it has weakened sufficiently, wiping with a course cloth should remove the residue.

It is unclear in my searching whether time is a significant factor in the susceptibility of PVA glue to heat. It is a resin, so there may be some long-term curing that prevents the glue from re-softening, but I couldn't find a definitive source one way or the other.

As an additional consideration, exposure to extended heat, chemical treatments, and physical cleaning may impact the surface quality of your bricks. Additionally, if the solvents present in the glue when it was applied to the surface also affect ABS, the glue may be bonded to the structure of the brick, not just the surface. If this is the case, you will not be able to salvage the brick without a destructive process like sanding that will inevitably leave signs.

If you can identify a small chunk of bricks to test the process on, you can at least see if heat and vinegar are a potential solution for the rest of your bricks.

Answer 2

Self-answer to let you all know how things went.

Warm water was having some effect but it took forever. So Saturday morning I went to the DIY store and got myself a 5 liter jerrycan of white vinegar.

Taking my small test-clump I dropped it in a a bucket with a 50/50 mix of warm water and vinegar. In about 5 minutes the top 2-3 millimeter of the glue had turned in a slimy gooey layer. Rinsing that of with a brush and exposing the still solid glue underneath started the dissolve the glue underneath as well.

Took less than 15 minutes to break up the whole clump and to brush the Lego pieces more or less clean. The more I could break up the clump the quicker it went. After that I gave them a second rinse in another bucket with water/vinegar mix just to get rid of the remaining residue and finally rinsed them off under running tap-water.

The first bucket now contained a very nasty slimy water/vinegar/glue mix.
I threw that away and refilled with fresh warm water/vinegar.
Stuck the large clump in (it was too large to submerge completely, part of it stuck above water) and let it soak for another 10 minutes.
Was then able to break up the under-water section in smaller pieces so eventually I was able to get everything soaking.

After another 10 minutes I had broken up the entire clump into small clumps each containing maybe 10 to 15 Lego pieces. Left these to soak some more.
Another 15 minutes later I had freed all Lego pieces and just needed to brush/rinse the remaining goo off.

Conclusion: Vinegar worked really well. Mixing it with warm water might have somewhat sped up the process as well.
There doesn't seem to be any negative impact on the Lego bricks.